Astrocytes from Na+-K+-Cl- cotransporter-null mice exhibit absence of swelling and decrease in EAA release

We reported previously that inhibition of Na+-K+-Cl- cotransporter isoform 1 (NKCC1) by bumetanide abolishes high extracellular K+ concentration ([K+](o))-induced swelling and intracellular Cl- accumulation in rat cortical astrocytes. In this report, we extended our study by using cortical astrocytes from NKCC1-deficient (NKCC1(-/-)) mice. NKCC1 protein and activity were absent in NKCC1(-/-) astrocytes. [K+](o) of 75 mM increased NKCC1 activity approximately fourfold in NKCC1(+/+) cells (P < 0.05) but had no effect in NKCC1(-/-) astrocytes. Intracellular Cl- was increased by 70% in NKCC1(-/-) astrocytes under 75 mM [K+](o) (P < 0.05) but remained unchanged in NKCC1(-/-) astrocytes. Baseline intracellular Na+ concentration ([Na+](i)) in NKCC1(-/-) astrocytes was 19.0 +/- 0.5 mM, compared with 16.9 +/- 0.3 mM [Na+](i) in NKCC1(-/-) astrocytes (P < 0.05). Relative cell volume of NKCC1(+/+) astrocytes increased by 13 +/- 2% in 75 mM[K+](o), compared with a value of 1.0 +/- 0.5% in NKCC1(-/-) astrocytes (P < 0.05). Regulatory volume increase after hypertonic shrinkage was completely impaired in NKCC1(-/-) astrocytes. High-[K+](o)-induced C-14-labeled D-aspartate release was reduced by similar to30% in NKCC1(-/-) astrocytes. Our study suggests that stimulation of NKCC1 is required for high-[K+](o)-induced swelling, which contributes to glutamate release from astrocytes under high [K+](o).