Effects of Chinese herbs on multiple ion channels in isolated ventricular myocytes

Background Shensong Yangxin (SSYX) is one of the compound recipe of Chinese materia medica.This study was conducted to investigate the effects of SSYX on sodium current (I_(Na)),L-type calcium current (I_(Ca,L)),transient outward potassium current (I_(to)),delayed rectifier current (I_K),and inward rectifier potassium currents (I_(K1)) in isolated ventricular myocytes. Methods Whole cell patch-clamp technique was used to study ion channel currents in enzymatically isolated guinea pig or rat ventricular myocytes. Results SSYX decreased peak I_(Na) by (44.84±7.65)% from 27.21±5.35 to 14.88±2.75 pA/pF (n=5,P0.05).The medicine significantly inhibited the I_(Ca,L).At concentrations of 0.25,0.50,and 1.00 g/100 ml,the peak I_(Ca,L) was reduced by (19.22±1.10)%,(44.82±6.50)% and (50.69±5.64)%,respectively (n=5,all P0.05).SSYX lifted the Ⅰ-Ⅴ curve of both I_(Na) and I_(Ca,L) without changing the threshold,peak and reversal potentials.At the concentration of 0.5%,the drug blocked the transient component of I_(to) by 50.60% at membrane voltage of 60 mV and negatively shifted the inactive curve and delayed the recovery from channel inactivation.The tail current density of I_K was decreased by (30.77±1.11)% (n=5, P0.05) at membrane voltage of 50 mV after exposure to the medicine and the time-dependent activity of I_K was also inhibited.Similar to the effect on I_K,the SSYX inhibited I_(K1) by 33.10% at the test potential of-100 mV with little effect on reversal potential and the rectification property. Conclusions The experiments revealed that SSYX could block multiple ion channels such as I_(Na) I_(Ca,L),I_k,I_(to) and I_(K1), which may change the action potential duration and contribute to some of its antiarrhythmic effects. Chin Med J 2007;120(12):1068-1074