TRANSLATIONAL PHYSIOLOGY Increased tolerance to oxygen and glucose deprivation in astrocytes from Na /H exchanger isoform 1 null mice

Kintner, Douglas B., Gui Su, Brett Lenart, Andy J. Ballard, Jamie W. Meyer, Leong L. Ng, Gary E. Shull, and Dandan Sun. Increased tolerance to oxygen and glucose deprivation in astrocytes from Na /H exchanger isoform 1 null mice. Am J Physiol Cell Physiol 287: C12–C21, 2004. First published March 10, 2004; 10.1152/ajpcell.00560.2003.—The ubiquitously expressed Na /H exchanger isoform 1 (NHE1) functions as a major intracellular pH (pHi) regulatory mechanism in many cell types, and in some tissues its activity may contribute to ischemic injury. In the present study, cortical astrocyte cultures from wild-type (NHE1 / ) and NHE1deficient (NHE1 / ) mice were used to investigate the role of NHE1 in pHi recovery and ischemic injury in astrocytes. In the absence of HCO3 , the mean resting pHi levels were 6.86 0.03 in NHE1 / astrocytes and 6.53 0.04 in NHE1 / astrocytes. Removal of extracellular Na or blocking of NHE1 activity by the potent NHE1 inhibitor HOE-642 significantly reduced the resting level of pHi in NHE1 / astrocytes. NHE1 / astrocytes exhibited a rapid pHi recovery (0.33 0.08 pH unit/min) after NH4Cl prepulse acid load. The pHi recovery in NHE1 / astrocytes was reversibly inhibited by HOE-642 or removal of extracellular Na . In NHE1 / astrocytes, the pHi recovery after acidification was impaired and not affected by either Na -free conditions or HOE-642. Furthermore, 2 h of oxygen and glucose deprivation (OGD) led to an 80% increase in pHi recovery rate in NHE1 / astrocytes. OGD induced a 5-fold rise in intracellular [Na ] and 26% swelling in NHE1 / astrocytes. HOE642 or genetic ablation of NHE1 significantly reduced the Na rise and swelling after OGD. These results suggest that NHE1 is the major pHi regulatory mechanism in cortical astrocytes and that ablation of NHE1 in astrocytes attenuates ischemia-induced disruption of ionic regulation and swelling.