Crocin, a carotenoid component of Crocus sativus L. belonging to the Iridaceae family, has demonstrated cardioprotective effects. To investigate the cellular mechanisms of these cardioprotective effects, here we studied the influence of crocin on L-type Ca(2+)current (ICa-L), intracellular Ca2+ ([Ca2+](i)), and contraction of isolated rat cardiomyocytes by using the whole-cell patch-clamp technique and video-based edge detection and dual excitation fluorescence photomultiplier systems. Crocin inhibited ICa-L in a concentration-dependent manner with the half-maximal inhibitory concentration (IC50) of 45 mu mol/L and the maximal inhibitory effect of 72.195% +/- 1.54%. Neither current-voltage relationship of ICa-L, reversal potential of ICa-L, nor the activation/inactivation of ICa-L was significantly changed. Crocin at 1 mu mol/L reduced cell shortening by 44.64% +/- 2.12% and the peak value of the Ca2+ transient by 23.66% +/- 4.52%. Crocin significantly reduced amplitudes of myocyte shortening and [Ca2+](i) with an increase in the time to reach 10% of the peak (Tp) and a decrease in the time to 10% of the baseline (Tr). Thus, the cardioprotective effects of crocin may be attributed to the attenuation of [Ca2+](i) through the inhibition of ICa-L in rat cardiomyocytes and negative inotropic effects on myocardial contractility.