AJP - Endocrinology and Metabolism, Vol 250, Issue 4 402-E406, Copyright © 1986 by American Physiological Society
Insulin binding and glucose transport activity in cardiomyocytes of a diabetic rat
E. C. Almira, A. R. Garcia and B. R. Boshell
We studied insulin binding and glucose transport in isolated adult
cardiomyocytes from rats with 2-wk streptozotocin-induced diabetes. At 37
degrees C, cells from diabetic rats bound less 125I-insulin and exhibited
lower rates of 3-O-methylglucose transport than cells from control rats. In
contrast, the amount of 125I-insulin bound to myocytes at 4 degrees C was
the same in both groups. Preincubation of cells from both groups with
10-10,000 ng/ml insulin significantly increased their basal rates of
glucose transport by approximately 40%. However, the augmented rates in
diabetics were still approximately 36% lower than the corresponding
insulin-stimulated rates in the controls. When the glucose transport data
were expressed as percent maximal insulin effect and plotted as a function
of the amount of insulin bound, the curves obtained from both diabetic and
nondiabetic controls were superimposable. These data demonstrate that 1)
heart cells from diabetic rats bind less insulin than from control rats
under conditions in which they exhibit impaired glucose transport rates, 2)
there is no apparent difference in total receptor number between the two
groups, but internalization of intact insulin appears to be diminished in
diabetes, 3) coupling exists between insulin binding and glucose transport
in both groups, and 4) these impaired processes are completely reversed by
insulin treatment in vivo but not in vitro.
