Molecular and functional characterization of the electroneutral Na/HCO3 cotransporter NBCn1 in rat hippocampal neurons.
We examined molecular and electrophysiological properties of the electroneutral sodium/bicarbonate cotransporter (NBCn1) that is present in rat hippocampal neurons. By PCR, a deletion variant (NBCn1-E) that lacks 123 amino acids in the cytoplasmic N-terminal domain was found in adult neurons. The previously characterized NBCn1-B, which does not have the deletion, was detected in embryonic neurons. In Xenopus oocytes, NBCn1-E raised the intracellular pH in the presence of HCO(3) without significantly affecting the membrane potential. Despite this electroneutral cotransport activity, the transporter mediated a steady-state current that positively shifted the resting potential by almost 30 mV. The mean reversal potential of the steady-state current was -21.2 mV, close to the resting potential of -21.4 mV. The reversal potential shifted 26 mV in response to a 10-fold increase of external Na(+) for concentrations above 10 mm. The current activity mediated by the transporter was unaffected by K(+), Mg(2+), Ca(2+), or Cl(-). Stable expression of NBCn1-E in human embryonic kidney cells also evoked an inward current that shifted the resting potentials more positive compared with the sham-transfected controls. In primary cultures of embryonic hippocampal neurons, the NBCn1 protein was localized in somatodendrites and synapses. NBCn1 protein was partially colocalized with the postsynaptic density protein PSD-95. Single-cell PCR showed that NBCn1 mRNA expression was present in both gamma-aminobutyric acid (GABA)ergic and non-GABAergic neurons. We propose that NBCn1 in hippocampal neurons may affect neuronal activity by regulating local pH as well as steady-state inward currents at synapses.
Cooper
Deborah S
DS
Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Saxena
Nina C
NC
Yang
Han Soo
HS
Lee
Hye Jeong
HJ
Moring
Anisha G
AG
Lee
Amy
A
Choi
Inyeong
I
D000818:Animals; D002460:Cell Line; D005260:Female; D006624:Hippocampus / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009474:Neurons / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D027982:Sodium-Bicarbonate Symporters / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology*; D013569:Synapses / Q000378:metabolism; D014981:Xenopus
C498898:SLC4A4 protein, human; C422004:Slc4a4 protein, rat; D027982:Sodium-Bicarbonate Symporters