Changes in intracellular pH following egg activation and during the early cell cycle of the amphibian Pleurodeles waltlii, coincide with changes in MPF activity.

Previous work on Xenopus laevis suggests a temporal coincidence between inactivation of the M-phase promoting factor (MPF) and intracellular pH (pHi) increase during egg activation. In addition, we recently showed that during the early cell cycle of Xenopus eggs, MPF activity cycling and pHi oscillations were temporally and functionally related. In the present work, using eggs of another amphibian, Pleurodeles waltlii, which has a natural cell cycle considerably longer than that of Xenopus laevis, we show a temporal coincidence between MPF activity and pHi changes, both at the time of egg activation and at each of the following cell cycles. Egg activation-induced pHi changes in Pleurodeles did not involve classical plasma membrane ion exchangers, and were not due to the activation of a H+ conductance. On the other hand, the pHi oscillations intervening at each cell cycle were suppressed by inhibitors of protein synthesis or phosphorylation, as were their counterparts in Xenopus eggs. We propose that physiological pHi changes in Pleurodeles and Xenopus eggs might have a metabolic origin, in direct relation with the cascade of phosphorylations-dephosphorylations of proteins implicated in the control of the cell cycle.