[Role of fast Na--Ca current channels in effecting parathyroid hormone action].

Under conditions of incomplete tetrodotoxin (TTX) blockade of the fast channels, the parathyroid hormone augmented the AP amplitude, accelerated development of ascending depolarization, and enhanced the AP plateau in the frog myocardium cells. The TTX appears to activate Ca++ transport both in the slow and fast Ca++--Na+ channels which participate in formation of the AP slow phase of ascending depolarization in the frog myocardium cells.