Nuclear Precipitates in Pyroantimonate-osmium Tetroxide-fixed Tissues

Recent biochemical studies indicate a significant role for sodium ions in nuclear metabolism. Protein and nucleic acid syntheses in the nucleus depend upon sodium, apparently through a stimulating effect of this cation on the transport of amino acid, purine, and pyrimidine into the nucleus (1). The nuclei of avian erythrocytes and calf thymocytes appear to contain higher sodium concentrations than the cytoplasm (5), and the nuclei of frog oocytes actively incorporate and concentrate sodium as shown by radioautography with Na (1). An ultrastructural method developed by Komnick (8) presumably localizes tissue sodium by precipitating this cation with pyroantimonate (antimonate) ions included in the osmium tetroxide fixative. This method was employed in the present study in an effort to localize the sodium reported to be abundant in the nucleus and to evaluate the possibility of visualizing nucleic acidlinked cations. Use of this technique has yielded results which indicate an abundance of cation, presumably sodium, in the heterochromatin and