[Blockade of thrombocyte calcium channels by cardiotropic compounds]

The effect of calcium antagonists (verapamil, nicardipine, nifedipine), nitrates (glycerin trinitrate, isosorbide dinitrate and sodium nitroprusside) and of antiarrhythmic drugs (ethmozin, ethacizin) on the increase of platelet Ca2+ concentration brought about by aggregation inductors was studied. All the analyzed substances produced an inhibitory effect on the induction of cellular Ca2+ level increase due to the action of platelet aggregation factor, ADP, vasopressin and endoperoxide PGH2 stable analogue. The degree of this inhibitory effect of calcium antagonists and nitrates was independent of the nature of the stimulator used. Calcium-blocking action of calcium antagonists and nitrates was due to suppression of the entry of Ca2+ into the cells. The action of nitrates on platelets was accompanied by an acceleration of cGMP and cAMP synthesis. Unlike nitrates, antiarrhythmic drugs did not influence the intracellular level of cyclic nucleotides. On the basis of the data obtained it is suggested that calcium-blocking action of different types of compounds can be mediated by different intracellular mechanisms.