Unitary cardiac Na+,Ca2+ exchange current magnitudes determined from channel-like noise and charge movements of ion transport

被引:63
作者
Hilgemann, DW
机构
[1] Department of Physiology, Univ. Texas Southwestern Med. C., Dallas
[2] Department of Physiology, University of Texas Southwestern, Medical Center at Dallas, Dallas, TX 75235-9040
关键词
D O I
10.1016/S0006-3495(96)79275-5
中图分类号
Q6 [生物物理学];
学科分类号
071011 ;
摘要
The cardiac Na+,Ca2+ exchanger (NCX1) is thought to achieve a high turnover rate, but all estimates to date are indirect. Two new strategies demonstrate that maximum unitary exchange currents are about 1 fA (6000 unitary charges per s) and that they fluctuate between on and off levels similar to ion channel currents. First, exchange current noise has been identified in small cardiac patches with properties expected for a gated transport process. Noise power density spectra correlate well with exchanger inactivation kinetics, and the noise has a predicted bell-shaped dependence on the activation state of the exchanger. From the magnitudes of exchange current noise, maximum unitary exchange currents are estimated to be 0.6-1.3 fA. Second, charge movements with rates of similar to 5000 s(-1) have been isolated for the transport of both Na+ and Ca2+ in giant membrane patches using nonsaturating ion concentrations. The Na+ transport reactions are disabled or ''immobilized'' by exchanger inactivation reactions, thus confirming that inactivation generates fully inactive exchanger states.
引用
收藏
页码:759 / 768
页数:10
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