THE UPTAKE OF RADIOACTIVE CALCIUM BY SEA URCHIN EGGS. I. ENTRANCE OF CA45INTO UNFERTILIZED EGG CYTOPLASM

Abstract

The uptake of radiocalcium by the unfertilized eggs of Tripneustes gratilla was studied by incubating intact eggs and eggs without jelly coats in sea water containing Ca45. Direct measurements of these eggs showed that both types of eggs took up radio-calcium but eggs without jelly coats took up much more. When washed with surface active agents, eggs without jelly coats retained 6 to 11 times as much radiocalcium as intact eggs. Autoradiographs of whole eggs showed the presence of Ca45 in the jelly coat and on the vitelline membrane. The approximate position of radiocalcium taken into the cytoplasm of both types of eggs was shown by autoradiographs of histological sections of these eggs. No significant difference in total calcium has been found by chemical analysis of groups of eggs having different radio-. activity through incubation for various periods of time in sea water containing Ca45. Entrance of radiocalcium into egg cytoplasm through an exchange with stable calcium of the unfertilized egg is indicated.