Abstract
Intracellular Cl− concentration ([Cl−]i) in immature neurons is higher than that expected for a passive distribution, resulting in that GABA renders immature neurons depolarizing. The higher [Cl−]i in immature neurons is thought to be attributed to the uptake of Cl− mediated by NKCC1 (Na+, K+-2Cl− cotransporter). Thus, a dysfunction of this transporter could affect synaptic development through a GABAA receptor-mediated pathway. To test this possibility, we examined the effects of a Cl− -uptake inhibitor on the development of synaptic activities of rat neocortical neurons in culture. Chronic treatment with bumetanide at 10 μM during the culture diminished the amplitude of synaptically-driven rhythmic depolarizing potentials (RDPs) in neurons and also decreased the frequency of sIPSCs but not of sEPSCs. Chronic treatment with bumetanide decreased vesicular GABA transporter (VGAT)-immunopositive particles without affecting paired-pulse ratio of evoked IPSCs (eIPSCs), indicating a decrease in the number of functional GABAergic synapses. These results suggest that the uptake of Cl− by NKCC1 affects the development of inhibitory synapses by promoting a depolarizing GABA-mediated response. [J Physiol Sci. 2007;57 Suppl:S144]
