We studied the effects of glucose on specific insulin binding to cultured endothelial cells from the bovine aorta. We cultured the cells in Dulbecco's modified Eagle's medium, containing 100 or 300 mg/dl glucose or 100 mg/dl glucose plus 200 mg/dl mannitol. We added 125I-insulin to monolayers of these cells and counted the radioactivity resulting. Specific insulin binding increased with time and dosage. Maximal binding resulted from 0.17 nM 125I-insulin being incubated for 30 min at 37°C, and amounted to 0.35% per 105 cells being bound in cultures of 100 mg/dl glucose. The higher concentration of glucose led to significantly less binding (P < 0.05) (0.24 ± 0.03% vs. 0.38 ± 0.02%, n = 6). The addition of mannitol, on the other hand, did not affect binding. All three incubation conditions produced curvilinear competition curves. Scatchard analysis showed that insulin bound significantly less (P < 0.05) to endothelial cells in 300 mg/dl glucose than to those in 100 mg/dl glucose (4.0 ± 1.2 nmol/l vs. 12.8 ± 3.1, n = 6, mean ± SEM). Insulin binding capacity, however, did not change. We conclude that glucose can reduce insulin binding to endothelial cells and that it may reduce receptor-related insulin transport into and out of the cells.
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