Inhibitory Effects of Diltiazem and Verapamil, Calcium Antagonists, on Fertilization-Induced Increase in the Phosphorylase Reaction in Echiuroid Eggs: (diltiazem/verapamil/phosphorylase/glycolysis/echiuroid eggs).

The calcium antagonists diltiazem and verapamil at 100 μM caused considerable inhibition of the glycolysis system in recently fertilized eggs of the echiuroid, Urechis unicinctus. The levels of glycolytic intermediates in eggs were found to be higher 5 min after insemination than before fertilization while the levels of adenine nucleotides and inorganic phosphate were almost the same before and after fertilization. Addition of diltiazem or verapamil 30 sec after insemination did not inhibit fertilization, but resulted in maintenance of as low levels of glycolytic intermediates as in unfertilized eggs. The apparent mass action ratio in the phosphorylase step, calculated from the levles of glucose-1-phosphate and inorganic phosphate was normally higher in fertilized eggs than in unfertilized eggs, but was maintained at as low a level as in unfertilized eggs by adding these compounds 30 sec after insemination. Phosphorylase a activity also normally increased after insemination, but was maintained at a low level in fertilized eggs by adding these compounds. These compounds also inhibited the increased Ca uptake normally observed after fertilization. These results suggest that after fertilization, the Ca level increases associated with fertilization-induced Ca influx and that this stimulates Ca dependent protein kinase to phosphorylate phosphorylase b, resulting in an increased rate of the phosphorylase reaction.