Stimulation of Na-K-2Cl cotransporter in neurons by activation of non-NMDA ionotropic receptor and group-I mGluRs

In a previous study, we found that Na+-K+-2Cl(-) cotransporter in immature cortical neurons was stimulated by activation of the ionotropic N-methyl-D-aspartate (NMDA) glutamate receptor in a Ca2+-dependent manner. In this report, we investigated whether the Na+-K+-2Cl(-) cotransporter in immature cortical neurons is stimulated by non-NMDA glutamate receptor-mediated signaling pathways. Expression of the Na+-K+-2Cl(-) cotransporter and metabotropic glutamate receptors (mGluR1 and 5) was detected in cortical neurons via immunoblotting and immunofluorescence staining. Significant stimulation of cotransporter activity was observed in the presence of both trans-(+/-)-1-aminocyclopentanetrans-1,3-dicarboxylic acid (trans-ACPD) (10 muM), a metabotropic glutamate receptor (mGluR) agonist, and (RS)-3,5-dihydroxyphenyl-glycine (DHPG) (20 muM), a selective group-I mGluR agonist. Both trans-ACPD and DHPG-mediated effects on the cotransporter were eradicated by bis-(o-aminophenoxy)-N,N,N',N' -tetraacetic acid-AM, a Ca2+ chelator. In addition, DHPG-induced stimulation of the cotransporter activity was inhibited in the presence of mGluRs antagonist (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) (1 mM) and also with selective mGluR1 antagonist 7-(hydroxyimino)cyclopropa[b]chromen-la-carboxylate ethyl eater (CPCCOEt) (100 muM). A DHPG-induced rise in intracellular Ca2+ in cortical neurons was detected with Fura-2. Moreover, DHPG-mediated stimulation of the cotransporter was abolished by inhibition of Ca2+/CaM kinase II. Interestingly, the cotransporter activity was increased by activation of alpha -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor. These results suggest that the Na+-K+-2Cl(-) cotransporter in immature cortical neurons is stimulated by group-I mGluR- and AMPA-mediated signal transduction pathways. The effects are dependent on a rise of intracellular Ca2+.