title: Down-regulation of insulin receptors in the heart: studies on primary cultured adult cardiac myocytes.
abstract: Primary cultured cardiac myocytes from adult rats have been used to study insulin receptor regulation. Culturing of cells in the presence of insulin induced a dose-dependent down-regulation of insulin binding with a maximal effect of 35% at an insulin concentration of 1.7 X 10(-7) mol/l. The number of high-affinity sites decreased from 110 000 to 70 000 sites per cell in control and down-regulated cells, respectively, with no change in the apparent affinity constant. Down-regulation was found to be rapid (t 1/2 = 3 h) and fully reversible. Culturing of cells in the presence of cycloheximide (0.1 mmol/l) or Tris (35 mmol/l) resulted in a further time-dependent increase in insulin-induced receptor loss with no effect on insulin binding to control cells. The action of both agents was found to be additive reaching a down-regulation of 51% after a culture period of 16 h. Recovery of insulin binding activity after removal of insulin remained unaffected in the presence of cycloheximide, whereas Tris inhibited this process by 74%. In conclusion our results show that the concept of insulin-induced receptor down regulation can be extended to the adult heart muscle. Moreover the data suggest involvement of protein synthesis and receptor recycling in this process.
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003864:Depression, Chemical; D007328:Insulin / Q000494:pharmacology*; D009124:Muscle Proteins / Q000096:biosynthesis; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D011972:Receptor, Insulin / Q000187:drug effects* / Q000378:metabolism; D014325:Tromethamine / Q000494:pharmacology
chemical_list: D007328:Insulin; D009124:Muscle Proteins; D014325:Tromethamine; D003513:Cycloheximide; D011972:Receptor, Insulin