Fig. 3.

Activation of D-³H aspartate release by ATP with moderate and substantial swelling and effects of Ca²⁺ and changes in osmolarity. A. Moderate cell swelling was induced by 5% reduction in medium osmolarity (-14.5 mosmol). Ten micromoles of ATP was applied simultaneously with hypoosmotic medium. The data are the mean values ±SEM of seven experiments performed on three different cell culture preparations. B. Substantial cell swelling was induced by a 30% reduction in medium osmolarity (-90 mosmol). Ten micromolar ATP was applied simultaneously with hypoosmotic medium. The open squares show the ATP-induced D-[³H]aspartate release values in moderately swollen cells for comparison. The data are the mean values ±SEM of five experiments performed on two cell culture preparations. When not indicated, SEMs were less than symbols. C. Simultaneous measurements of the ATP-induced D-[³H]aspartate and [¹⁴C]taurine release from moderately swollen cultured astrocytes. Astrocytes were preloaded overnight with D-[³H]-aspartate and [¹⁴C]taurine. The data are means ±SEM of five experiments. D. ATP-induced organic osmolyte release in astrocytes is dependent on intracellular [Ca²⁺]. Cells were preincubated with 10 μM BAPTA-AM for 20 min, followed by a 5-min wash to remove extracellular BAPTA-AM. Then, astrocytes were exposed to a 5% reduction in medium osmolarity plus 10 μM ATP. The data are the means ±SEM of five experiments performed on two cell culture preparations. E. ATP-induced release is inhbited by an increase in medium osmolarity. Cells were exposed to 10 μM ATP and the simultaneous changes in medium osmolarity shown during 21st to 30th min of superfusion. F. Summary of the osmotic dependence of D-[³H]aspartate release in the presence or absence of 10 μM ATP shown in E. Open triangles represent an ATP-induced increment in EAA release. Data are the means ±SEM of 3–10 experiments performed on 2–4 different astrocyte culture preparations (from Mongin and Kimelberg, 2002, 2005).