title: Ventral medulla pHi measured in vivo by 31P NMR is not regulated during hypercapnia in anesthetized rat.
abstract: Chemoreceptors in the ventral medulla contribute to the respiratory response to hypercapnia. Do they 'sense' intracellular pH (pHi)? We measured pHi in the ventral medulla or cortex (control) using 31P-NMR obtained via a novel 3 x 5 mm2 surface coil in anesthetized rats breathing air or 7% CO2. During air breathing over 240 min, pHi decreased slightly from 7.13 +/- 0.02 to 7.05 +/- 0.02 (SEM; n = 5; 2 cortex, 3 ventral medulla). During 180 min of hypercapnia, cortical pHi (n = 4) decreased from 7.17 +/- 0.02 to 6.87 +/- 0.01 by 90 min and recovered by 150 min. Ventral medulla pHi showed no such regulation. It decreased from 7.11 +/- 0.02 to 6.88 +/- 0.02 at 90 min and recovered only after cessation of hypercapnia (n = 5), results consistent with pHi being the chemoreceptor stimulus. However, non-chemoreceptor neurons that contribute to our medullary NMR signal also do not appear to regulate pHi in vitro. Regional differences in pHi regulation between cortex and ventral medulla may be due to both chemosensitive and non-chemosensitive neurons.
authors.affiliation: Department of Physiology, Dartmouth Medical School, 706E Borwell Building, Lebanon, NH 03756-0001, USA. eugene.nattie@dartmouth.edu
authors.forename: Eugene
authors.initials: E
authors.lastname: Nattie
authors.forename: Aihua
authors.initials: A
authors.lastname: Li
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Meyerand
authors.forename: Jeff F
authors.initials: JF
authors.lastname: Dunn
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001784:Blood Gas Analysis / Q000379:methods; D002540:Cerebral Cortex / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D006935:Hypercapnia / Q000378:metabolism*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008526:Medulla Oblongata / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D010758:Phosphorus; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D010710:Phosphates; D010725:Phosphocreatine; D010758:Phosphorus; D000251:Adenosine Triphosphatases