Elevated potassium regulates astrocyte water permeability.

<p>(A) Representative recordings from two independent primary astrocytes showing changes in calcein fluorescence (2.5mM potassium, dashed line; 10mM potassium, solid line) in water permeability measurements. The grey bar depicts the part of the curve used for calculation of plasma membrane water permeability (s; seconds). (B) Fluorescence intensity change induced by isosmotic high potassium: bars show quantified fluorescence intensity at 2min before high potassium (-2min), at start (0min) and after 1min and 5min of indicated potassium concentrations, respectively. Values were normalized to the initial intensity at 2.5mM potassium. Right hand panels show fluorescence intensity curves for isosmotic high potassium (grey: 10mM; black: 35mM) within the time window (∼20s) of water permeability recordings after 1 or 5 minutes. Arrows indicate starting points. Values are means and error bars of each individual acquired time point, n = 48–65. (C) Water permeability in primary astrocytes exposed to 10mM potassium for 1min and 5min, respectively. 10mM potassium caused a significant water permeability increase at 1min and 5min (*p<0.001), n = 57–92. (D) 35mM potassium caused a transient astrocyte water permeability increase at 1min (*p<0.001). The effect was abolished after 5min (NS; not significant p = 0.52), n = 53–92. (E) AQP4 specific water permeability calculated from astrocyte cell line. 10mM potassium significantly increased AQP4 water permeability at 1min (*p<0.001) and 5min (*p<0.05), N = 5-7. (F) 35mM potassium did not increase AQP4 water permeability either at 1min (p = 0.62) or 5min (p = 0.89), N = 5–16. (G) Water permeability in AQP4-negative astrocyte cell line. 10mM potassium for 1min did not have any effect on water permeability in AQP4-negative cells. A small but significant water permeability was observed after 5min of 10mM potassium (P = 0.045), n = 43–130. (H) 35mM potassium did not have any effect on water permeability in AQP4-negative astrocyte cell line (1min, p = 0.62; 5min p = 0.89), n = 33–119. Values are means±SEM, n; number of cells, N; number of plates.