Effects of Altered Calcium Concentrations on AV Conduction and Interactions of Verapamil and Sodium or Calcium

Abstract

In recent years, the importance of slow inward currents in the genesis of transmembrane action potentials of cardiac fibers has been well established as the result of various experimental observations [1–4]. Such slow inward currents are considered responsible for the maintenance of prolonged plateau characteristic of cardiac action potentials, and for the slowly rising action potentials (so-called slow responses) observed in damaged or partially depolarized myocardial fibers. In fibers of the sinoatrial (SA) and atrioventricular (AV) nodes, which physiologically show reduced membrane potentials and typical slow responses, the action potentials are said to depend predominantly on these slow inward currents [5–10]. Since it has been shown that calcium is one major charge carrier through the slow channel [1–4,6,11–15], the effects of altered calcium concentrations on AV conduction were studied in the present series of experiments using isolated hearts of the rabbit.