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

摘要

class="enumerated" style="list-style-type:decimal">The effects of external anions on the decay kinetics of Ca²⁺-activated Cl⁻ currents (ICl(Ca)) were studied in smooth muscle cells isolated from rabbit portal vein using the perforated patch whole-cell voltage clamp technique.In normal NaCl-containing external solution the decay of spontaneous Ca²⁺-activated Cl⁻ currents (STICs) and Ca²⁺-activated Cl⁻‘tail’ currents (Itail) was described by a single exponential with a time constant (τ) 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 τ of STICs and Itail.There was a positive correlation between the ability of an external anion to affect the decay τ of ICl(Ca) and its permeability relative to Cl⁻.The voltage dependence of STIC and Itail decay was not affected by external or internal anions.External permeating anions were not obligatory for activation of ICl(Ca) and STIC τ was not altered in Cl⁻-free external solution.Modulation of τ by mole fractions of SCN⁻ and Cl⁻ ions was fitted by a logistic curve, suggesting competition between SCN⁻ and Cl⁻ ions for a binding site.In conclusion, external anions affect the decay of ICl(Ca) by a mechanism compatible with an interaction with a binding site which modulates Cl⁻ channel kinetics.