Location of inexchangeable sodium in the nucleus and cytoplasm of oocytes of Bufo bufo exposed to sodium-free solutions.

1. In oocytes exposed to Ringer solution in which Li substitutes for Na, 13-62% Na is inexchangeable with Li.2. Nuclei of oocytes isolated by dissection in salt solutions swell irrespective of the concentration or ionic components of the solution. When isolated in 4% bovine albumin solutions, swelling is negligible.3. When the nuclei of cells exposed to Li are isolated in 4% albumin solution, less than 6% of the inexchangeable Na is found in the nucleus, while 36-88% of it is found in the cytoplasmic fragments remaining after removal of the nucleus.4. When a Li-exposed cell is crushed in a cellophane bag and dialysed against Ringer or Li-substituted Ringer, 86-92% of the inexchangeable Na diffuses out.5. It thus appears that the inexchangeable Na is located almost entirely in the cytoplasm and hardly at all in the nucleus, and is not bound to macromolecules within the cell.