Modulation of the decay of Ca2+-activated Cl- currents in rabbit portal vein smooth muscle cells by external anions

1. The effects of external anions on the decay kinetics of Ca2+-activated C l- currents (I-Cl(ca)) were studied in smooth muscle cells isolated from ra bbit portal vein using the perforated patch whole-cell voltage clamp techni que. 2. In normal NaCl-containing external solution the decay of spontaneous Ca2 +-activated Cl- currents (STICs) and Ca2+-activated Cl- 'tail' currents (I- tail) was described by a single exponential with a time constant (tau) that was prolonged by external anions which are more permeable than Cl- (Br-, I - and SCN-) and accelerated by less permeant anions. However, intracellular I- did not affect the tau of STICs and I-tail. 3. There was a positive correlation between the ability of an external anio n to affect the decay tau of I-Cl(Ca) and its permeability relative to Cl-. 4. The voltage dependence of STIC and I-tail decay was not affected by exte rnal or internal anions. 5. External permeating anions were not obligatory for activation of I-Cl(Ca ) and STIC tau was not altered in Cl--free external solution. 6. Modulation of tau by mole fractions of SCN- and Cl- ions was fitted by a logistic curve, suggesting competition between SCN- and Cl- ions for a bin ding site. 7. In conclusion, external anions affect the decay of I-Cl(Ca) by a mechani sm compatible with an interaction with a binding site which modulates Cl- c hannel kinetics.