The carnosine C-2 proton's chemical shift reports intracellular pH in oxidative and glycolytic muscle fibers

The appearance of new peaks in the 7.7-8.6 and 6.8-7.4 ppm regions of the postexercise H-1 spectrum of frog muscle is reported. These new peaks result from the splitting of single pre-exercise carnosine C-2 and C-4 peaks into two peaks, representing the intracellular pH (pH(l)) of oxidative and glycolytic fibers. The following data support this conclusion: 1) comparison of means and regression analysis indicates equivalence of the pH(l) measurements by H-1 and P-31 NMR; 2) the pre- and poststimulation concentrations of carnosine are equal; 3) in ischemic rat hindlimb muscles, the presence of a single, more acidic peak in the plantaris; a single, less acidic peak in the soleus; and two peaks (more and less acidic) in the gastrocnemius correspond to published values for the fiber-type composition of these muscles; and 4) in muscles treated with iodoacetate prior to and during stimulation, a second peak never appears. These data indicate that it is feasible to measure separately the pH(l) of oxidative and glycolytic fibers using H-1 NMR spectroscopy. (C) 2003 Wiley-Liss, Inc.