Differential sensitivity of the insulin receptor to proteolysis after beta-adrenergic stimulation.
The cellular mechanism by which the specific binding of [125I]insulin to intact rat adipocytes is inhibited by isoproterenol has been studied. By exposing control and isoproterenol-treated cells to trypsin (0-150 micrograms/ml for 20 min at 4 degrees C) and measuring the intact insulin receptor pool following detergent solubilization, a differential sensitivity to proteolysis of the cell membrane receptor was observed. At low trypsin concentration (less than 30 micrograms/ml), approximately 40% of the specific insulin binding in isoproterenol-treated cells was insensitive to proteolysis as compared to control cells. At higher levels of trypsin (50-150 micrograms/ml) both groups displayed similar levels of trypsin-insensitive receptors which, at the highest trypsin concentration, accounted for 10% of the total receptors in intact cells. Detergent-solubilized receptors from isoproterenol-treated cells, on the other hand, exhibited the same sensitivity to trypsin proteolysis as solubilized receptors from control cells. The time course of the onset and reversal of the isoproterenol-induced binding alteration in intact adipocytes has been analyzed by mild trypsinization (20 micrograms/ml). Results indicated that insulin receptors resistant to trypsin under these conditions mediated the decreased surface binding and were re-expressed on the cell surface upon removal of isoproterenol. Experiments in which adipocytes were fractionated into plasma membrane and Golgi-enriched fractions indicated that the loss of surface insulin binding was not accompanied by a decrease in the proportion of receptors in the adipocyte plasma membrane.(ABSTRACT TRUNCATED AT 250 WORDS)
Sandra
A
A
Department of Anatomy, University of Iowa, Iowa City 52242.
Marshall
S J
SJ
D000273:Adipose Tissue / Q000166:cytology / Q000187:drug effects / Q000648:ultrastructure; D000320:Adrenergic Fibers / Q000378:metabolism; D000319:Adrenergic beta-Antagonists / Q000502:physiology; D000818:Animals; D007328:Insulin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011972:Receptor, Insulin / Q000187:drug effects* / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism / Q000494:pharmacology
D000319:Adrenergic beta-Antagonists; D007328:Insulin; D011972:Receptor, Insulin; D014357:Trypsin