牛视杆外段中的钠钙交换需要并转运钾离子。

Na+-Ca2+ exchange in bovine rod outer segments requires and transports K+.

作者信息

Schnetkamp P P, Basu D K, Szerencsei R T

机构信息

Department of Medical Biochemistry, University of Calgary, Alberta, Canada.

出版信息

Am J Physiol. 1989 Jul;257(1 Pt 1):C153-7. doi: 10.1152/ajpcell.1989.257.1.C153.

DOI:10.1152/ajpcell.1989.257.1.C153

PMID:2502022

Abstract

Intact outer segments isolated from bovine retinas (bovine ROS) display a high activity of Na+-Ca2+ exchange, and Na+-Ca2+ exchange appears to be the only functional ion transporter present. Here we demonstrate for the first time that Na+-Ca2+ exchange requires and transports K+ from the following observations. 1) Na+-Ca2+ exchange in bovine ROS required the simultaneous presence of K+ and Ca2+ on one side of the membrane and the presence of Na+ on the other side. 2) Na+-stimulated Ca2+ release from bovine ROS was accompanied by an equally large release of K+. We used the electrogenic protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) as an added electrical shunt; in the intact rod cell, electrogenic Na+-Ca2+ exchange is shunted by K+ channels present in the rod inner segment. In the presence of FCCP, an inward Na+-Ca2+ exchange current was accompanied by an outward current of protons with a stoichiometry of 1 H+/Ca2+; in the absence of FCCP, no Na+-induced proton current was observed. Addition of FCCP did not uncouple Na+-induced K+ release from Na+-induced Ca2+ release. We conclude that Na+-Ca2+ exchange in bovine rod photoreceptors operates at an electrogenic stoichiometry of 4 Na+:(1 Ca2+ + 1 K+). In isolated ROS and in the absence of an external electrical shunt, Na+-Ca2+ exchange operated at an electroneutral stoichiometry of 3 Na+:(1 Ca2+ + 1 K+).

摘要

从牛视网膜分离出的完整外段（牛视网膜外段，bovine ROS）表现出高活性的Na⁺-Ca²⁺交换，并且Na⁺-Ca²⁺交换似乎是唯一存在的功能性离子转运体。在此，我们通过以下观察首次证明Na⁺-Ca²⁺交换需要并转运K⁺。1）牛视网膜外段中的Na⁺-Ca²⁺交换需要膜的一侧同时存在K⁺和Ca²⁺，另一侧存在Na⁺。2）Na⁺刺激牛视网膜外段释放Ca²⁺的同时伴有等量的K⁺释放。我们使用质子载体羰基氰化物对三氟甲氧基苯腙（FCCP）作为额外的电分流器；在完整的视杆细胞中，电生Na⁺-Ca²⁺交换被视杆细胞内段存在的K⁺通道分流。在FCCP存在的情况下，内向的Na⁺-Ca²⁺交换电流伴随着质子的外向电流，化学计量比为每Ca²⁺ 1个H⁺；在没有FCCP的情况下，未观察到Na⁺诱导的质子电流。添加FCCP并没有使Na⁺诱导的K⁺释放与Na⁺诱导的Ca²⁺释放解偶联。我们得出结论，牛视杆光感受器中的Na⁺-Ca²⁺交换以4个Na⁺:(1个Ca²⁺ + 1个K⁺)的电生化学计量比运行。在分离的视网膜外段且没有外部电分流的情况下，Na⁺-Ca²⁺交换以3个Na⁺:(1个Ca²⁺ + 1个K⁺)的电中性化学计量比运行。