Regulation of intracellular pH in cultured hippocampal neurons by an amiloride-insensitive Na+/H+ exchanger.
Regulation of intracellular pH (pHi) in single cultured rat hippocampal neurons was investigated using the fluorescent pHi indicator dye bis-carboxyethylcarboxyfluorescein. Resting pHi was dependent on the presence of bicarbonate and external Na+ but was not altered significantly by removal of Cl- or treatment with the anion exchange inhibitor diisothiocyanatostilbene-2,2'-disulfonate. Recovery of pHi from acute acid loading was due, in large part, to a pharmacologically distinct variant of the Na+/H+ antiporter. In nominally HCO3(-)-free solutions, this recovery exhibited a saturable dose dependence on extracellular Na+ (Km = 23-26 mM) or Li+. The antiporter was activated by decreasing pHi and was unaffected by collapse of the membrane potential with valinomycin. Like the Na+/H+ antiporter described in other cell systems, the hippocampal activity was inhibited by harmaline, but in sharp contrast, neither amiloride nor its more potent 5-amino-substituted analogues were able to prevent the recovery from an acid load. These data indicate that Na(+)-dependent mechanisms dominate pHi regulation in hippocampal neurons and suggest a role for a novel variant of the Na+/H+ antiporter.
Raley-Susman
K M
KM
Department of Biological Sciences, Stanford University, California 94305-5020.
Cragoe
E J
EJ
Sapolsky
R M
RM
Kopito
R R
RR
D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001639:Bicarbonates; D002352:Carrier Proteins / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D006246:Harmaline / Q000494:pharmacology; D006624:Hippocampus / Q000737:chemistry* / Q000166:cytology; D006863:Hydrogen-Ion Concentration; D009474:Neurons / Q000737:chemistry*; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D017923:Sodium-Hydrogen Exchangers
D001639:Bicarbonates; D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D010042:Ouabain; D000584:Amiloride; D006246:Harmaline