Isoproterenol stimulates phosphorylation of the insulin-regulatable glucose transporter in rat adipocytes.
We have examined the acute effects of insulin and isoproterenol on the phosphorylation state of the insulin-regulatable glucose transporter (IRGT) in rat adipocytes. The IRGT was immunoprecipitated from either detergent-solubilized whole-cell homogenates or subcellular fractions of 32P-labeled fat cells and subjected to sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The 32P-labeled IRGT was detected by autoradiography as a species of apparent Mr 46,000. Insulin stimulated translocation of the IRGT from low-density microsomes to the plasma membrane but did not affect phosphorylation of the transporter in either fraction. Isoproterenol inhibited insulin-stimulated glucose transport by 40% but was without effect on the subcellular distribution of the transporter in either the presence or absence of insulin. Isoproterenol stimulated phosphorylation of the IRGT 2-fold. Incubating cells with dibutyryl-cAMP and 8-bromo-cAMP also stimulated phosphorylation 2-fold, and the transporter was phosphorylated in vitro when IRGT-enriched vesicles were incubated with cAMP-dependent protein kinase and [gamma-32P]ATP. These results suggest that isoproterenol stimulates phosphorylation of the IRGT via a cAMP-dependent pathway and that phosphorylation of the transporter may modulate its ability to transport glucose.
James
D E
DE
Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO 63110.
Hiken
J
J
Lawrence
J C
JC
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002087:Butyrates / Q000494:pharmacology; D020148:Butyric Acid; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology; D007328:Insulin / Q000494:pharmacology*; D007545:Isoproterenol / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains
D002087:Butyrates; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D020148:Butyric Acid; D015124:8-Bromo Cyclic Adenosine Monophosphate; D003994:Bucladesine; D000242:Cyclic AMP; D007545:Isoproterenol