PROPERTIES OF OSMOLYTE FLUXES ACTIVATED DURING REGULATORY VOLUME DECREASE IN CULTURED CEREBELLAR GRANULE NEURONS

Efflux pathways for amino acids, K, and Cl activated during regulatory volume decrease (RVD) were characterized in cultured cerebellar granu le neurons exposed to hyposmotic conditions. Results of this study fav or diffusion pores (presumably channels) over energy-dependent transpo rters as the mechanisms responsible for the efflux of these osmolytes. The selectivity of osmolyte pathways activated by RVD was assessed by increasing the extracellular concentrations of cations, anions, and a mino acids to such an extent that upon opening of the pathway, a perme able compound will enter the cell and block RVD by reducing the efflux of water carried by the exit of intracellular osmolytes. The cationic pathway was found selective for K (and Rb), whereas the anionic pathw ay was rather unselective being permeable to Cl, nitrate, iodine, benz oate, thiocyanate, and sulfate but impermeable to gluconate. Glutamate and aspartate as K but not as Na salts were permeable through the ani on channel. RVD was slightly inhibited by quinidine but otherwise was insensitive to known K channel blockers. RVD was inhibited by 4,4'-dii sothiocyanostilbene-2-2'-disulfonic acid (DIDS), niflumic acid, and di pyridamole. Gramicidin did not affect cell volume in isosmotic conditi ons but greatly accelerated RVD, suggesting that cell permeability to Cl is low in isosmotic conditions but increases markedly during RVD ma king K permeability the rate limit of the process. The permeability pa thway for amino acids activated during RVD was permeable to short chai n alpha- and beta-amino acids, but excluded glutamine and basic amino acids. (C) 1994 Wiley-Liss, Inc.