Membrane Potentials in Normal, Isolated, Perfused Frog Hearts

1957 ◽  
Vol 190 (2) ◽  
pp. 194-200 ◽  
Author(s):  
Frederick Ware ◽  
A. L. Bennett ◽  
A. R. McIntyre
Keyword(s):  
Action Potential ◽  
Graphical Method ◽  
Membrane Potentials ◽  
Resting Potential ◽  
Perfusion Fluid ◽  
Time Curve ◽  
Oscilloscope Trace ◽  
Average Maximum ◽  
Cathode Follower ◽  
Upstroke Velocity

Intracellular potentials from isolated normal frog hearts were measured in a series of 29 experiments, using microelectrodes of less than 1 micron tip diameter, a cathode follower input, direct coupled amplifier, and photographic registration of an oscilloscope trace. The perfusion fluid was Clark's solution, containing 1.08 mm calcium and 1.88 mm potassium. The average of 485 measurements of the normal resting potential was 84.5 mv. The average of 421 measurements of overshoot was 18.9 mv; and the average of 421 measurements of action potential was 102.5 mv. In eight experiments, including 141 values, the maximum depolarization rate was determined, using a graphical method of analysis. The average maximum upstroke velocity was 33.9 v/sec. The voltage-time curve of the action potential during the repolarization sequence showed considerable variation from fiber to fiber, but in most cases some evidence of a ‘spike’ component was seen.

Effects of ethanol on cellular membrane potentials and contractility of isolated rat atrium

1962 ◽  
Vol 203 (1) ◽  
pp. 194-196 ◽  
Author(s):  
Alvaro L. Gimeno ◽  
Martha F. Gimeno ◽  
J. Leyden Webb
Keyword(s):  
Action Potential ◽  
Direct Action ◽  
Cellular Membrane ◽  
Membrane Potentials ◽  
Resting Potential ◽  
Mechanical Activity ◽  
Characteristic Change ◽  
Electrical Characteristics ◽  
Ectopic Beats ◽  
The Relationship

The simultaneous effects of ethanol on the contractility and electrical characteristics of atrial cells were examined. Single cell membrane potentials were determined using microelectrodes; the mechanical activity was recorded from a sensitive strain gauge. Ethanol at concentrations between 24 and 192 mm (110–880 mg/100 ml) depresses the contractility of the rat atria, the relationship between contractile depression and concentration being essentially linear. The effects are reversible in all cases. A definite shortening of the action potential, simultaneous with the reduction in contractility, is the most characteristic change in the electrical properties. This results from a more rapid rate of repolarization. The magnitude of the action potential is decreased slightly, whereas the resting potential and the depolarization rate are unaffected by ethanol. The depression of the contractility can be partially attributed to the shortening of the action potential but, in addition, there would appear to be some more direct action on the contractile mechanism. The decrease in the duration of the action potential may predispose the atria to dysrhythmias, such as ectopic beats and fibrillation.

Effects of calcium deficiency on cell membrane potentials of isolated frog hearts

1960 ◽  
Vol 198 (3) ◽  
pp. 547-551 ◽  
Author(s):  
F. Ware ◽  
A. L. Bennett ◽  
A. R. McIntyre
Keyword(s):  
Cell Membrane ◽  
Action Potential ◽  
Calcium Deficiency ◽  
Membrane Potentials ◽  
Resting Potential ◽  
Early Repolarization ◽  
Depolarization Rate ◽  
Significant Fall

Membrane potentials were recorded in isolated frog hearts. Observations were made on the effects of calcium deficiency upon resting potential, action potential, overshoot, maximum depolarization rate and action potential contour. Calcium deficiency caused a significant fall in all observed potentials. Maximum depolarization rate was increased. Early repolarization rate was markedly decreased. Chelation of calcium caused changes indistinguishable from those caused by omission of the ion from the perfusate. These results are discussed in relation to current concepts.

Potassium currents contributing to action potential repolarization and the afterhyperpolarization in rat vagal motoneurons

1992 ◽  
Vol 68 (5) ◽  
pp. 1834-1841 ◽  
Author(s):  
P. Sah ◽  
E. M. McLachlan
Keyword(s):  
Action Potential ◽  
Time Constant ◽  
Action Potentials ◽  
Potassium Current ◽  
Outward Current ◽  
Potassium Currents ◽  
Membrane Potentials ◽  
Calcium Currents ◽  
Resting Potential ◽  
Action Potential Repolarization

1. Intracellular recordings were made from neurons in the dorsal motor nucleus of the vagus (DMV) in transverse slices of rat medulla maintained in vitro at 30 degrees C. Neurons had a resting potential of -59.8 +/- 1.4 (SE) mV (n = 39) and input resistance of 293 +/- 23 M omega (n = 44). 2. Depolarization elicited overshooting action potentials that were blocked by tetrodotoxin (TTX; 1 microM). In the presence of TTX, two types of action potentials having low and high thresholds could be elicited. The action potentials were blocked by cobalt (2 mM) indicating they were mediated by calcium currents. 3. Under voltage clamp, depolarization of the cell from membrane potentials negative of the resting potential activated a transient potassium current. This current was selectively blocked by 4-aminopyridine (4-AP) (5 mM) and catechol (5 mM) indicating that it is an A-type current. This current inactivated with a time constant of 420 ms and recovered from inactivation with a time constant of 26 ms. 4. When calcium currents were blocked by cadmium or cobalt, the rate of action potential repolarization was slower. In the presence of tetraethylammonium (TEA; 200-400 microM) or charybdotoxin (CTX; 30 nM) a small "hump" appeared on the repolarizing phase of the action potential that was abolished by addition of cadmium. These results indicate that a calcium-activated potassium current (IC) contributes to action potential repolarization. 5. Actions potentials elicited from hyperpolarized membrane potentials repolarized faster than those elicited from resting membrane potential. This effect could be blocked by catechol, indicating that voltage-dependent potassium currents (IA) can also contribute to action-potential repolarization. In the presence of catechol and calcium channel blockers, action potentials still had a significant early afterhyperpolarization suggesting that another calcium independent outward current is also active during repolarization. This fast afterhyperpolarizations (AHP) was not blocked by TEA. 6. Action potentials were followed by prolonged AHPs, which had two phases. The initial part of the AHP was blocked by apamin (100 nM) indicating that it results from activation of SK type calcium-activated potassium channels. The slow phase was selectively blocked by catechol suggesting that it is due to activation of IA. 7. It is concluded that a TTX-sensitive sodium current and two calcium currents contribute to the action potential in rat DMV neurons. At least three different currents contribute to action-potential repolarization: IC, IA, and a third unidentified calcium-insensitive outward current.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrophysiological properties of cultured adult rat ventricular cardiac muscle cells

1986 ◽  
Vol 250 (5) ◽  
pp. H731-H735
Author(s):  
C. F. Meier ◽  
G. M. Briggs ◽  
W. C. Claycomb
Keyword(s):  
Action Potential ◽  
Cultured Cells ◽  
Resting Potential ◽  
Myocardial Tissue ◽  
Myocardial Cells ◽  
Isolated Cells ◽  
Cardiac Muscle Cells ◽  
Electrophysiological Properties ◽  
Adult Rat ◽  
Average Maximum

Action and resting potential characteristics of isolated adult rat myocardial cells maintained in culture for 10–28 days are described. Resting potentials averaged -76.3 +/- 2 mV in 5 mM extracellular [K+] ([K+]o). Resting potentials changed by 54.3 mV/decade change in [K+]o for concentrations greater than 5 mM. The average maximum rate of rise of action potential (Vmax) was 117.7 +/- 10 V/s with overshoots of 34.6 +/- 2.5 mV. Action potential durations (APD) to 0 and -40 mV and full repolarization were 21.8 +/- 3.9, 36.3 +/- 6.0, and 206 +/- 16.9 ms respectively. Action potential configurations were qualitatively similar to those previously reported by others for rat myocardial tissue or freshly dissociated cells. Tetrodotoxin (4 micrograms/ml) decreased Vmax to less than 24 V/s and decreased overshoot and APD. Isoproterenol (10(-8) M) decreased APD with slight elevation of the overshoot. Verapamil (10(-5) to 10(-4) M) depressed overshoot and plateau while slowing the final phase of repolarization. Verapamil (10(-4) M) depressed upstroke velocity and blocked excitability. While APDs recorded from these cultured cells are apparently longer than those reported by others for rat myocardial APDs, the values of all other electrophysiological parameters recorded are within the limits previously reported for normal rat myocardial tissue. These data indicate that adult rat myocardial cells maintained in tissue culture for 10–28 days possess electrophysiological properties and responses to pharmacological agents similar to adult rat myocardial tissue or undamaged freshly isolated cells.

Effect of high K, low K, and quinidine on QRS duration and ventricular action potential

1962 ◽  
Vol 203 (6) ◽  
pp. 1135-1140 ◽  
Author(s):  
Leonard S. Gettes ◽  
Borys Surawicz ◽  
James C. Shiue
Keyword(s):  
Action Potential ◽  
Resting Potential ◽  
Qrs Complex ◽  
High Potassium ◽  
Conduction Disturbances ◽  
High K ◽  
Low Potassium ◽  
Qrs Duration ◽  
Low K ◽  
Upstroke Velocity

Perfusion of isolated rabbit hearts with high potassium, low potassium, and quinidine solutions caused a diffuse widening of the QRS complex with no change in shape. These QRS changes were correlated with the magnitude and upstroke velocity of the ventricular transmembrane potential. An increase of QRS duration by 132% produced by high K was accompanied by a decrease of the action potential, resting potential, and upstroke velocity. A similar increase in QRS duration produced by quinidine was accompanied by a slow upstroke velocity but no change in magnitude of the action potential or resting potential. An increase of QRS duration by 49% produced by low K was accompanied by an increased action and resting potential, and upstroke velocity. We attributed the QRS changes produced by high K and quinidine, at least partly, to a slow conduction in the ventricle, caused by a slow upstroke velocity of the action potential. The QRS changes produced by low K could be explained by hyperpolarization. Early arrhythmias caused by low K were due to atrioventricular conduction disturbances.

Disopyramide phosphate: is it just another quinidine

1978 ◽  
Vol 56 (2) ◽  
pp. 326-331 ◽  
Author(s):  
Teresa Kus ◽  
Betty I. Sasyniuk
Keyword(s):  
Steady State ◽  
Action Potential ◽  
Membrane Potentials ◽  
Terminal Phase ◽  
Plateau Phase ◽  
Therapeutic Concentration ◽  
Order Of Magnitude ◽  
Maximum Rate Of Rise ◽  
State Curve ◽  
Upstroke Velocity

We compared the effects of a therapeutic concentration of disopyramide with those of quinidine and lidocaine on the action potential characteristics and on the steady-state relationship between membrane potential and the maximum rate of rise of the action potential in the same normal Purkinje fiber in which constant impalement was maintained for more than 7 h. All the drugs depressed the steady-state upstroke velocity in the following order of magnitude: quinidine > disopyramide > lidocaine. Both lidocaine and disopyramide shifted the normalized steady-state curve to more negative membrane potentials indicating a greater depression of upstroke velocity at lower membrane potentials. Quinidine did not shift this curve. Lidocaine abbreviated all phases of repolarization while both disopyramide and quinidine shortened the plateau phase and lengthened the terminal phase of the action potential. The results suggest that the actions of disopyramide on upstroke velocity resemble those of lidocaine, while its effects on action potential duration resemble those of quinidine. The actions of this drug are therefore more complex than previously assumed.

scholarly journals Loading effect of fibroblast-myocyte coupling on resting potential, impulse propagation, and repolarization: insights from a microstructure model

2008 ◽  
Vol 294 (5) ◽  
pp. H2040-H2052 ◽  
Author(s):  
Vincent Jacquemet ◽  
Craig S. Henriquez
Keyword(s):  
Action Potential ◽  
Cardiac Cells ◽  
Resting Potential ◽  
Impulse Propagation ◽  
A Cell ◽  
Microstructure Model ◽  
Potential Impact ◽  
Electrical Connections ◽  
Fibroblast Density ◽  
Upstroke Velocity

The numerous nonmyocytes present within the myocardium may establish electrical connections with myocytes through gap junctions, formed naturally or as a result of a cell therapy. The strength of the coupling and its potential impact on action potential characteristics and conduction are not well understood. This study used computer simulation to investigate the load-induced electrophysiological consequences of the coupling of myocytes with fibroblasts, where the fibroblast resting potential, density, distribution, and coupling strength were varied. Conduction velocity (CV), upstroke velocity, and action potential duration (APD) were analyzed for longitudinal and transverse impulse propagation in a two-dimensional microstructure tissue model, developed to represent a monolayer culture of cardiac cells covered by a layer of fibroblasts. The results show that 1) at weak coupling (<0.25 nS), the myocyte resting potential was elevated, leading to CV up to 5% faster than control; 2) at intermediate coupling, the myocyte resting potential elevation saturated, whereas the current flowing from the myocyte to the fibroblast progressively slowed down both CV and upstroke velocity; 3) at strong couplings (>8 nS), all of the effects saturated; and 4) APD at 90% repolarization was usually prolonged by 0–20 ms (up to 60–80 ms for high fibroblast density and coupling) by the coupling to fibroblasts. The changes in APD depended on the fibroblast resting potential. This complex, coupling-dependent interaction of fibroblast and myocytes also has relevance to the integration of other nonmyocytes in the heart, such as those used in cellular therapies.

scholarly journals EFFECTS OF EXTERNAL IONS ON MEMBRANE POTENTIALS OF A LOBSTER GIANT AXON

1958 ◽  
Vol 41 (3) ◽  
pp. 529-542 ◽  
Author(s):  
John C. Dalton
Keyword(s):  
Action Potential ◽  
Sea Water ◽  
Giant Axon ◽  
Membrane Potentials ◽  
Squid Giant Axon ◽  
Resting Potential ◽  
Magnesium Concentration ◽  
Constant Field ◽  
Order Of Magnitude ◽  
External Calcium

The effects of varying external concentrations of normally occurring cations on membrane potentials in the lobster giant axon have been studied and compared with data presently available from the squid giant axon. A decrease in the external concentration of sodium ions causes a reversible reduction in the amplitude of the action potential and its rate of rise. No effect on the resting potential was detected. The changes are of the same order of magnitude, but greater than would be predicted for an ideal sodium electrode. Increase in external potassium causes a decrease in resting potential, and a decrease in potassium causes an increase in potential. The data so obtained are similar to those which have been reported for the squid giant axon, and cannot be exactly fitted to the Goldman constant field equation. Lowering external calcium below 25 mM causes a reduction in resting and action potentials, and the occasional occurrence of repetitive activity. The decrease in action potential is not solely attributable to a decrease in resting potential. Increase of external calcium from 25 to 50 mM causes no change in transmembrane potentials. Variations of external magnesium concentration between zero and 50 mM had no measurable effect on membrane potentials. These studies on membrane potentials do not indicate a clear choice between the use of sea water and Cole's perfusion solution as the better external medium for studies on lobster nerve.

Transmembrane Activity Gradients of K and cl in the Muscle Fibres of Osmoconforming Marine Decapod Crustaceans

1978 ◽  
Vol 72 (1) ◽  
pp. 127-140
Author(s):  
ROBERT W. FREEL
Keyword(s):  
Sea Water ◽  
Membrane Potentials ◽  
Resting Potential ◽  
Muscle Fibres ◽  
Salinity Adaptation ◽  
Decapod Crustaceans ◽  
Marine Crustaceans ◽  
Equilibrium Distributions

1. The resting membrane potentials (Em) and the transmembrane activity gradients for K and Cl were measured in the muscle fibres of osmoconforming (Callianassa and Cancer) and weakly osmoregulating (Pachygrapsus) marine crustaceans acclimated to various osmotic conditions. 2. The muscle membranes of sea water acclimated crabs behave as good K electrodes. However, a slight contribution of Na to the resting potential was demonstrated in all species. The ratio PNa/PK was about 0.01. Equilibrium potentials (measured with ion-selective microelectrodes) for Cl were equal to Em, while EK was always more negative than Em as a result of the slight Na contribution. 3. Acclimation to dilute or concentrated sea water had little effect on the K electrode properties or Na permeabilities of these fibres. The muscle fibres were depolarized in crabs acclimated to concentrated sea water and were hyperpolarized in crabs adapted to dilute sea water. These changes resulted solely from alterations in (aK)i/ (aK)O which were in turn brought about by changes in cellular and haemolymph hydration. 4. Since the Na contribution to Em was so small in all conditions, it was concluded that the distributions of K and Cl are best considered in terms of Donnan equilibria, and that the cellular K and Cl adjustments observed during salinity adaptation reflect the passive re-establishment of new equilibrium distributions for these ions.

Electrophysiology of the Giant Nerve Cell Bodies of Limnaea Stagnalis (L.) (Gastropoda: Pulmonata)

1974 ◽  
Vol 60 (3) ◽  
pp. 653-671
Author(s):  
D. B. SATTELLE
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Cell Types ◽  
Resting Potential ◽  
Constant Field ◽  
Bathing Medium ◽  
Mean Values ◽  
Relative Contribution ◽  
External Potassium ◽  
Limnaea Stagnalis

1. A mean resting potential of -53.3 (S.D. ±2.7) mV has been obtained for 23 neurones of the parietal and visceral ganglia of Limnaea stagnalis (L.). Changes in the resting potential of between 28 and 43 mV accompany tenfold changes in [K+0]. A modified constant-field equation accounts for the behaviour of most cells over the range of external potassium concentrations from 0-5 to 10.o mM/1. Mean values have been estimated for [K+1, 56.2 (S.D.± 9-0) mM/1 and PNa/PK, 0-117 (S.D.±0-028). 2. Investigations on the ionic basis of action potential generation have revealed two cell types which can be distinguished according to the behaviour of their action potentials in sodium-free Ringer. Sodium-sensitive cells are unable to support action potentials for more than 8-10 min in the absence of sodium. Sodium slopes of between 29 and 37 mV per decade change in [Na+0] have been found for these cells. Tetrodotoxin (5 x 10-5 M) usually blocks action potentials in these neurones. Calcium-free inger produces a marked reduction in the overshoot potential and calcium slopes of about 18 mV per decade change in [Ca2+o] are found. Manganous chloride only partially reduces the action potential overshoot in these cells at concentrations of 10 mM/l. 3. Sodium-insensitive neurones maintain action potentials in the absence of external sodium. Stimulation only slightly reduces the amplitude of the action potential under these conditions and such cells are readily accessible to potassium ions in the bathing medium. A calcium-slope of 29 mV per decade change in [Ca2+o] has been observed in these cells in the absence of external sodium. 4. It is concluded that both sodium and calcium ions can be involved in the generation of the action potential in neurones of Limnaea stagnate, their relative contribution varying in different cells.

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