INSULIN RECEPTORS AND INSULIN RECEPTOR PROTEIN KINASE ACTIVITY IN MUSCLES OF ENDURANCE TRAINED RATS

1985 ◽  
Vol 17 (2) ◽  
pp. 240
Author(s):  
G. L. Dohm ◽  
J. F. Caro ◽  
M. K. Sinha
1987 ◽  
Vol 252 (2) ◽  
pp. E170-E175
Author(s):  
G. L. Dohm ◽  
M. K. Sinha ◽  
J. F. Caro

Exercise has been shown to increase insulin sensitivity, and muscle is quantitatively the most important tissue of insulin action. Since the first step in insulin action is the binding to a membrane receptor, we postulated that exercise training would change insulin receptors in muscle and in this study we have investigated this hypothesis. Female rats initially weighing approximately 100 g were trained by treadmill running for 2 h/day, 6 days/wk for 4 wk at 25 m/min (0 grade). Insulin receptors from vastus intermedius muscles were solubilized by homogenizing in a buffer containing 1% Triton X-100 and then partially purified by passing the soluble extract over a wheat germ agglutinin column. The 4 wk training regimen resulted in a 65% increase in citrate synthase activity in red vastus lateralis muscle, indicating an adaptation to exercise. Insulin binding by the partially purified receptor preparation s was approximately doubled in muscle of trained rats at all insulin concentrations, suggesting an increase in the number of receptors. Training did not alter insulin receptor structure as evidenced by electrophoretic mobility under reducing and nonreducing conditions. Basal insulin receptor protein kinase activity was higher in trained than untrained animals and this was likely due to the greater number of receptors. However, insulin stimulation of the protein kinase activity was depressed by training. These results demonstrate that endurance training does alter receptor number and function in muscle and these changes may be important in increasing insulin sensitivity after exercise training.


1987 ◽  
Vol 245 (2) ◽  
pp. 325-331 ◽  
Author(s):  
P A Wilden ◽  
J E Pessin

The purified human placental insulin-receptor beta-subunit autophosphorylating activity was found to be inhibited, in a time- and concentration-dependent manner, by the specific thiol-alkylating agents N-ethylmaleimide and 5,5′-dithiobis-(2-nitrobenzoic acid). The insulin-receptor kinase was observed to be more sensitive to inhibition by N-ethylmaleimide in the presence [IC50 (concn, giving 50% inhibition) = 25 +/- 3 microM] than in the absence (IC50 = 73 +/- 6 microM) of insulin. Similarly, inhibition by 5,5′-dithiobis-(2-nitrobenzoic acid) occurred with IC50 = 30 +/- 6 microM in the presence and 155 +/- 35 microM in the absence of insulin. Examination of the exogenous-substrate protein kinase activity demonstrated that the differential sensitivity to N-ethylmaleimide was due to direct inhibition of protein kinase activity, as opposed to blockade of the phospho-acceptor properties of the insulin receptor. In contrast, iodoacetamide had essentially no effect on the insulin-receptor beta-subunit autophosphorylating activity and was able to protect partially against the N-ethylmaleimide inhibition in both the presence and the absence of insulin. Consistent with these findings, none of the thiol-specific agents were able to alter significantly insulin binding at concentrations which maximally inhibited the beta-subunit autophosphorylation. Further, in the presence of insulin, the insulin-receptor kinase activity was also observed to be more sensitive to oxidation by H2O2 and FeCl3/ascorbate compared with insulin receptors in the absence of insulin. These results indicate that there is a critical thiol group(s) necessary for the beta-subunit autophosphorylating activity of the insulin-receptor kinase and that in the presence of insulin is more susceptible to exogenously added thiol and oxidizing agents.


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