Guanine nucleotide and NaF stimulation of phospholipase C activity in rat cerebral-cortical membranes. Studies on substrate specificity.
Guanyl-5'-yl imidodiphosphate (p[NH]ppG) stimulated a rapid phospholipase C-mediated breakdown of exogenously added phosphatidylinositol 4,5-bisphosphate (PIP2) in rat cerebral-cortical membranes, with half-maximal activation at approx. 33 microM. NaF stimulated phospholipase C activity, with half-maximal activation at 0.5 mM. Stimulation of phospholipase C activity by NaF exhibited pH optima at approx. 5.5 and 7.0, with the stimulatory activity at pH 7.0 greater than that at pH 5.5. With p[NH]ppG, only stimulation at pH 7.0 was observed. Neither p[NH]ppG nor NaF stimulated hydrolysis of added phosphatidylinositol (PI) or phosphatidylinositol 4-phosphate (PIP). Mg2+ (0.5 mM) potentiated p[NH]ppG-stimulated breakdown of PIP2. Ca2+ increased basal and p[NH]ppG-stimulated breakdown of PIP2. PI breakdown was stimulated only by high Ca2+ concentrations and was unaffected by p[NH]ppG at any Ca2+ concentration examined. These results indicate that, in cerebral-cortical membranes, activation of phospholipase C by guanine nucleotides or fluoride directly increases a phospholipase C activity which specifically hydrolyses PIP2.
Litosch
I
I
Department of Pharmacology, University of Miami School of Medicine, FL 33101.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology; D002540:Cerebral Cortex / Q000187:drug effects / Q000201:enzymology*; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology*; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012969:Sodium Fluoride / Q000494:pharmacology*; D013379:Substrate Specificity; D010738:Type C Phospholipases / Q000378:metabolism*
D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; D006165:Guanylyl Imidodiphosphate; D006160:Guanosine Triphosphate; D012969:Sodium Fluoride; D010738:Type C Phospholipases; D008274:Magnesium; D002118:Calcium