RESUMO
AIMS: The fast transient outward current, I(to,fast) , is the most extensively studied cardiac K(+) current in diabetic animals. Two hypotheses have been proposed to explain how type-1 diabetes reduces this current in cardiac muscle. The first one is a deficiency in channel expression due to a defect in the trophic effect of insulin. The second one proposes flawed glucose metabolism as the cause of the reduced I(to,fast) . Moreover, little information exists about the effects and possible mechanisms of diabetes on the other repolarizing currents of the human heart: I(to,slow) , I(Kr) , I(Ks) , I(Kur) , I(Kslow) and I(K1) . METHODS: We recorded cardiac action potentials and K(+) currents in ventricular cells isolated from control and streptozotocin- or alloxan-induced diabetic mice and rabbits. Channel protein expression was determined by immunofluorescence. RESULTS: Diabetes reduces the amplitude of I(to,fast) , I(to,slow) and I(Kslow) , in ventricular myocytes from mouse and rabbit, with no effect on I(ss) , I(Kr) or I(K1) . The absence of changes in the biophysical properties of the currents and the immunofluorescence experiments confirmed the reduction in channel protein synthesis. Six-hour incubation of myocytes with insulin or pyruvate recovered current amplitudes and fluorescent staining. The activation of AMP-K reduced the same K(+) currents in healthy myocytes and prevented the pyruvate-induced current recovery. CONCLUSION: Diabetes reduces K(+) current densities in ventricular myocytes due to a defect in channel protein synthesis. Activation of AMP-K secondary to deterioration in the metabolic status of the cells is responsible for K(+) channel reductions.
