The role of osmotic pressure and membrane potential in K(+)-stimulated taurine release from cultured astrocytes and LRM55 cells

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Abstract
The effects of [K+]o on taurine release from glial cells were studied with primary cultures of cerebellar astrocytes and with LRM55 cells, a continuous glial cell line. The characteristics of K(+)-stimulated taurine release were virtually identical in the 2 cell types. Both cerebellar astrocytes and LRM55 cells released taurine when stimulated with high-K+ medium prepared by isosmotically substituting KCl for NaCl, but neither cell type released taurine when stimulated with hyperosmotic high-K+ medium prepared by adding solid KCl to control medium. The membrane potential of LRM55 cells was measured by intracellular recording and was insensitive to changes in [K+]o below 20 mM. LRM55 cells released taurine when stimulated with nondepolarizing concentrations of K+ (13–22 mM) if the isosmotically prepared high-K+ medium was used, but the cells did not release taurine when treated with a depolarizing concentration of K+ (50 mM) if hyperosmotic high-K+ medium was used. The time course of K(+)- stimulated taurine release was quite slow, having a time to peak of 10– 15 min. Small changes (2.5–10%) in the osmolarity of the medium strongly affected taurine release by cerebellar astrocytes and LRM55 cells. K(+)-stimulated taurine release from both cell types was inhibited when the osmolarity was increased with sucrose or NaCl and was enhanced when the osmolarity was reduced. Similarly, baseline taurine release was suppressed by small elevations in osmolarity and increased by reduced osmolarity.(ABSTRACT TRUNCATED AT 250 WORDS)