Equivalence of intracellular pH of differentiating Dictyostelium cell types

Abstract

During the development of the cellular slime moulds, spore and stalk cells arise from vegetative amoebae. The intracellular pH (pH_i) of the developing cells has been postulated to be important in the choice of morphogenetic programmes¹. This hypothesis stems from the observation that the addition to the culture medium of weak (membrane-permeable) acids or bases favours the differentiation of pre-stalk or pre-spore cells respectively^1–3. Similarly, compounds that are known to inhibit a Dictyostelium plasma membrane proton pump induce preferential pre-stalk development^1,4,5; and a stalk-specific Dictyostelium morphogen, ‘DIF’, has been suggested to act via intracellular acidification^6,7. However, in these studies the pH_i values of pre-spore and pre-stalk amoebae were unknown, and the actual effects of the various agents mentioned above on pH_i were also unknown. By monitoring the intracellular fluorescence of a pH-sensitive dye, I have measured the relative intracellular pH of pre-spore compared with pre-stalk amoebae. I report here that, contrary to the above hypothesis, there is no significant difference in the pH_i of the two cell types.