WHOLE-CELL PATCH-CLAMP MEASUREMENTS AND BERBERINE INHIBITION OF HYPERPOLARIZATION-ACTIVATED INWARD CURRENT IN RABBIT SINOATRIAL NODE CELLS

Single rabbit sinoatrial node (SAN) cells were isolated by means of an enzymatic dispersion procedure and used for the whole-cell patch clam p experiment. At a holding potential of - 40 mV , a time- and voltage- dependent inward current, I(f), was activated at different hyperpolari zation potentials from - 60 mV to - 110 mV. The current-voltage relati on curve showed that I(f) was activated at potential more negative tha n - 40 mV. Five min after treatment by CsCl2 mmol . L-1-containing Tyr ode solution, I(f) was almost completely blocked. At a hyperpolarizati on potential of - 110 mV , I(f) was reduced from 1. 7 +/- 0. 2 nA of t he control to 1. 2 +/- 0.4 nA after superfusing with Tyrode solution c ontaining berberine (Ber) 1 mumol . L-1 for 5 min. And it was difficul t to wash out this action. Ber also had inhibitory effects on other cu rrents to a certain extent. The results indicate that I(f) is a Cs+-se nsitive current and that the negative chronotropic effect of Ber may b e due to the inhibition of I(f) that functions as an important pacemak ing modulator for the spontaneous depolarization of SAN tissue.