Peroxide inactivates calcium pumps in pig coronary artery
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To study the effects of hydrogen peroxide, pig coronary artery smooth muscle subcellular fractions enriched in plasma membrane (F2) or sarcoplasmic reticulum (F3) were incubated in various concentrations of peroxide and 5 mM azide. ATP-dependent azide-insensitive oxalate-stimulated Ca2+ uptake was determined for F3 and phosphate-stimulated uptake for F2. Only 1.5-5 microM hydrogen peroxide was required for 50% inhibition of the Ca2+ uptake by F3, but the corresponding concentration for F2 was 10-50 microM. This effect was not prevented by superoxide dismutase. Hydrogen peroxide inhibited the Ca(2+)-dependent formation of a 115-kDa acylphosphate band in F3 and 140- and 115-kDa bands in F2. The inhibition of Ca2+ uptake in F3, however, exceeded the inhibition of the acylphosphate formation. Efflux of Ca2+ from F2 and F3 was enhanced by hydrogen peroxide but F3 was more sensitive than F2. We conclude that hydrogen peroxide has dual effect on Ca2+ dynamics in the coronary artery smooth muscle, i.e., it inactivates the Ca2+ pumps and increases membrane permeability to Ca2+. The effect is more pronounced on sarcoplasmic reticulum than on plasma membrane. Intrinsic catalase may, however, provide partial protection against such damage.
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