Restoration of cardiac transient outward potassium current by norepinephrine in diabetic rats

In cardiac ventricle, the density of the transient outward potassium curren t, I-to, is clearly related to sympathetic nervous system integrity. This s ympathetic regulation of I-to expression may be greatly significant to the genesis of cardiac complications of several diseases such us diabetes melli tus. Autonomic neuropathy, including cardiac neuropathy, is a complication of chronic diabetes. The objective of the present study was to identify the possible role of cardiac sympathetic neuropathy in the reduction of I-to c urrent density in diabetic ventricular myocardium. Thus, we employed the pa tch-clamp technique to test whether I-to can be restored in diabetic myocyt es incubated with norepinephrine. We also measured, using HPLC, the catecho lamine content of the stellate ganglion, which is responsible for cardiac s ympathetic innervation, in normal and diabetic animals. The main result of the present study was to show that a 24-h incubation of diabetic cells with norepinephrine restores I-to density to control values. The restoration of I-to current density by norepinephrine suggests that the diabetes-induced reduction of I-to is at least partially attributable to a reduced trophic e ffect of norepinephrine on the expression of I-to.