Regulation of cytoplasmic pH in the differentiating cell types of the cellular slime mould Dictyostelium discoideum

Abstract

The regulation of cytoplasmic pH (pH i ) in prestalk and prespore cells of Dictyostelium discoideum was investigated by analysing pH i recovery following addition of the weak acid potassium propionate. By taking advantage of the sensitivity of the plasma membrane H + -ATPase to diethylstilbestrol, it was possible to separate pH i recovery into two distinct components: intracellular buffering capacity and proton-pump activity. Prespore cells had a higher intracellular buffering capacity (35.6 mequiv/pH unit per l) than prestalk cells (26.2 mequiv/pH unit per l). They also showed a roughly 4-fold higher proton pump activity. This activity increased as pH i decreased in both cell types. The permeability of propionic acid through the cell membrane was estimated to be 10.74 · 10 −5 cm/s for prestalk cells and 8.12 · 10 −5 cm/s for prespore cells. These results indicate that the greater resistance of prespore cells to acid load is primarily due to higher plasma membrane proton pump activity.