STIMULATION OF NA-K+-2CL(-) COTRANSPORTER IN NEURONAL CELLS BY EXCITATORY NEUROTRANSMITTER GLUTAMATE()

Na+-K+-2Cl(-) cotransporters are important in renal salt reabsorption and in salt secretion by epithelia. They are also essential in mainten ance and regulation of ion gradients and cell volume in both epithelia l and nonepithelial cells. Expression of Na+-K+-2Cl(-) cotransporters in brain tissues is high; however, little is known about their functio n and regulation in neurons. In this study, we examined regulation of the Na+-K+-2Cl(-) cotransporter by the excitatory neurotransmitter glu tamate. The cotransporter activity in human neuroblastoma SH-SY5Y cell s was assessed by bumetanide-sensitive K+ influx, and protein expressi on was evaluated by Western blot analysis. Glutamate was found to indu ce a dose- and time-dependent stimulation of Na+-K+-2Cl(-) cotransport er activity in SH-SY5Y cells. Moreover, both the glutamate ionotropic receptor agonist N-methyl-D-aspartic acid (NMDA) and the metabotropic receptor agonist (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD) significantly stimulated the cotransport activity in the se cells. NMDA-mediated stimulation of the Na+-K+-2Cl(-) cotransporter was abolished by the selective NMDA-receptor antagonist (+)-MK-801 hy drogen maleate. trans-ACPD-mediated effect on the cotransporter was bl ocked by the metabotropic receptor antagonist (+)-alpha-methyl-(4-carb oxy-phenyl)glycine. The results demonstrate that Na+-K+-2Cl(-) cotrans porters in neurons are regulated by activation of both ionotropic and metabotropic glutamate receptors.