Effects of 5-hydroxytryptamine on intracellular free Ca~(2+) of myocardium

5-HT was found to increase intracellular free Ca~(2+) concentration in a dose-dependent manner. The addition of lacidipine, a dihydropyridine calcium antagonist, to the cells could partly abolish the 5-HT-induced response. Similarly the addition of ryanodine, an regulator of sarcoplasmic reticulum ryanodine receptor, showed the same action on 5-HT-induced response. When extracellular free Ca~(2+) was chelated by EGTA, the increase of free Ca~(2+) stimulated by 5-HT was curtailed significantly. Moreover, cyprohatidine, a 5-HT_(2)R antagonist, could also partly diminish the 5-HT-induced response.