Intracellular pH of single crustacean muscle fibres by the DMO and electrode methods during acid and alkaline conditions.

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Abstract
The intracellular pH of intact single muscle fibers of the giant barnacle was measured directly with a glass micro-electrode following prolonged (2-5 h) equilibration in 1 of 3 solutions: normal Ringer, CO2 Ringer and NH4+ Ringer. The intracellular pH of identically-prepared fibers from the same specimen was measured indirectly from the distribution of DMO [5,5-dimethyloxazolidine-2,4-dione] following prolonged equilibration in the same solutions. The DMO-pH compared favorably with the electrode-pHi provided DMO-pHi was calculated from the values of the indicator compounds, [14C]DMO and [3H]inulin, obtained by extrapolating the slow uptake phase to time zero. On prolonged equilibration, the transmembrane H+ ion distribution varied with the membrane potential but not in accordance with a simple Gibbs-Donnan equilibrium. A model which recognizes the existence of 2 independent net fluxes for H+ across the membrane is developed to explain the results. One of the fluxes represents passive diffusion and the other represents the so called H+-pump. The model predicts the H+-pump rate increases by 2 orders of magnitude when pHi is reduced from 7.2 to 6.7.