Ionic milieu and volume adjustments in detergent-extracted thymic nuclei

Detergent-extracted isolated thymic lymphocyte nuclei were incubated in buffers containing 3 mM Ca++ and Mg++ and varying concentrations of Na+ and K+. Nuclei in 15 mM K+, 15 mM Na+ had a smaller size, smaller interchromatin spaces, and less packed chromatin than nuclei in the absence of these ions, but their water content relative to dry mass was not significantly different. NMR relaxation properties of water protons in these different nuclei were different, and nuclei in 15 mM K+, 15 mM Na+ contained twice as much K and Na as in the buffer solution. These findings indicate that the hydration of chromatin bodies and the size of the interchromatin spaces are sensitive to the free monovalent ion concentrations. When isolated nuclei were exposed to solutions containing 150 mM total concentration of K + Na, the nucleoplasm became disrupted and the hydration index was greater. The results are discussed in regard to possible mechanisms of nuclear volume control in cells.