Cardiotoxin from cobra venom affects the Ca-Mg-ATPase of cardiac sarcolemmal membrane vesicles.
Highly purified sarcolemmal (SL) membrane vesicles were prepared from bovine cardiac tissue and used to evaluate the effects of cardiotoxin (CTX) on Ca2+ transport systems of the SL membrane. The addition of CTX, at 1.0 microM and 10 microM, stimulated the ATP-dependent transport of 45Ca2+ by the Ca2(+)-Mg2(+)-ATPase to 138% and 193% of control levels, respectively. The increase in Ca2+ accumulation by the SL vesicles in the presence of CTX was not affected by 100 microM ouabain but was reduced to 50% of control uptake levels by the addition of 0.5 mM dicyclohexylcarbodiimide. Additionally, no effect of CTX (1.0 microM to 10 microM) was seen on 45Ca2+ transport by the Na-Ca exchange system. These effects of CTX on the SL membrane do not appear to be due to non-specific membrane disruption since SL vesicles preloaded with 45Ca2+ did not release (efflux) the accumulated Ca2+ more rapidly in the presence of CTX (1.0 microM to 250 microM). The rate of hydrolysis of ATP by the SL Ca2(+)-Mg2(+)-ATPase was observed to increase (29% to 52%) as CTX concentration increased (1.0 microM to 10 microM). The same concentrations of CTX had no effect on ATP hydrolysis by Na(+)-K(+)-ATPase. We conclude that 10 microM CTX stimulates the rate of ATP hydrolysis and Ca2+ transport by the SL Ca2(+)-Mg2(+)-ATPase.
Huang
J L
JL
Department of Bacteriology and Biochemistry, University of Idaho, Moscow 83843.
Trumble
W R
WR
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000187:drug effects*; D002417:Cattle; D004179:Cobra Cardiotoxin Proteins / Q000633:toxicity*; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D004546:Elapid Venoms / Q000633:toxicity*; D006321:Heart / Q000187:drug effects*; D006868:Hydrolysis; D009206:Myocardium / Q000201:enzymology; D012508:Sarcolemma / Q000187:drug effects* / Q000201:enzymology; D012964:Sodium / Q000378:metabolism
D004179:Cobra Cardiotoxin Proteins; D004546:Elapid Venoms; D004024:Dicyclohexylcarbodiimide; D000255:Adenosine Triphosphate; D012964:Sodium; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium