Cardiac pacemaker potentials at different extra- and intracellular K concentrations

Vassalle, Mario

doi:10.1152/ajplegacy.1965.208.4.770

Cited by 167 publications

(87 citation statements)

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“…When the osmolarity of bathing medium was increased twice or havled, the spontaneous beating was arrested. Since the spontaneous action potential was resumed by the protocol which may reduce the driving force for K+, the result supports the idea proposed by VASSALLE (1965) that an increase in intracellular K + concentration by cell shrinkage will increase K+ efnux in Purkinje fibers.…”

Section: Discussionsupporting

confidence: 85%

Effects of tonicity on the pacemaker activity of guinea-pig sino-atrial node.

Ohba

1986

Jpn.J.Physiol

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Spontaneously beating sino-atrial node (S-A node) of guineapig was superfused with solutions of various osmolarities. The changes in the rate of spontaneous beating and in action potentials were measured. In the solution of normal tonicity, the rate of spontaneous beating was 214±6 beats/min (mean + S.E.) and the maximum rate of rise was 9.7 + 2.5 V/s. When extracellular Na " was reduced by 33%, isotonically replaced with sucrose, the heart rate was reduced to 177±8 beats/min and the maximum rate of rise was reduced to 7.6 ± 1.2 V/s. Decreasing the osmolarity by 30% increased the heart rate by 6% and increasing the osmolarity to 130, 150, and 170% decreased the heart rate to 94, 89, and 73%, respectively, in low Na+ medium. The tonicity dependence of the heart rate was not affected by TTX, atropine, phentolamine, or propranolol. When the tonicity was either increased twice or decreased half, the spontaneous beating stopped. Adding either K + or Rb + of 6 mM to the solution which was two times as hypertonic as the normal, could activate the beating again. Substances inhibiting the potassium conductance such as tetraethylammonium (TEA), 4-aminopyridine (4-AP), and cesium chloride (CsCI) could also reactivate the spontaneity. Although lowering extracellular Cat + concentration could reactivate the spontaneity in the hypertonic medium, increasing Mgt + inhibited the reactivation. The contribution of K + current in the effects of changing osmolarity on the spontaneous beating is discussed.

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Section: Discussionsupporting

confidence: 85%

Effects of tonicity on the pacemaker activity of guinea-pig sino-atrial node.

Ohba

1986

Jpn.J.Physiol

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“…The feature of subthreshold oscillations resembled that of the end-plate potential which is hypothesized to be produced by a large non-selective increase in ion permeability (Fatt & Katz, 1951). According to results obtained from the present study and studies already done, subthreshold oscillations seem to appear in conjunction with a reduction of [K+]o (Vassalle, 1965) when the membrane permeability to K+ is low , and in conjunction with the presence of isoproterenol (West, 1961) and cardiac noradrenaline; but they seem to be depressed by elevation of [Ca2+]0 (West, 1961) and of [K+]o (Vassalle, 1965), by a reduction of [Na+]o, and by the application of endogenous and exogenous acetylcholine (Toda & West, 1967). The amplitude and the rate of subthreshold oscillations produced by Na+-deficiency were increased by sympathetic nerve stimulation.…”

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confidence: 84%

Influence of sodium ions on the membrane potential of the sino‐atrial node in response to sympathetic nerve stimulation

Toda¹

1968

The Journal of Physiology

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SUMMARY1. Sympathetic nerve-atrial preparations isolated from rabbits were used in the present study. Transmembrane potentials were recorded from sino-atrial (S-A) nodal pace-maker fibres.2. A reduction of [Na+]o (extracellular concentration of sodium ions) decreased the maximal diastolic potential, reduced the size of the overshoot, prolonged the depolarization time, increased the rate of early repolarization and decreased the rate of late repolarization.3. A Na+-deficiency markedly augmented the positive chronotropic effect of stimulation of post-ganglionic sympathetic nerves at a frequency of 5/sec but slightly augmented the effect of stimulation at 1 and 20/sec. 4. The marked membrane effect of sympathetic nerve stimulation at low [Na+]o was an increase in the slope of slow depolarization during diastole.Corresponding to an induced acceleration of S-A nodal rate, the 90 % duration of the action potential was decreased but the other action potential parameters measured were not influenced.5. A reduction of [Na+]o to 51 7 mm produced in the pace-maker membrane, subthreshold oscillations the rate and the amplitude of which were increased by sympathetic nerve stimulation until conducted potentials were generated.6. It is presumed that cardiac noradrenaline elicits an increase in the slope of slow depolarization during late diastole which is due to an increase in Na+ permeability, a decrease in K+ permeability or a nonselective increase in ion permeability, but that it does not influence the pace-maker membrane during systole.

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“…Figure 4 shows the relationship between the slope of diastolic depolarization and (K)0. As is well known (17), diastolic depolarization increased as (K)0 was lowered. During the control period, slow diastolic depolarization was observed with (K)0 values of 4 mM or less.…”

Section: Methodssupporting

confidence: 64%

Effect of External Potassium and Acetylstrophanthidin on Conduction Velocity of Isolated Canine Purkinje Fibers

Hashimoto

Moe

1985

Japanese Journal of Pharmacology

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Abstract-Isolatedlong Purkinje fibers were perfused in oxygenated Tyrode's solution.The conduction velocity of action potentials driven from one end of a fiber at cycle lengths of 300 and 1000 msec was measured using silver wire surface electrodes.Action potentials were recorded using glass microelectrodes. Tyrode's solutions of different potassium concentrations were used, and preparations were equilibrated for 10 min. Prior to acetylstrophanthidin, maximum conduction velocities reaching 2.3 m/sec were recorded at (K)0=6 mM. The conduction velocity was not directly proportional to maximum dV/dt or action potential amplitude at (K)0 between 2 and 6 mM; maximum dV/dt and action potential amplitude were greater although conduction velocity was decreased.In this range of (K)0, mem brane excitability may be an important factor. Acetylstrophanthidin (10-7 and 5x10-8 g/ml for slowly and rapidly driven preparations, respectively) increased diastolic depolarization and slowed conduction at (K)0 less than 6 mM, but it did not increase automaticity or decrease conduction at (K)0 over 6 mM. The added effect of high potassium on digitalis-induced slowing of conduction, reported in whole animal experiments, was not observed.

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Cardiac pacemaker potentials at different extra- and intracellular K concentrations

Cited by 167 publications

References 0 publications

Effects of tonicity on the pacemaker activity of guinea-pig sino-atrial node.

Effects of tonicity on the pacemaker activity of guinea-pig sino-atrial node.

Influence of sodium ions on the membrane potential of the sino‐atrial node in response to sympathetic nerve stimulation

Effect of External Potassium and Acetylstrophanthidin on Conduction Velocity of Isolated Canine Purkinje Fibers

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