Effects of Xinjining(心悸宁) Extract on Inward Rectifier Potassium Current in Ventricular Myocytes of Guinea Pig

Objective： To study the effect of Xinjining extract （心悸宁, XJN） on inward rectifier potassium current （IKI） in ventricular myocyte （VMC） of guinea pigs and its anti-arrhythmic mechanism on ion channel level. Methods： Single VMC was enzymatically isolated by zymolisis, and whole-cell patch clamp recording technique was used to record the Ikl in VMC irrigated with XJN of different concentrations （1.25, 2.50, 5.00 g/L; six samples for each）. The stable current and conductance of the inward component of IK1 as well as the outward component of peak IK1 and conductance of it accordingly was recorded when the test voltage was set on -110 mV. Results： The suppressive rate of XJN on the inward component of IK1 was 9.54% ± 5.81%, 34.82% ± 15.03%, and 59.52% ± 25.58% with a concentration of 1.25, 2.50, and 5.00 g/L, respectively, and that for the outward component of peak IK1 was 23.94%± 7.45%, 52.98%± 19.62%, and 71.42% ± 23.01%, respectively （all P〈0.05）. Moreover, different concentrations of XJN also showed effects for reducing IK1 conductance. Conclusion： XJN has inhibitory effect on IK1in guinea pig＇s VMC, and that of the same concentration shows stronger inhibition on outward component than on inward component, which may be one of the mechanisms of its anti-arrhythmic effect.

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 ofalloxan （145mg/kg, Lv. ）. 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 -5.404-1.08 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） （J Geriatr Cardio12010; 7：25-29）.