Inhibitory Action of Mibefradil on T-Type Calcium Channels in Early Embryonic Mouse Ventricular Myocytes

Mibefradil has been reported to preferentially block T-type Ca 2 + channel currents in many different tissues including heart with variable potencies. We recorded T-type Ca 2 + currents (I C a - T ) in early embryonic (9.5day post coitum (dpc)) mouse ventricular myocytes using a whole-cell patch clamp method and studied the effects of mibefradil. I C a - T were inhibited by mibefradil in a concentration-dependent manner with half inhibitory concentration (IC 5 0 ) at 3.4 ′ 0.2 μM. This value is higher than those reported for native adult and neonatal atrial myocytes (0.1-1.5 μM). Factors affecting the mibefradil sensitivity of I C a - T , in particular different subtypes of al subunits, are discussed.