Inhibition and acceleration of Na+/Ca2+/K+ exchange fluxes by Ag+ in bovine retinal rod outer segments.
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.
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002352:Carrier Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D002417:Cattle; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D008623:Mercaptoethanol / Q000494:pharmacology; D012374:Rod Cell Outer Segment / Q000378:metabolism*; D012834:Silver / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger; D013997:Time Factors
D002121:Calcium Channel Blockers; D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; C074530:potassium-dependent sodium-calcium exchanger; D012834:Silver; D008623:Mercaptoethanol; D012964:Sodium