Calcium uptake and release by dividing sea urchin eggs

During early cleavage stages the sea urchin egg, when supplied with 45Ca in the sea water shows distinct peaks of activity representing uptake and release of the 45Ca. Three distinct peaks corresponding with prophase, metaphase and 50% cleavage, were observed during each division cycle. The 45Ca inside the cells appeared to be free and capable of efflux when exogenous 40Ca was supplied. The observed 45Ca peaks were discussed in relation to ( a) viscosity changes in egg cytoplasm; ( b) formation of the mitotic apparatus; ( c) regional membrane contraction and relaxation; ( d) cyclic changes in membrane permeability; ( e) cofactor requirements.