Inhibition and acceleration of Na+/Ca2+/K+ exchange fluxes by Ag+ in bovine retinal rod outer segments
Schnetkamp, P.P.; Szerencsei, R.T.; Tucker, J.E.; Van den Elzen, P.
American Journal of Physiology 269(5 Pt 1): C1147-C1152
1995
ISSN/ISBN: 0002-9513 PMID: 7491903 Document Number: 441993
The effect of Ag+ on Ca-2+ fluxes mediated by the retinal rod Na+/Ca-2+/K+ exchanger was investigated in intact bovine rod outer segments (ROS). Intracellular Na+ concentration ((Na+)-in-dependent Ca-2+ influx and extracellular Na I concentration ((Na+)-out)-dependent Ca-2+ efflux were monitored by changes in cytosolic free Ca-2+ measured with the fluorescent Ca-2+-indicating dye fluo 3. Ag+ was the most effective inhibitor of Na+/Ca-2+/K+ exchange fluxes described to date, with half-maximal inhibition observed at 2-8 mu-M 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 Ca-2+ but not of (Na+)-i-dependent Ca-2+ influx. We suggest that Ag+ inhibits and accelerates Na+/Ca-2+/K+ exchange fluxes by binding to cysteine residues on the cytosolic surface of the exchanger protein.