Effect of extracellular acid-base disturbances on the intracellular pH of neurones cultured from rat medullary raphe or hippocampus.
Previous reports suggest that an important characteristic of chemosensitive neurones is an unusually large change of steady-state intracellular pH in response to a change in extracellular pH (DeltapH(i)/DeltapH(o)). To determine whether such a correlation exists between neurones from the medullary raphe (a chemosensitive brain region) and hippocampus (a non-chemosensitive region), we used BCECF to monitor pH(i) in cultured neurones subjected to extracellular acid-base disturbances. In medullary raphe neurones, respiratory acidosis (5%--> 9% CO(2)) caused a rapid fall in pH(i) (DeltapH(i) approximately 0.2) with no recovery and a large DeltapH(i)/DeltapH(o) of 0.71. Hippocampal neurones had a similar response, but with a slightly lower DeltapH(i)/DeltapH(o) (0.59). We further investigated a possible link between pH(i) regulation and chemosensitivity by following the pH(i) measurements on medullary raphe neurones with an immunocytochemistry for tryptophan hydroxylase (a marker of serotonergic neurones). We found that the DeltapH(i)/DeltapH(o) of 0.69 for serotonergic neurones (which are stimulated by acidosis) was not different from either the DeltapH(i)/DeltapH(o) of 0.75 for non-serotonergic neurones (most of which are not chemosensitive), or from the DeltapH(i)/DeltapH(o) of hippocampal neurones. For both respiratory alkalosis (5%--> 3% CO(2)) and metabolic alkalosis (22 mm--> 35 mm HCO(3)(-)), DeltapH(i)/DeltapH(o) was 0.42-0.53 for all groups of neurones studied. The only notable difference between medullary raphe and hippocampal neurones was in response to metabolic acidosis (22 mm--> 14 mm HCO(3)(-)), which caused a large pH(i) decrease in approximately 80% of medullary raphe neurones (DeltapH(i)/DeltapH(o)= 0.71), but relatively little pH(i) decrease in 70% of the hippocampal neurones (DeltapH(i)/DeltapH(o)= 0.09). Our comparison of medullary raphe and hippocampal neurones indicates that, except in response to metabolic acidosis, the neurones from the chemosensitive region do not have a uniquely high DeltapH(i)/DeltapH(o). Moreover, regardless of whether neurones were cultured from the chemosensitive or the non-chemosensitive region, pH(i) did not recover during any of the acid-base stresses.
Bouyer
Patrice
P
Department of Cellular & Molecular Physiology, SHM B-133, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA. patrice.bouyer@yale.edu
Bradley
Stefania Risso
SR
Zhao
Jinhua
J
Wang
Wengang
W
Richerson
George B
GB
Boron
Walter F
WF
D000142:Acidosis, Respiratory / Q000139:chemically induced / Q000503:physiopathology; D000472:Alkalosis, Respiratory / Q000139:chemically induced / Q000503:physiopathology; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D002245:Carbon Dioxide / Q000494:pharmacology; D002478:Cells, Cultured; D045604:Extracellular Fluid / Q000187:drug effects / Q000502:physiology*; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000187:drug effects / Q000502:physiology*; D008526:Medulla Oblongata / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D011903:Raphe Nuclei / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D001639:Bicarbonates; D002245:Carbon Dioxide