The role of ClC-3 in volume-activated chloride currents and volume regulation in bovine epithelial cells demonstrated by antisense inhibition

1. A chloride current with mild outward rectification was induced in the na tive bovine nonpigmented ciliary epithelial (NPCE) cells by a 23% hypotonic solution. The current showed no or little inactivation at depolarized step s. 2. ATP blocked 88 and 61% of the outward and inward components of the volum e-activated chloride current (I-Cl,I-vol) with an IC50 of 5.3 and 9.6 mM, r espectively. 3. The volume-activated chloride current was decreased and the activation o f the current was delayed by inhibiting endogenous ClC-3 expression using a ClC-3 antisense oligonucleotide. The inhibition of the current as a functi on of antisense concentration was asymptotic with a maximum about 60 %. The remaining current was probably not derived from ClC-3 and was inhibited by ATP. 4. ClC-3 expression in the bovine NPCE cells was verified by immunofluoresc ence studies. ClC-3 immunofluorescence was distributed throughout the cells but with the predominant location within the nucleus. The expression of Cl C-3 protein was diminished by the ClC-3 antisense oligonucleotide with the greatest diminution occurring in the nuclear region. 5. The size of the volume-activated chloride current was positively correla ted with the ClC-3 immunofluorescence level. 6. Regulatory volume decrease of the NPCE cells was reduced by ClC-3 antise nse oligonucleotide. 7. We conclude that endogenous ClC-3 is associated with the volume-activate d chloride current and is involved in cell volume regulation, but that it c an only contribute towards a proportion of the current in NPCE cells. 8. The nuclear predominance of ClC-3 immunofluorescence in NPCE cells, the absence of basal activity of chloride current and the marked pharmacologica l differences between IClC-3 and I-Cl,I-vol argue against ClC-3 being the o nly, or even the main, volume-activated chloride channel in NPCE cells.