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Changes in the phosphorylation state of the inhibitory guanine-nucleotide-binding protein Gi-2 in hepatocytes from lean (Fa/Fa) and obese (fa/fa) Zucker rats.
- Source :
-
European journal of biochemistry [Eur J Biochem] 1990 Sep 11; Vol. 192 (2), pp. 537-42. - Publication Year :
- 1990
-
Abstract
- Treatment of intact, 32Pi-labelled hepatocytes from lean Zucker rats with a range of agents including 12-O-tetradecanoyl-phorbol 13-acetate (TPA), vasopressin, and angiotensin II elicited substantial increases in the phosphorylation of the alpha-subunit of the inhibitory G protein of adenylate cyclase (alpha Gi-2). These agonist-induced phosphorylations of alpha Gi-2 were associated with loss of Gi function as assessed by the ability of low concentrations of guanylyl 5'-[beta,gamma imido]triphosphate (p[NH]ppG) to inhibit forskolin-stimulated adenylate cyclase activity. Hepatocytes from obese Zucker rats displayed a resistance to both agonist-induced phosphorylation of alpha Gi-2 and to p[NH]ppG-mediated inhibition of adenylate cyclase. The basal level of alpha Gi-2 phosphorylation in hepatocytes from obese Zucker rats was considerably greater at 1.06 +/- 0.09 mol phosphate/mol alpha Gi-2 than in hepatocytes from lean animals which gave 0.54 +/- 0.09 mol phosphate/mol alpha Gi-2. Incubation with TPA (10 ng/ml, 15 min) approximately doubled the level of phosphorylation of alpha Gi-2 in the hepatocytes from lean animals but had little effect on the phosphorylation of alpha Gi-2 in hepatocytes from obese animals. Incubation of hepatocytes from lean animals with ligands which lead to the phosphorylation of alpha Gi-2 abolished the ability of low concentrations of p[NH]ppG to inhibit adenylate cyclase expressed in isolated membranes. Treatment of hepatocyte plasma membranes from lean but not obese Zucker rats with pure protein kinase C led to the phosphorylation of alpha Gi-2. The resistance to protein-kinase-C-mediated phosphorylation in hepatocyte membranes from obese animals could be overcome by treatment of the membranes with alkaline phosphatase. These results indicate that the defect in guanine-nucleotide-mediated 'Gi function' seen in obese Zucker rats may be due to an inactivating phosphorylation of alpha Gi-2.
- Subjects :
- Adenylyl Cyclases metabolism
Angiotensin II pharmacology
Animals
Cell Membrane metabolism
Cells, Cultured
Kinetics
Male
Phosphates metabolism
Phosphorylation
Rats
Reference Values
Tetradecanoylphorbol Acetate pharmacology
Vasopressins pharmacology
GTP-Binding Proteins metabolism
Liver metabolism
Rats, Zucker metabolism
Subjects
Details
- Language :
- English
- ISSN :
- 0014-2956
- Volume :
- 192
- Issue :
- 2
- Database :
- MEDLINE
- Journal :
- European journal of biochemistry
- Publication Type :
- Academic Journal
- Accession number :
- 2120055
- Full Text :
- https://doi.org/10.1111/j.1432-1033.1990.tb19258.x