title: Evidence for direct involvement of the sarcoplasmic reticulum Ca(2+)-ATPase in a passive monovalent cation (K+/Na+) exchange.
abstract: A specific inhibitor of SERCA-pumps, thapsigargin (TG) was used to demonstrate the direct involvement of the SR Ca(2+)-ATPase in passive K+/Na+ exchange. The K(+)-potential variations across vesicle membranes were measured in the absence of ATP with a fluorescent probe: 3,3'-dipropylthiodicarbocyanine iodide. Addition of EGTA dissipates the K(+)-potential whereas the presence of TG abolishes this effect. Our data prove that the Ca(2+)-ATPase translocates monovalent cations at a rate similar to the E2-->E1 conformational change.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002474:Cell-Free System; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006096:Gramicidin / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007476:Ionophores / Q000494:pharmacology; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D012964:Sodium / Q000378:metabolism*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D007476:Ionophores; D013729:Terpenes; D006096:Gramicidin; D014634:Valinomycin; D019284:Thapsigargin; D012964:Sodium; D000252:Calcium-Transporting ATPases; D011188:Potassium; D002118:Calcium