Volume-activated Cl- channels (VACCs) can be activated by hypotonic solutions and
have been identified in many cell types. Here, we investigated the effects of different
statins on VACCs in monocytes. Whole-cell patch clamp recordings demonstrated that
a hypotonic solution induced 5-nitro-2- (3-phenylpropylamino) benzoic acid (NPPB)-
and 4,4'-diisothiocyanatostilbene-2, 2'-disulfonic acid (DIDS)-sensitive VACC currents
in human peripheral monocytes and RAW 264.7 cells. The VACC currents were inhibited
by the lipophilic statin (simvastatin) but not by the hydrophilic simvastatin acid
and pravastatin. A low-molecular-weight superoxide anion scavenger (tiron, 1 mM) and
inhibitor of NADPH oxidase (DPI 10 μM) was able to abolish the VACC currents. A hypotonic
solution increased the reactive oxygen species (ROS) detected by the fluorescence
of dichlorodihydrofluorescein (DCF), which was abolished by tiron and DPI. NPPB, DIDS,
and simvastatin but not pravastatin decreased the fluorescence of DCF. Simvastatin
could not further decrease VACC currents when pretreated with tiron or DPI, whereas
exogenous H2O2 (100 μM), increased the VACC currents and overcame the blockade of
VACC currents by simvastatin. Functionally, hypotonic solution increased the TNF-α
mRNA expression, which could be decreased by tiron, DPI, NPPB, DIDS and simvastatin
but not pravastatin. However, simvastatin could not decrease the TNF-α expression
further when pretreatment with tiron, DPI, NPPB or DIDS. We conclude that lipophilic
(simvastatin) rather than hydrophilic statin inhibit VACCs and decrease hyposmolality
induced inflammation in monocytes by inhibiting NADPH oxidase.