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 (14)C-labeled D-aspartate release was reduced by approximately 30% 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).