Cleavage in a saponin model of the sea urchin egg.

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Abstract
A cell model, in which cleavage could be induced, was obtained from fertilized sea urchin eggs by putting eggs that were in the 1st cleavage into a solution containing 3 .times. 10-5 g/ml saponin and suitable amounts of ATP and Ca2+. The cell membrane became freely permeable to ATP and Ca2+ within 1 min. The respective optimal concentrations of ATP and Ca2+ that advanced the cleavage furrow in this model were 2 mM and 10-8 M. With the optimal ATP and Ca2+ concentrations, the cleavage furrow of the model advanced at a rate that differed little from that in living eggs. The cleavage furrow soon receded when the concentration of ATP was decreased to less than 1 mM or increased to more than 3 mM, as well as when the concentration of Ca2+ was increased to more than 10-7 M.