The Simultaneous Determination of Muscle

At an external pH of 7.40, pH DMO was 7.17 while pH nicotine was 6.69-a pH difference of 0.48 pH units (P <0.001). In either respiratory or metabolic alkalosis both DMO and pH nicotine rose so that differences between them remained essentially constant. Metabolic acidosis induced a decrease in both values though they fell more slowly than did extracellular pH. In contradistinction, in respiratory acidosis, decreasing extracellular pH from 7.40 to 6.80 resulted in 0.35 pH unit drop in pH DMO while pH nicotine remained constant. In every experiment, under all external conditions, pH DMO exceeded pH nicotine. These results indicate that there is significant pH heterogeneity within diaphragm muscle, but the degree of heterogeneity may vary under different external conditions. The metabolic implications of these findings are discussed. In addition, the data show that true overPresented in part at the meeting of the American Federation for Clinical Research and published in abstract form: 1970. Clin. Res. 18: 493. Received for publication 21 July 1971 and in revised form 17 September 1971. all cell pH is between 6.69 and 7.17-a full pH higher than would be expected from thermodynamic considerations alone. This implies the presence of active processes to maintain cell pH.