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

Abstract

SUMMARY1. 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 %0 bovine albumin solutions, swelling is negligible.3. When the nuclei of cells exposed to Li are isolated in 4 0 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.

The distribution of sodium, potassium and chloride in the nucleus and cytoplasm of Bufo bufo oocytes measured by electron microprobe analysis.

“…The present studies thus confirm previous studies which indicate the presence of an internal fraction of Na in the oocyte which is inexchangeable or very slowly exchangeable with external Li (Dick & Lea, 1964;Dick & McLaughlin, 1969;Dick et al 1970;De Laat et al 1974;Dick & Fry, 1973. This fraction lies in the cytoplasm but is readily dialysable against either Na or Li (Dick & Fry, 1973).…”

“…This fraction lies in the cytoplasm but is readily dialysable against either Na or Li (Dick & Fry, 1973). It seems likely therefore that the inexchangeable or sequestered Na is located within cytoplasmic membrane-bounded vesicles rather than bound to proteins or other macromolecules.…”

“…Autoradiographic studies have shown that the fraction of Na which does not readily exchange with Li, the so-called sequestered fraction, lies in the cytoplasm rather than the nucleus (Dick, Fry, John & Rogers, 1970), and dialysis studies have suggested that it is contained in some membrane-bounded vesicular component of the cytoplasm rather than bound to protein or other macromolecules (Dick & Fry, 1973).…”

The effect of lowering external sodium on the intracellular sodium activity of crab muscle fibres.

“…The fast changes of aNa could only be explained in terms of a reduction of the passive Na+ influx if the ATP-dependent Na pump in crab muscle was both extremely active and extremely ouabain-resistant. (Dick & Fry, 1973;McLaughlin & Hinke, 1966) but these only exchange slowly with the sarcoplasm and the extracellular environment and anyway, would be expected to be depleted rather than enriched in low-Na solution. However, the possibility exists that aNa which can itself exchange directly with the exterior might also be able to rapidly exchange indirectly via a second compartment like the sarcoplasmic reticulum which is extrasarcoplasmic in origin.…”

Evidence for the Existence of Globular Units in the Supranucleosomal Organization of Chromatin

“…It is obvious that extended nucleosomal filaments as shown in Fig. 1 a do not occur in the living cell nucleus since the ion concentrations determined in nuclei of living cells (Century et al 1970;Century and Horowitz 1974;Dick and Fry 1973;Paine et al 1975;Riemann et al 1969) favor the arrangement of nucleosomes into higher order structures. The important question therefore is: What is the organization of the chromatin in the nucleus of the living cell?…”