pH Heterogeneity in skeletal muscle extracellular fluid

Oxygen and carbon dioxide are known to be heterogeneously distributed in tissues. Extracellular skeletal muscle tissue pH (pH_t) also exhibits a spatial variability in vitro, but this has not been examined in vivo. pH_t distributions in resting skeletal muscle and the effect of the dispersion of pH_t on ischemia and normoxic hypercarbia was therefore studied in an animal model with a multichannel pH microelectrode. Under resting conditions and spontaneous breathing, local pH_t (from all animals, n = 10) was found to vary between 6.96 and 7.68 (range), and 70% of the values were withina pH of 7.00-7.32. In each animal the maximum pH_t differences (maximum range between the 6 channels of the microelectrode) found were 0.32 ± 0.11 pH units (mean ± SD).During tissueacidosis, induced by ischemia, no significant change in the local pH_t differences in each animal was seen. During normoxic hypercarbia a 2-fold increase in pH_t variability within each animal was noticed (p < 0.01), which suggests thatcarbon dioxide and buffering effects of the blood are significant factors for the pH_t distribution. The pH_t distribution range found is of similar magnitude as previouslydescribed in in vitro studies on skeletal muscle. Locally varying pH_t levels may be of importance as they will affectcellular H⁺ extrusion, membrane potential and volume control of different cell populations differently.