Release of taurine from astrocytes during potassium‐evoked swelling

Abstract

Cultured astrocytes superfused with isosmotic solutions containing high concentrations of potassium, i.e., 25, 56, 75, and 100 mM, showed a proportional increase in cell volume corresponding to 25, 36, 57, and 75% greater than the cell volume in physiological solutions. This volume increase was abolished in low chloride or hypertonic solutions. The release of ³H‐taurine previously accumulated by astrocytes was stimulated by potassium at all concentrations examined. During 4‐minute exposure to 25, 56, 75, or 100 mM of potassium, cells released 13.5, 15.6, 20.2, or 36.2%, respectively, of the total labeled taurine accumulated during the preloading period. The potassium‐stimulated release of ³H‐taurine was calcium‐independent and insensitive to BaCl₂ and bumetanide. Substitution of chloride by gluconate to concentrations necessary to maintain the K⁺ × Cl⁻ product constant abolished the potassium‐stimulated release of ³H‐taurine. Superfusion with solutions made hypertonic with sucrose also decreased the potassium‐elicited efflux of ³H‐taurine. In both conditions, the depolarizing effect of potassium measured with ³H‐TPP⁺ was unchanged. High potassium concentrations and hyposmotic solutions released ³H‐taurine by a nonadditive mechanism. These results indicate that in cultured astrocytes high concentrations of potassium produce both swelling and depolarization, but only swelling elicits the release of taurine. These observations suggest an involvement of taurine in cell‐volume regulation in astrocytes.