Measurements of intracellular pH and its relevance to cell differentiation in Dictyostelium discoideum.

A method was developed in this study to measure the intracellular pH (pHi) of Dictyostelium discoideum cells with a pH-sensitive fluorescence dye, carboxyfluorescein dibutyrate, and the pHi values of cells on the stalk and spore pathways were compared. The pHi of prestalk cells was lower than that of prespore cells by approximately 0.3 pH unit. In monolayer cultures of sporogenous mutants, which can differentiate into stalk cells and spores without cell contact, the pHi of the amoebae depended on the medium: media in which the majority of cells eventually become stalk cells reduced the pHi while conditions favouring spore formation increased the pHi. Addition of weak acids lowered the pHi. These results are in good accordance with the model presented by Gross and coworkers, which proposes that the choice between alternative pathways of cell differentiation is regulated via pHi and that low pHi favours stalk differentiation whereas high pHi favours spore formation.