Recovery from NMDA-induced intracellular acidification is delayed and dependent on extracellular bicarbonate.
A 30-s exposure to N-methyl-D-aspartate (NMDA) produced a dose-dependent and long-lasting (10-20 min) reduction in intracellular pH in cultured cortical neurons, detected by the fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. This intracellular acidification could be blocked by addition of the NMDA antagonist, D-(-)-2-amino-5-phosphonovalerate, or by removal of extracellular Ca2+. Removal of extracellular HCO3- markedly impaired recovery from NMDA-induced intracellular acidification. Recovery was also impaired when 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid or 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid, inhibitors of HCO3- transport, were added to the cultures immediately after NMDA exposure. In contrast, the Na+/H+ exchange blocker, 5-(N-ethyl-N-isopropyl)amiloride, did not affect pH recovery. Removal of extracellular Cl- partially prevented pH recovery after NMDA stimulation. In addition, extracellular HCO3- increased intracellular Na+ after NMDA exposure, consistent with HCO3- activation of a Na(+)-dependent exchanger. These results demonstrate that stimulation of cortical neuronal NMDA receptors is followed by long-lasting intracellular acidification and that the presence of extracellular HCO3- is important in the subsequent recovery of normal intracellular pH, likely acting at least in part via the Na(+)-dependent Cl-/HCO3- exchanger.
Canzoniero
L M
LM
Center for the Study of Nervous System Injury, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Sensi
S L
SL
Choi
D W
DW
D000143:Acids / Q000378:metabolism*; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism*; D051379:Mice / Q000196:embryology; D016202:N-Methylaspartate / Q000494:pharmacology*; D009474:Neurons / Q000378:metabolism*; D013997:Time Factors
D000143:Acids; D001639:Bicarbonates; D005452:Fluoresceins; D005456:Fluorescent Dyes; D016202:N-Methylaspartate; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein