Increased tolerance to oxygen and glucose deprivation in astrocytes from Na(+)/H(+) exchanger isoform 1 null mice.
The ubiquitously expressed Na(+)/H(+) exchanger isoform 1 (NHE1) functions as a major intracellular pH (pH(i)) 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 NHE1-deficient (NHE1(-/-)) mice were used to investigate the role of NHE1 in pH(i) recovery and ischemic injury in astrocytes. In the absence of HCO(3)(-), the mean resting pH(i) 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 pH(i) in NHE1(+/+) astrocytes. NHE1(+/+) astrocytes exhibited a rapid pH(i) recovery (0.33 +/- 0.08 pH unit/min) after NH(4)Cl prepulse acid load. The pH(i) recovery in NHE1(+/+) astrocytes was reversibly inhibited by HOE-642 or removal of extracellular Na(+). In NHE1(-/-) astrocytes, the pH(i) 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 approximately 80% increase in pH(i) recovery rate in NHE1(+/+) astrocytes. OGD induced a 5-fold rise in intracellular [Na(+)] and 26% swelling in NHE1(+/+) astrocytes. HOE-642 or genetic ablation of NHE1 significantly reduced the Na(+) rise and swelling after OGD. These results suggest that NHE1 is the major pH(i) regulatory mechanism in cortical astrocytes and that ablation of NHE1 in astrocytes attenuates ischemia-induced disruption of ionic regulation and swelling.
Kintner
Douglas B
DB
Department of Neurosurgery, University of Wisconsin Medical School, Madison, WI 53792, USA.
Su
Gui
G
Lenart
Brett
B
Ballard
Andy J
AJ
Meyer
Jamie W
JW
Ng
Leong L
LL
Shull
Gary E
GE
Sun
Dandan
D
D000222:Adaptation, Physiological; D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D015687:Cell Hypoxia / Q000502:physiology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D005947:Glucose / Q000172:deficiency*; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics; D009994:Osmolar Concentration; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
D017923:Sodium-Hydrogen Exchangers; C069139:growth factor-activatable Na-H exchanger NHE-1; D012964:Sodium; D005947:Glucose