AJP - Regulatory, Integrative and Comparative Physiology, Vol 266, Issue 2 638-R645, Copyright © 1994 by American Physiological Society
A method for calculating the distribution of pH in tissues and a new source of pH error from the 31P-NMR spectrum
R. A. Graham, A. H. Taylor and T. R. Brown
Department of Nuclear Magnetic Resonance and Medical Spectroscopy, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111.
The true distribution of the pH in tissues can be determined from the in
vivo 31P-nuclear magnetic resonance (NMR) spectrum by converting the parts
per million (PPM) axis of the pH responsive resonance to pH using the
Henderson-Hasselbalch equation. In addition, the intensity axis of the
resonance must be divided by the derivative of the Henderson-Hasselbalch
equation to correct for the nonlinear relationship between pH and PPM. This
nonlinear relationship causes the apparent center of the resonance in PPM
to be dependent not only on the center of the pH distribution but also on
its width and distance from the pKa, where Ka is the association constant.
Therefore, the pH determined from uncorrected spectra may be in significant
error, particularly if the pH distribution is distant from the pKa and is
broad. The method was applied to the isolated perfused Morris hepatoma
5123C to determine the distribution of intracellular pH (pHi) using
resonances from two intracellular compounds. The two resonances did not
report the same pHi unless the spectral data were properly corrected. The
method should be of interest to anyone interested in pHi.
