Considerations for brain pH assessment by 31P NMR.
Recently in vivo NMR spectroscopy has been used to measure brain pH non-invasively. Both the inorganic orthophosphate (Pi) chemical shift (delta) and the difference between the chemical shifts of phosphocreatine (PCr) and Pi(delta delta PCr-Pi) have been proposed as indicators of brain pH. However, the precise delta of Pi may be difficult to determine under normoxic conditions as is the delta of PCr under hypoxic/ischemic conditions. Ideally one needs a NMR delta parameter that: (1) linearly changes between pH 6.0-8.0, (2) is either relatively unaffected or predictably affected by cations (e.g., Mg2+) other than H+, and that (3) comes from readily observable 31P NMR resonances whose delta's can be accurately assessed under all physiological conditions. Therefore, we undertook a systematic 31P NMR study of the pH and Mg2+ titration curves for 16 phosphorus-containing metabolites observed in brain by 31P NMR. On the basis of the titration curves, the delta delta's for PCr-Pi, phosphoethanolamine (PE)-Pi, and PCr-PE fulfill criteria (1) and (2), but not criterion (3). However, the delta delta of ATP gamma-alpha fulfills all three criteria and potentially provides information on the intracellular Mg2+ concentration.
Pettegrew
J W
JW
Department of Psychiatry, University of Pittsburgh, PA 15213.
Withers
G
G
Panchalingam
K
K
Post
J F
JF
D000255:Adenosine Triphosphate / Q000032:analysis; D001923:Brain Chemistry; D004983:Ethanolamines / Q000032:analysis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D009682:Magnetic Resonance Spectroscopy; D010710:Phosphates / Q000032:analysis; D010725:Phosphocreatine / Q000031:analogs & derivatives / Q000032:analysis
D004983:Ethanolamines; D010710:Phosphates; D010725:Phosphocreatine; C025403:phosphocreatinine; C005448:phosphorylethanolamine; D000255:Adenosine Triphosphate