THE PENETRATION OF RADIOACTIVE PHOSPHATE INTO MARINE EGGS ,

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Abstract
1. A method is described for measuring the concentration of radioactive isotope in cells without washing the cells free of the surrounding radioactive medium. 2. P32 as orthophosphate penetrates the unfertilized eggs of all species at a slow and constant rate. 3. During the first 10 to 15 minutes following the insemination of Strongylocentrotus purpuratus and S. franciscanus eggs, the rate of P32 uptake is essentially identical to that of the unfertilized eggs. The rate of uptake increases by 15 to 20 minutes, and reaches a maximum by 50 to 90 minutes after insemination. There after, through the first three cleavages the rate remains constant, within the limits of error of the method, as long as the concentration of P in the medium is in excess of 20 µg P/liter. 4. Following insemination of Urechis caupo eggs, the rate of P32 uptake does not increase. After the second cleavage, however, the rate of P32 uptake increases, and a maximum rate has not been attained even after the fourth cleavage. 5. When fertilized eggs containing P32 are suspended in non-radioactive sea water, they slowly lose P32 to the external medium. On the other hand, no P32 is lost from fertilized eggs containing radioactive phosphate when they are washed in non-radioactive sea water. 6. P32 is not absorbed to the extraneous coats of fertilized eggs. 7. The rate of penetration of phosphate into the unfertilized and fertilized eggs has been calculated in terms of the µg P entering one ml. eggs/minute. The rate at which phosphate enters fertilized Strongylocentrotus eggs is relatively independent of the external concentration, as long as this exceeds 20 µg P/liter. Phosphate enters fertilized Strongylocentrotus eggs 86 to 132 times faster that it penetrates the unfertilized eggs.