Clapp L H, Gurney A M
Department of Pharmacology, United Medical School, St Thomas's Hospital, London, UK.
Pflugers Arch. 1991 Jun;418(5):462-70. doi: 10.1007/BF00497774.
Using the patch-clamp technique, we have characterised the inward current from enzymatically dispersed rabbit pulmonary arterial cells, and investigated the effects of the vasodilator, nitroprusside (NP), on these and other membrane currents. With Cs(+)-filled pipettes, inward currents were recorded during brief depolarizing voltage steps in both physiological Ca2+ and 10 mM Ba2+. The threshold for current activation was positive to -40 mV and the current peaked at 0 mV for Ca2+ and +10 mV for Ba2+. During the first few minutes of recording, inward currents increased or "ran-up". This could not be attributed to blockade of outward current or the inclusion of adenosine triphosphate (ATP) in the patch pipette. Experiments revealed that all the inward current was carried through a single type of voltage-activated Ca2+ channel, namely the high-threshold, dihydropyridine-sensitive channel. It was unaffected by tetrodotoxin but was abolished at all potentials by low concentrations of Cd2+ (100 microM) or nifedipine (1-2 microM). NP (1 microM) suppressed peak inward Ba2+ current at +10 mV by approximately 45%. Higher concentrations (50 microM) did not produce further blockade of the current. This decrease was associated with increased inactivation of the current, and both effects required the presence of ATP in the patch pipette. In physiological Ca2+, using K(+)-filled pipettes, NP was found to induce spontaneous bursts of outward currents, which are probably activated by the release of Ca2+ from Ca(2+)-overloaded stores. These results are consistent with NP lowering cytosolic Ca2+, and hence causing vasodilation, by inhibiting Ca2+ influx through voltage-gated Ca2+ channels and by promoting Ca2+ uptake into the sarcoplasmic reticulum.
运用膜片钳技术，我们已对酶解分散的兔肺动脉细胞的内向电流进行了特性描述，并研究了血管舒张剂硝普钠（NP）对这些电流及其他膜电流的影响。使用充满Cs⁺的微电极，在生理Ca²⁺和10 mM Ba²⁺条件下，于短暂的去极化电压阶跃期间记录内向电流。电流激活阈值正向于-40 mV，对于Ca²⁺，电流在0 mV时达到峰值，对于Ba²⁺，电流在+10 mV时达到峰值。在记录的最初几分钟内，内向电流增加或“上升”。这不能归因于外向电流的阻断或膜片微电极中加入三磷酸腺苷（ATP）。实验表明，所有内向电流均通过单一类型的电压激活Ca²⁺通道传导，即高阈值、对二氢吡啶敏感的通道。它不受河豚毒素影响，但在所有电位下均被低浓度的Cd²⁺（100 μM）或硝苯地平（1 - 2 μM）阻断。NP（1 μM）使+10 mV时的内向Ba²⁺电流峰值抑制约45%。更高浓度（50 μM）并未进一步阻断该电流。这种降低与电流失活增加相关，且两种效应均需要膜片微电极中存在ATP。在生理Ca²⁺条件下，使用充满K⁺的微电极，发现NP可诱导外向电流的自发爆发，这可能是由Ca²⁺超载储存库中Ca²⁺的释放所激活。这些结果与NP通过抑制电压门控Ca²⁺通道的Ca²⁺内流以及促进Ca²⁺摄取到肌浆网中来降低细胞质Ca²⁺从而引起血管舒张相一致。
