title: Up-regulation of insulin receptors in rat liver plasma membranes.
abstract: Kinetic experiments (uptake versus time) were utilized to examine the effects of occupancy on insulin receptor availability in rat liver plasma membranes in vitro. The following observations were made: 1) at 4 degrees C, a 3-h exposure of membranes to 100 nM native insulin, followed by removal of unbound hormone, resulted in a subsequent decrease of 125I-insulin binding at 4 degrees C. In a similar experiment at 23 degrees C, no decrease of 125I-insulin binding was observed. 2) At 23 degrees C, 131I-insulin (5 nM) was bound to membranes in a slowly reversible manner after a 3-h association. After removal of free hormone, the 131I-insulin-treated membranes displayed similar binding of 125I-insulin (1 nM) relative to controls despite persistent high level occupancy of receptors by 131I-insulin. 3) At 23 degrees C, phospholipase pretreatment of membranes enhanced 125I-insulin uptake (approximately 40%). Phospholipase-digested membranes exposed to 100 nM native insulin for 3 h bound more 125I-insulin (approximately 40%) than did nondigested membranes preincubated without native insulin. The results allowed speculation that rat liver membranes up-regulated insulin receptors after treatment with insulin and that this was mediated by exposure of cryptic binding sites.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D007328:Insulin / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D010740:Phospholipases; D051381:Rats; D011972:Receptor, Insulin / Q000187:drug effects / Q000378:metabolism*
chemical_list: D007328:Insulin; C008147:insulin, iodo-; D011972:Receptor, Insulin; D010740:Phospholipases