Two phases of inositol polyphosphate and diacylglycerol production at fertilisation

Abstract

[³H]Inositol and [³H]arachidonic acid were used to label polyphosphoinositide phospholipids in sea urchin eggs. Both [³H]inositol polyphosphate (InsP₃) and [³H]diacylglycerol (DAG) increase at fertilisation. An early increase in InsP₃ occurs as the sperm‐induced calcium transient crosses the egg and exocytosis occurs; a later increase in InsP₃, as calcium declines and the protein kinase C‐dependent Na/H antiporter causes the cytoplasmic pH to increase. These results support suggestions that a calcium‐induced hydrolysis of phosphatidylinositol bisphosphate occurs at fertilisation, that the production of diacylglycerol may be essential for exocytosis and that diacylglycerol production at fertilisation stimulates the Na/H antiporter. The increase in [³H]inositol polyphosphate as calcium declines indicates that this second messenger may have some function later in the cell cycle.