Figure 6.

Astrocytes overexpressing AQP4d swell faster in hypoosmotic conditions. (A) The average relative volume changes, obtained by measuring the average fluorescence intensity of sulphorhodamine 101 (SR101) in non-transfected (NTS) astrocytes, and in astrocytes overexpressing AQP4b or AQP4d in isoosmotic (Iso; A_i) and hypoosmotic (Hypo; A_ii) conditions. (B) The expanded section of the graph shown in A_ii represents the swelling phase (ΔV/V₀) in astrocytes after hypoosmotic stimulation (the addition of hypoosmotic stimulation is represented by the dashed line). (C_i) The swelling phase (τ swelling) was faster in cells overexpressing AQP4d than in NTS cells (p < 0.05, Kruskal–Wallis test, followed by Dunn’s method), whereas in cells overexpressing AQP4b, the swelling phase was similar to that in NTS cells (p > 0.05, Kruskal–Wallis test, followed by Dunn’s method). (C_ii) Time constants of the regulatory volume decrease (RVD) phase were similar for NTS cells and cells overexpressing AQP4b or AQP4d (p = 0.17, Kruskal–Wallis test). (D) Maximal amplitude of the volume increase (ΔV_max) and (E) recovery of the cell volume at 90 s (ΔV_t=90s) in the RVD phase were similar for NTS cells and cells overexpressing AQP4b or AQP4d (p = 0.44 and p = 0.77, respectively, Kruskal–Wallis test). Data represent means ± standard error of the mean from independent experiments equal to the number of animals: 6 (NTS), 3 (AQP4b), and 4 (AQP4d). The numbers above the bars represent the number of cells analysed.