The Simultaneous Determination of Muscle Cell pH Using a Weak Acid and Weak Base

Abstract

A B S T R A C T Should significant pH heterogeneity exist within cells then the simultaneous calculation of intracellular pH from the distribution of a weak acid will give a value closest to the highest pH in the system, whereas calculation from the distribution of a weak base will give a value closer to the lowest pH. These two values should then differ significantly. Intact rat diaphragms were exposed in vitro to varying bicarbonate concentrations (pure metabolic) and C02 tensions (pure respiratory), and steady-state cell pH was measured simultaneously either by distribution of the weak acid 5,5-dimethyloxazolidine-2,4-dione-"C (pH DMO) or by distribution of the weak base nicotine-'4C (pH nicotine). The latter compound was found suitable to measure cell pH since it was neither metabolized nor bound by rat diaphragms.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.

Intracellular pH, H ion flux and H ion permeability coefficient in bullfrog toe muscle

“…However, because nicotine causes the release of calcium ions from intracellular binding sites (Weiss, 1966), because a significant fraction of the cellular nicotine may be bound (Weiss, 1968a), and because nicotine may alter the normal pH, of frog skeletal muscle (Weiss, 1968b); it is probably poorly suited for the task. In addition, the fact that the pH, as indicated by nicotine is unaffected by respiratory acidosis (Adler, 1970) raises another serious doubt about the meaning of the nicotine calculation.…”

Micro‐electrode measurement of the intracellular pH and buffering power of mouse soleus muscle fibres.

“…This dependence of pHi on the C02 level has also been seen in mammalian cardiac preparations (Ellis & Thomas, 1976 Thomas, 1977) and with those obtained using DMO in vivo in various muscles of the rat, rabbit and dog (Schoerb, Blackburn & Grantham, 1967;Roos, 1971;Poole-Wilson & Cameron, 1975;Gonzalez, Gerbrandt & Brown, 1976). On the other hand studies in vitro of the effect of changing external pH in rat diaphragm using DMO (Adler, Roy & Relman, 1965;Adler, 1972;Heisler, 1975) have shown no change in pHi for changes in external pH between about 7-1 and 7*4. This difference could be explained by the inclusion of deteriorating, or even dead, innermost fibres of the in vitro preparation in the determination of pHi.…”

Active H+ transport in the turtle urinary bladder. Coupling of transport to glucose oxidation.

“…Alterations in the serosal pH probably do not result in significant changes in the cell pH. Large changes of ambient pH at constant pCO~ result in much smaller changes in the intracellular pH of mammalian renal tubular epithelial cells (31) and muscle (1). In the turtle urinary bladder the apparent cell pH determined by the DMO distribution method changed from 7.56 to 7.42 when the ambient pCO2 was increased from near zero to 40 mm Hg (27).…”