PHARMACOLOGICAL CHARACTERIZATION OF SWELLING-INDUCED D-[H-3]ASPARTATERELEASE FROM PRIMARY ASTROCYTE CULTURES

During stroke or head trauma, extracellular K+ concentration increases , which can cause astrocytes to swell. In vitro, such swelling causes astrocytes to release excitatory amino acids, which may contribute to excitotoxicity in vivo. Several putative swelling-activated channels h ave been identified through which such anionic organic cellular osmoly tes can be released. In the present study, we sought to identify the s welling-activated channel(s) responsible for D-[H-3]aspartate release from primary cultured astrocytes exposed to either KCI or hypotonic me dium. KCl-induced D-[H-3]aspartate release was inhibited by the anion channel inhibitors 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), dideoxy-forskolin, L-644711, ATP, ITP, 3'-azido-3'-deoxythymidine, DI DS, and tamoxifen but not by cAMP The cell swelling caused by raised K Cl was not inhibited by extracellular ATP or tamoxifen as measured by an electrical impedance method, which suggests that these anion channe l inhibitors directly blocked the channel responsible for efflux. Extr acellular nucleotides and DIDS, however, had no or only partial effect s on D-[H-3]aspartate release from cells swollen by hypotonic medium, but such release was inhibited by NPPB, dideoxyforskolin, and tamoxife n. Of the swelling-activated channels so far identified, our data sugg est that a volume-sensitive outwardly rectifying channel is responsibl e for D-[H-3]aspartate release from primary cultured astrocytes during raised extracellular K+ and possibly during hypotonic medium-induced release.