Contribution of chloride channels to volume regulation of cortical astrocytes.

The objective of this study was to determine the relative contribution of Cl(-) channels to volume regulation of cultured rat cortical astrocytes after hypotonic cell swelling. Using a Coulter counter, we showed that cortical astrocytes regulate their cell volume by approximately 60% within 45 min after hypotonic challenge. This volume regulation was supported when Cl(-) was replaced with Br(-), NO(3)(-), methanesulfonate(-), or acetate(-) but was inhibited when Cl(-) was replaced with isethionate(-) or gluconate(-). Additionally, substitution of Cl(-) with I(-) completely blocked volume regulation. Volume regulation was unaffected by furosemide or bumetanide, blockers of KCl transport, but was inhibited by Cl(-) channel blockers, including 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and niflumic acid. Surprisingly, the combination of Cd(2+) with NPPB, DIDS, or niflumic acid inhibited regulation to a greater extent than any of these drugs alone. Volume regulation did not differ among astrocytes cultured from different brain regions, as cerebellar and hippocampal astrocytes exhibited behavior identical to that of cortical astrocytes. These data suggest that Cl(-) flux through ion channels rather than transporters is essential for volume regulation of cultured astrocytes in response to hypotonic challenge.