Hamilton S L, Yatani A, Brush K, Schwartz A, Brown A M
Mol Pharmacol. 1987 Mar;31(3):221-31.
To investigate the mechanism of action of dihydropyridines on calcium channels, both receptor binding and the electrophysiological effects of optically pure enantiomers of Bay k 8644, Sandoz 202-791, nimodipine, and PN200-110 were studied in a guinea pig ventricular preparation. The radioligand binding studies are consistent with other reports that the inhibitory and excitatory dihydropyridines share a single binding site. The patch clamp method was used for recording whole cell calcium currents. (-)-Bay k 8644 and (+)-202-791 produced voltage-dependent increases in the calcium currents. The magnitude of the effect was dependent on the holding potential. At holding potentials between -40 and -90 mV these activators increased calcium currents in a concentration-dependent manner with EC50 values of 25 nM and 80 nM, respectively. The inhibitors (+)-Bay k 8644, (-)-202-791, (+)- and (-)-nimodipine, and (+)-PN200-110 blocked the calcium currents with potencies that depended upon holding potential. The IC50 values for these enantiomers measured at a holding potential of -80 mV were, respectively, 8000, 200, 2000, 450, and 400 nM, and IC50 values measured at a holding potential of -30 mV were 26, 1.0, 52, 4.0, and 4.5 nM. The dissociation constants calculated for some dihydropyridines are similar to the Kd values determined by radioligand binding. However, for other dihydropyridines, large discrepancies between the concentrations giving rise to half-maximal electrophysiological effects and the Kd values from binding studies could not be reconciled by voltage-dependent binding alone. We suggest that each dihydropyridine also produces unique effects on the voltage-dependent gating of calcium channels.
为了研究二氢吡啶对钙通道的作用机制，我们在豚鼠心室标本中研究了光学纯对映体Bay k 8644、Sandoz 202 - 791、尼莫地平和PN200 - 110的受体结合及电生理效应。放射性配体结合研究与其他报告一致，即抑制性和兴奋性二氢吡啶共享一个单一结合位点。采用膜片钳方法记录全细胞钙电流。(-)-Bay k 8644和(+)-202 - 791使钙电流产生电压依赖性增加。效应的大小取决于钳制电位。在-40至-90 mV的钳制电位下，这些激活剂以浓度依赖性方式增加钙电流，EC50值分别为25 nM和80 nM。抑制剂(+)-Bay k 8644、(-)-202 - 791、(+)-和(-)-尼莫地平以及(+)-PN200 - 110阻断钙电流的效力取决于钳制电位。在-80 mV钳制电位下测得的这些对映体的IC50值分别为8000、200、2000、450和400 nM，在-30 mV钳制电位下测得的IC50值分别为26、1.0、52、4.0和4.5 nM。为一些二氢吡啶计算的解离常数与通过放射性配体结合测定的Kd值相似。然而，对于其他二氢吡啶，仅靠电压依赖性结合无法解释产生半数最大电生理效应的浓度与结合研究中的Kd值之间的巨大差异。我们认为每种二氢吡啶对钙通道的电压依赖性门控也会产生独特的影响。
