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 1 H 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 I ) of oxidative and glycolytic fibers. The following data support this conclusion: 1) comparison of means and regression analysis indicates equivalence of the pH I measurements by 1 H and 31 P 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 I of oxidative and glycolytic fibers using 1 H NMR spectroscopy. Magn Reson Med 49:233–240, 2003. © 2003 Wiley‐Liss, Inc.