title: Ca-2+-dependent inhibitory effects of Na+ and K+ on Ca-2+ transport in sarcoplasmic reticulum vesicles.
abstract: Effects of Na+ and K+ on Ca-2+ transport by sarcoplasmic reticulum vesicles were studied in a medium containing high Mg-2+ and ATP (2mM) and low Ca-2+ (0.44muM) concentrations. Under these conditions, Na+ and K+ inhibit Ca-2+ uptake, ATPase activity and membrane phosphorylation by ATP. Since the concentrations of ATP and Ca-2+ used are consistent with relaxation in vivo, the results suggest that under physiological resting conditions the Ca-2+ pump of the sarcoplasmic reticulum operates below its maximal capacity.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D009132:Muscles / Q000378:metabolism; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D008094:Lithium; D012964:Sodium; D011188:Potassium; D002118:Calcium