Muscarinic cholinergic stimulation of exogenous phosphatidylinositol hydrolysis is regulated by guanine nucleotides in rabbit brain cortical membranes.
Rabbit brain cortical membranes, which have been extracted with 2 M KCl, hydrolyze exogenously added [3H]phosphatidylinositol [( 3H]PI) in a guanine nucleotide- and carbachol-dependent manner. Both oxotremorine-M and carbachol are full agonists with EC50 values of 8 and 73 microM, respectively. Pirenzepine and atropine inhibit carbachol-stimulated [3H]PI hydrolysis. The hydrolysis-resistant guanine nucleotide analog guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) is the most potent in supporting carbachol-stimulated hydrolysis of PI. There is no effect of carbachol in the absence of guanine nucleotides or in the presence of 100 microM adenosine 5'-O-(3-thiotriphosphate), adenosine-5'-(beta, gamma-imido)triphosphate, or sodium pyrophosphate. Guanylyl-5'-(beta,gamma-imido)triphosphate [Gpp(NH)p] in the presence of carbachol also stimulates PI hydrolysis although much less than that seen with GTP gamma S. GDP and Gpp(NH)p are potent antagonists of the GTP gamma S-dependent carbachol response. Optimal stimulation by carbachol and GTP gamma S was observed at 0.3-1 microM free Ca2+ and 6 mM MgCl2. Limited trypsinization resulted in loss of receptor-regulated PI breakdown and a slight decrease in basal activity. These results demonstrate that phospholipase C hydrolysis of exogenous PI by rabbit cortical membranes may be stimulated by carbachol in a guanine nucleotide-dependent manner.
Carter
H R
HR
Department of Biochemistry, University of Tennessee, Memphis 38163.
Fain
J N
JN
D000818:Animals; D002540:Cerebral Cortex / Q000378:metabolism; D006150:Guanine Nucleotides / Q000502:physiology*; D006153:Guanosine Diphosphate / Q000494:pharmacology; D006868:Hydrolysis; D008297:Male; D008566:Membranes / Q000378:metabolism; D010277:Parasympathomimetics / Q000494:pharmacology*; D010447:Peptide Hydrolases / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D011817:Rabbits; D010738:Type C Phospholipases / Q000378:metabolism
D006150:Guanine Nucleotides; D010277:Parasympathomimetics; D010716:Phosphatidylinositols; D006153:Guanosine Diphosphate; D010738:Type C Phospholipases; D010447:Peptide Hydrolases