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Multielectrode arrays (MEA) are used extensively for basic and applied electrophysiological research of neuronal- and cardiomyocyte-networks. Whereas immense progress has been made in realizing sophisticated MEA platforms of thousands of addressable, high-density, small diameter, low impedance sensors, the quality of the interfaces formed between excitable cells and classical planar sensor has not improved. As a consequence in vitro and in vivo MEA are “blind” to the rich and important “landscape” of sub-threshold synaptic potentials generated by individual neurons. Disregarding this essential fraction of network signaling repertoire has become the standard and almost the “scientific ideology” of MEA users. To overcome the inherent limitations of substrate integrated planar MEA platforms that only record extracellular field potentials, a number of laboratories have developed in vitro MEA for intracellular recordings. Most of these novel devices use vertical nano-rods or nano-wires that penetrate the plasma membrane of cultured cells and record the electrophysiological signaling in a manner similar to sharp intracellular microelectrodes. In parallel, our laboratory began to develop a bioinspired approach in-which cell biological energy resources are harnessed to self-force a cell into intimate contact with extracellular gold mushroom-shaped microelectrodes to record attenuated synaptic- and action-potentials with characteristic features of intracellular recordings. Here we describe some of the experiments that helped evolve the approach and elaborate on the biophysical principles that make it possible to record intracellular potentials by an array of extracellular electrode. We illustrate the qualities and limitations of the method and discuss prospects for further improvement of this technology.

Non-technical summary What is known about gastric electrophysiology and used in motility clinics throughout the world is mostly deduced from animal studies and extracellular recordings from human patients. Extracellular recording from gastrointestinal muscles, however, is prone to extensive motion artifact, and it is not clear that animal models can be translated directly to human physiology. Therefore, we have performed a detailed analysis of electrical activity from carefully mapped specimens of gastric muscle removed from humans during surgery for gastric cancers. Our data show several important differences in electrical activity recorded with intracellular microelectrodes and accepted gastric electrophysiological dogma. We observed ongoing electrical slow wave activity in the gastric fundus; we also found no evidence for a slow wave frequency gradient. Muscles from all regions through the thickness of the muscularis demonstrated intrinsic pacemaker activity, and this corresponded with the widespread distribution of pacemaker cells.

Cardiological research greatly rely on the use of cultured primary cardiomyocytes (CMs). The prime methodology to assess CM network electrophysiology is based on the use of extracellular recordings by substrate-integrated planar Micro-Electrode Arrays (MEAs). Whereas this methodology permits simultaneous, long-term monitoring of the CM electrical activity, it limits the information to extracellular field potentials (FPs). The alternative method of intracellular action potentials (APs) recordings by sharp- or patch-microelectrodes is limited to a single cell at a time. Here, we began to merge the advantages of planar MEA and intracellular microelectrodes. To that end we cultured rat CM on micrometer size protruding gold mushroom-shaped microelectrode (gMμEs) arrays. Cultured CMs engulf the gMμE permitting FPs recordings from individual cells. Local electroporation of a CM converts the extracellular recording configuration to attenuated intracellular APs with shape and duration similar to those recorded intracellularly. The procedure enables to simultaneously record APs from an unlimited number of CMs. The electroporated membrane spontaneously recovers. This allows for repeated recordings from the same CM a number of times (>8) for over 10 days. The further development of CM-gMμE configuration opens up new venues for basic and applied biomedical research.

1. Intracellular microelectrodes were used to identify three major electrophysiological categories of neurone in both the internal and external submucous plexuses of the porcine small intestine. 2. Two classes of neurone with a long-lasting after-hyperpolarization following their action potential were differentiated by the presence or absence of fast excitatory synaptic inputs (EPSPs) and were termed AH neurones. S neurones received fast EPSPs but did not display after-hyperpolarizations. 3. The mean resting membrane potentials of the three groups of neurones showed a similar trend in both plexuses, with significantly higher values for the two populations of AH neurone than for S neurones. No significant variation of input resistance with cell type was detected. Neuronal input resistance was significantly greater in the internal submucous plexus than in the external submucous plexus. 4. Over 80% of AH neurones in the internal submucous plexus displayed fast EPSPs but a similar percentage of AH neurones in the external submucous plexus did not show fast EPSPs. S neurones constituted 60% of cells studied in the internal submucous plexus but less than 30% of the cell population in the external submucous plexus. 5. This study of porcine submucous neurones has revealed both similarities and differences to previous work in the guinea-pig small intestine. The most contrasting features are the relative abundance and subclassification of AH neurones in the pig in addition to the apparent paucity of slow synaptic potentials. The differences in the neuronal profiles of the internal and external submucous plexuses may reflect a differentiation of function between the two enteric nerve networks.

The effects of lindane, a gamma-isomer of hexachlorocyclohexane, were studied on transmembrane potentials and currents of frog atrial heart muscle using intracellular microelectrodes and the whole cell voltage-clamp technique. Lindane (0.34 microM to 6.8 microM) dose-dependently shortened the action potential duration (APD). Under voltage-clamp conditions, lindane (1.7 microM) increased the amplitude of the outward current (Iout) which developed in Ringer solution containing TTX (0.6 microM), Cd2+ (1 mM) and TEA (10 mM). The lindane-increased Iout was not sensitive to Sr2+ (5 mM). It was blocked by subsequent addition of quinidine (0.5 mM) or E-4031 (1 microM). E-4031 lengthened the APD; it prevented or blocked the lindane-induced APD shortening. In conclusion, our data revealed that lindane increased the quinidine and E-4031-sensitive rapid delayed outward K+ current which contributed to the AP repolarization in frog atrial muscle.

In the following, an attempt will be made to discuss the role of the K+ conductive pathway in the nephron. The aim of Table 1 is to give a systematic summary of what is known about K+-conductive pathways along the nephron. This table provides references to pertinent experimental work. In addition, this table clearly documents that a K+ conductive pathway is present in most, if not all cells of the different nephron segments; its functional role, however, may be quite different. Rather than giving a systematic overview, the present text seeks to provide new insights into the functional role of the K+-conductive pathways in several segments of the nephron. After an introduction into the two most important methods to examine the conductive properties of the nephron, namely the use of intracellular microelectrodes and the patch clamp technique, we shall focus on three issues: 1) the need for K+ recycling across the basolateral membrane in proximal tubule segments; 2) the specific role of the apical K+-conductance in the diluting segment as a means to recycle K+; and 3) the role of the apical K+-conductance in the collecting tubule for net K+ secretion.

The electrical membrane properties of the marine (brackish-water) ciliate Paramecium calkinsi were investigated under constant-current and voltage-clamp conditions, using two intracellular microelectrodes. The action potential and membrane currents were extremely tolerant to changes in the salinity of the bathing medium. Current-voltage relationships exhibited a moderate inward-going rectification of the membrane upon hyperpolarization, and a prominent outward-going rectification upon depolarization of the membrane. Ion substitution experiments showed that the electrically excitable response is a graded Ca2+-action potential, similar to that found in freshwater ciliates.

The electrophysiological properties of subendocardial Purkinje fibers surviving in myocardial infarcts were studied with intracellular microelectrodes in isolated superfused preparations and correlated with subsequent light and electron microscopic studies. Transmembrane action potentials could always be recorded from one or two cell layers of subendocardial Purkinje fibers in infarcted regions 3 days to 7 weeks after coronary artery occlusion; ventricular muscle action potentials were rarely found. Microscopic studies also demonstrated several layers of intact subendocardial Purkinje fibers; the subjacent ventricular muscle cells were irreversibly injured and replaced by scar. At all time intervals, surviving Purkinje fibers had significantly reduced maximum diastolic potentials, action potential amplitudes, and depolarization velocities as well as prolonged action potential durations. These parameters normalized between 24 hours and 7 weeks after coronary artery occlusion. Surviving Purkinje fibers with electrophysiological abnormalities at 24 hours and 3 days contained vast lipid deposits. Lipid was less prevalent at 10 days when action potential characteristics had improved. By 7 weeks, action potentials were nearly normal and lipid was absent. Subendocardial Purkinje fibers surviving in infarcts are subject to conditions which cause electrophysiological and ultrastructural abnormalities. Persistent abnormalities in the electrophysiological properties of these surviving Purkinje fibers may cause persistent altered electrophysiological properties of the infarcted heart.

The propagation process of the atrial excitation was investigated during ectopic atrial rhythms evoked by electrical pacing through stimulation at several sites in 35 isolated rabbit atria using intracellular microelectrodes. Excitation sequences was correlated with the atrial deflections in a distant bipolar electrogram representing a cranio-caudal atrial activation. The conduction velocity was faster along the crista terminalis but slower across the coronary sinus ostium than in the ordinary atrial muscle. These differences in conduction velocity resulted in the upward artial deflection on the distant bipolar electrogram in the rhythm which was produced by stimulation at the right side of the lower interatrial septum. On a function as a preferential conduction pathway in the case of left to right direction of excitation, as in left atrial rhythm. On stimulation of the postero-inferior region of the left atrium, the region around the coronary sinus ostium was the first area in the right atrium to be activated. Inversely, the impulse originating from the coronary sinus ostium wasconducted relatively fast to the postero-inferior region of the left atrium. These findings suggested that there might be a preferential conduction pathway along the coronary sinus vein or its neighbouring tissues.

Right atria were excised from the hearts of 20 young dogs (15 +/- 5 weeks old) and maintained in vitro in order to perform microelectrode impalements. The atria contracted spontaneously for at least 6 hours at a stable rate of 127/min when they were perfused with Krebs-Ringer bicarbonate solution through the sinus node artery. Cells within a small area near the sinus node artery and between the superior vena cava and right atrium consistently yielded transmembrane potentials typical of pacemaker cells. This area was verified histologically to be the midportion of the sinus node. Electrical characteristics of these sinus node pacemaker cells were: maximum diastolic potential, -56 +/- 7 mV (mean +/- 1 SD); action potential amplitude, 56 +/- 8 mV; overshoot, 0 +/- 2 mV. Smooth transitions from phase 4 to phase 0 were always present. From these experiments we conclude that the excised perfused canine right atrium provides a useful new experimental cardiac preparation because it maintains stable spontaneous activity for many hours in vitro and the sinus node within it is readily accessible for study by intracellular microelectrodes.

1. E.p.s.p.s and terminal potentials (t.p.s) produced by the action of single medial gastrocnemius Ia afferent fibres were examined with intracellular microelectrodes in cat triceps surae motoneurones. 2. Simple terminal potentials (t.p.s) appeared as positive-negative diphasic waves with a single positive peak. Shape indices of excitatory post-synaptic potentials (e.p.s.p.s) recorded in conjunction with simple t.p.s indicate that these e.p.s.p.s were generated at an electrotonically confined compartment on the motoneurone somadendritic membrane. 3. Compound t.p.s. were similar ones, except that they had two or more positive peaks. Shape indices of e.p.s.p.s recorded in conjunction with compound t.p.s indicate that these e.p.s.p.s were generated at two or more electrotonically separate compartments. 4. E.p.s.p. latency and post-synaptic electrotonic delay were determined for a group of single fibre e.p.s.p.s with simple t.p.s. The shortest recorded latency was 0.26 msec. By subtracting estimated electrotonic delay, the shortest synaptic delay obtained for a medial gastrocnemius Ia single fibre e.p.s.p. was 0.17 msec. 5. The finding of a significant synaptic delay supports the hypothesis that the Ia-motoneurone synapse is a chemically mediated synapse.

Experiments were performed on the hearts of open-chest anesthetized dogs and on isolated rabbit hearts. Intracellular microelectrodes and bipolar surface electrodes were used for recording from and for stimulating the atria, AV node, bundle of His, bundle branches and ventricles. Atrial or ventricular premature beats which were usually blocked or delayed within the AV node were facilitated when ectopic activity caused preexcitation and early recovery of the site of block or delay. Ectopic atrial, ventricular, nodal, and bundle of His responses allowed previously blocked or delayed antegrade and retrograde beats to be conducted only when the ectopic activity arrived at an appropriate time at the site of block within the AV node. Therefore, apparent supernormal AV conduction may occur in the human heart by this mechanism, and some reported cases of supernormal conduction may be due to the preexcitation and early recovery of a refractory barrier by ectopic activity.

Electrocardiograms, ventricular monophasic action potentials registered with suction and intracellular microelectrodes, and pressure curves were recorded simultaneously in isolated rabbit hearts perfused with oxygenated Krebs-Henscleit solution containing varying calcium/magnesium ratios. The duration of the action potential and Q-T interval was not affected by low and high magnesium concentrations unless calcium was omitted or significantly reduced. When Mg was completely absent, solutions free of calcium or with one-sixteenth of the "normal" Ca concentration caused a progressive prolongation of the action potential and Q-T interval until they occupied the entire cardiac cycle. When Mg concentration was low (0.075 to 0.6 mM/L.), the prolongation occurred at a slower rate and was less pronounced. With higher Mg concentrations (1.2 to 19.2 mM/L.), the initial lengthening of the action potential and Q-T interval was followed by a gradual shortening. The higher the Mg concentration employed, the shorter was the period of the initial lengthening, and the more pronounced was the subsequent shortening. These observations can be best explained by assuming that calcium-like action of Mg on the plateau of the action potential becomes apparent only when Ca is absent or significantly decreased. The depression of contractility by calcium deficiency proceeded at the same rate at all studied Mg concentrations. The findings are discussed in relation to the electrocardiographic patterns encountered in clinical cal cium and magnesium deficiency.

The preparation was stimulated externally and transmembrane action potentials were recorded with intracellular microelectrodes. The relationship between the area of the first action potential after a pause in stimulation and the duration of the pause was examined. It was found that the area retained its dependence on the pattern of stimulation prior to the pause. These experiments confirm one of the predictions of a mathematical model (Gibbs et al., 1963) which describes the relationship between the area of action potentials and the pattern of stimulation.

Electrophysiologic mapping experiments on the excitation of the A-V node of isolated rabbit heart have been performed with intracellular microelectrodes. An area of tissue showing peculiar physiologic characteristics was shown to coincide, at least in part, with the histologic A-V node and His bundle. Three functional regions have been determined in the physiologic mapping of the A-V node. The middle layer (N) shows signs of decremental conduction and is the site of the slowest propagation velocity in the A-V node. The other layers are transitional regions between the N layer and atrium (AN) or the His bundle (NH). The AN layer shows a progressively slower propagation velocity as the N region is approached. The same holds for the NH region. A precise correlation between these findings and the 3 existent histologic layers remains to be determined. The existence of an area of peculiar tissue just above the A-V valves and encircling the A-V orifice has been confirmed. This area is continuous with the AN layer of the functional A-V node and has been named the atrioventricular ring (AVR) on the assumption that it is a remnant of the embryonic A-V ring. Wenckebach cycles and A-V block of nodal origin are tentatively explained as resulting from increased decrement in the middle nodal layer (N).

SUMMARY Some basic physiological mechanisms which may be involved in epileptic disturbances of brain function have been reviewed with particular reference to temporal lobe automatisms (psychomotor or psychoparetic seizures). Microelectrode studies of the firing patterns of individual neurones, and changes in membrane potential in neurones whose activity has been recorded with intracellular microelectrodes has shown that inactivation by prolonged depolarization, and arrest of discharge by prolonged inhibition are as important as excitatory events in epileptic discharge. Profound alterations in the behaviour of single cells may occur without evidence of high-voltage electrical activity in the usual EEG. Emphasis is placed upon changes in patterns of discharge in response to incoming sensory information which must cause important distortions in information processing by the brain, even during periods between gross overt clinical attacks. Amnesia and irrelevant automatic behaviour does not follow after-discharge in amygdaloid and hippocampal structures in man unless epileptic activity spreads to affect brain stem structures, and unless there is significant change in neo-cortical function. The “activation” pattern which characterizes the EEG over temporal and other cortical regions at the onset of such attacks is associated with striking changes in unitary activity in the temporal neo-cortex of both hemispheres. It is concluded that it is the epileptic “activation paralysis” of limbic and brain stem circuits essential to the consolidation of memories in neo-cortex which are necessarily involved in the typical temporal lobe automatism with amnesia. The importance of William Lennox's views on the neurochemical mechanisms involved in seizures is stressed, particularly in view of the growing evidence that chemical mechanisms are involved in the storage of memory, and certainly in excitatory and inhibitory processes of epileptic discharge. The rapid growth of knowledge in the field of genetically determined metabolic defects, as well as rapid technical advances in neurochemistry, should make it possible to advance our knowledge of the chemistry of seizures much more rapidly than it has been possible in the past. It was suggested that this might be an appropriate major concern of the American Epilepsy Society, as a tribute to William G. Lennox, its founder. RESUME Des mecanismes basaux physiologiques pouvant etre impliques dans des troubles epileptiques de la fonction cerebrale ont ete, en particulier, considered quant aux automatismes du lobe temporal (crises psychomotrices ou psychoparesiques). Des etudes microelectrodiques des “firing patterns” de neurones individuels et des changements du potentiel membraneux dans des neurones dont l'activite a ete enregistree avec des microelectrodes intracellulaires ont montre que l'inactivation par la depolarisation prolongee, et arret de la decharge par l'inhibition prolongee sont aussi importants que des evenements excitatoires dans la decharge epileptique. De profondes alterations du comportement de cellules solitaires peuvent survenir sans qu'il soit certain qu'il y ait une activiteelectrique de haut voltage dans l'EEG habituel. Il est insiste sur des changements se produisant dans des types de decharges en reponse a l'information sensorielle, laquelle doit causer d'importantes alterations dans le proces d'information du cerveau, meme pendant des periodes situees entre des attaques cliniques manifestes. Amnesie et comportement automatique hors de propos ne suivent pas la post-decharge dans des structures amygdaloides et hippocampales humaines a moins qu'une activiteepileptique ne s‘etende jusqu’a affecter des structures du tronc cerebralet a moins qu'il n'y ait un changement significatif de la fonction neocorticale. Le type d‘“activation” qui caracterise l'EEG des regions temporales et autres regions corticales au debut des attaques de ce genre est associea des changements frappants dans l'activite unitaire dans le neocortex temporal des deux hemispheres. La conclusion de ces etudes est que c'est l‘“activation paralytique”epileptique des circuits du limbique et du tronc cerebral, essentiels a la consolidation de la memoire dans le neocortex, qui est necessairement impliquee dans l'automatisme du lobe temporal typique avec l'amnesie. L'importance des apercus de William Lennox sur les mecanismes neurochimiques impliques dans les crises a ete soulignee, en vue specialement de l'evidence croissante de ce que des mecanismes chimiques sont impliques dans la mise en reserve de la memoire et, certainement, dans les proces excitateurs et inhibiteurs de la decharge epileptique. La rapide croissance de nos connaissances dans le domaine des defectuosites metaboliques genetiquement determines, tout comme les rapides progres techniques obtenus dans la neurochimie pourront peut-etre contribuer a augmenter nos apercus de la chimie des crises, bien plus rapidement que dans le passe. L'auteur suggere la possibilite que ceci puisse etre un objet d'interet majeur pour l'American Epilepsy Society en tant que tribut a William G. Lennox, son fondateur.

The electrical activity of macrophages derived from human blood monocytes was recorded in vitro with intracellular microelectrodes and was analyzed with computer-assisted data acquisition and analysis techniques. In cells impaled 6 to 8 days after the cultures were prepared, the resting potentials reached a maximum value of -72 millivolts. The cells were electrically excitable; spikes exhibited a slow upstroke, a fast downstroke, a discrete threshold, a large overshoot, and a brief undershoot. Repetitive firing was induced by a maintained depolarizing current. A positive relation was observed between transmembrane currents and resting potential. Voltage-current relations were nonrectifying for subthreshold current injections. Since these cells had not been treated with any specific activation factors, the electrical activity recorded is evidence for the presence of voltage-dependent inward and outward currents in the membranes of mature macrophages. The electrical signals generated by these cells may be useful for the assay of sensor and effector functions of macrophages, such as chemotaxis, receptor-ligand interactions, and phagocytosis.

Initially dissociated spinal cord and muscle cells derived from chick embryos differentiate sufficiently in tissue culture to form functional synaptic contacts. Spontaneous and evoked potentials recorded with intracellular microelectrodes resemble synaptic responses of adult spinal cord and neuromuscular junctions.

The effects of temperature on the inhibitory junctional potential (i.j.p.) and the electrotonic potential, recorded in the circular smooth muscle of the guinea-pig ileum, were studied with intracellular microelectrodes. The amplitude and time course of the i.j.p. were both dependent on the ambient temperature, the i.j.p. becoming smaller and more prolonged as the temperature was lowered. In contrast, the electrotonic potential was not much affected by temperature. The atropine-resistant 'late' depolarization was also dependent on temperature. These results are consistent with the mechanism of release, of the nonadrenergic noncholinergic inhibitory transmitter, being sensitive to temperature and with the inhibitory conductance change, underlying the i.j.p., being long compared to the membrane time constant of the circular smooth muscle.

The ability of N. flexilis and N. translucens to survive exposure to magnetic fields up to 1.6 T for extended periods of time was tested. Internodal cells subjected to such fields for as long as 72 h showed no evidence of damage. The active response of internodal cells was studied using an especially constructed sample chamber which allowed the use of intracellular microelectrodes. Action potentials in longitudinal and transverse fields as large as 2.0 T appeared identical to those in zero field. The results are in sharp contrast to observations reported by Arajs et al. (1975, Proceedings of the International Conference on Magnetism and Magnetic Materials).

Individually identified neurones are sufficiently large and accessible in grasshopper embryos to permit visualisation and impalement with intracellular microelectrodes from the time of their birth to their maturation. In this article part of the temporal pattern of differentiation from an identified neuroblast (precursor cell) to a group of identified neurones is described.

Intracellular microelectrodes were used to study a cluster of neurosecretory ‘Light Yellow’ Cells (LYC) in the central nervous system of Lymnaea stagnalis. LYC usually have a spontaneous firing pattern of bursts, lasting 10-600 s, alternating with periods of silence. Experiments on isolated single cells showed that the bursting activity has an endogenous origin. Each action potential is followed by a depolarizing afterpotential (DAP), with an amplitude of about 10 mV, lasting several seconds. Bursts end with a subthreshold DAP. It is concluded that two pace-maker mechanisms are responsible for the bursting properties, one initiating and the other (the DAP) maintaining the burst. The relationship between the electrical and the neurosecretory properties of the cells is discussed.

An intense (up to 20 μA/cm 2 ) steady electrical current enters the anterior or nurse cell end of the growing follicle (or oocyte—nurse cell complex) of the Cecropia moth and is balanced by a more diffuse current leaving elsewhere. In late growth stages, the total transfollicular current is about 100 nA. Moreover, a separate small current, of about 1 nA, seems to leave the furrow between the oocyte and the nurse cells. After the nurse cells collapse, but before shell formation, the transfollicular current is redistributed so that a second relatively localized inward current appears at the posterior pole of the follicle. Thus, at this later stage currents enter both poles of the follicle and leave its sides. Previous measurements, with intracellular microelectrodes, seem to imply a very large (order of 1000 nA) back current across the cytoplasmic bridge between the oocyte and nurse cells. A simple model is presented that attributes the apparent bridge current, and the more directly measured transfollicular and furrow currents, to the action of an ion pump lying within the nurse cell face of the furrow membrane.

The effects of catecholamines (adrenaline, noradrenaline and isoproterenol) on ionic conductance changes during the generation of action potentials of bullfrog sympathetic and spinal ganglion cells were studied with intracellular microelectrodes. In sympathetic ganglion cells, adrenaline (3X10(-5)-1X10(-3)M) reversibly decreased the peak amplitude and positive after-potential of action potentials, and prolonged the duration of spike potentials without changes in the resting membrane potential and conductance in the Ringer solution. The maximum rates of rise and fall of spike potentials were also decreased. The action of noradrenaline was similar to that of adrenaline, but isoproterenol did not show any effects. Adrenaline (3X10(-5)-3X10(-4)M) markedly depressed the peak amplitude and maximum rate of rise of both TEA-potential and Ca-potential produced either in TEA solution containing TTX or in the isotonic CaCl2 solution. Similar actions were observed with noradrenaline but not isoproterenol. In spinal ganglion cells, catecholamines did not show any effects of the action potentials in Ringer and TEA solutions. It was concluded that adrenaline inhibited the increases in Ca2+, K+ and Na+ conductances during the generation of action potentials of sympathetic ganglion cells.

The effects of germine monoacetate (GMA) on neuromuscular transmission were studied with intracellular microelectrodes in isolated sciatic nerve-sartorius muscle preparations of the frog (Rana temporaria). In muscle fibers treated with 5 X 10-7 g/ml of d-tubocurarine (dTc) or 5 × 10-6 g/ml of succin

Electrical resistance measurements, made with intracellular microelectrodes on a system consisting of two giant intemodal cells of Nitella translucens joined by a node, show that the specific resistance of the node is 50 times smaller than the specific resistance of the intemodal cell plasmalemma. The node is a complex structure of small cells which separate the intemodal cells by a single layer at the nearest point of approach. Information on the size and distribution of the plasmodesmata in the node, obtained from electron micrographs, suggests that the specific resistance of the node should be smaller than the observed value by a factor of 330. It must therefore be assumed that there is some restriction on the diffusion of ions in the plasmodesmata. The electrical coupling between some internodal cells is sufficient for an action potential in one cell to initiate an action potential in the neighbouring cell.

The sucrose-gap method was adapted to record the action potentials of bullfrog cardiac muscles. The size and configuration of action potentials recorded from atrial or ventricular strips with the sucrose-gap method were similar to those recorded with intracellular microelectrodes. Action potentials could be maintained at a constant amplitude and time-course for up to 3 hours. Furthermore, during recording of action potentials, it was possible to apply DC current to hyperpolarize or depolarize the muscle membrane. Thus the present method in combination with the intracellular microelectrode method will provide valuable information concerning the physiology of cardiac muscle fibers.

1. Using single intracellular microelectrodes in a bridge circuit, the effect of electrotonus on the activity of motoneurons was explored in excised spinal cords of toads.2. A linear relationship was found between the applied current and the changes of the membrane potential, usually within a range of ±2.5 × 10-9 A, which caused shifts of the membrane potential by ±6 to 8 mV. With stronger currents, the rectifying action of the membrane was usually observed.3. The overshoot of the spike antidromically evoked remained almost constant, either when the membrane was depolarized or hyperpolarized to a certain extent. Stronger such polarizations, however, brought about insufficient or over-compensation.4. The effects of electrotonus on the afterpotentials were studied with similar results to those known from other cells.5. The size of PSP's was reduced by depolarization and augmented within a certain range of hyperpolarization. Monosynaptic EPSP was ineffective in evoking motoneuron spikes in the normal state, but sometimes became effective when the membrane had been suitably depolarized.6. With the combined application of two long square pulses, the motoneurons were excited directly under various background polarizations. Depolarized motoneurons showed responses only with short latency and a rather constant threshold depolarization. On the contrary, hyperpolarized motoneurons responded even with long latencies, the spike arising from a level of depolarization which becomes markedly higher with an increase in the latent time. The accommodation of motoneurons is discussed in connection with these findings.

WE have previously reported1 that the application of acetylcholine by perfusion or local injection to different central neurones of the mollusc Aplysia depilans, impaled with intracellular microelectrodes, always produced one of the two following reactions: (a) cells of one type, conventionally designated by us as H-neurones, are hyperpolarized and inhibited by the drug (Fig. 1, H1), and (b) cells of another type, or D-neurones, are depolarized and excited (Fig. 1, D1).

1. With intracellular microelectrodes electric responses of the catfish Mauthner cell to antidromic stimulation were recorded. The responses were composed the parts, namely of brief cell-body responses and long dendritic responses.2. The duration of the cell-body response was 1-1.5 msec. and that of the dendritic response longer than 7 msec.3. Due to this great difference in the spike-duration and the difference in refractoriness between the cell body and the dendrites, multipe responses of the cell body were frequently observed during the course of a single dendritic response.4. The possibility of injuring a neurone by insertion of a microelectrode was stressed.

Aldosterone plays a major role in atrial structural and electrical remodeling, in particular through Ca2+-transient perturbations and shortening of the action potential. The Ca2+-activated non-selective cation channel Transient Receptor Potential Melastatin 4 (TRPM4) participates in atrial action potential. The aim of our study was to elucidate the interactions between aldosterone and TRPM4 in atrial remodeling and arrhythmias susceptibility. Hyperaldosteronemia, combined with a high salt diet, was induced in mice by subcutaneously implanted osmotic pumps during 4 weeks, delivering aldosterone or physiological serum for control animals. The experiments were conducted in wild type animals (Trpm4+/+) as well as Trpm4 knock-out animals (Trpm4-/-). The atrial diameter measured by echocardiography was higher in Trpm4-/- compared to Trpm4+/+ animals, and hyperaldosteronemia-salt produced a dilatation in both groups. Action potentials duration and triggered arrhythmias were measured using intracellular microelectrodes on the isolated left atrium. Hyperaldosteronemia-salt prolong action potential in Trpm4-/- mice but had no effect on Trpm4+/+ mice. In the control group (no aldosterone-salt treatment), no triggered arrythmias were recorded in Trpm4+/+ mice, but a high level was detected in Trpm4-/- mice. Hyperaldosteronemia-salt enhanced the occurrence of arrhythmias (early as well as delayed-afterdepolarization) in Trpm4+/+ mice but decreased it in Trpm4-/- animals. Atrial connexin43 immunolabelling indicated their disorganization at the intercalated disks and a redistribution at the lateral side induced by hyperaldosteronemia-salt but also by Trpm4 disruption. In addition, hyperaldosteronemia-salt produced pronounced atrial endothelial thickening in both groups. Altogether, our results indicated that hyperaldosteronemia-salt and TRPM4 participate in atrial electrical and structural remodeling. It appears that TRPM4 is involved in aldosterone-induced atrial action potential shortening. In addition, TRPM4 may promote aldosterone-induced atrial arrhythmias, however, the underlying mechanisms remain to be explored.

Spontaneous junctional potentials (SJP) in guinea-pig vas deferens were investigated with intracellular microelectrodes. In some of the cells examined, SJP was atropine-sensitive and presumably cholinergic in nature. This finding stands in contrast to the generally accepted concept that all of SJPs in vas deferens are atropine-resistant and noradrenergic in nature. It seems more likely from this result that there exist two types of SJPs in vas deferens; one is noradrenergic type and the other is cholinergic type.