McCarron J G, Walsh J V, Fay F S
Department of Physiology, University of Massachusetts, Worcester 01605.
Pflugers Arch. 1994 Feb;426(3-4):199-205. doi: 10.1007/BF00374772.
The sodium/calcium (Na+/Ca2+) exchanger is often considered to be a key regulator of the cytoplasmic calcium concentration ([Ca2+]) in smooth muscle but neither its precise role in Ca2+ homeostasis nor even its existence in smooth muscle are generally agreed upon. Here we directly assessed the role Na+/Ca2+ exchange plays in regulating [Ca2+] in single voltage-clamped smooth muscle cells. Following an elevation of [Ca2+], its decline was found to have both voltage-dependent and voltage-independent components. The voltage-dependent component was abolished when Na+ was removed from the external bathing solution. During the fall of [Ca2+] a small and declining Na(+)-dependent inward current was observed of a magnitude predicted by 3:1 Na+/Ca2+ exchange stoichiometry. At [Ca2+] above 400 nM the principal efflux of Ca2+ above rest was attributed to this Na(+)-dependent removal mechanism. These results establish that a Na+/Ca2+ exchanger exists in smooth muscle and argue that it can regulate [Ca2+] at physiological Ca2+ concentrations.
钠/钙（Na⁺/Ca²⁺）交换体通常被认为是平滑肌细胞质钙浓度（[Ca²⁺]）的关键调节因子，但对于其在钙稳态中的精确作用以及在平滑肌中的存在与否，人们尚未达成普遍共识。在此，我们直接评估了Na⁺/Ca²⁺交换在调节单个电压钳制平滑肌细胞[Ca²⁺]方面所起的作用。[Ca²⁺]升高后，发现其下降具有电压依赖性和非电压依赖性成分。当从外部浴液中去除Na⁺时，电压依赖性成分消失。在[Ca²⁺]下降期间，观察到一个小的且逐渐减小的Na⁺依赖性内向电流，其大小由3:1的Na⁺/Ca²⁺交换化学计量比预测。在[Ca²⁺]高于400 nM时，静息状态以上Ca²⁺的主要外流归因于这种Na⁺依赖性清除机制。这些结果表明平滑肌中存在Na⁺/Ca²⁺交换体，并表明它可以在生理钙浓度下调节[Ca²⁺]。
