Sustained depolarizing shift of the GABA reversal potential by glutamate receptor activation in hippocampal neurons.
The inhibitory action of GABA is a consequence of a relatively hyperpolarized Cl(-) reversal potential (E(Cl)), which results from the activity of K(+)-Cl(-) cotransporter (KCC2). In this study we investigated the effects of glutamate and glutamatergic synaptic activity on E(Cl). In dissociated culture of mature hippocampal neurons, the application of glutamate caused positive E(Cl) shifts with two distinct temporal components. Following a large transient depolarizing state, the sustained depolarizing state (E(Cl)-sustained) lasted more than 30 min. The E(Cl)-sustained disappeared in the absence of external Ca(2+) during glutamate application and was blocked by both AP5 and MK801, but not by nifedipine. The E(Cl)-sustained was also induced by NMDA. The E(Cl)-sustained was blocked by furosemide, a blocker of both KCC2 and NKCC1, but not bumetanide, a blocker of NKCC1. On the other hand, in immature neurons having less expression of KCC2, NMDA failed to induce the sustained depolarizing E(Cl) shift. In organotypic slice cultured neurons, repetitive activation of glutamatergic afferents also generated a sustained depolarizing E(Cl) shift. These results suggest that Ca(2+) influx through NMDA receptors causes the down-regulation of KCC2 and gives rise to long lasting positive E(Cl) shifts, which might contribute to hyperexcitability, LTP, and epileptiform discharges.
Department of Developmental Physiology, National Institute for Physiological Sciences, Okazaki 444-8585, Japan.
Akihiko
A
Kitamura
Hitoshi
H
Ishibashi
Miho
M
Watanabe
Yusuke
Y
Takatsuru
Malcolm
M
Brodwick
Junichi
J
Nabekura
D000704:Analysis of Variance; D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism; D004558:Electric Stimulation / Q000379:methods; D004622:Embryo, Mammalian; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018683:Excitatory Amino Acid Agents / Q000494:pharmacology; D005665:Furosemide / Q000494:pharmacology; D018755:GABA Agonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology*; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology; D009118:Muscimol / Q000494:pharmacology; D009433:Neural Inhibition / Q000187:drug effects; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects* / Q000502:physiology*; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D051381:Rats; D017470:Receptors, Glutamate / Q000502:physiology*; D049994:Sodium Potassium Chloride Symporter Inhibitors / Q000494:pharmacology; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D002712:Chlorides; D004791:Enzyme Inhibitors; D018683:Excitatory Amino Acid Agents; D018755:GABA Agonists; D017470:Receptors, Glutamate; D049994:Sodium Potassium Chloride Symporter Inhibitors; D002034:Bumetanide; D009118:Muscimol; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D005665:Furosemide; D002118:Calcium