The effects of hypothermia on a cloned human brain glutamate transporter (hGLT-1) expressed in Chinese hamster ovary cells: -[3H]L-glutamate uptake study.

Abstract

Hypothermia provides neuroprotection that inhibits increases in extracellular glutamate concentration during ischemia; however, the effect of hypothermia on the glutamate transporter is uncertain. A human glial glutamate transporter (hGLT-1) cDNA, isolated by screening a cDNA, library was cloned and stably transfected into Chinese hamster ovary cells. We assessed the effects of temperature on transporter activity in [3H]L-glutamate flux experiments at 23, 32, and 37 degrees C. Hypothermia of 23 degrees C and 32 degrees C decreased [3H]L-glutamate uptake at 60 min, to 76.7%+/-7.3% (P < 0.05, n = 5) and 70.7%+/-7.5% (P < 0.05, n = 5) of uptake at 37 degrees C, respectively. Reversed uptake of preloaded [3H]L-glutamate via hGLT-1 was not observed at any temperature. The specific uptakes (Q10 values) for 37 degrees C to 32 degrees C and 32 degrees C to 23 degrees C at 30 min were 3.48 and 2.37, whereas they were 2.17 and 0.91, respectively, for 60 min. These changes suggest that hypothermia attenuates uptake of extracellular glutamate via hGLT-1 in a temperature- and time-dependent manner. Under certain pathologic conditions, including cerebral ischemia and traumatic brain injury, glutamate neurotoxicity may initially be propagated by hypothermia due to relative failure of glutamate uptake via Human Glial Glutamate Transporter before a subsequent recovery of uptake.