Absence of pH changes during altered work in the in vivo sheep heart: a 31P-NMR investigation.
Saturation transfer from gamma-ATP to inorganic phosphate was used to assign the intracellular inorganic phosphate resonance of the phosphorus-31 nuclear magnetic resonance spectrum of heart obtained from adult sheep under Halothane anesthesia. The 31P chemical shift of intracellular inorganic phosphate was then used as a probe of myocardial pH. Resting myocardial pH was found to be 7.03 +/- 0.02. The effects of increasing myocardial work on myocardial pH were examined using external pacing and phenylephrine infusion alone or in combination to produce steady-state increases in the rate-pressure product. No alteration in myocardial pH was observed with up to 4-fold increases in rate-pressure product. No changes in high-energy phosphates were observed except at the highest rate-pressure products obtained, where small increases in inorganic phosphate and decreases in the phosphocreatine/ATP ratio were observed. In addition, the transition to a new steady state was studied with a 20-s time resolution after initiation of pacing. Again, no changes in pH or levels of phosphates were detected during the transition to increased work.
Detre
J A
JA
Department of Biological Sciences, Carnegie Mellon University, Pittsburg, PA 15213.
Koretsky
A P
AP
Williams
D S
DS
Ho
C
C
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D007261:Infusions, Intra-Arterial; D008274:Magnesium / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D010656:Phenylephrine / Q000008:administration & dosage / Q000494:pharmacology; D010725:Phosphocreatine / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism
D010725:Phosphocreatine; D010656:Phenylephrine; D010758:Phosphorus; D000255:Adenosine Triphosphate; D008274:Magnesium