Potassium currents in ventricular myocytes from genetically diabetic rats

Abstract

Our previous study demonstrated the longer duration of action potential in ventricular myocytes from genetically diabetic WBN/Kob rats without change in calcium channel density compared with age-matched controls [Tsuchida, K., H. Watajima, and S. Otamo. Am. J. Physiol. 267 (Heart Circ. Physiol. 36): H2280-H2289, 1994]. In the present study we examined the alteration of potassium currents, especially transient outward current, in ventricular myocytes of genetically diabetic WBN/Kob rats. WBN/Kob rats gradually develop hyperglycemia with aging and show some similarity to non-insulin-dependent diabetes mellitus models, which differ from the insulin-dependent streptozotocin-treated rat model. The density of the intracellular calcium ion-independent transient outward current (I(to)) from 17- to 19-mo diabetic rat myocytes was significantly smaller than that from age-matched control rat myocytes. In addition, the density of I(to) from 17- to 19-mo rat myocytes was significantly less than that from 2-mo rat myocytes, suggesting that aging-induced alteration of I(to) was accelerated by the diabetic state. The steady-state inactivation curves of I(to), the recovery from I(to) inactivation, and the other outward currents were not significantly altered between diabetic myocytes and age-matched control myocytes. In conclusion, the prolonged duration of action potential from genetically diabetic rat myocytes is mainly due to the depressed I(to).