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NKCC1 activity modulates formation of functional inhibitory synapses in cultured neocortical neurons
Author(s) -
Nakanishi Keiko,
Yamada Junko,
Takayama Chitoshi,
Oohira Atsuhiko,
Fukuda Atsuo
Publication year - 2007
Publication title -
synapse
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.809
H-Index - 106
eISSN - 1098-2396
pISSN - 0887-4476
DOI - 10.1002/syn.20352
Subject(s) - bumetanide , inhibitory postsynaptic potential , excitatory postsynaptic potential , depolarization , postsynaptic potential , neuroscience , cotransporter , chemistry , biophysics , gabaergic , biology , membrane potential , gabaa receptor , synapse , receptor , biochemistry , organic chemistry , sodium
Intracellular Cl − concentration ([Cl − ] i ) in immature neurons is higher than that expected for a passive distribution, therefore the equilibrium potential for chloride is more positive than the resting membrane potential, and the resulting GABA renders immature neurons depolarization. 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 GABA A 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 spontaneous inhibitory postsynaptic currents (sIPSCs) but not of spontaneous excitatory postsynaptic currents (sEPSCs). Chronic treatment with bumetanide decreased vesicular GABA transporter (VGAT)‐immunopositive particles without affecting paired‐pulse ratio of evoked IPSCs (eIPSCs), indicating decrease in the number of functional GABAergic synapses. Acute treatment with bumetanide (10 μM) decreased neuronal [Cl − ] i , the amplitude of RDPs, and neuronal excitability, while bumetanide had no effect on RDPs and neuronal excitability in the presence of bicuculline. These results suggest that the uptake of Cl − by NKCC1 affects the development of inhibitory synapses by promoting a depolarizing GABA‐mediated response. Synapse 61:138–149, 2007. © 2006 Wiley‐Liss, Inc.