The role of taurine in the regulation of brain cell volume in chronically hyponatraemic rats

Cells in slices prepared from the superficial cerebral cortex of normonatra emic rats underwent moderate swelling when exposed to low Na+ medium (122 m mol/l) accompanied by a large increase in the rate of efflux of preloaded t aurine. In contrast, cells in slices from chronically (4 day) hyponatraemic rats did not increase in volume and the rate of taurine efflux was unchang ed. The anion transport inhibitor 4,4'-diisothiocyanato-stilbene-2,2'-sulph onic acid (25 mu mol/l) caused marked (-44%) reduction in taurine efflux in cells from normonatraemic rats; this response was strongly attenuated (-16 %) by hyponatraemia. When slices from hyponatraemic rats were acutely expos ed to medium containing 142 mmol/Na+ cells exhibited marked and paradoxical swelling. This response was completely abolished by the NaCl co-transport inhibitor bumetanide (50 mu mol/l) and was not observed in slices that had not been pre-loaded with taurine. Forty eight hours after the start of the remission of hyponatraemia, cells from post-hyponatraemic rats displayed no rmal responses (i.e., moderate swelling and greatly accelerated taurine eff lux) on exposure to 122 mmol/Na+. But at 24 h there was only partial restor ation of the efflux response to 122 mmol/Na+, with an enhanced cell swellin g response that was not significantly affected by bumetanide. II is conclud ed that (i) during chronic hyponatraemia, unlike acute hyposmotic stress, c ortical cells preserve their volume and that this is not associated with an y increase in the rate of taurine loss; there does however, appear to be a decrease in the anionic component of cellular taurine efflux; (ii) acute re -incubation of slices in medium containing 142 mmol/l Na+ is associated wit h cell swelling that may reflect up-regulation of Na/Cl/taurine co-transpor t; (iii) following restoration of normonatraemia the pattern of normal cell ular response to acute hyposmotic stress is only gradually re-established. (C) 1998 Elsevier Science Ltd. All rights reserved.