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AIM:To study the effects of palmatine,a known inhibitoron delayed rectifier potassium current and L-type calciumcurrent(I_(Ca,L))in guinea pig ventricular myocytes,on thepotassium and calcium currents in isolated rat hepatocytes.METHODS:Tight-seal whole-cell patch-clamp techniqueswere performed to investigate the effects of palmatine onthe delayed outward potassium currents(I_K),inward rectifierpotassium current(I_(K1))and Ca~(2+)release-activated Ca~(2+)current(I_(CRAC))in enzymatically isolated rat hepatocytes.RESULTS:Palmatine 0.3-100 μM reduced I_K in a concentration-dependent manner with EC_(50)of 41.62±10.11 μM and n_H,0.48±0.07(n=8).The effect of the drug was poorly reversibleafter washout.When the bath solution was changed totetraethylammonium(TEA)8 raM,I_K was inhibited.Palmatine 10 μM and 100 μM shifted the Ⅰ-Ⅴ curves of I_Kdownward,and the block of I_K was voltage-independent.Palmatine 0.3-100 μM also inhibited I_(CRAC)in a concentration-dependent manner.The fitting parameters were as follows:EC_(50)=51.19±15.18 μM,and nH=0.46±0.07(n=8).The peakvalue of I_(CRAC)in the Ⅰ-Ⅴ relationship was decreased bypalmatine 10 μM and 100 μM.But the reverse potential ofI_(CRAC)occurred at Voltage=0 mV in all cells.Palmatine 0.3-100 μM failed to have any significant effect on either inwardor outward components of I_(K1)at any membrane potentialexamined.CONCLUSION:The inhibitory effects on I_K and I_(CRAC)couldbe one of the mechanisms that palmatine exerts protectiveeffect on hepatocytes.
AIM: To study the effects of palmatine, a known inhibitor of delayed rectifier potassium current and L-type calcium current (I_ (Ca, L)) in guinea pig ventricular myocytes, on the potassium and calcium currents in isolated rat hepatocytes. METHODS: Tight- whole-cell patch-clamp techniqueswere performed to investigate the effects of palmatine on the delayed outward potassium currents (I_K), inward rectifierpotassium current (I_ (K1)) and Ca 2+ release- activated Ca 2+ current I_ (CRAC)) in enzymatically isolated rat hepatocytes. RESULTS: Palmatine 0.3-100 μM reduced I_K in a concentration-dependent manner with EC_ (50) of 41.62 ± 10.11 μM and n_H, 0.48 ± 0.07 (n = 8) of the drug was poorly reversible after washout. The bath solution was changed totetraethylammonium (TEA) 8 raM, I_K was inhibited. Palmatine 10 μM and 100 μM shifted the I-V curves of I_Kdownward, and the block of I_K was voltage-independent. Palmatine 0.3-100 μM also inhibited I_ (CRAC) in a concentration-dependent manner. The fitti ng values were as follows: EC 50 = 51.19 ± 15.18 μM, and nH = 0.46 ± 0.07 (n = 8). The peak value of I_ (CRAC) in the Ⅰ -Ⅴ relationship was decreased by palmatine 10 μM and 100 μM. But the reverse potential of I_ (CRAC) occurred at Voltage = 0 mV in all cells. Partmatine 0.3-100 μM failed to have any significant effect on either inwardor outward components of I_ (K1) at any membrane potentialexamined. CONCLUSION: The inhibitory effects on I_K and I_ (CRAC) could be one of the mechanisms that palmatine exerts protective effect on hepatocytes.