AJP - Cell Physiology, Vol 269, Issue 5 C1147-C1152, Copyright © 1995 by American Physiological Society
Inhibition and acceleration of Na+/Ca2+/K+ exchange fluxes by Ag+ in bovine retinal rod outer segments
P. P. Schnetkamp, R. T. Szerencsei, J. E. Tucker and P. Van den Elzen
Department of Medical Biochemistry, University of Calgary, Alberta, Canada.
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.
