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Although KATP channels have been proposed as playing a role in most types of myocardial damage associated with ischemia/reperfusion, the potential benefits of KATP channel modulators against the biochemical and electrical disturbances observed during ischemia remain unclear. We have thus studied the effects of glibenclamide and cromakalim, KATP channel blocker and opener respectively, on membrane lipid injury and arrhythmias, in a model of ischemic-reperfused guinea-pig myocardium. Ventricular strips were prelabeled with [3H] arachidonic acid, then subjected to normal conditions (Time-related Control) or to simulated ischemic-reperfused conditions in absence of drug (Control) or in presence of glibenclamide 10 microM or cromakalim 10 microM. The release of radioactive compounds was counted by liquid scintillation spectrometry, while action potentials (AP) were recorded with intracellular microelectrodes. Reperfusion induced a significant increase of arachidonic acid release (P0.05 versus Time-related Control). Glibenclamide inhibited the reperfusion-induced arachidonic acid release while cromakalim only delayed it (respectively 483 +/- 87 dpm/g, P0.05 and 790 +/- 143 dpm/g. NS versus 838 +/- 80 dpm/g for Control, after 30 min of reperfusion). Unlike glibenclamide, cromakalim was proarrhythmic during reperfusion (in 100% of preparations versus 33% in Control or in presence of glibenclamide, P0.05). This in vitro study shows that glibenclamide prevented the reperfusion-induced membrane arachidonic acid release, without proarrhythmic effect, whereas cromakalim, associated with proarrhythmicity, was unable to protect myocardium from cell lipid damage.

At present, the prime methodology for studying neuronal circuit-connectivity, physiology and pathology under in vitro or in vivo conditions is by using substrate-integrated microelectrode arrays. Although this methodology permits simultaneous, cell-non-invasive, long-term recordings of extracellular field potentials generated by action potentials, it is 'blind' to subthreshold synaptic potentials generated by single cells. On the other hand, intracellular recordings of the full electrophysiological repertoire (subthreshold synaptic potentials, membrane oscillations and action potentials) are, at present, obtained only by sharp or patch microelectrodes. These, however, are limited to single cells at a time and for short durations. Recently a number of laboratories began to merge the advantages of extracellular microelectrode arrays and intracellular microelectrodes. This Review describes the novel approaches, identifying their strengths and limitations from the point of view of the end users--with the intention to help steer the bioengineering efforts towards the needs of brain-circuit research.

1. Bovine ventricular myocytes isolated according to isenberg and Klockner (1982a) were superfused with Tyrode solution ([Ca]0-3.6 mM, 35°C) and investigated with intracellular microelectrodes. The properties of the action potential (AP) were compared to those published for multicellular ventricular tissue. 2. At 1 Hz stimulation, the AP had 4 clearly discernible phases with a trapezoidal configuration and a duration of 276 ±38 ms. At [Ca]0=1.8 mM the 4 phases were less clear. Following a 1 min rest period, 1 Hz stimulation shortened the AP by 28% ([Ca]0=3.6 mM) or by 12% ([Ca]0=1.8 mM). 3. The AP started with a sodium spike which rose with\(\dot V_{\max }\) of 250±60 V/s to an overshoot of +40±5 mV. The sodium spike was blocked by 60 μM TTX.\(\dot V_{\max }\) was modified with 2s conditioning pre-pulses; the resultingh∞ curve showed half maximal inactivation atV0.5=−65 mV and a slope factork=5.5 mV. Reduction of [Ca]0 to 1.8 mM shiftedh∞ by −5 mV but did not modifyk. However, large shifts inh∞ curves were measured in myocytes depolarized by 20 mM or 0 mM [K]0. 4. Slow AP's were studied when the sodium spike was inactivated by high [K]0 or blocked by TTX. The slow AP's rose with\(\dot V_{\max }\) of 11±5 V/s to a maximum plateau potential of 36±4 mV;\(\dot V_{\max }\) increased up to 24 V/s when the latency was shortened by increased stimulus strength.\(\dot V_{\max }\), plateau and duration were increased by 0.1 μM adrenaline, reduced by 1.8 mM [Ca]0 and blocked by Ni, Co or D600. 5. Changes in [K]0 modified the resting potential (Vm) as discribed in multicellular ventricular tissue.Vmax was −84 ±4 mV at [K]0=5.4 mM and −54±3 mV at [K]0=20 mM; the latter value suggests [K]i=152±8 mM. The increase in [K]0 abolished the sodium spike and shortened the AP, but did not change the maximum plateau potential. In voltage clamp experiments the i-v relation of the repolarizing late outward currents was N-shaped. The sensitivity of these currents to [Cs]0 and [K]0 indicated that the inward rectifying potassium conductance declines with [K]0. 6. The experimental interventions used in the present study changed the AP of the isolated myocyte in a way similar to that reported for multicellular ventricular tissue, i.e. no electrophysiological peculiarity was observed. We conclude that the enzymatic isolation procedure did not significantly alter the properties of the Na-, Ca- or K-channels.

1. Spike propagation across the nonhomogeneous section of the giant axon in ganglion T3 of the cockroach was analyzed by intracellular microelectrodes recording at the posterior and anterior ends of T3. Ascending and descending potentials were evoked by stimulation of A5-A6 and T2-T3 connectives. 2. At high frequencies, descending and ascending impulses exhibit the following: a) consecutive reduction in the spike amplitude, b) a decrease in the afterhyperpolarization; c) gradual appearance of a prepotential together with an increase in delay of spike initiation; d) failure of full spike invasion into the recording area, showing only a decremental potential. 3. The duration of a train required to block spike propagation when the whole connective is stimulated is much shorter (about 6 times) than that required when a single giant axon is stimulated. 4. The conduction block is associated with a marked decrease in effective membrane resistance, greater than that expected from depolarization and delayed rectification. 5. Synaptic potentials could be recorded in the giant axons in the caudal base of ganglion T3 after stimulation of either the ipsilateral or contralateral connectives at both ends of the ganglion. These synaptic potentials could be blocked by d-tubocurarine (d-TC) or low Ca2+-high Mg2+. 6. Activation of these synapses produces a marked increase in membrane conductance, blocking propagation of spike trains through the ganglion. 7. After these synapses are blocked by d-TC or low Ca2+-high Mg2+, high-frequency stimulation still produces a conduction block. 8. It seems that conduction of spike during repetitive stimulation is affected both by accumulation of extracellular potassium, which depolarizes the membrane and causes sodium inactivation, and by activation of synaptic inputs to shunt the membrane in this region. 8. Each of these two mechanisms by itself can produce conduction block along the giant axons in ganglion T3.

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.

(1) Depolarizing after-potentials (DAPs) of hippocampal pyramidal cells were studied with intracellular microelectrodes in rabbits anesthetized with Nembutal and, in addition, curarized. (2) DAPs were classified into two types. One was linearly related in magnitude to the spike and the membrane potential of the cell body while the other was not. Therefore, the former was tentatively called the true DAP and the latter the pseudo-DAP. (3) In accordance with reduction in the membrane potential, the magnitude of the true DAP diminished and at a membrane potential of −60 to −50 mV, the true DAP disappeared. On further reduction in the membrane potential, a hyperpolarization-going dip appeared in place of the true DAP. (4) The pseudo-DAP usually appeared when the membrane potential of the cell body was reduced beyond −60 to −50 mV. But the pseudo-DAP was not quantitatively related to the membrane potential. It was shown that the pseudo-DAP was a nonsynaptic process, and its possible relation to the dendritic spike was discussed. (5) It was demonstrated that it was the pseudo-DAP that led to the genesis of the so-called inactivation response,i.e. a large and prolonged depolarization of the cell membrane with a strong tendency to spike inactivation.

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.

The hearts of 7–12 week old human embryos were investigated by means of intracellular microelectrodes. Average heart rate was 91 beats per minute. The cardiac pacemaker was localized in the sinus venosus. The mean amplitude of action potentials amounted in the pacemaker fibres to 58 mV, in the atrium to 90 mV and in the ventricles to 110 mV. The isolated left auricle exhibits spontaneous activity. The atria are electrically isolated from the ventricles and excitation is conducted by a preferential pathway, most probably by the atrio-ventricular node and bundle.

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.

The effects of the chlorinated hydrocarbon insecticides, DDT and dieldrin, on the electrical activity of skeletal muscle fibres of the clawed toad, Xenopus laevis , were investigated by means of intracellular microelectrodes. Both compounds caused an increase in the amplitude of the negative afterpotential and a slowing-down of the falling phase of the action potential, without affecting the resting potential. Neither DDT nor dieldrin caused repetitive activity. It is concluded that the increase in the duration of the action potential, measured at a potential level of −50 mV, may be responsible for part of the effects of these insecticides on the mechanical response of skeletal muscle.

Kolmodin, G. M. and C. R. Skoglund. Influence of asphyxia on membrane potential level and action potentials of spinal moto- and interneurons. Acta physiol. scand. 1959. 45. 1–18. — Asphyxial changes in spinal moto- and interneurons of decapitate cats were studied by means of intracellular microelectrodes. In both types of neurons the first change in membrane potential was usually observed after about 30 sec in the form of a depolarization of 5–10 mV which after some 30 sec was followed by a phase of more rapidly developing depolarization of larger amplitude; during recovery a phase of increased polarization may be observed. Interneurons showed signs of being more resistant to asphyxia than moto-neurons. The spib potential underwent a. successive diminution in amplitude, at first owing to the decrease in membrane potential value, later also due to a change in spike peak level. During the later stage of asphyxia a decrease of both the rate of rise of the ascending and the rate of decay of the descending spike phases could be demonstrated. Rhythmical interneuron discharges showed periods of increased and decreased frequency before final blocking.

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 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).

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.

Previous studies indicate that cardiac hypertrophy is associated with altered mechanical properties including prolonged contraction times and mechanical refractory periods and exaggerated aftercontractions in isolated rat papillary muscle preparations. The present study was designed to ascertain whether changes in transmembrane potentials accompany the altered mechanical properties. Responses of papillary muscles from hypertrophied hearts of deoxycorticosterone acetate-treated Wistar Kyoto (WKY) rats were compared to those of nonhypertrophied, sham-treated WKYs. Muscles connected to a force transducer in a bathing chamber containing a 27° oxygenated physiological salt solution were subjected to field stimulation and isometric tension measured. Intracellular microelectrodes were used to measure transmembrane potentials of single impaled cells. When compared to nonhypertrophied controls, the hypertrophied preparations had (1) longer action potentials and contraction times, (2) longer electrical and ...

We used intracellular microelectrodes to study the effect of histamine on oscillatory afterpotentials (OAPs). OAPs were induced by exposing cardiac Purkinje fibers to barium (10(-5) M) and to strophanthidin (3 X 10(-7) M). Histamine consistently increased the amplitude of the barium-induced OAPs. Similar results were obtained in strophanthidin-treated preparations: histamine, in fact, was able to increase the OAPs amplitude and eventually to induce triggered activity. The effect of histamine was antagonized by cimetidine (10(-5) M). The possible role of the OAPs in the arrhythmogenic action of histamine is discussed.

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.

THERE is considerable indirect evidence for cyclic AMP as the mediator of the chronotropic effects of adrenaline in heart cells. Adrenaline-like changes in electrical activity have been evoked in cardiac preparations by exposure to inhibitors of cyclic AMP phosphodiesterase1,2 or butyryl cyclic AMP derivatives (refs 2 and 3, but compare ref. 4), which are thought to mimic adrenaline because of their presumed ability to raise intracellular cyclic AMP concentrations. This approach has been widely used5 but the interpretation depends heavily on assumptions as to the mode of action of the particular exogenous compound4. We have approached the problem more directly by examining the electrical effects of iontophoretic injection of cyclic AMP from intracellular microelectrodes in cardiac Purkinje fibres.

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. 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.