title: Insulin-stimulated glucose transport and insulin internalization share a common postbinding step in adipocytes.
abstract: We recently demonstrated that chymotrypsin substrate analogues inhibit receptor-mediated insulin internalization in isolated rat adipocytes. In this study, the effect on glucose transport of inhibiting insulin internalization with these agents was examined. Glucose transport was assayed by measuring [3H]-2-deoxyglucose uptake, and internalized insulin was measured after rapidly dissociating surface-bound insulin with an acidic buffer. The chymotrypsin substrate analogue N-acetyl-Tyr ethyl ester inhibited insulin internalization by 85% while increasing surface-bound insulin by 80-110%. Under these conditions, ATP levels were minimally altered, and basal glucose transport was unchanged; however, insulin-stimulated glucose transport was decreased by 86%. The inhibition of insulin-stimulated glucose transport was not overcome by supramaximal concentrations (400 ng/ml) of insulin. When insulin internalization and insulin-stimulated glucose transport were measured in the presence of increasing concentrations of N-acetyl-Tyr ethyl ester (0.1-1 mM), a strong and highly significant correlation (r = .97, P less than .001) was found between inhibition of insulin internalization and inhibition of insulin-stimulated glucose uptake. Fragments of N-acetyl-Tyr ethyl ester that do not inhibit insulin internalization were also without effect on insulin-stimulated glucose transport. In addition to N-acetyl-Tyr ethyl ester, four other chymotrypsin substrate analogues that are effective inhibitors of insulin internalization also markedly inhibited insulin-stimulated glucose transport. These results indicate that insulin internalization and insulin-stimulated glucose transport share a common postbinding step in adipocytes and that this step is inhibitable by chymotrypsin substrate analogues.
mesh_terms: D000255:Adenosine Triphosphate / Q000032:analysis; D000273:Adipose Tissue / Q000032:analysis / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002918:Chymotrypsin / Q000378:metabolism; D003847:Deoxyglucose / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D007329:Insulin Antagonists / Q000494:pharmacology; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014443:Tyrosine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D007328:Insulin; D007329:Insulin Antagonists; D014443:Tyrosine; C007651:ethyl N-alpha-acetyl-tyrosinate; D000255:Adenosine Triphosphate; D003847:Deoxyglucose; C025787:N-acetyltyrosine; D002918:Chymotrypsin; D005947:Glucose