EFFECTS OF NACL REMOVAL ON OSMOLYTE FLUXES AND REGULATORY VOLUME DECREASE IN CULTURED ASTROCYTES

Cultured cerebellar astrocytes exhibit regulatory volume decrease (RVD ) after anisosmotic swelling by extrusion of potassium (K), chloride ( Cl), and organic osmolytes. The volume decay curve after swelling in 5 0% hyposmotic solutions has a first-order rate constant k min(-1) of 0 .18 and 70% cell volume recovery is attained after 15 min. Replacing N aCl in the hyposmotic medium by sugars and polyalcohols markedly accel erated RVD increasing k to 0.37-0.39 min(-1) and full recovery in 3-5 min. NaCl removal increased (80%) K efflux (measured as Rb-86), delaye d the inactivation of Cl efflux (measured as I-125) and enhanced tauri ne and D-aspartate release by 25%, These effects appear due to NaCl re moval rather than to specific actions of the organic molecules. Replac ing Na by other cations or Cl by gluconate increased k to 0.22 min(-1) and 0.26 min(-1), respectively, and Rb-86 efflux by 4-23% and 39, res pectively. It is concluded that the electrochemical gradient after NaC l removal increasing the K driving force, delaying the equilibrium of Cl and increasing amino acid efflux, accounts for the observed RVD acc eleration. Other consequences of NaCl removal possibly modulating the K efflux pathway include changes in the surface charge screening, decr eased ion strength, a rise in [Ca](i) and a decrease in intracellular Na. J. Neurosci. Res. 53:195-202, 1998. (C) 1998 Wiley-Liss, Inc.