Change in Na+, K+ -ATPase activity in embryos of the sea urchin, Hemicentrotus pulcherrimus, during early development

Ouabain-sensitive Na⁺, K⁺-ATPase activity in plasma membrane fraction, which was detectable in unfertilized eggs, scarcely altered before hatching and began to increase at the mesenchyme blastula stage. The activity reached to a maximum at the gastrula stage and thereafter decreased gradually. The increase of this ATPase activity was mainly found in ectodermal cells.