title: The effect of cardiotoxin on (Ca2+ + Mg2+)-ATPase of the erythrocyte and sarcoplasmic reticulum.
abstract: The effects of cardiotoxin on the ATPase activity and Ca2+-transport of guinea pig erythrocyte and rabbit muscle sarcoplasmic reticulum (Ca2+ + Mg2+)-ATPase (E.C.3.6.1.3) were investigated. Erythrocyte (Ca2+ + Mg2+)-ATPase was inhibited by cardiotoxin in a time- and dose-dependent fashion and inhibition appears to be irreversible. Micromolar calcium prevented this inhibitory effect. Specificity for (Ca2+ + Mg2+)-ATPase inhibition by cardiotoxin was indicated since a homologous neurotoxin had no effect. Cardiotoxin did not affect (Ca2+ + Mg2+)-ATPase activity from sarcoplasmic reticulum, but Ca2+-transport was 50% inhibited. This inhibition was not due to an increased Ca2+-efflux and could be the result of an intramolecular uncoupling of ATPase activity from Ca2+-transport. Inhibition of Ca2+-transport by cardiotoxin could not be prevented by millimolar concentrations of Ca2+. It is suggested that the biological effects of cardiotoxin could be a consequence of inhibition of plasma membrane (Ca2+ + Mg2+)-ATPases.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D004179:Cobra Cardiotoxin Proteins / Q000494:pharmacology*; D004546:Elapid Venoms / Q000494:pharmacology*; D004912:Erythrocytes / Q000201:enzymology*; D006168:Guinea Pigs; D007700:Kinetics; D011817:Rabbits; D012508:Sarcolemma / Q000201:enzymology; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
chemical_list: D004179:Cobra Cardiotoxin Proteins; D004546:Elapid Venoms; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium