Mechanism of calcium channel block by D600 in single smooth muscle cells from rabbit ear artery

S Hering, T B Bolton, D J Beech, S P Lim
1989 Circulation Research  
This study investigated the action of the calcium antagonist D600 on calcium channel currents recorded in high barium solution from single, enzymatically isolated smooth muscle cells from the rabbit ear artery using the whole cell configuration of the patch-damp technique. D600 (1-100 fiM) was applied by bath perfusion or by a new technique that allowed a concentration jump during the current. Application of D600 at rest (holding potential, -60 mV) did not alter the peak inward current elicited
more » ... rd current elicited on depolarization, but the activation of the channels led to a marked block and an acceleration of the current decay. The mechanism of block of calcium channels by D600 was studied by using pulse protocols with different pulse length and different interpulse intervals. The results were consistent with the hypothesis that D600 has a low affinity for the caldum channels in the resting state and that they have to pass to the open state before the drug affects the calcium channel current. A fast onset of the calcium channel block by D600 (time constant, msec) could be shown by rapid application of D600 during the sustained current component of the barium inward current. However, experiments did not definitely distinguish whether binding occurred to the open or to the inactivated state (although there was some evidence of a long-lasting binding to an inactivated state). (Circulation Research 1989;64:928-936) U ntil now, the action of D600 has been examined principally in multicellular smooth muscle preparations. According to these studies, 1 there is much evidence that the relaxant effect of this drug is a consequence of inhibition of voltage-dependent calcium channels. Detailed voltage-clamp studies on the action of calcium antagonists on the calcium channels in smooth muscle have been complicated in part by methodological problems of voltage clamp in multicellular preparations and also because of residual outward currents occurring simultaneously with the calcium inward currents. 2 -4 Calcium or barium inward currents in smooth muscle that are similar to calcium currents in heart muscle with respect to voltage dependence and kinetic properties have
doi:10.1161/01.res.64.5.928 pmid:2539923 fatcat:v2xbgi3ztvbgzd2lb73y7if2ia