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 exhib its 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 ther efore studied in an animal model with a multichannel pH microelectrode . Under resting conditions and spontaneous breathing, local pH(t) (fro m all animals, n = 10) was found to vary between 6.96 and 7.68 (range) , and 70% of the values were within a 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 tissue acidosis, induced by ischemia, no significant change in the local pH(t) differences in each animal was seen. During normoxic h ypercarbia a 2-fold increase in pH(t) variability within each animal w as noticed (p < 0.01), which suggests that carbon dioxide and bufferin g effects of the blood are significant factors for the pH(t) distribut ion. The pH(t) distribution range found is of similar magnitude as pre viously described in in vitro studies on skeletal muscle. Locally vary ing pH(t) levels may be of importance as they will affect cellular Hextrusion, membrane potential and volume control of different cell pop ulations differently.