演題番号 : P1-a23
井上 浩一 / Koichi Inoue:1 古川 智範 / Tomonori Furukawa:1 熊田 竜郎 / Tatsuro Kumada:1 山田 順子 / Junko Jamada:2 王 天英 / Tianying Wang:1 福田 敦夫 / Atsuo Fukuda:1
1:浜松医大・医・一生理 / Dept Physiol, Hamamatsu Univ Sch of Med, Hamamatsu 2:弘前大・医・脳神経生理 / Dept Neurophysiol, Hirosaki Univ Sch of Med, Hirosaki
K+-Cl- cotransporter 2 (KCC2) is a neuron-specific ion transporter which effluxes Cl- out of cells, and relatively low intracellular Cl- concentration ([Cl-]i) elicits inhibitory action of neurotransmitters such as GABA and glycine. Lowering [Cl-]i takes place along with developmental upregulation of KCC2, but some cases are also reported that KCC2 does not function to extrude Cl- in spite of its apparent expression. Taurine is another inhibitory neurotransmitter and abundant in mammalian brains, especially in embryonic stages. Here we examined the effect of taurine on KCC2 activity. Rat embryonic cerebral cortices were dissected and KCC2-expressing plasmids were then transfected before plating for primary culture. Transfected cells were either untreated or treated with taurine for 3 days and then whole-cell patch-clamp recording was performed with low Cl--pipette solution to estimate reversal potential of GABA (EGABA). EGABA of cells without taurine was -49.5 ± 0.4 mV, while that of cells with taurine was -45.3 ± 0.3 mV (p < 0.05), suggesting that taurine inhibited KCC2 transporter activity. When staurosporine, a broad spectrum kinase inhibitor, was applied to taurine-treated KCC2-expressing cells, EGABA of the cells shifted to the negative direction, but this shift was neither obtained from taurine-untreated KCC2-expressing cells nor taurine-treated KCC2-unexpressing cells. These results suggest that KCC2 activity was inhibited by taurine in a kinase activity-dependent manner. Unexpectedly, strychinine and bicuculline, blockers of glycine and GABAA receptor, respectively, did not affect EGABA of KCC2-expressing cells when they were added along with taurine. Instead, application of GES, an inhibitor of taurine transporter, shifted EGABA of the cells to the negative direction. Taken together, intracellularly incorporated taurine may be implicated in developmental regulation of KCC2 activity. The detail effect is further studied.