Effect of Aldose Reductase Inhibition on Calcium homeostasis in adult rat ventricular myocytes subjected to stimulated ischemia

Abstract

Cardiovascular disease represents the major cause of morbidity and mortality in patients with diabetes mellitus. Recently, it has been found that aldose reductase (AR), a key enzyme in the pathogenesis of diabetic complications, is involved in myocardial infarction. The mechanism is assumed to be due to the depletion of ATP level by increasing the cytosolic NADH/NAD+ ratio. Previous studies showed that the activity of cardiac RyR decreased in the presence of NADH and increased with NAD+. We hypothesized that the I/R-induced increase in NADH/NAD+ by the activation of polyol pathway impaired the Ca2+ handling at multiple sites. To test the hypothesis, we therefore determine how the ryanodine receptor (RyR) and sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) handled Ca2+ in rat ventricular myocytes followed by either inhibiting AR or sorbitol dehydrogenase (SDH) with 5uM zopolrestat (CP-83,750) or SDH inhibitor (CP-470,711), and subsequently subjected to stimulated ischemia. We determine the following: Ca2+ transient induced by the electrical stimulation, which provided the overall picture for Ca2+ homeostasis; expression of RyR and SERCA by Western blot analysis in rat ventricular myocytes. We found that inhibition of AR or SDH attenuated the I/R-induced decrease in the activity of RyR and SERCA, but the expression of RyR and SERCA remained unchanged. The results are evidence that AR may contribute to the severity of I/R injury of the rat hearts by impairing Ca2+ homeostasis at multiple sites (RyR and SERCA).