Effects of hypercapnia on brain pHi and phosphate metabolite regulation by 31P-NMR.
The ability of brain cells to regulate intracellular pH (pHi) and several phosphate metabolites was evaluated during 1 h of hypercapnia (inspiratory CO2 fraction of 0.10 and 0.05) in anesthetized rats by 31P high-field (145.6 MHz) nuclear magnetic resonance spectroscopy. Body temperature was maintained at 37 +/- 0.5 degrees C. Fully relaxed spectra were obtained for controls and 30-50 min after CO2 loading and CO2 withdrawal. Spectra were taken serially every 2.5 min after gas mixtures were changed. Brain pHi decreased 0.10 +/- 0.02 units [7.06 +/- 0.01 (SE)] to 6.96 +/- 0.01 (P less than 0.001) after 30-50 min of 10% CO2 breathing, and arterial pH decreased 0.24 +/- 0.01 units. Brain pHi decreased by 0.045 +/- 0.01 units (7.05 +/- 0.01 to 7.01 +/- 0.01, P less than 0.05) during 5% CO2 breathing. Brain pHi returned to control values after 30-50 min of CO2 washout in both groups. In three of six animals breathing 10% CO2, there was an undershoot in brain pHi by 0.07-0.09 units between 2.5 and 20 min of hypercapnia. Three animals exhibited an overshoot in pHi by 0.06-0.11 units between 7.5 and 17.5 min during CO2 washout. Phosphocreatine-to-Pi and Pi-to-beta-ATP ratios changed during hypercapnia and returned to base line after withdrawal of CO2. The findings of a smaller brain pHi change than arterial pH change and undershoots and overshoots in pHi support the view that pHi regulation involves active processes such as transmembrane ion transport.
Nishimura
M
M
Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts 02114.
Johnson
D C
DC
Hitzig
B M
BM
Okunieff
P
P
Kazemi
H
H
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002245:Carbon Dioxide / Q000097:blood*; D002560:Cerebrovascular Circulation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D010710:Phosphates / Q000378:metabolism*; D010725:Phosphocreatine / Q000378:metabolism*; D010758:Phosphorus; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values
D010710:Phosphates; D010725:Phosphocreatine; D002245:Carbon Dioxide; D010758:Phosphorus; D000255:Adenosine Triphosphate