The ionic mechanisms of long QT interval in diabetic rabbits

Objective Abnormal QT prolongation associated with arrhythmias is considered the major cardiac electrical disorder and a significant predictor of mortality in diabetic patients. The precise ionic mechanisms for diabetic QT prolongation remained unclear. The present study was designed to analyze the changes of ventricular repolarization and the underlying ionic mechanisms in diabetic rabbit hearts. Methods Diabetes was induced by a single injection of alloxan (145mg/kg, i.v. ). After the development of diabetes (10 weeks), ECG was measured. Whole-cell patch-clamp technique was applied to record the action potential duration (APD50, APD90), slowly activating outward rectifying potassium current (IKs), L-type calcium current (ICa-L) and inward rectifying potassium current (IK1). Results The action potential duration (APD50 and APD90) of ventricular myocytes was obviously prolonged from 271.5±32.3 ms and 347.8±36.3 ms to 556.6±72.5 ms and 647.9±72.2 ms respectively (P< 0.05). Meanwhile the normalized peak current densities of IKs in ventricular myocytes investigated by whole-cell patch clamp was smaller in diabetic rabbits than that in control group at test potential of +50mV (1.27±0.20 pA/pF vs 3.08±0.67 pA/pF, P<0.05). And the density of the ICa-L was increased apparently at the test potential of 10 mV (-2.67±0.41 pA/pF vs -5.40±1.08 pA/pF, P<0.05). Conclusion Ventricular repolarization was prolonged in diabetic rabbits, it may be partly due to the increased L-type calcium current and reduced slow delayed rectifier K+ current (IKs).