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,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 Ca(2+) release-activated Ca(2+) current (I(CRAC)) in enzymatically isolated rat hepatocytes. RESULTS: Palmatine 0.3-100 microM reduced I(K) in a concentration-dependent manner with EC(50) of 41.62+/-10.11 microM 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, IK was inhibited. Palmatine 10 microM and 100 microM shifted the I-V curves of I(K) downward, and the block of I(K) was voltage-independent. Palmatine 0.3-100 microM also inhibited I(CRAC) in a concentration-dependent manner. The fitting parameters were as follows: EC(50)=51.19+/-15.18 microM, 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 microM and 100 microM. But the reverse potential of I(CRAC) occurred at Voltage=0 mV in all cells. Palmatine 0.3-100 microM 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.