Ca2+ influx and stimulation of protein synthesis in sea urchin eggs

Acid release, Ca2+ influx and stimulation of protein synthesis were investigated with sea urchin eggs submitted to an excess of KCl, to NH4Cl, and to a combination of both. KCl, though unable to promote any acid release, triggers a large 45Ca uptake by eggs and slightly stimulates protein synthesis, provided that external Ca2+ is present. NH4Cl, which induces an intracellular pH increase, triggers a late and small 45Ca uptake but highly stimulates protein synthesis. The combined use of NH4Cl + KCl allows a large 45Ca uptake to occur but the level of protein synthesis is similar to that obtained with NH4Cl alone and is identical whether external Ca2+ is present or not. In contrast to previous works, our results show that the large stimulation of protein synthesis triggered by an intracellular pH increase, as after NH4Cl activation, cannot be enhanced by a Ca2+ influx. This suggests that the Ca2+ influx occurring after fertilization has only a minimal effect on the overall stimulation of protein synthesis.