Effects of palmatine on potassium and calcium currents in isolated rat hepatocytes

AIM: To study the effects of palmatine, a known inhibitor on delayed rectifier potassium current and L-type calcium current (I-Ca,I-L) in guinea pig ventricular myocytes, on the potassium and calcium currents in isolated rat hepatocytes. METHODS: Tight-seal whole-cell patch-clamp techniques were performed to investigate the effects of palmatine on the delayed outward potassium currents (I-K), inward rectifier potassium current (I-K1) and Ca2+ release-activated Ca2+ current (I-CRAC) in enzymatically isolated rat hepatocytes. RESULTS: Palmatine 0.3-100 muM reduced IK in a concentration-dependent manner with EC50 of 41.62+/-10.11 muM and n(H), 0.48+/-0.07 (n=8). The effect of the drug was poorly reversible after washout. When the bath solution was changed to tetraethylammonium (TEA) 8 MM, I-K was inhibited. Palmatine 10 muM and 100 muM shifted the I-V curves Of IK downward, and the block Of IK was voltage-independent. Palmatine 0.3-100 muM also inhibited I-CRAC in a concentration-dependent manner. The fitting parameters were as follows: EC50=51.19+/-15.18 muM, and n(H)=0.46+/-0.07 (n=8). The peak value of I-CRAC in the I-V relationship was decreased by palmatine 10 muM and 100 muM But the reverse potential of I-K I-CRAC occurred at Voltage=0 mV in all cells. Palmatine 0.3-100 muM failed to have any significant effect on either inward or outward components Of I-K1 at any membrane potential examined. CONCLUSION: The inhibitory effects on I-K and I-CRAC could be one of the mechanisms that palmatine exerts protective effect on hepatocytes.