Suction Pipette Research Articles

High selectivity of calcium channels in single dialysed heart cells of the guinea-pig.

Membrane currents and action potentials were recorded in single ventricular cells obtained from guinea-pig hearts by enzymatic dissociation. Ca2+ channel currents carried by Ba2+ or Ca2+ were recorded with a suction pipette (5-10 microns diameter) for voltage clamp and internal dialysis. Currents through Na+, K+ and non-selective monovalent cation channels were suppressed by suitable holding potentials and external and internal solutions. The dialysis method allowed exchange within minutes of alkali metal cations (e.g. Cs+) and small molecules (e.g. quaternary derivatives of lidocaine and verapamil). Nevertheless, Ca2+ channels remained functional for considerable periods, typically 20 min and sometimes more than 1 h. With Ba2+ outside and Cs+ inside, current flow through Ca2+ channels changed from inward to outward at strongly positive levels beyond a clear-cut reversal potential Erev. Several methods for defining Erev were in close agreement: (1) zero-crossing of leak-subtracted peak current, (2) inversion of time-dependent current changes during channel activation or inactivation, (3) inversion of drug-sensitive current as defined by channel blockers such as Cd2+ or D-600. Erev varied with external Ba2+ or internal Cs+. Erev increased by 29 mV per 10-fold increase in Ba2+. Interpreted with constant-field theory, Erev values correspond to PBa/PCs of approximately 1360. With 5 mM-Ca2+ outside and 151 mM-Cs+ inside, Ca2+ channel current reversed near + 75 mV, corresponding to PCa/PCs approximately 6000. Earlier measurements of Erev (Lee & Tsien, 1982) suggest that PCa/PK greater than 1000. At strongly positive membrane potentials where channel activation is maximal, the Ca2+ channel current-voltage relationship is strongly non-linear, with conductance increasing on either side of an inflexion point near Erev. Activation of inward or outward currents through Ca2+ channels follows a sigmoid time course, as expected if activation were a multi-step process.

Isolation and kinetic analysis of inward currents in neuroblastoma cells

The suction pipette method for combined voltage clamp and intracellular dialysis was applied to isolate the two components of voltage-gated inward current across membranes of NIE-115 neuroblastoma cells. In order to anlayze the kinetic behavior of the Na + and Ca 2+ channels responsible for generating these components, current through K + channels was effectively blocked by substituting impermeant Cs + for internal and external K +. Block was confirmed independently by examining the effects of the application of external tetraethylammonium or Cd 2+; and comparing the time course of Ca 2+ tail currents with the decay of current during a maintained depolarization. Na + currents studied at 8–10°C, developed as a fourth order process giving a maximum e-fold conductance change for a 3 mV depolarization, with half activation occurring at −10 mV. The instantaneous current-voltage relationship was linear. Time constants of the activation parameter ( m) varied from 0.5ms (−50 mV) to 3–4 ms (−10 to −40 mV) at 10°C. Inactivation ( h) was a first order process having a time constant between 4 ms (+10 to +60mV) and 225ms (−60 mV). Steady-state inactivation for Na + channels attained a value of 0.5 at −50 mV. A slow inactivation process, however, also is involved in gating of Na + channels, and has a time course at least two orders of magnitude slower than that for h. The temperature sensitivity of Na + currents was found to be similar to that found for other preparations. Ca 2+ currents were studied at 24–29°C in the presence of internal ethyleneglycolbis-(aminoethylether)-tetra-acetate (EGTA) and an external Ca 2+ concentration of 20 mM. Ca 2+ channel activation could also be described by a fourth order process giving an e-fold conductance change for a 5–6 mV change in potential and the half activation potential of −13 mV. Internal EGTA (20 mM) did not abolish inactivation of Ca 2+ currents and no recovery from inactivation caused by a prepulse could be measured as the prepulse potential approached the null potential for Ca 2+ influx. Time constants of both activation and inactivation of Ca 2+ channels were measured between −20 and +50 mV. Currents through K + channels could be completely eliminated by substitution of K + with Cs +, although a residual non-linear leakage current remained, in addition to currents through the Na + and Ca 2+ channels. Na + channels of these mammalian neuronal cell bodies were found to have kinetics most similar to those of neurons in gastropods, and were much slower than axonal Na + channel kinetics in either mammals or poikilothermic animals, when compared at the same temperature. Measurements of the time course of both Ca 2+ channel inactivation and activation also point to a similarity between mammalian and gastropod neuronal cell bodies. Kinetics of Ca 2+ channels were found to be 20 times slower than those for Na + channels in this preparation when the latter were scaled to the same temperature. This difference explains the generation of the late depolarization phase of the action potential in these cells by Ca 2+ currents. Under the conditions described, inactivation in these cells appears to be primarily a voltagedependent process rather than one dependent on the concentration of intracellular Ca 2+.

Intracellular calcium ions and calcium currents in perfused neurones of the snail, Lymnaea stagnalis.

Neuronal somata of Lymnaea stagnalis were internally perfused and voltage clamped using the suction pipette method. The cells were exposed to internal solutions buffered to various concentrations of Ca2+ while the cytoplasmic Ca2+ activity [( Ca2+]i) was monitored with a Ca2+ -sensitive micro-electrode. [Ca2+]i was usually about 10(-7) M when the cell was perfused with a solution buffered to any level of Ca2+ from 9 X 10(-7) to below 10(-8) M. With internal solutions buffered to 10(-6) M-Ca2+ or greater, [Ca2+]i increased rapidly and overshot the perfusate Ca2+ activity by up to two orders of magnitude. It was thus virtually impossible to hold [Ca2+]i steady at any levels other than about 10(-7) M or 10(-4) M using internal perfusion of simple ionic internal solutions. The excess Ca2+ which caused the overshoot of [Ca2+]i entered the cell from the external solution through Cd2+ -sensitive channels. Cd2+ in the external solution prevented or reversed the overshoot of [Ca2+]i and brought [Ca2+]i to near the perfusate level. ATP added to the internal solution also prevented [Ca2+]i from overshooting the perfusate level during perfusion with high-Ca2+ buffers. By monitoring [Ca2+]i with a Ca2+ -sensitive micro-electrode, we were able to estimate the relationship between [Ca2+]i and the Ca2+ current (ICa) measured under voltage clamp. ICa was completely blocked as [Ca2+]i was raised to 10(-6) M. We believe that the discrepancy between our data and other estimates of the ICa vs. [Ca2+]i relationship using internal perfusion of molluscan nerve cells results from the incorrect assumption that [Ca2+]i is controlled adequately during internal perfusion.

Adhesivity and rigidity of erythrocyte membrane in relation to wheat germ agglutinin binding.

Binding of the plant lectin wheat germ agglutinin (WGA) to erythrocyte membranes causes membrane rigidification. One of our objectives has been to directly measure the effects of WGA binding on membrane rigidity and to relate rigidification to the kinetics and levels of WGA binding. Our other objective has been to measure the strength of adhesion and mechanics of cell separation for erythrocytes bound together by WGA. The erythrocyte membrane rigidity was measured on single cells by micropipette aspiration. The slope of the suction pressure-length data for entry into the pipette provided the measure of the membrane extensional modulus. Data were collected for cells equilibrated with WGA solutions in the range of concentrations of 0.01-10 micrograms/ml. Erythrocyte-erythrocyte adherence properties were studied by micropipette separation of two-cell aggregates. First, a "test" cell was selected from a WGA solution by aspiration into a small micropipette, then transferred to a separate chamber that contained erythrocytes in WGA-free buffer. Here, a second cell was aspirated with another pipette and maneuvered into close proximity of the test cell surface, and adhesive contact was produced. The flaccid cell was separated from the test cell surface in steps at which the force of attachment was derived from the pipette suction pressure and cell geometry. In addition, we measured the time-dependent binding and release of fluorescently labeled WGA to single erythrocytes with a laser microfluorometry system. The results showed that the stiffening of the erythrocyte membrane and binding of fluorescently labeled WGA to the membrane surface followed the same concentration and time dependencies. The threshold concentration for membrane stiffening was at approximately 0.1 microgram/ml where the time course to reach equilibrium was close to 1 h. The maximal stiffening (almost 30-fold over the normal membrane elastic modulus) occurred in concentrations greater than 2 micrograms/ml where the time to reach equilibrium took less than 1 min. The WGA binding also altered the normal elastic membrane behavior into an inelastic, plastic-like response which indicated that mechanical extension of the membrane caused an increase in cross-linking within the surface plane. Similar to the stiffening effect, we observed that the membrane adhesivity of cells equilibrated with WGA solutions greatly increased with concentration greater than 0.1 microgram/ml.(ABSTRACT TRUNCATED AT 400 WORDS)

Internal perfusion studies demonstrating GABA-induced chloride responses in frog primary afferent neurons.

Cl- current in gamma-aminobutyric acid (GABA)-sensitive neurons of the frog dorsal root ganglia was separated from other ionic components (i.e., Na+, Ca2+, and K+ currents) using a suction pipette technique, which allowed internal perfusion and current clamp. The GABA-induced depolarization response increased slightly on substituting Na+ by tris(hydroxymethyl)amino-methane+ or Ca2+ by Mg2+ in the external solution. Additional replacement of external and internal K+ with Cs+ further enhanced the GABA response. The GABA response was virtually unaffected when the internal perfusate contained, in addition to 60 mM Cl-, large organic anions such as isethionate-, aspartate-, and citrate- (each 70 mM) as well as aspartate- and GABA (each 35 mM). The reversal potential of GABA-induced Cl- response (EGABA) was equal to Cl- equilibrium potential (ECl) and behaved as a simple Cl- electrode following changes of external and internal Cl- concentrations. These observations indicate the adequacy of internal perfusion. The GABA-induced Cl- response increased in a sigmoidal dose-dependent manner, in which the threshold GABA concentration was around 10(-7) M and the GABA response reached ECl at 10(-4) M. When GABA concentration was higher than 6 X 10(-6) M, the responses were always accompanied by a rapid desensitization.

Separation of ionic currents in the somatic membrane of frog sensory neurons.

Electrical properties of isolated frog primary afferent neurons were examined by suction pipette technique, which combines internal perfusion with current or voltage clamp using a switching circuit with a single electrode. When K+ in the external and internal solutions was totally replaced with Cs+, extremely prolonged Ca spikes, lasting for 5 to 10 sec, and Na spikes, having a short plateau phase of 10 to 15 msec, were observed in Na+-free and Ca2+-free solutions, respectively. Under voltage clamp, Ca2+ current (ICa) appeared at around -30 mV and maximum peak current was elicited at about 0 mV. With increasing test pulses to the positive side, ICa became smaller and flattened but did not reverse. Increases of [Ca]o induced a hyperbolic increase of ICa and also shifted its I-V curve along the voltage axis to the more positive direction. Internal perfusion of F- blocked ICa time-dependently. The Ca channel was permeable to foreign divalent cations in the sequence of ICa greater than IBa greater than ISr much greater than IMn greater than IZn. Organic Ca-blockers equally depressed the divalent cation currents dose- and time-dependently without shifting the I-V relationships, while inorganic blockers suppressed these currents dose-dependently and the inhibition appeared much stronger in the order of IBa = ISr greater than ICa greater than IMn = IZn.

Low resting potentials in single isolated heart cells due to membrane damage by the recording microelectrode

Single myocytes from adult rat hearts were prepared following the method of Powell and co-workers (9, 10, 11). Low resting potentials (Em) could be improved by three techniques. (i) Elevation of Cao to 7.2 mM which, however, mostly resulted in spontaneity and irreversible contracture. (ii) Pre-incubation in a "KB medium" (6). (iii) Use of suction pipettes instead of tapered microelectrodes for intracellular recordings (2). It is concluded that low Em measured previously (11) were due to membrane damage upon microelectrode impalement accompanied by insufficient healing of the membrane around the electrode insertion.

Light-Activated Channels in Limulus Ventral Photoreceptors

We have investigated the light-dependent conductance of the ventral photoreceptor of Limulus by using the patchclamp technique. Our results show that ionic channels open in response to the sensory stimulus in these cells. To prepare the photoreceptors for patch-clamp recording, the glial cells and connective tissue that surround the photoreceptor were removed by teasing them away using a suction pipette (20-,m diam), after treating the preparation with 2% pronase (Calbiochem, La Jolla, CA) for -1 min (1). Although this procedure exposed the photoreceptor membrane (1), further treatment was necessary to obtain good patch recordings from the light-sensitive part of the photoreceptor because of the presence of microvilli on the membrane of this region of the cell (1). We found that mild sonication of the preparation allowed us to obtain patch-clamp recordings from this region, possibly because of alterations in the morphology of the cell surface. The sonication procedure did not, however, cause any obvious alteration in the physiology of the photoreceptor.

Electrophysiological properties of isolated ventricular myocytes.

There is no doubt that major advances have been made in cardiac electrophysiology using single heart cells. Accurate analysis of rapid inward sodium current and the second inward current carried by calcium has resulted in a major re-examination of the steps involved in excitation-contraction coupling in the heart. Future work using glass microelectrodes, suction pipettes and patch pipettes will yield a vast amount of information highly relevant to mechanisms involved in the initiation of the heartbeat.

Effects of various intracellular Ca ion concentrations on the calcium current of guinea-pig single ventricular cells.

The effects of changing the intracellular Ca concentration ([Ca]i) on the calcium current (iCa) were studied in isolated single ventricular cells of the guinea-pig. [Ca]i was varied by an intracellular perfusion technique using a suction pipette. iCa measured from internally perfused cells at a pCa lower than 9.0 was dependent on the extracellular Ca concentration ([Ca]o). Increasing [Ca]o from 1.8 to 5.4 mM increased the amplitude of iCa, and reduction of [Ca]o from 1.8 to 0.01 mM decreased the amplitude. The inactivation time course of iCa became faster as [Ca]o was increased and slower as [Ca]o was reduced. By decreasing the pCa of the internal perfusate from 9.0 to 6.8, the amplitude of iCa was decreased markedly, but no significant change was observed in its time course. Analysis of the I-V curve led to the conclusion that a change in the driving force was not a major factor in the reduction of iCa. The "steady state inactivation" of iCa was measured by a double-pulse method. The amplitude of iCa elicited by the test pulse was smaller at pCa 7.4 than at pCa 9.0 at potentials of between -27 and +33 mV. By normalizing the iCa amplitude, however, the "steady state inactivation" curve in the control and at high [Ca]i overlapped. Similar results were obtained in Sr-Tyrode solution. The degree of "steady state inactivation" of iCa at the potentials positive to +10 mV was larger in Ca-Tyrode than in Sr-Tyrode solution. It is proposed that the reduction in amplitude of iCa at higher [Ca]i is caused by a reduction of the maximum conductance of iCa (gCa) and that Ca ions passing through iCa channels have a remarkable effect on its inactivation.

Effects of a new antiarrhythmic compound SUN 1165 [N-(2,6-dimethylphenyl)-8-pyrrolizidineacetamide hydrochloride] on the sodium currents in isolated single rat ventricular cells.

The effects of a new antiarrhythmic compound, SUN 1165 (which resembles lidocaine in chemical structure) on sodium currents (INa) of enzymatically isolated, single rat ventricle cells were studied under current or voltage clamp conditions. A suction pipette technique was used for current injection and internal perfusion. Potassium currents were blocked by replacing K+ with Cs+ in the internal and external solutions, and calcium current by replacing Ca2+ with Co2+ in the external solution. When cells were stimulated infrequently (less than 1 HZ), SUN 1165 decreased INa without changing the position of the current-voltage curve. The inactivation curve of INa shifted to negative potentials along the voltage axis. The drug also produced an additional use-dependent block of INa, which depended on the frequency of the voltage clamp pulse. The effects of SUN 1165 on INa resemble those of lidocaine, although the relative importance of use-dependent action versus tonic blockade differs from that of lidocaine.

P-232) - Analysis of actions of antiarrhytlimic agents on myocardial electrical activities using an extracellular suction pipette technique

P-232) - Analysis of actions of antiarrhytlimic agents on myocardial electrical activities using an extracellular suction pipette technique

Barbiturates increase the rate of voltage-dependent inactivation of the calcium current in snail neurones.

Effects of barbiturates (thiopentone, pentobarbitone, phenobarbitone and barbitone) on the calcium current (ICa) in identified Helix neurones were studied, using a conventional suction pipette technique. Barbiturates depressed the maximal peak amplitudes (MPA) of ICa in a dose-dependent manner without shifting the current-voltage relationships along the voltage axis. Barbiturates accelerated the decay phase of ICa at high concentrations (1 X 10(-4) to 3 X 10(-3) M), at which concentrations double-pulse experiments showed the increased rate of a voltage-dependent inactivation of ICa. It is concluded that the acceleration of the decay phase of ICa by barbiturates may be due to the increased rate of the voltage-dependent inactivation of ICa.

A description of activation and conduction in calcium channels based on tail and turn-on current measurements in the snail.

Turn-on of Ca currents, or activation, was compared with turn-off, or deactivation. The experiments were done on nerve cell bodies of Helix aspersa separated by dissection, voltage-clamped and internally perfused using a combined suction pipette--micro-electrode method. Ca currents were isolated by suppression of Na and K currents. The turn-off or tail currents were large and fast; this required that the limitations of the voltage clamp be established. A second micro-electrode was inserted to determine temporal and spatial control of potential, and it was found that the cells were essentially equipotential within 60 microsec during the largest tail currents. Series resistance was less than 5 k omega as measured by a small-perturbation, pseudorandom noise-current signal and presented negligible error in the measurements. Activation was complicated by the presence of asymmetry currents which required evaluation. This was done after Co replacement for Ca. The asymmetry currents were sufficiently small for their contribution to the tail currents to be ignored. Addition of Cd to Ca solutions could not be used since relatively large inward tail currents persisted in the presence of Cd. Tail currents were fitted by sums of two or three exponentials; each was sensitive to Ca-channel blockers but only two were due to closure of Ca channels. The two faster components with time constants tau F and tau S, for fast and slow respectively, were produced by brief, 3.0 msec voltage pulses and were present in all cells. The third and slowest component with time constant tau VS, for very slow, activated much more slowly and was not always present. The amplitudes of tau F and tau S were reduced by cooling and were increased when Ca was replaced by Ba extracellularly or when the external Ca concentration was increased. Hence, these components were due to closure of Ca channels. The third component activated faster in Ba solution. When fully activated it had the same amplitude in either Ba or Ca solution despite the differences in amplitude of Ba and Ca currents during the voltage-clamp step. The amplitude of the third component was also not changed by increasing external Ca concentration; hence it was not due to closure of Ca channels. Cooling also had very little effect. The third component was abolished by Ca blockers, but it does not appear to be related to previously described Ca-activated currents.(ABSTRACT TRUNCATED AT 400 WORDS)

Characteristics of manganese current and its comparison with currents carried by other divalent cations in snail soma membranes

Characteristics of currents carried by Mn2+ and other divalent cations were studied in the isolated identified neuron in the circumesophageal ganglia ofHelix aspersa using a suction pipette technique which allows internal perfusion of the cell body and voltage clamp. Increases in [Mn2+]0 induced not only saturation of the peak ofIMn but also shifts theI–V relationships along the voltage axis to the more positive potentials. Internal perfusion with F−, which blocks Ca channels, depressedIMn. Diltiazem, an organic Ca blocker, inhibitedIMn over the entire range of theI–V relation without shifting the threshold and peak voltage of theI–V relation. Co2+, Ni2+, Cd2+ and La3+ also suppressedIMn. Relative maximum peak currents of the divalent cations wereIBa=ISr>ICa>IMn=IZn. Time constants for activation (τm) and inactivation (τh) of these cations were voltage dependent, and both time constants were greater in the sequence ofIMn=IZn>IBa=ISr>ICa over the whole voltage range.

Accelerating effects of pentobarbitone on the inactivation process of the calcium current in Helix neurones.

The effect of pentobarbitone on Ca2+ current (ICa), separated from other ionic currents was studied under voltage clamp using a suction pipette technique in Helix neurones. Pentobarbitone depressed the maximal peak amplitude (MPA) of ICa in a concentration-dependent manner without shifting the current-voltage (I-V) relationships along the voltage axis. Increases in external Ca2+-concentration [( Ca2+]o) overcame the inhibitory action of the agent on MPA. Pentobarbitone markedly accelerated the decay phase of ICa which took a distinctly different time course from that of the control. The accelerating action of the agent on the decay phase of ICa was not overcome by increases in [Ca2+]o. In the presence of internal EGTA (20 mM), pentobarbitone also accelerated the decay of ICa. Changes in pH of the external perfusing solution altered the potency of pentobarbitone in depressing MPA; in the presence of pentobarbitone (3 X 10(-4) M) at pH of 7.0, 8.0 and 9.0, fractional inhibition was approx. 46%, 21% and 4%, respectively. Internal application of pentobarbitone (10(-4)-10(-3) M) inhibited MPA, but exerted no effect on the decay phase of ICa. Pentobarbitone (10(-4) M) markedly accelerated the decrease of MPA of ICa induced by repetitive stimuli applied at an interval of 150 ms, indicating a use-dependent depression of MPA. Results provide evidence that pentobarbitone has a dual action on ICa, inhibiting MPA and accelerating the decay phase of ICa.

Modulation by intracellular ATP and cyclic AMP of the slow inward current in isolated single ventricular cells of the guinea-pig.

Effects of ATP and of cyclic AMP on membrane current systems were investigated in isolated single ventricular cells from guinea-pig hearts by applying the suction electrode method. The intracellular milieu was dialysed with various solutions which were perfused continuously through the suction pipette. The presence of ATP, cyclic AMP and EGTA in the perfusion solution kept the plateau phase of the action potential almost intact for as long as 30 min. With depolarizing voltage-clamp pulses from holding potentials between -30 and -40 mV, the slow inward current (isi) was activated at potentials positive to -20 mV. The inactivation time course of isi was fitted by two exponential components in the potential range between -10 mV and +30 mV. By increasing ATP from 2 to 9.5 mM in the solution, the amplitude of isi was increased and the slow component of inactivation was accelerated. The steady-state current-voltage relationship (I-V curve), exhibited a negative slope that became steeper after increasing the ATP concentration. The current was shifted towards the outward direction between -40 mV and -10 mV and became more inward between -10 mV and +40 mV. Increase of the cyclic AMP concentration from 30 to 60 microM also enhanced the amplitude of isi, but the negative slope in the steady-state I-V curve was unaffected. Assuming that the concentration of free Ca2+ in the cell was well buffered at a low level by the EGTA-Ca buffer solution in the pipette, it was concluded that [ATP]i and [cyclic AMP]i exert a direct influence on membrane current systems of the ventricular cell.

Voltage- and use-dependent effects of lidocaine on sodium current in rat single ventricular cells.

We compared the blocking effects of the local anesthetics, lidocaine and benzocaine, on the sodium current, using single rat ventricular cells to obtain further information about the voltage dependence and kinetics of local anesthetic interaction with cardiac sodium channels. We used a hybrid voltage clamp system which employed a suction pipette for passing current and internal perfusion, and a microelectrode for membrane potential measurement. Lidocaine (20 microM) and benzocaine (100 microM) produced qualitatively similar effects on sodium current when test pulses were applied infrequently. Both of these agents decreased the peak sodium current without producing a shift of the current-voltage curve. They did, however, shift the inactivation curves of sodium current to hyperpolarized potentials; the V0.5 was shifted by -9.5 mV for lidocaine and by -5 mV for benzocaine. Lidocaine produced a significant use-dependent effect that was proportional to the duration of the voltage step. Benzocaine produced only minimal use-dependent effects. The characteristics of the lidocaine block suggest that this agent binds preferentially to inactivated sodium channels and that dissociation from resting channels is voltage-dependent. The differences in lipid solubility and molecular weight between lidocaine and benzocaine may explain the differences in their use-dependent blocking effects on sodium current.

Protons block the dark current of isolated retinal rods.

Membrane currents of isolated frog rods were recorded with the suction pipette technique and tested by perfusion techniques for their sensitivity to H+. The following facts have been established. (i) Increased [H+] suppresses the Na+ conductance of the outer segment rapidly and reversibly. (ii) H+ acts in the rod interior. (iii) The [H+] necessary to cause a 50% decrement in Na+ conductance is inversely related to the [Ca2+] over 5 orders of magnitude. (iv) The sensitivity to H+ and the sensitivity to light, as a function of [Ca2+], have the same slope. Thus, H+ act like light in effecting membrane current suppression but behave as if their effect is mediated through Ca2+. Based on these results and properties of rod disk membrane phosphodiesterase, we propose that protons produced in the light-activated hydrolysis of cGMP liberate Ca2+ from the disks by ion exchange.

Analysis of actions of antiarrhythmic agents on electrical activity of ischemic myocardium in situ.

To study actions of antiarrhythmic agents on electrical activities of ischemic myocardium in situ, we have developed two methods; 1) transplanted cardiac cells into the renal capsular space examined by microelectrode techniques in the rat and 2) ischemia of myocardium examined by suction pipette techniques in the dog. The cardiac transplant showed normal resting and action potentials(AP). One-2 min after ligation of the renal artery of the host rat, APs with the prolonged duration and decreased rate of rise were recorded, and then the cardiac cells were markedly depolarized. APs spontaneously occurring or electrically evoked ceased within 20 min after the ligation. Topical application of TTX abolished the APs with low amplitude and short duration induced by ischemia, but verapamil (1-10 μM) did not. Myocardial electrical activity (MEA) recorded using a suction pipette showed close resemblance to intracellular APs. After coronary ligation, the ischemic myocardium initiated MEA with the low amplitude, decreased rate of rise and short duration. Lidocaine depressed the MEA and prolonged the conduction time, but verapamil did not. Results suggest that the abortive APs may be initiated mainly by the sodium current.