title: Increased Ca2+ binding by a cardiac cell membrane preparation after cyclic AMP-enhanced intrinsic membrane protein phosphorylation.
abstract: Ca2+ binding to a sarcolemma-enriched membrane fraction from pig myocardium possessing an intrinsic cyclic AMP-dependent protein kinase occurs at several classes of low affinity binding sites and at two high affinity binding sites with binding constants  of about 1.5-1.7x10(7) M-1 (0.3 nmole of Ca2+/mg protein) and 0.9-2.9x10(6) M-1 (0.8 nmole of Ca2+/mg protein). Ca2+ binding properties are not affected by verapamil and ouabain, whereas ruthenium red depresses Ca2+ binding at the low affinity binding sites and La3+ ions strongly reduce both low and high affinity Ca2+ binding. A profound inhibition of the high affinity Ca2+ binding sites was observed in the presence of Na+ ions, half-maximal inhibition at a free Ca2+ concentration of 2x10(-8) M being achieved by 11 mM NaC1. High affinity Ca2+ binding is also diminished after pretreatment of the membranes with trypsin and phospholipase A. Phosphorylation of one or two of the membrane proteins by the endogenous cyclic AMP-dependent protein kinase leads at both classes of high affinity Ca2+ binding sites to an approximately 4-fold increase in affinity, the number of these sites remaining unchanged. The high affinity Ca2+ binding sites may possibly be involved in Ca2+ extrusion from the cell and in the relaxation process.
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology*; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology; D009124:Muscle Proteins / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism*; D011955:Receptors, Drug; D012430:Ruthenium Red / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D009124:Muscle Proteins; D011955:Receptors, Drug; D012430:Ruthenium Red; D010042:Ouabain; D007811:Lanthanum; D012964:Sodium; D014700:Verapamil; D000242:Cyclic AMP; D011494:Protein Kinases