title: Apparent cooperativity of [3H]ouabain binding to myocytes obtained from guinea-pig heart.
abstract: Kinetics of [3H]ouabain binding to intact cardiac cells were examined using myocytes obtained from guinea-pig heart. In intact cells, the use of excess unlabeled ouabain results in an under-estimation of nonspecific binding, presumably due to cytotoxic effects of the unlabeled glycoside; estimation of the specific binding, as that to rapidly releasing sites yields more accurate results. Specific [3H]ouabain binding to myocytes is promoted by an increase in Na+ influx, indicating that normal intracellular Na+ concentration is insufficient to fully stimulate glycoside binding. High concentrations of [3H]ouabain seem to increase the apparent affinity of binding sites for the glycoside via increases in intracellular Na+ concentration resulting from sodium-pump inhibition; hence the binding reaction may be regarded as having a novel type of cooperativity. This cooperativity has kinetics different from those of classical positive cooperativity based on binding-site interactions, and is apparent with toxic concentrations of the glycoside that cause marked increases in intracellular Na+ concentrations.
authors.affiliation: Department of Pharmacology and Toxicology, Michigan State University, East Lansing.
authors.forename: P
authors.initials: P
authors.lastname: Stemmer
authors.forename: T
authors.initials: T
authors.lastname: Akera
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002498:Centrifugation; D005374:Filtration; D006168:Guinea Pigs; D007700:Kinetics; D008985:Monensin / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D010042:Ouabain / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014316:Tritium
chemical_list: D014316:Tritium; D010042:Ouabain; D008985:Monensin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium