Modulation Of ICl(Ca) in vascular smooth muscle cells by oxidizing and cysteine-reactive reagents

The present study investigated the effect of redox agents on Ca2+-activated Cl- currents (I-Cl(Ca)) recorded in smooth muscle cells isolated from rabbit portal vein. In perforated-patch experiments on portal vein cells the amplitude of I-Cl(Ca) evoked by either spontaneous release of Ca2+ from internal stores or Ca2+ influx through voltage-dependent Ca2+ channels was markedly and irreversibly enhanced by the non-specific oxidant, diamide (10-200 muM). Diamide also prolonged the decay of both currents. The reductant dithiothreitol had no effect on control I-Cl(Ca) but reversed the increase of current amplitude produced by diamide. Diamide also increased global intracellular Ca2+ at rest but had no effect on the time-course of Ca "sparks" determined by confocal microscopy. Diamide and the endogenous oxidant hydrogen peroxide increased the amplitude and prolonged the kinetics of I-Cl(Ca) evoked by pipette solutions containing free Ca2+ clamped at 500 nM. Similar effects were observed with the hydrophilic thiol-reactants thimerosal and p-chloromercuriphenylsulphonic acid (PCMPS). Therefore, the gating and activation of Ca2+-activated Cl- conductance is sensitive to redox modification.