Abstract

Using standard microelectrode techniques, we studied the electrophysiologic effects of dopamine on sheep cardiac Purkinje fibers. Dopamine had no significant effect on the relation between transmembrane potential and maximum velocity of the upstroke of the action potential. Dopamine slightly increased or had no effect on conduction velocity. Dopamine had a consistently positive chronotropic effect and increased the slope of spontaneous diastolic depolarization. These effects were greatly reduced by propranolol and practolol suggesting that the effect of dopamine is mediated via beta adrenergic receptors. Maximum diastolic potential was slightly increased in the presence of dopamine. Threshold potential and current were apparently unchanged under the influence of dopamine. Action potential duration was decreased and the initial level of the plateau was shifted to slightly more positive values after brief exposure to dopamine. Prolonged exposure increased the action potential duration. Experiments with tyramine and cocaine indicate that the effect of dopamine does not require the release of endogenous catecholamines. The time course of dopamine effect as well as the dose-response relation suggest that dopamine, rather than some metabolic derivative, exerts the effects observed. The electrophysiologic effects of dopamine are similar to those reported for other catecholamines although its biphasic effect on action potential duration is unusual.