Effects of mild versus deep hypothermia on a cloned human brain glutamate transporter (GLT-1) expressed in Chinese hamster ovary cells

Glutamate transporters, widely distributed in the brain and spinal cord, ma intain extracellular glutamate concentrations below neurotoxic levels. In c erebral ischemia/anoxia, the glutamate transporter runs in reverse and rele ases glutamate into the extracellular space, causing irreversible neuronal damage. Although hypothermia reduces the elevation of extracellular glutama te concentration during cerebral ischemia/ anoxia, little is known about th e effect of hypothermia on the glutamate transporter. A human glial glutama te transporter (hGLT-1) cDNA was isolated by screening a human cerebral cor tical library, and cloned cDNA was stably transfected in Chinese hamster ov ary (CHO) cells. Effects of deep hypothermia (22 to 23 degrees C) on uptake and release of L-glutamate via hGLT-1 were investigated by whole-cell patc h-clamp. The control study was performed at 34 to 35 degrees C, The hGLT-1 transporter had the capacity to take up extracellular L-glutamate under ess entially physiological ionic conditions, whereas this transporter promoted release of L-glutamate under a nonphysiological condition mimicking complet e ischemia. Deep hypothermia decreased a) uptake and b) release of L-glutam ate via hGLT-1 to a) 4.8 +/- 4.8 (P < .01, n = 7) and b) 19.0 +/- 4.5% (P < .01, n = 15) of control values, respectively. The results suggest that dee p hypothermia is a potent inhibitor of glutamate uptake by intact glial cel ls as well as glutamate release from glial cells under certain pathophysiol ogical circumstances. The balance between these antagonistic effects of hyp othermia may attenuate the elevation of the extracellular glutamate concent ration during ischemia/anoxia.