Insulin binding and action in isolated cardiocytes from spontaneously diabetic BB rats

Isolated cardiac myocytes from control and insulin treated diabetic BB rats were used to study cellular alterations related to partly controlled diabetes. Scatchard analysis of equilibrium binding data showed an unaltered affinity and number of insulin receptors in cardiocytes from both groups of animals. Moreover, insulin internalization was found to be identical under these conditions. Insulin action was determined by measuring the effect of the hormone on initial velocities of 3-0-methylglucose influx. Basal activity of the glucose transporter and maximal transport stimulation by insulin remained unaffected. In contrast, the sensitivity of the carrier towards stimulation by insulin was markedly reduced in cardiocytes from diabetic rats with a half-maximal action occurring at an insulin concentration of 3 X 10(-10) mol/l and 9 X 10(-9) mol/l in control and diabetic animals, respectively. The onset of insulin action was much slower in cells from diabetic BB rats exhibiting an increase in the coupling time by 400% from 5 to 20 min, respectively. The data suggest an association of partly controlled diabetes with myocardial alterations located at the postreceptor level.