Dual modulation of swelling-activated chloride current by NO and NO donors in rabbit portal vein myocytes.

1. The effects of authentic NO and the NO donor S-nitroso-N-acetylpenicillamine (SNAP) on swelling-activated chloride currents (Iswell) were investigated in freshly dispersed rabbit portal vein smooth muscle cells. Iswell was recorded with the perforated patch configuration of the whole-cell patch clamp technique. 2. In approximately 50 % of cells NO and SNAP inhibited the amplitude of Iswell by about 45 % in a voltage-independent manner. Iswell was also inhibited by an inhibitor of NO-sensitive guanylate cyclase (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and by KT5823, an inhibitor of cGMP-dependent protein kinase. 3. In other cells both NO and SNAP enhanced Iswell by about 40 % in a voltage-independent manner. A similar increase was produced by application of the cell-permeable cGMP analogue 8-bromo-guanosine 3', 5'-cyclic monophosphate (8-Br-cGMP). However, 8-Br-cGMP had no effect on current amplitude in cells pre-treated with KT5823. In contrast 8-Br-cGMP increased the amplitude of Iswell in cells which had been pre-treated with ODQ. 4. SNAP also modulated Iswell recorded in the conventional whole-cell configuration with internal solutions containing 10 mM EGTA to rule out any contribution from Ca2+-activated Cl- currents. 5. These data suggest that the amplitude of Iswell can be enhanced by NO via a cGMP-dependent phosphorylation and inhibited by NO in a cGMP-independent manner.