Insulin-induced reduction of membrane receptor concentrations in isolated fat cells and lymphocytes. Independence from receptor occupation and possible relation to proteolytic activity of insulin.

Incubation of cultured human lymphocytes or isolated rat fat cells at 37 degrees with insulin results in a time-dependent fall in the ability of the thoroughly washed cells to bind 125I-labeled insulin. Although this effect is dependent on the concentration of insulin used in the preincubation period, the concentration dependence pattern varies directly with the length of this incubation, and kinetically (i.e. at early times) it is virtually impossible to demonstrate saturability with respect to insulin concentration. Significant effects are demonstrable at very early times (e.g. 1 to 3 hours) provided sufficiently high insulin concentration (i.e. 5 mug/ml or more) are used...