RADIOACTIVE SODIUM PERMEABILITY AND EXCHANGE IN FROG EGGS

¹ Department of Terrestrial Magnetism, Carnegie Institution of Washington
² National Cancer Institute

1. The ovarian egg of the frog Rana pipiens is freely permeable to Na²⁴.

2. At least two different types of binding limit the internal diffusibility of sodium within the egg. Only 12 per cent of the normal sodium is readily exchangeable. The remainder exchanges very slowly.

3. The implications of finding non-equilibration of such a simple ion as sodium are presented.

4. A new technique for making radio-autographs of single cells shows that after half an hour sodium is distributed almost uniformly throughout the cytoplasm.

5. Calculations based on rate of exchange of sodium into the egg plus radio-autograph evidence give a value of 2.6 x 10^-7 cm²./sec. for the diffusion coefficient of sodium within the egg.

6. At equilibrium the nucleus possesses approximately twice as much traced sodium per unit volume as the cytoplasm.

7. By direct chemical analysis the sodium content of frog eggs was found to be 0.082 per cent of the wet weight.