TETRAHYDROBERBERINE SUPPRESSES DOPAMINE-INDUCED POTASSIUM CURRENT IN ACUTELY DISSOCIATED CA1 PYRAMIDAL NEURONS FROM RAT HIPPOCAMPUS

Effects of tetrahydroberberine (THE) on dopamine (DA)-induced response have been investigated in single pyramidal neurons freshly dissociate d from CA1 area of the hippocampus using the nystatin perforated patch -clamp, whole-cell recording technique under voltage-clamp configurati on. At a holding potential (V-H) of -20 mV, DA-induced responses inclu ded a transient outward current, a slow inward current and a combinati on of the two. The outward current had a reversal potential of -83.5 /- 8.0 mV which was close to K+ equilibrium potential and was sensitiv e to TEA, suggesting that this outward current was carried by K+. Appl ication of THB reversibly suppressed three type responses induced by D A with different degrees of inhibitory ratio. THE inhibited the DA-ind uced outward current in a concentration-dependent manner with an IC50 of 13 mu M. The maximal value of the concentration-response curve for DA-induced outward current was suppressed by THE, suggesting a non-com petitive inhibition. The results support the hypothesis that THE acts as a novel dopaminergic system antagonist. Furthermore, THE inhibits t he DA-induced K+ current non-competitively in single dissociated cells , implying that THE may exhibit other pharmacological action on the ce ntral nervous system.