A swelling-activated chloride current in rat sympathetic neurones

1. We have tested whether neurones show a swelling-induced Cl- current following hypotonic shock, by recording membrane current responses and cell volume changes in voltage clamped isolated rat sympathetic neurones during application of hypotonic solutions. 2. Using both whole-cell and perforated patch recording methods, hypotonic solution caused cell swelling and the activation of an inward Cl- current at -6O MV. This current showed weak outward rectification with no obvious time dependence. It was inhibited by SITS (0.3-1mM), NPPB (30-300 mu M) and niflumic acid (50-200 mu M), but not by tamoxifen (10 mu M). 3. Hypotonic solution did not cause a rise in intracellular Ca2+ concentration as measured by simultaneous indo-1 fluorescence. Also, neither the volume change nor Cl- current were affected by the removal of external Ca2+ or internal Ca2+ buffering to less than or equal to nM with EGTA. 4. The Cl- current was unaffected by an inhibitor of protein kinase C (PKC; GF109203X, 3 mu M) or by omission of ATP from the pipette solution. 5. Cells exhibited a regulatory volume decrease during sustained exposure to hypotonic solution. This was completely inhibited by 0.5 mM niflumic acid. 6. It is concluded that osmotic swelling induces an outwardly rectifying, Ca2+- and PKC-independent Cl- current in these nerve cells. It is suggested that this current may be involved in volume regulatory mechanisms.