[Phosphatidylinositol-specific phospholipase C in hypoxic rat myocardium].
Phosphatidylinositol-specific phospholipase C (PI-PLC) was characterized in rat myocardium, and the effect of hypoxia on its activity was investigated. It had a substrate specificity toward phosphatidylinositol (PI) and was predominantly located in cytosol. Its optimal pH was 7.4 and it required 5 mM of Ca2+ for maximum activity, but did not hydrolyze phosphatidylcholine (PC), phosphatidylethanolamine (PE), or phosphatidylserine (PS). Vmax and Km were 51.5 nmol/mg/min, and 231 microM, respectively. Sodium deoxycholate increased its activity at a concentration of 0.05%, while Triton X-100 inhibited its activity at any concentrations examined. PI-PLC was partially purified 260 fold over the crude cytosol, with ammonium sulphate fractionation, DEAE-cellulose, Sephadex G-100, Hydroxylapatite, and Sephadex G-150 column chromatographies. In order to elucidate the biochemical function of myocardial PI-PLC in hypoxia, PI-PLC along with phospholipase A2 (PLA2) was investigated in N2 gas-saturated buffer up to for 24 hours. The activity of PI-PLC did not change during the first 2 hours, and then gradually attenuated. Substrate specificity or subcellular localization of PI-PLC unchanged during 24 hour 9 of hypoxia. PLA2 was predominantly located in microsome and had a substrate specificity toward PE in normoxic state. In hypoxia, on the other hand, it hydrolyzed PC besides PE and was activated on and after 2 hours of hypoxic incubation. PI-PLC did not seem to contribute in releasing arachidonate from membrane lipid-bilayers during myocardial ischemia. But some biochemical mechanism suggested to inhibit its activity protecting the abrupt cell damage.
Makita
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Department of Cardiovascular Medicine, Hokkaido University, School of Medicine, Sapporo, Japan.
D000818:Animals; D003600:Cytosol / Q000201:enzymology; D000860:Hypoxia / Q000201:enzymology*; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D010727:Phosphoric Diester Hydrolases / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D010727:Phosphoric Diester Hydrolases; D054801:Phosphoinositide Phospholipase C; D043265:Phosphatidylinositol Diacylglycerol-Lyase