[Effect of parathyroid hormone on electrical and contractile processes in myocardial cells].

In normal ionic milieau, the parathyroid hormone (PTH) generated a biphasic effect: the initial increase in amplitude and duration of A at the plateau level, and the following decrease in amplitude and duration of AP of the myocardial cells at every level of repolarization. The contractile activity steadily decreased under the PTH effect. The negative inotropic effect of the PTH in its quantitative and temporal aspects was diminished by a preliminary administration of calcitonin. The PTH effect is supposed to be based on an increase in the calcium flow through slow CaNa channels and on Ca binding in intracellular sites of storage.