Role of guanine nucleotide regulatory proteins in insulin stimulation of glucose transport in rat adipocytes. Influence of bacterial toxins.
The potential role of guanine nucleotide regulatory proteins (G-proteins) in acute insulin regulation of glucose transport was investigated by using bacterial toxins which are known to modify these proteins. Cholera-toxin treatment of isolated rat adipocytes had no effect on either 2-deoxyglucose transport or insulin binding. Pertussis-toxin treatment resulted in an inhibition of both insulin binding and glucose transport. Insulin binding was decreased in pertussis-toxin-treated cells by up to 40%, owing to a lowering of the affinity of the receptor for hormone, with no change in hormone internalization. The dose-response curve for insulin stimulation of glucose transport was strongly shifted to the right by pertussis-toxin treatment [EC50 (half-maximally effective insulin concn.) = 0.31 +/- 0.04 ng/ml in control cells; 2.29 +/- 1.0 in treated cells), whereas cholera toxin had only a small effect (EC50 = 0.47 +/- 0.02 ng/ml). Correcting for the change in hormone binding, pertussis toxin was found to decrease the coupling efficiency of occupied receptors (50% of maximal insulin effect with 928 molecules bound/cell in control and 3418 in treated cells). Pertussis-toxin inhibition of insulin sensitivity was slow in onset, requiring 2-3 h for completion. Under conditions where pertussis-toxin inhibition of insulin sensitivity was maximal, a 41,000 Da protein similar to the alpha subunit of Gi (the inhibitory G-protein) was found to be fully ribosylated. These results are consistent with the concept that pertussis-toxin-sensitive G-protein(s) can modify the insulin-receptor/glucose-transport coupling system.
Ciaraldi
T P
TP
Veterans Administration Medical Center, Medical Research Service, San Diego, CA 92161.
Maisel
A
A
D000243:Adenosine Deaminase / Q000494:pharmacology; D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism; D003837:Deoxy Sugars / Q000378:metabolism*; D003847:Deoxyglucose / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000502:physiology*; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D009243:NAD / Q000378:metabolism; D037342:Pertussis Toxin; D051381:Rats; D011919:Rats, Inbred Strains; D011972:Receptor, Insulin / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D003837:Deoxy Sugars; D007328:Insulin; D010566:Virulence Factors, Bordetella; D009243:NAD; D002772:Cholera Toxin; D003847:Deoxyglucose; D000242:Cyclic AMP; D037342:Pertussis Toxin; D011972:Receptor, Insulin; D000243:Adenosine Deaminase; D019204:GTP-Binding Proteins