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Departments of
1 Cellular & Molecular Physiology
2 Neurology, Yale University, New Haven, CT 06520, USA
3 Veteran's Affairs Medical Center, West Haven, CT 06516, USA
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 (
pHi/pHo). 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 pHi in cultured neurones subjected to extracellular acid–base disturbances. In medullary raphe neurones, respiratory acidosis (5%
9% CO2) caused a rapid fall in pHi (pHi
0.2) with no recovery and a large pHi/pHo of 0.71. Hippocampal neurones had a similar response, but with a slightly lower pHi/pHo (0.59). We further investigated a possible link between pHi regulation and chemosensitivity by following the pHi measurements on medullary raphe neurones with an immunocytochemistry for tryptophan hydroxylase (a marker of serotonergic neurones). We found that the pHi/pHo of 0.69 for serotonergic neurones (which are stimulated by acidosis) was not different from either the pHi/pHo of 0.75 for non-serotonergic neurones (most of which are not chemosensitive), or from the pHi/pHo of hippocampal neurones. For both respiratory alkalosis (5% 3% CO2) and metabolic alkalosis (22 mM 35 mM HCO3–), pHi/pHo 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 HCO3–), which caused a large pHi decrease in 80% of medullary raphe neurones (pHi/pHo= 0.71), but relatively little pHi decrease in 70% of the hippocampal neurones (pHi/pHo= 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 pHi/pHo. Moreover, regardless of whether neurones were cultured from the chemosensitive or the non-chemosensitive region, pHi did not recover during any of the acid–base stresses.
(Received 10 May 2004;
accepted after revision 4 June 2004;
first published online 11 June 2004)
Corresponding author P. Bouyer: Cellular & Molecular Physiology, SHM B-133, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA. Email: patrice.bouyer{at}yale.edu
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