Coronary artery acidosis: pH and calcium pump stability

To study the effects of prolonged exposure to different pH, pig coronary artery smooth muscle subcellular fraction F3 enriched in sarcoplasmic reticulum was preincubated at 0 or 37 degrees C and pH 6.4-7.8 and then used for monitoring the rate of the oxalate-stimulated component of the ATP-dependent azide-insensitive Ca2+ uptake at constant pH (6.8) and temperature (37 degrees C). Ca2+ uptake by F3 decreased with the increasing preincubation pH. The loss of Ca2+ uptake was more rapid upon preincubation at 37 degrees C than at 0 degrees C. Dithiothreitol (DTT), when included in the preincubation solution, protected against the loss. Sucrose, KCl, ATP, and ATP plus CaCl2 protected slightly, and glutathione, catalase, superoxide dismutase, azide, ascorbate, CaCl2, ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, mannitol, mercaptopropionylglycine, and FeSO4 had only marginal or no effects. Efflux of accumulated Ca2+ was more rapid from membranes that had been preincubated at 37 degrees C than from those preincubated at 0 degrees C, but it was not affected by the preincubation pH or by DTT. The loss of Ca2+ uptake due to incubation at pH 7.8 accompanied a decrease in the 115-kDa Ca(2+)-dependent acylphosphate formation due to the Ca2+ pump. The presence of DTT in the preincubation mixture increased the acylphosphate level in the control and protected against its loss at the preincubation pH 6.8 or 7.8. Thus, in the membranes isolated from coronary artery, acidosis may protect against damage to the sarcoplasmic reticulum Ca2+ pump by protonation of a key sulfhydryl group.(ABSTRACT TRUNCATED AT 250 WORDS)