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Functional magnetic resonance imaging (fMRI) suggests that the hypoxic ventilatory response is facilitated by the AMP-activated protein kinase (AMPK), not at the carotid bodies, but within a subnucleus (Bregma -7.5 to -7.1 mm) of the nucleus tractus solitarius that exhibits right-sided bilateral asymmetry. Here, we map this subnucleus using cFos expression as a surrogate for neuronal activation and mice in which the genes encoding the AMPK-α1 (Prkaa1) and AMPK-α2 (Prkaa2) catalytic subunits were deleted in catecholaminergic cells by Cre expression via the tyrosine hydroxylase promoter. Comparative analysis of brainstem sections, relative to controls, revealed that AMPK-α1/α2 deletion inhibited, with right-sided bilateral asymmetry, cFos expression in and thus activation of a neuronal cluster that partially spanned three interconnected anatomical nuclei adjacent to the area postrema: SolDL (Bregma -7.44 mm to -7.48 mm), SolDM (Bregma -7.44 mm to -7.48 mm) and SubP (Bregma -7.48 mm to -7.56 mm). This approximates the volume identified by fMRI. Moreover, these nuclei are known to be in receipt of carotid body afferent inputs, and catecholaminergic neurons of SubP and SolDL innervate aspects of the ventrolateral medulla responsible for respiratory rhythmogenesis. Accordingly, AMPK-α1/α2 deletion attenuated hypoxia-evoked increases in minute ventilation (normalised to metabolism), reductions in expiration time, and increases sigh frequency, but increased apnoea frequency during hypoxia. The metabolic response to hypoxia in AMPK-α1/α2 knockout mice and the brainstem and spinal cord catecholamine levels were equivalent to controls. We conclude that within the brainstem an AMPK-dependent, hypoxia-responsive subnucleus partially spans SubP, SolDM and SolDL, namely SubSol-HIe, and is critical to coordination of active expiration, the hypoxic ventilatory response and defence against apnoea. [ABSTRACT FROM AUTHOR]

We recently demonstrated that the hypoxic ventilatory response (HVR) is facilitated by the AMP-activated protein kinase (AMPK) in catecholaminergic neural networks that likely lie downstream of the carotid bodies within the caudal brainstem. Here, we further subcategorise the neurons involved, by cross-comparison of mice in which the genes encoding the AMPK-α1 (Prkaa1) and AMPK-α2 (Prkaa2) catalytic subunits were deleted in catecholaminergic (TH-Cre) or adrenergic (PNMT-Cre) neurons. As expected, the HVR was markedly attenuated in mice with AMPK-α1/α2 deletion in catecholaminergic neurons, but surprisingly was modestly augmented in mice with AMPK-α1/α2 deletion in adrenergic neurons when compared against a variety of controls (TH-Cre, PNMT-Cre, AMPK-α1/α2 floxed). Moreover, AMPK-α1/α2 deletion in catecholaminergic neurons precipitated marked hypoventilation and apnoea during poikilocapnic hypoxia, relative to controls, while mice with AMPK-α1/α2 deletion in adrenergic neurons entered relative hyperventilation with reduced apnoea frequency and duration. We conclude, therefore, that AMPK-dependent modulation of non-adrenergic networks may facilitate increases in ventilatory drive that shape the classical HVR, whereas AMPK-dependent modulation of adrenergic networks may provide some form of negative feedback or inhibitory input to moderate HVR, which could, for example, protect against hyperventilation-induced hypocapnia and respiratory alkalosis. [ABSTRACT FROM AUTHOR]

Oxygen is a vital element for the survival of cells in multicellular aerobic organisms such as mammals. Lack of O2 availability caused by environmental or pathological conditions leads to hypoxia. Active oxygen distribution systems (pulmonary and circulatory) and their neural control mechanisms ensure that cells and tissues remain oxygenated. However, O2-carrying blood cells as well as immune and various parenchymal cells experience wide variations in partial pressure of oxygen (PO2) in vivo. Hence, the reactive modulation of the functions of the oxygen distribution systems and their ability to sense PO2 are critical. Elucidating the physiological responses of cells to variations in PO2 and determining the PO2-sensing mechanisms at the biomolecular level have attracted considerable research interest in the field of physiology. Herein, we review the current knowledge regarding ion channel–dependent oxygen sensing and associated signalling pathways in mammals. First, we present the recent findings on O2-sensing ion channels in representative chemoreceptor cells as well as in other types of cells such as immune cells. Furthermore, we highlight the transcriptional regulation of ion channels under chronic hypoxia and its physiological implications and summarize the findings of studies on the post-translational modification of ion channels under hypoxic or ischemic conditions. [ABSTRACT FROM AUTHOR]

Carotid body physiology meets cytochrome c oxidase crystallography Commentary to Ortega-Sáenz P, López-Barneo J. Physiology of the Carotid Body: From Molecules to Disease. Changing gas composition of the super-fusion medium from 20% O SB 2 sb , 3% CO SB 2 sb , 77% N SB 2 sb (normoxia) to 97% N SB 2 sb , 3% CO SB 2 sb (full hypoxia) is followed by a characteristic hypoxia-induced increased chemoreceptor sinus nerve activity (registration in black) serving as control. 1 CcO crystallographic changes of about 3 Ångström are displayed by CB chemoreceptor discharge. a Chemoreceptor discharge under normoxic and hypoxic CO application (red registration line) The effect of CO is shown as a percentage of peak chemoreceptor activity induced by 4-min hypoxia. [Extracted from the article]

Carotid body (CB) hyperactivity promotes hypertension in response to chronic intermittent hypoxia (CIH). The plasma concentration of adrenaline is reported to be elevated in CIH and our previous work suggests that adrenaline directly activates the CB. However, a role for chronic adrenergic stimulation in mediating CB hyperactivity is currently unknown. This study evaluated whether beta-blocker treatment with propranolol (Prop) prevented the development of CB hyperactivity, vascular sympathetic nerve growth and hypertension caused by CIH. Adult male Wistar rats were assigned into 1 of 4 groups: Control (N), N + Prop, CIH and CIH + Prop. The CIH paradigm consisted of 8 cycles h−1, 8 h day−1, for 3 weeks. Propranolol was administered via drinking water to achieve a dose of 40 mg kg−1 day−1. Immunohistochemistry revealed the presence of both β1 and β2-adrenoceptor subtypes on the CB type I cell. CIH caused a 2–3-fold elevation in basal CB single-fibre chemoafferent activity and this was prevented by chronic propranolol treatment. Chemoafferent responses to hypoxia and mitochondrial inhibitors were attenuated by propranolol, an effect that was greater in CIH animals. Propranolol decreased respiratory frequency in normoxia and hypoxia in N and CIH. Propranolol also abolished the CIH mediated increase in vascular sympathetic nerve density. Arterial blood pressure was reduced in propranolol groups during hypoxia. Propranolol exaggerated the fall in blood pressure in most (6/7) CIH animals during hypoxia, suggestive of reduced sympathetic tone. These findings therefore identify new roles for β-adrenergic stimulation in evoking CB hyperactivity, sympathetic vascular hyperinnervation and altered blood pressure control in response to CIH. [ABSTRACT FROM AUTHOR]

Regulation of ion channels is central to the mechanisms that underlie immediate acute physiological responses to changes in the availability of molecular oxygen (O). A group of cation-permeable channels that are formed by transient receptor potential (TRP) proteins have been characterized as exquisite sensors of redox reactive species and as efficient actuators of electric/ionic signals in vivo. In this review, we first discuss how redox-sensitive TRP channels such as TRPA1 have recently emerged as sensors of the relatively inert oxidant O. With regard to the physiological significance of O sensor TRP channels, vagal TRPA1 channels are mainly discussed with respect to their role in respiratory regulation in comparison with canonical pathways in glomus cells of the carotid body, which is a well-established O-sensing organ. TRPM7 channels are discussed regarding hypoxia-sensing function in ischemic cell death. Also, ubiquitous expression of TRPA1 and TRPM7 together with their physiological relevance in the body is examined. Finally, based upon these studies on TRP channels, we propose a hypothesis of 'O remodeling.' The hypothesis is that cells detect deviation of O availability from appropriate levels via sensors and adjust local O environments in vivo by controlling supply and consumption of O via pathways comprising cellular signals and transcription factors downstream of sensors, which consequently optimize physiological functions. This new insight into O adaptation through ion channels, particularly TRPs, may foster a paradigm shift in our understanding in the biological significance of O. [ABSTRACT FROM AUTHOR]

Oxygen (O) sensing by the carotid body and its chemosensory reflex is critical for homeostatic regulation of breathing and blood pressure. Carotid body responses to hypoxia are not uniform but instead exhibit remarkable inter-individual variations. The molecular mechanisms underlying variations in carotid body O sensing are not known. Hypoxia-inducible factor-1 (HIF-1) and HIF-2 mediate transcriptional responses to hypoxia. This article reviews the emerging evidence that proper expression of the HIF-α isoforms is a key molecular determinant for carotid body O sensing. HIF-1α deficiency leads to a blunted carotid body hypoxic response, which is due to increased abundance of HIF-2α, elevated anti-oxidant enzyme activity, and a reduced intracellular redox state. Conversely, HIF-2α deficiency results in augmented carotid body sensitivity to hypoxia, which is due to increased abundance of HIF-1α, elevated pro-oxidant enzyme activity, and an oxidized intracellular redox state. Double heterozygous mice with equally reduced HIF-1α and HIF-2α showed no abnormality in redox state or carotid body O sensing. Thus, mutual antagonism between HIF-α isoforms determines the redox state and thereby establishes the set point for hypoxic sensing by the carotid body. [ABSTRACT FROM AUTHOR]

The carotid body (CB) is the principal arterial chemoreceptor that mediates the hyperventilatory response to hypoxia. Our understanding of CB function and its role in disease mechanisms has progressed considerably in the last decades, particularly in recent years. The sensory elements of the CB are the neuron-like glomus cells, which contain numerous transmitters and form synapses with afferent sensory fibers. The activation of glomus cells under hypoxia mainly depends on the modulation of O-sensitive K channels which leads to cell depolarization and the opening of Ca channels. This model of sensory transduction operates in all mammalian species studied thus far, including man. However, the molecular mechanisms underlying the modulation of ion channel function by changes in the O level are as yet unknown. The CB plays a fundamental role in acclimatization to sustained hypoxia. Mice with CB atrophy or patients who have undergone CB resection due to surgical treatments show a marked intolerance to even mild hypoxia. CB growth under hypoxia is supported by the existence of a resident population of neural crest-derived stem cells of glia-like phenotype. These stem cells are not highly affected by exposure to low O tension; however, there are abundant synapse-like contacts between the glomus cells and stem cells (chemoproliferative synapses), which may be needed to trigger progenitor cell proliferation and differentiation under hypoxia. CB hypo- or hyper-activation may also contribute to the pathogenesis of several prevalent human diseases. [ABSTRACT FROM AUTHOR]

A functional role for the mitochondria in acute O sensing in the carotid body (CB) remains undetermined. Whilst total inhibition of mitochondrial activity causes intense CB stimulation, it is unclear whether this response can be moderated such that graded impairment of oxidative phosphorylation might be a mechanism that sets and modifies the O sensitivity of the whole organ. We assessed NADH autofluorescence and [Ca] in freshly dissociated CB type I cells and sensory chemoafferent discharge frequency in an intact CB preparation, in the presence of varying concentrations of nitrite (NO), a mitochondrial nitric oxide (NO) donor and a competitive inhibitor of mitochondrial complex IV. NO increased CB type I cell NADH in a manner that was dose-dependent and rapidly reversible. Similar concentrations of NO raised type I cell [Ca] via L-type channels in a PO-dependent manner and increased chemoafferent discharge frequency. Moderate inhibition of the CB mitochondria by NO augmented chemoafferent discharge frequency during graded hypoxia, consistent with a heightened CB O sensitivity. Furthermore, NO also exaggerated chemoafferent excitation during hypercapnia signifying an increase in CB CO sensitivity. These data show that NO can moderate the hypoxia sensitivity of the CB and thus suggest that O sensitivity could be set and modified in this organ by interactions between NO and mitochondrial complex IV. [ABSTRACT FROM AUTHOR]

Two-pore domain K (K) channels are involved in a variety of physiological processes by virtue of their high basal activity and sensitivity to various biological stimuli. One of these processes is secretion of hormones and transmitters in response to stimuli such as hypoxia, acidosis, and receptor agonists. The rise in intracellular [Ca] ([Ca]) that is critical for the secretory event can be achieved by several mechanisms: (a) inhibition of resting (background) K channels, (b) activation of Na/Ca-permeable channels, and (c) release of Ca from intracellular stores. Here, we discuss the role of TASK and TREK in stimulus-secretion mechanisms in carotid body chemoreceptor cells and adrenal medullary/cortical cells. Studies show that stimuli such as hypoxia and acidosis cause cell depolarization and transmitter/hormone secretion by inhibition of TASK or TREK. Subsequent elevation of [Ca] produced by opening of voltage-dependent Ca channels then activates a Na-permeable cation channel, presumably to help sustain the depolarization and [Ca]. Agonists such as angiotensin II may elevate [Ca] via multiple mechanisms involving both inhibition of TASK/TREK and Ca release from internal stores to cause aldosterone secretion. Thus, inhibition of resting (background) K channels and subsequent activation of voltage-gated Ca channels and Na-permeable non-selective cation channels may be a common ionic mechanism that lead to hormone and transmitter secretion. [ABSTRACT FROM AUTHOR]

Arterial chemoreceptors play a vital role in cardiorespiratory control by providing the brain with information regarding blood oxygen, carbon dioxide, and pH. The main chemoreceptor, the carotid body, is composed of sensory (type 1) cells which respond to hypoxia or acidosis with a depolarising receptor potential which in turn activates voltage-gated calcium entry, neurosecretion and excitation of adjacent afferent nerves. The receptor potential is generated by inhibition of Twik-related acid-sensitive K channel 1 and 3 (TASK1/TASK3) heterodimeric channels which normally maintain the cells' resting membrane potential. These channels are thought to be directly inhibited by acidosis. Oxygen sensitivity, however, probably derives from a metabolic signalling pathway. The carotid body, isolated type 1 cells, and all forms of TASK channel found in the type 1 cell, are highly sensitive to inhibitors of mitochondrial metabolism. Moreover, type1 cell TASK channels are activated by millimolar levels of MgATP. In addition to their role in the transduction of chemostimuli, type 1 cell TASK channels have also been implicated in the modulation of chemoreceptor function by a number of neurocrine/paracrine signalling molecules including adenosine, GABA, and serotonin. They may also be instrumental in mediating the depression of the acute hypoxic ventilatory response that occurs with some general anaesthetics. Modulation of TASK channel activity is therefore a key mechanism by which the excitability of chemoreceptors can be controlled. This is not only of physiological importance but may also offer a therapeutic strategy for the treatment of cardiorespiratory disorders that are associated with chemoreceptor dysfunction. [ABSTRACT FROM AUTHOR]

It has been proposed that endogenous HS mediates oxygen sensing in chemoreceptors; this study investigates the mechanisms by which HS excites carotid body type 1 cells. HS caused a rapid reversible increase in intracellular calcium with EC ≈ 6 μM. This [Ca] response was abolished in Ca-free Tyrode. In perforated patch current clamp recordings, HS depolarised type 1 cells from −59 to −35 mV; this was accompanied by a robust increase in [Ca]. Voltage clamping at the resting membrane potential abolished the HS-induced rise in [Ca]. HS inhibited background K current in whole cell perforated patch and reduced background K channel activity in cell-attached patch recordings. It is concluded that HS excites type 1 cells through the inhibition of background (TASK) potassium channels leading to membrane depolarisation and voltage-gated Ca entry. These effects mimic those of hypoxia. HS also inhibited mitochondrial function over a similar concentration range as assessed by NADH autofluorescence and measurement of intracellular magnesium (an index of decline in MgATP). Cyanide inhibited background K channels to a similar extent to HS and prevented HS exerting any further influence over channel activity. These data indicate that the effects of HS on background K channels are a consequence of inhibition of oxidative phosphorylation. Whilst this does not preclude a role for endogenous HS in oxygen sensing via the inhibition of cytochrome oxidase, the levels of HS required raise questions as to the viability of such a mechanism. [ABSTRACT FROM AUTHOR]

In this study, we explored the presence of aquaporins (AQPs), a family of membrane water channel proteins, in carotid body (CB) type I chemoreceptor cells. The CB is a polymodal chemoreceptor whose major function is to detect changes in arterial O2 tension to elicit hyperventilation during hypoxia. The CB has also been proposed to function as a systemic osmoreceptor, thus we hypothesized that the presence of AQPs in type I cell membrane may confer higher sensitivity to osmolarity changes and hence accelerate the activation of chemoreceptor cells. We detected the expression of AQP1, AQP7, and AQP8 in the CB and confirmed the location of AQP1 in type I cells. We have also shown that inhibition of AQP1 expression clearly reduced type I cell swelling after a hyposmotic shock, demonstrating that AQP1 has a major contribution in transmembrane water movement in these chemoreceptor cells. Interestingly, CB AQP1 expression levels change during postnatal development, increasing during the first postnatal weeks as the organ matures. In conclusion, in this study, we report the novel observation that AQPs are expressed in the CB. We also show that AQP1 mediates water transport across the cell membrane of type I cells, supporting the contribution of this protein to the osmoreception function of the CB. [ABSTRACT FROM AUTHOR]

Acute hypoxia increases the endogenous release of nitric oxide (NO) in rat carotid body and the expression of nitric oxide synthases is modulated by chronic hypoxia. The aim of the study was to examine hypoxia-induced NO generation in rat carotid body adapted to chronic hypoxia with inspired oxygen at 10% for 4 weeks. The concentration of NO was measured electrochemically with a Pt/Nafion/Pd-IrOx/POAP modified electrode inserted into the isolated carotid body superfused with bicarbonate-buffer saline at 35°C. Acute hypoxia increased the concentration of NO by 471.3±71.4 nM in the carotid body of chronically hypoxic (CH) rats. The amount of NO release induced by hypoxia was significantly augmented when compared with that of the normoxic control (87.6±15.9 nM). The hypoxia-induced NO generation was markedly attenuated by pretreatment with L-NG-nitroarginine methylester (L-NAME; 500 µM), a non-selective nitric oxide synthase (NOS) inhibitor and also by removal of extracellular calcium with the calcium chelator EGTA (5 mM). Additionally, NO generation during hypoxia was reduced by 30% in the CH carotid body treated with S-methylisothiourea (SMT; 50 µM), a specific blocker of inducible NOS (iNOS). Immunohistochemical study revealed that positive iNOS protein immunoreactivity was detected in clusters of glomus cells in the carotid bodies of CH rats, but not in the normoxic group. Thus, chronic hypoxia enhances hypoxia-induced NO generation mediated by calcium-dependent NOSs and iNOS in the carotid body. Extracellular recording of sinus nerve activity of CH carotid bodies showed that L-NAME treatment enhanced the afferent discharge in response to hypoxia, confirming that the generation of NO suppresses the activities of carotid chemoreceptors. Taken together, our results suggest that hypoxia-induced NO production increases in the rat carotid body adapted to chronic hypoxia and that constitutive and inducible NOSs are involved in the NO generation. The enhancement of NO generation may play a physiological role in blunting the hypoxic chemosensitivity during chronic hypoxia. [ABSTRACT FROM AUTHOR]

The nitric oxide (NO) donor S-nitroso-acetylpenicillamine (SNAP) enhanced Ca2+-dependent K+ channel activity in rat carotid body chemoreceptor cells. Ca2+-dependent K+ channel activity was enhanced by SNAP in 38% (whole-cell configuration) and 67% (cell-attached mode) of the cells tested and was not affected by intracellular Ca2+ chelation with BAPTA-AM. Enhancement of Ca2+-dependent K+ channel activity by SNAP was blocked by the cGMP-dependent protein kinase G inhibitor 8-[(4-chlorophenyl)thio]-guanosine 3′,5′-cyclic monophosphothioate Rp diastereomer (Rp-8-pCPT-cGMPS). NO thus enhances Ca2+-dependent K+ channel activity through cGMP-dependent protein kinase G. The NO-mediated increase in Ca2+-dependent K+ channel activity is likely to alter the function of carotid body chemoreceptor cells and could explain the decreased chemosensitivity of the carotid body in response to NO released from efferent nerves or vascular endothelial cells. [ABSTRACT FROM AUTHOR]

Endothelin-1 (ET-1) excites carotid body (CB) chemoreceptors and induces mitosis of the chemoreceptors in chronic hypoxia. The aim of the present study was to examine the hypothesis that up-regulation of both ETA receptor and endogenous ET-1 expression in CB chemoreceptors enhances the response of intracellular Ca2+ to ET-1 following adaptation to chronic hypoxia (10% inspired O2 for 3–4 weeks). Cytosolic free [Ca2+] ([Ca2+]i) in type-I (glomus) cells freshly dissociated from rat CBs was measured by spectrofluorometry. Application of exogenous ET-1 (1–100 nM) concentration-dependently elevated [Ca2+]i in the glomus cells. This response to ET-1 (100 nM) was 49% greater in the chronically hypoxic (CH) group. The ET-1 response was abolished completely by the ETA receptor antagonist BQ610 (1 µM), but not by the ETB antagonist BQ788 (1 µM). The transient [Ca2+]i elevation induced by caffeine (30 mM) in the normoxic group was similar to that in the CH group, suggesting no differences in the intracellular Ca2+ stores. In situ hybridization with a digoxigenin-labelled antisense ETA receptor mRNA oligonucleotide probe revealed very intense and ubiquitous specific expression of ETA receptors in the lobules of glomus cells in the CH group, whereas staining in normoxic controls was light. Immunohistochemical studies revealed intense cytoplasmic staining for ET-1-immunoreactivity in most of the cell clusters in glomera in the CBs of CH rats but was faint in normoxic CBs. These findings indicate increased expression of both the ETA receptor and ET-1 in CB chemoreceptors during chronic hypoxia. Taken together, our results suggest that the [Ca2+]i response to ET-1 in rat CB chemoreceptors is augmented by up-regulation of ETA receptors and ET-1 expression. The enhancement of the paracrine/autocrine effect of ET-1 on the chemoreceptors is consistent with an excitatory and mitogenic role of the ET-1 and ETA receptor in the CB during chronic hypoxia. [ABSTRACT FROM AUTHOR]

In acute hypoxia, the release of nitric oxide (NO) produced in rat carotid body is unclear. The concentration of NO was measured electrochemically with a Pt/Nafion/Pd-IrOx/POAP-modified electrode placed on the surface of isolated carotid bodies superfused with bicarbonate-buffer saline at 35°C. In hypoxia, the concentration of NO in the carotid body was increased by 17±2 nM. The amount of NO release during hypoxia was augmented by increasing the number of carotid bodies surrounding the electrode and also in the presence of L-arginine. In addition, the hypoxia-induced elevation of NO was abolished by pretreatment with a nitric oxide synthase (NOS) inhibitor, L-NG-nitroarginine methylester (L-NAME). The results suggest that endogenous NO production in the carotid body increases during hypoxia. Electrophysiological measurement of single fiber activity in the sinus nerve revealed that L-NAME treatment enhances the afferent discharge in response to hypoxia. This confirms that the hypoxia-induced elevation of NO suppresses the carotid chemoreceptor response to hypoxia. Taken together, it is concluded that acute hypoxia increases NO generation in the rat carotid body, and that the elevated levels of NO suppress carotid chemoreceptor activity during hypoxia. Hence, NO may play an active inhibitory role in the control of carotid chemoreceptor activity during hypoxia. [ABSTRACT FROM AUTHOR]

Angiotensin II increases afferent discharge from the carotid body in vitro. We hypothesized that angiotensin II receptors (AT receptors) are expressed functionally in the type-I cell of the carotid body. Cytosolic free [Ca2+] ([Ca2+]i) in type-I cells freshly dissociated from rat carotid bodies was measured spectrofluorimetrically. Angiotensin II (10–100 nM) concentration-dependently increased [Ca2+]i in type-I cells. The [Ca2+]i response was blocked by pretreatment with losartan (1 µM), an AT1 receptor antagonist, but not by blockade of AT2 receptors with PD-123319 (1 µM). Moreover, the gene expression of AT1 receptors was assessed by the reverse transcriptase polymerase chain reaction and gene transcripts of both AT1a and AT1b receptors were detected in the carotid body. In addition, immunohistochemical study revealed that AT1 immunoreactivity was localized in lobules of type-I cells in the carotid body. Taken together, these results suggest that type-I cells in the rat carotid body express functional angiotensin II receptors. The binding of angiotensin II to the AT1 receptors increases [Ca2+]i, a key step of the intracellular signalling cascade following the activation of the receptors. It is concluded that angiotensin II modulates carotid body chemoreceptor function directly via AT1 receptors in the type-I cell. [ABSTRACT FROM AUTHOR]

In order to better understand the post-natal increase in peripheral chemoreceptor responsiveness to hypoxia, chemoreceptors of newborn (1–2 days) and older (10–12 days, 30 days, adult) rabbits were isolated and superfused, in vitro. The free tissue catecholamine concentration was measured using carbon-fiber voltammetry and pauci-fiber nerve activity was recorded from the sinus nerve during stimulation (4 min) with graded hypoxia or increased potassium. Both the peak catecholamine and peak nerve responses to stimulation with 10% and 0% oxygen increased with age, particularly between 10 and 30 days of age. In contrast, peak nerve and peak catecholamine responses to increased potassium did not significantly change with age. For a better understanding of how responsiveness increases with age, the fast Na+ and the Ca2+ currents were measured from isolated glomus cells of newborn and older rabbits, but the magnitude of the currents when normalized to membrane area was not significantly different between ages. We conclude that: (1) rabbit chemoreceptors mature in the newborn period (10–30 days) and part of this maturation is an increase in catecholamine secretion, (2) maturation of hypoxia transduction primarily occurs in steps prior to depolarization since potassium-evoked responses were not affected, and (3) an increase in the magnitude of glomus cell fast Na+ or Ca2+ currents is not a likely mechanism for the maturational change, but changes in the oxygen sensitivity of these currents cannot be excluded. [ABSTRACT FROM AUTHOR]

Long-term hypoxia induces changes in neuropeptide-Y-like immunoreactivity (NPY-LI) and/or in the content of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) at the central level. To determine whether these alterations depend on the integrity of carotid body (CB) chemoreceptors, intact rats or those whose carotid sinus nerve was transected (CSNT) were exposed to hypoxia (10% O2) or to normoxia for 14 days. Thereafter, NPY-LI, 5-HT and 5-HIAA levels in discrete brain regions were determined. The increase in NPY-LI in the ventrolateral medulla oblongata (VLM) of intact hypoxic rats was mostly abolished after CSNT and therefore is mainly mediated by CB chemoreceptors. In contrast, other hypoxia-induced changes were similar or even enhanced in CSNT as compared to intact rats and therefore do not depend on the integrity of CB chemoreceptors. This was the case for the increase of NPY-LI in the striatum and the caudal dorsomedian medulla oblongata (DMM), as well as for all the changes in 5-HT and 5-HIAA in the DMM, the VLM, the raphe nuclei, the striatum and the frontal cortex. We propose that long-term hypoxia alters brain NPY-LI and indolamine content through the stimulation of CB chemoreceptors or ancillary chemoreceptors, as well as through local biochemical or morphological mechanisms. [ABSTRACT FROM AUTHOR]

In rabbit carotid bodies (CBs) superfused during 1-5 h, with an air-equilibrated medium containing no tyrosine (TYR), the dopamine (DA) content decreased by approximately 60% after 1 h and remained constant afterwards. TYR and 3,4-dihydroxyphenylacetic acid (DOPAC) decreased with the same time course. Noradrenaline (NA) content exhibited a biphasic decrease of lesser magnitude than that of DA. Superfusions with a TYR-containing medium did not prevent the reduction in DA and TYR. Large amounts of DA and DOPAC were recovered in the effluent during the first hour of superfusion but after 90 min the two substances had declined below the detection limits (i.e. 0.5 and 1 pmol/5 min, respectively). The DA efflux decreased exponentially during the first hour and was not altered by changing the oxygen partial pressure ( PO) of the medium. The DOPAC efflux declined after 40 min of superfusion and was modulated by PO. The DA and the DOPAC effluxes were not suppressed by omitting calcium ions from the superfusing medium. In 4 cat CBs equal amounts of DA and NA were recovered from the effluent during the first hour of superfusion. [ABSTRACT FROM AUTHOR]

With the aid of a new three-dimensional mathematical model local flow velocities in the specific carotid body tissue of the cat measured by hydrogen clearances were calculated to have a mean value of 0.006 cm/s at a perfusion pressure of 50 mm Hg, 0.014 cm/s at a perfusion pressure of 120 mm Hg, and 0.018 cm/s at a perfusion pressure of 170 mm Hg. These results indicate that the carotid body specific tissue possesses a distinct flow heterogeneity with normal capillary flow velocities and a high shunt flow. During hypoxia, the smallest decrease in tissue PO was significantly correlated with the highest decrease in flow velocity. This suggests that the carotid body capillary network itself exhibits a PO sensor mechanisms amplifying the chemoreceptive process in the specific cell elements. [ABSTRACT FROM AUTHOR]

The $$P_{O_2 }$$ histogram of the carotid body tissue was calculated on the basis of a microscopical serial reconstruction, published physiological data, and a mathematical model. The calculation was made for glomoid as the subunit of the carotid body and the total organ by varying the following parameters: arterial $$P_{O_2 }$$ , oxygen consumption, hematocrit, diameter of the vessels, perfusion pressure, and capillary length. The results provide explanations for differences in the literature about the tissue $$P_{O_2 }$$ distribution in the cat carotid body. Differences in the capillary length of the carotid bodies seem to be the main reason for different $$P_{O_2 }$$ histograms. Furthermore, it is shown that the local flow velocities in the carotid body are in the range of local flow velocities known from other organs. [ABSTRACT FROM AUTHOR]

Monoamines and their metabolites have been measured by high performance liquid chromatography with electrochemical detection, in control rabbit carotid bodies and under several experimental conditions: 1) at different times (3 h, 6 h, 24 h, 48 h) after intravenous injection of reserpine (5 mg/kg); 2) 14 days after sympathectomy; 3) 14 days after section of the carotid sinus nerve. The results were analyzed with probability plotting methods. Dopamine was the most important monoamine in the carotid body (CB) and its variations were very large. It was almost entirely depleted by reserpinization without simultaneous increase in 3,4-dihydroxyphenylacetic acid. Sympathectomy increased dopamine content but did not change noradrenaline content. However data analysis suggested that noradrenaline might be compartmented in two pools: one with a large variance, located in the type I cells was increased after sympathectomy, the other, more constant, located in the sympathetic nerve endings was entirely depleted after sympathectomy. Section of the carotid sinus nerve increased dopamine and noradrenaline and quadrupled the serotonin content of the CB. It is proposed that carotid sinus and sympathetic innervations regulate the monoamine metabolism of the CB. [ABSTRACT FROM AUTHOR]

In the specific tissue of the rabbit carotid body as well as in the connective tissue surrounding the organ, pO distribution was measured with membranecovered needle electrodes (tip diameter 1-2 μm). The histograms resulting from measurements in the specific tissue were shifted to low pO values as compared to other tissues. The oxygen blowing test, i.e. exposure of the carotid boyd to humidified 100% oxygen was employed to decide upon the site of measurement: pO increased when the electrode measured in the surrounding tissue (type 1 response); pO remained stable or slightly decreased when the electrode sampled in the specific carotid body tissue (type 2 response). After the experiment, the electrode track was reconstructed from histological serial sections and the type of reaction was related to the type of tissue. Low pO values were found to prevail in the specific carotid body tissue, which leads to the conclusion that the amount of low pO values determines the degree of chemoreceptor activity. [ABSTRACT FROM AUTHOR]

The possibility that carotid chemoreceptors respond to changes in plasma osmolality was investigated in the cat, perfusing the carotid artery with blood made hyper- or hypo-osmotic and recording chemoreceptor activity from carotid nerve fibers. Blood made hyperosmotic with sucrose or NaCl reduced the chemoreceptor discharge, while hypoosmotic blood increased chemoreceptor activity. The minimal osmolality variation necessary to obtain a detectable frequency change was 3-8% of the control. Frequency changes of 30% of the control were obtained with a 20% variation in osmolality. The frequency variations produced by the osmotic changes lasted as long as the infusion was maintained (up to 15 min). In some instances a rebound was observed when iso-osmotic saline was perfused again. A transient change in frequency and a clear rebound were obtained when blood made hyperosmotic with glycerol was perfused. These effects probably reflect a rapid change in intracellular osmolality due to the free passage of glycerol across cellular membranes. The modifications in chemoreceptor activity consecutive to osmolality variations are the opposite of those observed in isolated and superfused carotid bodies. As it is known that osmolality values affect the smooth muscle of the blood vessels, we conclude that our results are mainly produced by changes in carotid body blood flow due to a direct effect of hyper- and hypo-osmotic solutions on vascular muscle tone. Chemoreceptor excitation during a decrease in blood osmolality may contribute reflexly to the increased vascular resistance observed during acute osmolality reductions in man. [ABSTRACT FROM AUTHOR]

The early ventilatory response to transient hypoxia was examined in the anaesthetized rabbit. In intact spontaneously breathing animals, an increase in tidal volume ( V) with an accompanying slight increase in inspiratory duration ( T) and a decrease in the expiratory duration ( T) was observed. After vagotomy, the ventilatory response was distinguished by a greater increase in V and a significant decrease in T and T. In another group of artificially ventilated rabbits, an increase in inspiratory volume with a simultaneous decrease in breathing frequency was found to involve a smaller reflex increase in phrenic inspiratory discharge after onset of transient hypoxia. These observations suggest that afferents from pulmonary vagal stretch receptors inhibit those from arterial chemoreceptors. [ABSTRACT FROM AUTHOR]

With the aid of potassium-sensitive microclectrodes reinforced by bitumen (tip diameter, 1.5 μm), extracellular potassium activity ([K]) and DC potential were measured in the cat's carotid body. Under normoxic and normocapnic conditions, potassium values of 1-16 mM (mean value 7.2 mM, standard deviation 3.8 mM) and DC potential values of −11 mV to +13 mV were recorded. With hypoxia, [K] increased by between 1 mM and 9 mM; DC potential was reduced by between 0.5 and 3 mV. With hypercapnia, [K] decreased by between 1 mM and 5 mM: changes in DC potential were variable. The results suggest that, during hypoxia, potassium influences the nervous structures in the carotid body whereas this influence is absent during hypercapnia. [ABSTRACT FROM AUTHOR]

In cats anesthetized with chloralose-urethane, the central respiratory chemoreceptors were exposed to mock CSF of pH 7.02, 7.20, or 7.57. The right carotid body was simultaneously stimulated by intracarotid injections of 40, 80, or 160 μg sodium cyanide in 200 μl Ringer solution. The left carotid nerve and, in some animals, both vagosympathetic truncs were dissected. It could be demonstrated the the increase in ventilation produced by application of NaCN to the peripheral chemoreceptors is significantly larger at high than at low mock CSF pH (i.e. at low than at high central stimulus intensity). In vagotomized cats the responses of V and gelai to NaCN similarly depend upon CSF pH; they are somewhat larger, though, than in intact animals. These results are discussed as compared with results reported by different authors. [ABSTRACT FROM AUTHOR]

After perfusion stop a $$P_{{\text{O}}_{\text{2}} } $$ decrease has been measured in the carotid body tissue by means of elastically suspended $$P_{{\text{O}}_{\text{2}} } $$ needle electrodes. With the formula $${\text{U}}_{{\text{O}}_{\text{2}} } = \frac{\alpha }{{760}} \cdot \frac{{\Delta P_{{\text{O}}_{\text{2}} } }}{{\Delta t}} \cdot 10^5 $$ it is possible to calculate the oxygen consumption from this $$P_{{\text{O}}_{\text{2}} } $$ decrease. Our experiments have shown that the oxygen consumption of the non-perfused carotid body of the cat depends linearly on local $$P_{{\text{O}}_{\text{2}} } $$ . The $$\frac{{\Delta P_{{\text{O}}_{\text{2}} } }}{{\Delta t}}$$ measured in situ (Krebs-Henseleit perfusion) is with 6 Torr/s at a tissue $$P_{{\text{O}}_{\text{2}} } $$ of 100 Torr (37° C) two times higher than the values measured in vitro (Krebs-Henseleit-perfusion). The $$\frac{{\Delta P_{{\text{O}}_{\text{2}} } }}{{\Delta t}}$$ in vivo corresponds to an oxygen consumption of 1.2 ml O/100 g min at a $$P_{{\text{O}}_{\text{2}} } $$ of 100 Torr at 37° C. The $$P_{{\text{O}}_{\text{2}} } $$ dependence of the oxygen consumption of the carotid body might be caused by a special oxidase which may be involved in the chemoreceptive process. [ABSTRACT FROM AUTHOR]

Local $$\frac{{\Delta P_{O_2 } }}{{\Delta t}}$$ in the carotid body after perfusion stop depends on the oxygen consumption of the tissue and the apparent O solubility coefficient α of the blood. Oxygen consumption of the carotid body tissue can be determined by measuring the local $$\frac{{\Delta P_{O_2 } }}{{\Delta t}}$$ with $$P_{O_2 } $$ needle electrodes after Krebs-Henseleit perfusion. Assuming the same $$\frac{{\Delta P_{O_2 } }}{{\Delta t}}$$ for the blood-perfused carotid body the actual $$P_{O_2 } $$ decrease can be used to estimate the hemoglobin content of the tissue. The influence of hemoglobin is described by the factor α/α. Control values measured in the Krebs-Henseleit-perfused carotid body yielded values of α/α = 0.8 −3. In a series of 11 blood-perfused carotid body preparations with 105 perfusion stops the quotient α/α changed with arterial $$P_{O_2 } $$ values higher than 100 Torr α/α was between 0.8 and 2. This value thus was in the same range as the control values. Below 100 Torr higher values up to 11 were observed. Since a blood-perfused tissue (15 g % Hb) would have an α/α of about 128, we conclude that the carotid body is mainly perfused by plasma, and that with decreasing arterial $$P_{O_2 } $$ more red cells flowed through the carotid body. [ABSTRACT FROM AUTHOR]

The oxygen consumption of the isolated carotid body tissue measured in microchambers (volumes 12 and 20 μl) was 0.0051 μl O/mg wet weight min for an average of 54 measurements at 22±1°C, if the calculation was based on the oxygen pressure decrease of the surrounding medium measured polarographically in the range from 120 to 50 torr. It is bound to the presence of exogenous substrate and almost completely inhibited by antimycin but not significantly altered by addition of EGTA (4-16 mM) or Ca (2mM). Measurements performed at higher oxygen pressures (300 to 100 torr) in the medium show that the oxygen consumption of isolated carotid body tissue is independent of oxygen pressure at these high oxygen pressures. The findings obtained under the above conditions argue in favor of a mitochondrial oxygen consumption. The results are discussed with regard to data obtained with needle electrodes in the perfused organ. [ABSTRACT FROM AUTHOR]

The relationship between $$P_{GO_2 }$$ , $$P_{aO_2 }$$ , local blood flow, and the activity of individual chemoreceptor fiber units of the cat's carotid body was studied during changes in the arterial oxygen partial pressure and the arterial systemic blood pressure. The following results were obtained: [ABSTRACT FROM AUTHOR]

Catecholamines have been implicated in neuromodulation of peripheral chemosensitivity and central respiratory mechanisms. Because glucocorticoids can affect catecholamine metabolism in the carotid body and brainstem, this study explored the possibility that, in rats, dexamethasone or adrenalectomy affects catecholamine biosynthesis in carotid body chemoreceptors and the medullary areas (A2C2, A5, A6, A7) involved in the chemoreflex pathway and the hypoxic ventilatory response (HVR). One dexamethasone injection (1 mg/kg body wt.) stimulated tyrosine hydroxylase activity in the carotid body and had no effect in brainstem catecholamine areas, while HVR was reduced. Chronic dexamethasone (1 mg/kg body wt. daily for 10 days) had a stimulatory influence on tyrosine hydroxylase activity in the carotid body and an inhibitory effect on A2C2, A5 and A7 cell groups. Breathing pattern, but not HVR, was altered. Adrenalectomy elicited an increase in tyrosine hydroxylase activity in A2C2, which was accompanied by a decreased respiratory frequency in hypoxia. The data show that glucocorticoids have differential effects on catecholamine biosynthesis in peripheral and central structures involved in the chemoreflex pathway. Depending on the treatment, the neurochemical changes were accompanied by alterations of HVR or the breathing pattern, which are consistent with a neuromodulating influence of catecholamines on peripheral chemosensory inputs or the central respiratory network. [ABSTRACT FROM AUTHOR]

Intracellular pH (pHi) was measured in enzymically isolated, neonatal rat carotid body type-1 cells, using the fluorophore carboxy-SNARF-1 (AM-loaded), and using the nigericin technique for in situ fluorescence calibration (nigericin is a membrane-soluble K+-H+ exchanger). In CO2/HCO3 –-free media, inhibiting Na+-H+ exchange produced a prompt fall of pHi (background acid-loading), the rate of which was reduced by raising the extracellular K+ concentration, [K+]o. pHi recovery from an intracellular acid or alkali load was also sensitive to changes of [K+]o. These results are similar to those of Wilding et al. (J Gen Physiol 100:593–608, 1992), who proposed the existence of an acid-loading, K+-H+ exchanger (KHE) in the type-1 cell. However, when nigericin was not used for post-experimental calibration, and the superfusion system was flushed exhaustively with strong detergent, alcohol and distilled water, then background acid-loading was attenuated, and the K+ o sensitivity restored, when cells were monitored in a superfusion system which had previously been exposed to a single nigericin-calibration protocol (followed by a short system wash with strong detergent and distilled water). We conclude that the previously reported expression of KHE in carotid body type-1 cells is an artefact caused by nigericin contamination. We have therefore quantified the pHi insignificant. Background loading was increased again, and K+ o sensitivity restored, when cells were monitored in a superfusion system which had previously been exposed to a single nigericin-calibration protocol (followed by a short system wash with strong detergent and distilled water). We conclude that the previously reported expression of KHE in carotid body type-1 cells is an artefact caused by nigericin contamination. We have therefore quantified the pHi dependence of background loading in uncontaminated type-1 cells. We consider the possible implications of our work for reports of KHE in other cell types. [ABSTRACT FROM AUTHOR]

In the absence of pulmonary disease, hypoventilation is considered to be the primary cause of Chronic Mountain Sickness, and there is some reason to believe that chronic administration of respiratory analeptics could be useful for treatment of this disease. The present study was intended to define comparatively the influence of two potent ventilatory stimulants, namely a combination of progesterone and estrogen and the pharmacological agent almitrine, on catecholaminergic structures implicated in the chemoreflex pathway and on hypoxia-induced polycythemia. Three groups of young male rats born and living at high altitude (3 600 m) were examined: untreated animals ( n = 25), rats given ovarian steroids (progesterone plus 17β-estradiol, n = 25) or almitrine ( n = 25) for 6 weeks until sacrifice. Ovarian steroids or almitrine had pronounced neurochemical effects on the afferent chemoreflex circuitry. Both treatments inhibited norepinephrine (NE) and dopamine (DA) turnover in the carotid body, but central processing of chemosensory inputs differed between the two respiratory drugs. Ovarian steroids inhibited noradrenergic activity in the projection area of the chemosensory nerve fibers within the caudal portion (A2C) of the nucleus tractus solitarius (NTS). In contrast, almitrine stimulated neurochemical activity of other brainstem noradrenergic cell groups involved in cardiorespiratory control, i.e., the rostral portion (A2R) of the NTS, the nucleus reticularis lateralis (A1), the nucleus olivaris superior (A5) and the locus ceruleus (A6). Although both treatments increased chemoreflex drive and ventilation, only sex hormones decreased erythropoietin (EPO) levels and the degree of polycythemia. These results suggest that stimulation of ventilation through activation of peripheral arterial chemoreceptors activation alone is not sufficient for reducing EPO levels and polycythemia. The better efficiency of female sex hormone treatment as compared to almitrine could be related either to the central effects of progesterone and estrogen and/or to the impact of these hormones on erythropoiesis at the kidney/bone marrow level. [ABSTRACT FROM AUTHOR]

Mechanisms underlying sex-related differences in adaptation to high altitude were investigated by assessing the turnover of dopamine and noradrenaline in structures of the chemoafferent pathway, i.e. carotid body and brainstem noradrenergic cell groups (A1, A5, A6, A2 to which chemosensory fibres project). The influence of gender was assessed in male and female rats reared at an altitude of 3600 m, whereas the influence of endogenous sex hormones was evaluated by castration. Haematocrit, red blood cell count and plasma erythropoietin levels were lower in females than in males (–5%, –15%, –53%, respectively). Dopamine and noradrenaline turnover were higher in female structures (carotid body: +51%; A2: +140%; A1: +54%; A5: +27%). Dopamine and noradrenaline turnover in carotid body and brainstem cell groups were differently affected by castration, i.e. enhanced by orchidectomy (carotid body: +134%; A2: +120%; A1: +69%; A5: +67%) but inhibited by ovariectomy (carotid body: –33%; A2: –92%). Orchidectomy elicited a reduction in haematocrit (–10%), haemoglobin concentration (–8%) and red blood cell count (–24%), whereas haematological status remained unaltered after ovariectomy. Therefore, both gender and endogenous sex steroids may control catecholamine activity differently in structures involved in the chemoafferent pathway, thus providing a neurochemical basis for sex-related differences in adaptation to hypoxia. [ABSTRACT FROM AUTHOR]

Whole-cell patch-clamp recordings were used to evaluate the effects of the cyclic nucleotides adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) on ionic currents in type I carotid body cells isolated from rat pups, and to investigate whether cyclic nucleotides are involved in Kcurrent inhibition by hypoxia. In the presence of 500 μM isobutylmethylxanthine, currents were not significantly modified by 8-bromo-cAMP (2 mM), dibutyryl-cAMP (5 mM) or 8-bromo-cGMP (2 mM). Currents were also unaffected by the phosphodiesterase (PDE)-resistant protein kinase A activators Sp-cyclic adenosine-3′,5′-monophosphorothioate (Sp-cAMPS) and Sp-8-bromoadenosine-3′,5′-monophosphorothioate (Sp-8-bromo-cAMPS) (50 μM), or by β-phenyl-1, N-ethenoguanosine-3′,5′-cyclic monophosphate (PET-cGMP) (100 μM) or the nitric oxide donor S-nitroso- N-acetylpenicillamine (SNAP; 500 μM). Cachannel currents were also unaffected by Sp-8-Br-cAMPS, PET-cGMP and SNAP at the same concentrations. In the absence of cyclic nucleotide analogues, hypoxia (P17-23 mmHg) reversibly inhibited Kcurrents. This degree of hypoxic inhibition was not significantly altered by the PDE-resistant protein kinase A inhibitors Rp-cyclic adenosine-3′,5′-monophosphorothioate (Rp-cAMPS) (50 μM) or Rp-8-bromoadenosine-3′,5′-monophosphorothioate (Rp-8-bromo-cAMPS) (200 μM). Similarly, PET-cGMP (100 μM) and SNAP (500 μM) did not alter the degree of inhibition caused by hypoxia. At the same concentrations used in type I cell experiments, Sp-8-bromo-cAMPS, PET-cGMP and SNAP completely relaxed isolated guinea-pig basilar arteries preconstricted with 20 mM K-containing solutions. Our results indicate that cyclic nucleotides alone are not an important factor in the regulation by Otension of Kcurrents in rat type I carotid body cells. [ABSTRACT FROM AUTHOR]

We have investigated the effects of acidic stimuli upon [Ca] in isolated carotid body type I cells from the neonatal rat using indo-1 (AM-loaded). Under normocapnic, non-hypoxic conditions (23 mM HCO, 5% CO in air, pH=7.4), the mean [Ca] for single cells was 102±5.0 nM (SEM, n=55) with 58% of cells showing sporadic [Ca] fluctuations. A hypercapnic acidosis (increase in CO to 10%-20% at constant HCO, pH 7.15-6.85), an isohydric hypercapnia (increase in CO to 10% at constant pH=7.4) and an isocapnic acidosis (pH=7.0, constant CO) all increased [Ca] in single cells and cell clusters. The averaged [Ca] response to both hypercapnic acidosis and isohydric hypercapnia displayed a rapid rise followed by a secondary decline. The averaged [Ca] response to isocapnic acidosis displayed a slower rise and little secondary decline. The rise of [Ca] in response to all the above stimuli can be attributed to no single factor other than to a fall of pH. The hypercapnia-induced rise of [Ca] was almost completely abolished in Ca-free solution, suggesting a role for Ca influx in triggering and/or sustaining the [Ca] response. These results are consistent with a role for type I cell [Ca] in mediating pH/ PCO chemoreception. [ABSTRACT FROM AUTHOR]

We report the use of a new pH-sensitive dualemission fluoroprobe, carboxy-seminaphthorhodafluor-1 (carboxy-SNARF-1) for ratiometric recording of intracellular pH (pH) in small isolated cells. The method is illustrated with pH measurement in single type-1 cells (cell diameter ∼10 μm) isolated from the carotid body of the neonatal rat. Carboxy-SNARF-1 is loaded using bath application of the acetoxymethyl ester. When excited at 540 nm, the fluoroprobe gives strong, inversely related emission signals at 590 nm and 640 nm. Stable ratiometric recordings of pH can be achieved from a single cell (pH 8.5-6.5) for up to 50 min. Photobleaching of the probe is minimised by illuminating at relatively low light intensity (50 W xenon lamp with 0.2% transmission neutral density filter). The probe can be calibrated in situ using the nigericin technique and this is in good quantitative agreement with the independent null-point technique (extracellular weak acid/weak base application) of Eisner et al. (1989). This fluoroprobe offers certain advantages over the other commonly used probe for pH 2′,7′-bis-(2-carboxyethyl)-5(and -6)-carboxyfluorescein (BCECF): (i) because of its two strong pH-sensitive peak emissions, SNARF displays a good signal-to-noise ratio for ratiometric recording at low light intensities; (ii) unlike BCECF, the dual emisson of SNARF requires no sequential mechanical switching of excitation filters, thus simplifying the epifluorescence set-up; (iii) because carboxy-SNARF-1 emission signals are at the yellow/red end of the visible spectrum, fluorescent drugs like amiloride, ethyl-isopropyl-amibride (EIPA), 4,4′-diisothiocyanostilbene 2,2′-disulphonic acid (DIDS) and cinnamate analogues do not interfere with the pH recording, even when used at high concentrations. [ABSTRACT FROM AUTHOR]

A technique is described which enables the determination of local blood flow in different points of the carotid body. The blood flow measured in the middle zone of the catorid body at mean blood pressure of 120 to 130 mm Hg was about 2000 ml/100 gxmin and corresponded to the total flow values known thus far. It was found that the flow/g weight decreases from the arterial inflow towards the periphery. Under our experimental conditions no signs of autoregulation could be detected. Under special experimental conditions differnnt flow distributions were observed in the carotid body. [ABSTRACT FROM AUTHOR]

The oxygen consumption of the cat carotid body has been measured in vitro using a confinement method. The oxygen consumption of the organ appears to be very high (1.14 ml STPD·min per gram of dried tissue). The carotid body dry mass (0.044 mg) was much lower than the values found in the literature. The O consumption versus O tension relationship of this small organ shows no critical points as other organs generally do. [ABSTRACT FROM AUTHOR]

In the rabbit carotid body (CB) in vivo, the rate of dopamine metabolism was estimated to 44.4±3.9 (SD) pmol/CB/h from the decrease in dihydroxyphenylacetic acid content after pargyline inhibition of monoamine oxidase. [ABSTRACT FROM AUTHOR]