Contribution of Na+-K+-Cl- cotransporter to high-[K+]o-induced swelling and EAA release in astrocytes

We hypothesized that high extracellular K+ concentration ([K+](o))-mediated stimulation of Na+-K+-Cl- cotransporter isoform 1 (NKCC1) may result in a net gain of K+ and Cl- and thus lead to high[ K+](o)-induced swelling and glutamate release. In the current study, relative cell volume changes were determined in astrocytes. Under 75 mM [K+](o), astrocytes swelled by 20.2 +/- 4.9%. This high-[K+](o)-mediated swelling was abolished by the NKCC1 inhibitor bumetanide (10 muM, 1.0 +/- 3.1%; P < 0.05). Intracellular Cl-36(-) accumulation was increased from a control value of 0.39 +/- 0.06 to 0.68 +/- 0.05 μmol/mg protein in response to 75 mM [K+](o). This increase was significantly reduced by bumetanide (P < 0.05). Basal intracellular Na+ concentration ([Na+](i)) was reduced from 19.1 +/- 0.8 to 16.8 +/- 1.9 mM by bumetanide (P < 0.05). [Na+](i) decreased to 8.4 +/- 1.0 mM under 75 mM [K+](o) and was further reduced to 5.2 +/- 1.7 mM by bumetanide. In addition, the recovery rate of [Na+](i) on return to 5.8 mM [K+](o) was decreased by 40% in the presence of bumetanide (P < 0.05). Bumetanide inhibited high-[K+](o)-induced C-14-labeled D-aspartate release by similar to50% (P < 0.05). These results suggest that NKCC1 contributes to high-[K+](o)-induced astrocyte swelling and glutamate release.