[Effect of parathyroid hormone on the myocardium in the presence of ouabain-induced reduced membrane ATPase activity].

The effect of parathyroid hormone (PTH) on the action potential of myocardium cells under conditions of the oubain--reduced activity of transport ATPase tells in reduced duration of the plateau and in increased amplitude of evoked potentials. The form of the AP alters on administration of the hormone against the background of expressed activity of the cardiac glycoside. The increase in the AP amplitude and the appearance of the "peak"preseding the plateau phase due to the hormone administration seem to be entailed by an action of the hormone upon the transport of sodium ions and activity of the membrane Na, K--dependent ATPase. The effect of PTH upon the contractile activity of the myocardium cells under the oubain influence becomes inverse: instead of a decrease in the contractions amplitude the hormone administration entails an elongation of the "therapeutic" phase of oubain action. The elongation also occurs after a preliminary work of the myocardium strip in the PTH solution. The effect seems to follow the increase of amount of calcium in the cell under the hormone effect.