Stimulation of the Na/H exchanger of sea urchin eggs by phorbol ester

Abstract

On fertilization of a sea urchin egg, marked changes occur in the cytoplasmic concentration of calcium and hydrogen ions. These ionic signals represent the necessary and sufficient stimuli for the increased metabolism, protein synthesis and DNA synthesis that constitute egg activation^1–3. Cytoplasmic alkalinization, the major immediate cause of the increased rate of protein synthesis which occurs at fertilization⁴, arises because the sperm-induced intracellular calcium transient activates a coupled flux of sodium ions and hydrogen ions across the oolemma^5–7. The experiments reported here suggest that the second messenger which links the activation of the Na/H exchange to the calcium transient may be a substance which stimulates protein kinase C⁸, as 12-O-tetradecanoyl phorbol acetate (TPA), a known activator of protein kinase C⁹, appears to stimulate protein synthesis by turning on the Na/H exchanger and causing a cytoplasmic alkalinization. Our data indicate that one consequence of treating other tissues with TPA, a tumour promoter, may be an increase in intracellular pH^10–12.