Inhibition by Ca2+ of the incorporation of myo-inositol into phosphatidylinositol.
The incorporation of myo-[2-3H]inositol into phosphatidylinositol of the aorta and the vas deferens was measured and the effects of Ca2+ and other divalent cations were determined. When incubated in normal Krebs-Ringer buffer, only negligible radioactivity was incorporated into aorta slices. Mn2+ increased the incorporation greatly. The enhanced incorporation was attributable to an increase in CDP-diglyceride:inositol transferase activity, rather than the myo-inositol exchange reaction. Transferase activity was increased 20-fold by 1 mM Mn2+, in the presence of 20 mM Mg2+. The Mn2+-stimulated activity was strongly inhibited by Ca2+. In the absence of Mn2+, but presence of 20 mM Mg2+, transferase activity was inhibited 80% by 0.01 mM Ca2+. Removal of endogenous Ca2+ from the tissue by ionophore A23187 and EGTA increased the incorporation of myo-[2-3H]inositol into phosphatidylinositol. These findings indicate that Ca2+ inhibited the synthesis of phosphatidylinositol. The proposed action of cholinergic and alpha-adrenergic agonists in enhancing the degradation and turnover of phosphatidyl-inositol and in provoking the influx of Ca2+ should be unfavorable to the recovery of cellular phosphatidylinositol content.
D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000378:metabolism*; D051607:CDP-Diacylglycerol-Inositol 3-Phosphatidyltransferase; D002118:Calcium / Q000494:pharmacology*; D002712:Chlorides; D003567:Cytidine Diphosphate Diglycerides / Q000378:metabolism; D007294:Inositol / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D015636:Magnesium Chloride; D008297:Male; D008345:Manganese / Q000494:pharmacology; D017895:Manganese Compounds; D010716:Phosphatidylinositols / Q000378:metabolism*; D010770:Phosphotransferases / Q000378:metabolism; D011817:Rabbits; D017855:Transferases (Other Substituted Phosphate Groups); D014649:Vas Deferens / Q000187:drug effects / Q000378:metabolism*
D002712:Chlorides; D003567:Cytidine Diphosphate Diglycerides; D017895:Manganese Compounds; D010716:Phosphatidylinositols; D015636:Magnesium Chloride; D008345:Manganese; D007294:Inositol; D010770:Phosphotransferases; D017855:Transferases (Other Substituted Phosphate Groups); D051607:CDP-Diacylglycerol-Inositol 3-Phosphatidyltransferase; D008274:Magnesium; C025340:manganese chloride; D002118:Calcium