Na+/Ca2+ exchange of isolated sarcolemmal membrane: effects of insulin, oxidants and insulin deficiency.
In this study we prepared sarcolemmal fractions from bovine and rat hearts; their Na+K+ ATPase activities, measured in the presence of saponin to unmask latent Na+K+ ATPase, were 59.4 and 48.8 mu mol Pi/mg protein.h, respectively. The rate of Na+ dependent Ca2+ uptake was linear for the first 10 s and a plateau was reached in 3 min. Oxidation by free radical generation either with H2O2, FeSO4 plus DTT or xanthine oxidase plus hypoxanthine stimulated Na+/Ca2+ exchange in a time-dependent manner. The stimulation was abolished by deferoxamine or o-phenanthroline. By contrast, oxidation by HOCl inhibited Na+/Ca2+ exchange in proportion to its concentration, and this inhibition was antagonized by DTT. DTT alone had no effect on the exchange. Insulin stimulated Na+/Ca2+ exchange, its maximal effect was attained after 30 min incubation with 100 mu units/ml. N-ethylmaleimide inhibited the exchange both in the presence and in the absence of insulin. Sarcolemmal fractions prepared from hearts of alloxan-treated, acutely diabetic rats showed a significant decrease in Na+/Ca2+ exchange. Addition of insulin in vitro significantly stimulated Na+/Ca2+ exchange of both diabetic and control groups. The results indicate that sarcolemmal Na+/Ca2+ exchange function is modulated by oxidation-reduction states and by the presence of insulin.
Kato
M
M
Department of Physiology, University of Ottawa, School of Medicine, Ontario, Canada.
Kako
K J
KJ
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D002458:Cell Fractionation; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D019831:Sodium-Calcium Exchanger; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D002352:Carrier Proteins; D007328:Insulin; D019831:Sodium-Calcium Exchanger; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium