Effects of altered tonicity by sodium chloride on L-tryptophan binding to hepatic nuclei

This study was concerned with theeffects of NaCl administered in vivo or added in vitro to isolatednuclei on ³H]tryptophan binding to rat hepaticnuclei assayed in vitro. Hypertonic (10.7%) NaCl administered in vivoto rats caused at 10 min a marked decrease in in vitro binding (totaland specific) of ³H]tryptophan to hepaticnuclei. In vitro incubation of isolated hepatic nuclei, but not ofisolated nuclear envelopes, with added NaCl (particularly at 0.125 × 10⁴ M and 0.25 × 10⁴ M) revealed significant inhibition of³H]tryptophan binding. However, isolatedhepatic nuclear envelopes prepared after in vitro incubation ofisolated nuclei with added NaCl did show inhibition of³H]tryptophan binding (total and specific)compared with controls. Other salts (KCl, MgCl₂,NaHCO₃, NaC₂H₃O₂, NaF,or Na₂SO₄), at similar concentrations to thatof NaCl except for MgCl₂, when added to isolated nuclei didnot appreciably inhibit nuclear tryptophan binding. Kinetic studies ofin vitro nuclear ³H]tryptophan binding in thepresence of 0.125 × 10⁴ M NaCl revealed thatbinding decreased at 0.5 h and continued to 2 h compared with nuclear³H]tryptophan binding with controls (withoutNaCl addition). The results obtained in vivo in rats and those obtainedin vitro with isolated hepatic nuclei revealed NaCl-induced inhibitoryeffects on ³H]tryptophan binding to hepaticnuclei. Although the inhibitory effects were similar under the twodifferent experimental conditions, the mechanism for each may bedifferent in that the NaCl concentration in hepatic cells afteradministration of NaCl in vivo was appreciably higher than the lowlevels added in vitro to the isolated hepatic nuclei.