The Establishment Of Screening Models Of Ion Channels As A Target For Antiarrhythmic Drugs And Diuretics

In order to explore the changes of action potential and ionic currents induced by application of aconitine to single ventricular myocytes, whole cell patch clamp technique was used to record action potential duration (APD), sodium current (I_Na), L-type calcium current (I_Ca-L), inward rectifier potassium current (I_K1) and transient outward potassium current (I_to). Combined with the laser scanning confocal microscopic technique, the cytosolic [Ca²⁺]j was observed. Results showed: in single rat ventricular myocytes, aconitine 1 μmol · L^-1 prolonged the APD₅₀ and APD₉₀ from 103.4 ± 7.71 ms and 150.2 ± 7.02 to 176.4 ± 16.43 ms and 236.0 ± 23.22 ms respectively (P<0.01,n=12 from eight rats) . The APD90 prolonged by aconitine was further increased after perfusion of quinidine 10 μmol · L^-1. But the prolongation caused by aconitine was restored after verapamil 10 μmol · L^-1 was used. Oscillation of resting potential and delayed afterdepolarization and trigger activity was occurred when the higher dosage of aconitine(5 μmol · L^-1) was applied. In addition to prolongation of APD, aconitine increased I_Na, I_Ca-L and I_K1. The time constant of inactivation of I_Ca-L was delayed by aconitine. The voltage-dependent activation, inactivation and recovery of I_Ca-L showed no change. These results suggested that the arrhythmogenesis mechanism of aconitine may lie in its prolongation effect on APD of single ventricular myocytes. Enhancement of inward I_Na, I_Ca-L and decrease of outward potassium could be ionic mechnism of APD prolongation.[Ca²⁺]_i mobilization by KCl and caffeine were studied by the method of laser scanning confocal microscopy technique in single isolated rat ventricular myocytes. We found neither in the absence nor presence of extracellular calcium 1.8mmol/L FI value of [Ca²⁺]j in control resting level was changed by aconitine 1 μmol · L^-1. But FI value of [Ca²⁺]_i elevated by 60 mmol · L^-1 KCl was enhanced by aconitine. However, aconitine showed an inhibitory effect on caffeine-induce calcium release from sarcoplasmic reticulum. We can deduce from theses results that aconitine may have no effect on cardiac contractility although it increase L-type calcium current. And it gave us a hint that aconitine induced-permanent high [Ca²⁺]_i status might contribute to delayed...