Dual action of FRC8653, a novel dihydropyridine derivative, on the Ba2+ current recorded from the rabbit basilar artery.

Actions of FRC8653 on the macroscopic and unitary Ba2+ currents were studied using the rabbit basilar artery. Application of (+/-)-FRC8653 (less than 1 microM) increased the amplitude of the inward current when depolarization pulses more negative than -10 mV were applied but inhibited it when depolarization was more positive than 0 mV (in each case from a holding potential of -80 mV). At a holding potential of -40 mV, (+/-)-FRC8653 (greater than 0.1 nM) consistently inhibited the inward current. (-)-FRC8653 (greater than 1 nM) inhibited the amplitude of the inward current evoked by a depolarizing pulse more positive than -10 mV (the holding potential being -80 mV). At the holding potential of -80 mV, but not at -40 mV, (+)-FRC8653 (1 microM) enhanced the current amplitude evoked by a depolarizing pulse more negative than -10 mV but inhibited the current evoked by a pulse more positive than 0 mV. (+/-)-FRC8653 shifted the voltage-dependent inhibition curves to the left, and the slope of the curve became steeper (test pulse of +10 mV). Two types of single Ca2+ channel currents (12 and 23 pS) were recorded from the basilar artery by the cell-attached patch-clamp method. Opening of the 12-pS channel occurred with a depolarizing pulse (-20 mV) from a holding potential of -80 mV, but not from one of -60 mV. (+)-FRC8653 activated, and (-)-FRC8653 inhibited, the 23-pS channel.(ABSTRACT TRUNCATED AT 250 WORDS)