Glutamate Uptake into Synaptosomes of Rat Hypothalamic Paraventricular Nucleus (PVN): Characterization and Effect of Water Deprivation.

This study sought to compare high affinity glutamate transporter (GLUT) activity in the PVN of euhydrated versus water‐deprived Sprague‐Dawley rats. Control rats received water ad libitem . Treated rats were deprived of water for 48 h. After sacrifice, PVN synaptosomes were prepared and glutamate uptake was measured using [ 3 H]‐glutamate as substrate. Uptake was both saturable and Na + ‐dependent. In PVN synaptosomes from euhydrated rats (n=4) the K m of uptake was 17.6 ± 3.8 (SEM) nM and the V max was 541 ± 22 (SEM) pmol/min‐mg protein. In water deprived rats (n=4), the V max of uptake in PVN was 808 ± 58 pmol/min‐mg protein, which was significantly (p < 0.001) greater than in controls, whereas K m (21.2 ± 7.3 nM) was not different. Results indicate that water deprivation increases PVN synaptosomal glutamate uptake and suggests that local glutamatergic activity may be enhanced by water deprivation. These findings are consistent with evidence for ionotropic glutamate receptor activation in the PVN contributing to sympathetic excitation and maintenance of arterial pressure during water deprivation. Although mechanisms by which water deprivation stimulates glutamate uptake are not yet known, increased GLUT gene expression and trafficking of GLUT to the cell surface are presently under investigation. Support: HL071645.