Effects of active oxygen generated by DTT/Fe2+ on cardiac Na+/Ca2+ exchange and membrane permeability to Ca2+.
Sarcolemmal vesicles isolated from bovine heart were preincubated at 37 degrees C with an oxygen radical generating system consisting of 1 mM dithiothreitol (DTT) and 50 microM FeSO4. Exposure of the vesicles for 1 to 40 mins stimulated Na+/Ca2+ exchange about 2.5-fold. The DTT/Fe2+ treatment decreased the apparent Km for Ca2+ of Nai+-dependent Ca2+ uptake by 80% (from 63 to 13 microM). The effect on Vmax was much smaller however. The resulting stimulation of exchange activity was diminished by the presence of desferrioxamine (95%) or catalase (60%). In contrast, superoxide dismutase and sodium formate did not prevent the effects of DTT/Fe2+ on the exchanger. Neither Zn2+ nor Ga3+ could replace Fe2+ in the stimulation of Na+/Ca2+ exchange. Passive Ca2+ efflux was determined by first allowing Na+/Ca2+ exchange to continue to plateau values and then diluting the loaded vesicles in the presence of EGTA. Ca2+ leakage from the vesicles was slightly but significantly (P less than 0.05) increased by the action of DTT/Fe2+, the rate constants for the passive Ca2+ efflux being 0.22 and 0.26/min in control and treated groups, respectively. The calcium loading observed in myocytes in ischemia/reperfusion injury suggests that the stimulation of Na+/Ca2+ exchange by active oxygen may moderate the myocardial response to oxygen mediated injuries including ischemia/reperfusion injury. However, the clinical relevance of these phenomena is far from clear as the stimulation depends in part on the Km for Ca2+ prior to treatment.
Shi
Z Q
ZQ
Cardiac Membrane Research Lab., Simon Fraser University, Burnaby, BC, Canada.
Davison
A J
AJ
Tibbits
G F
GF
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002463:Cell Membrane Permeability / Q000187:drug effects; D004229:Dithiothreitol / Q000494:pharmacology*; D005290:Ferric Compounds / Q000494:pharmacology*; D005609:Free Radicals; D006321:Heart / Q000187:drug effects*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010100:Oxygen / Q000494:pharmacology*; D012508:Sarcolemma / Q000187:drug effects* / Q000378:metabolism
D000975:Antioxidants; D005290:Ferric Compounds; D005609:Free Radicals; C024823:ferric sulfate; D000251:Adenosine Triphosphatases; C034688:sodium calcium ATPase; D010100:Oxygen; D002118:Calcium; D004229:Dithiothreitol