Schnetkamp P P, Szerencsei R T, Tucker J E, Van den Elzen P
Department of Medical Biochemistry, University of Calgary, Alberta, Canada.
Am J Physiol. 1995 Nov;269(5 Pt 1):C1147-52. doi: 10.1152/ajpcell.1995.269.5.C1147.
The effect of Ag+ on Ca2+ fluxes mediated by the retinal rod Na+/Ca2+/K+ exchanger was investigated in intact bovine rod outer segments (ROS). Intracellular Na+ concentration ([Na+]in)-dependent Ca2+ influx and extracellular Na+ concentration ([Na+]out)-dependent Ca2+ efflux were monitored by changes in cytosolic free Ca2+ measured with the fluorescent Ca(2+)-indicating dye fluo 3. Ag+ was the most effective inhibitor of Na+/Ca2+/K+ exchange fluxes described to date, with half-maximal inhibition observed at 2-8 microM Ag+. Inhibition by Ag+ could be reversed by addition of beta-mercaptoethanol but not by addition of cysteine. Reversal by beta-mercaptoethanol resulted in a marked acceleration of [Na+]out-dependent lowering of cytosolic free Ca2+ but not of [Na+]in-dependent Ca2+ influx. We suggest that Ag+ inhibits and accelerates Na+/Ca2+/K+ exchange fluxes by binding to cysteine residues on the cytosolic surface of the exchanger protein.
在完整的牛视杆外段（ROS）中研究了Ag⁺对视网膜视杆Na⁺/Ca²⁺/K⁺交换体介导的Ca²⁺通量的影响。通过用荧光Ca²⁺指示染料fluo 3测量的胞质游离Ca²⁺的变化来监测细胞内Na⁺浓度（[Na⁺]in）依赖性的Ca²⁺内流和细胞外Na⁺浓度（[Na⁺]out）依赖性的Ca²⁺外流。Ag⁺是迄今为止所描述的对Na⁺/Ca²⁺/K⁺交换通量最有效的抑制剂，在2 - 8 microM Ag⁺时观察到半数最大抑制。添加β-巯基乙醇可逆转Ag⁺的抑制作用，但添加半胱氨酸则不能。β-巯基乙醇的逆转导致[Na⁺]out依赖性的胞质游离Ca²⁺降低显著加速，但[Na⁺]in依赖性的Ca²⁺内流没有加速。我们认为，Ag⁺通过与交换体蛋白胞质表面的半胱氨酸残基结合来抑制和加速Na⁺/Ca²⁺/K⁺交换通量。
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