EFFECTS OF CICLETANINE ON WHOLE-CELL CURRENTS OF SINGLE SMOOTH-MUSCLECELLS FROM THE GUINEA-PIG PORTAL-VEIN

1 Smooth muscle cells of the guinea-pig portal vein were dispersed by enzymatic treatment and recordings of membrane currents were made in t he whole-cell mode by the patch-clamp technique. The effects of extrac ellular application of cicletanine-hydrochloride on the whole-cell cur rents of isolated smooth muscle cells from the guinea-pig portal vein were studied in solutions containing a normal concentration of calcium (2.5 mm). 2 Cicletanine, 10 to 100 mum, reduced the voltage-dependent inward calcium current with an IC50 of 250 muM. These effects of cicl etanine were reversible. 3 The action of cicletanine on calcium curren ts can be interpreted as a decrease of the availability of calcium cha nnels but not by an alteration of the time course or voltage-dependenc y of inactivation. 3 The control calcium current was enhanced by appli cation of Bay K 8644. On this enhanced inward current, cicletanine als o exerted inhibitory effects which were not use-dependent. 5 Cicletani ne, 1 to 100 mum, did not enhance outward potassium currents. 6 It is concluded that at least one component of the vasorelaxant effects of c icletanine is produced by inhibition of calcium currents.