The effect of mibefradil, known as a T- and L-type Ca
2+ channel antagonist, on the histamine-induced Cl
− current and Ca
2+ entry was investigated in human aortic endothelial cells by the fluorescence measurement of intracellular Ca
2+ concentration ([Ca
2+]
i) combined with the patch clamp method. Mibefradil (10 μM) inhibited both the Cl
− current and Ca
2+ entry in a concentration-dependent manner with an IC
50 value of 4.8 and 2.6 μM for the Cl
− current and [Ca
2+]
i, respectively. These values were comparable to those reported for the inhibition of the T-type Ca
2+ channel and other Cl
− channels. The suppression of Ca
2+ entry is not caused by the inhibition of the Cl
− current and the resulting depolarization since the inhibition was still observed under the voltage clamp condition. These results suggest that mibefradil is a potent blocker not only for the agonist-induced Cl
− current but also Ca
2+ entry channels in vascular endothelial cells.
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