Caffeine‐induced inhibition of calcium channel current in cultured smooth muscle cells from pregnant rat myometrium

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Abstract
1 The inhibitory effect of caffeine on the calcium channel current was investigated in cultured myometrial cells isolated from pregnant rats. 2 Caffeine inhibited the calcium channel current elicited from a holding potential of — 70 mV in a concentration-dependent manner. The IC50 was estimated to be 35 mM. 3 The caffeine inhibition was not enhanced when calcium channels were opened by a conditioning depolarizing pulse sequence or when the number of inactivated calcium channels was increased at depolarized holding potentials. 4 Caffeine antagonized the specific binding of (+)-[3H]-isradipine to myometrial membranes. The IC50 value found in binding experiments was similar to the IC50 value for half-maximal inhibition of calcium channel current. Caffeine decreased the maximal binding capacity of (+)-[3H]-isradipine to myometrial membranes without any significant change in the dissociation constant. 5 The results indicate that caffeine interacts with a site closely associated with the voltage-dependent calcium channels in myometrial cells and, in turn, inhibits calcium influx.

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