High affinity choline uptake: ionic and energy requirements.

Abstract

Abstract— High affinity choline uptake into rat hippocampal synaptosomes was examined at 37°C when various ions were deleted from normal Kreb's‐Ringer media. When sodium chloride was replaced by sucrose, lithium chloride, cesium chloride or rubidium chloride, choline uptake was markedly reduced. When the sodium concentrations of the Kreb's media were gradually reduced to zero, the uptake was gradually reduced in parallel. A kinetic analysis performed at low and normal sodium concentrations revealed changes in Km and Vmax values.When several non‐chloride sodium salts were utilized, the uptake was reduced in all cases suggesting also a chloride‐dependence in addition to the sodium‐dependence. Omission of calcium chloride or magnesium sulfate from the media did not alter uptake.Sodium‐dependent choline uptake was examined over a range of potassium concentrations (0–35 DIM). It was found that uptake was maximal between potassium concentrations of 0.35–4.8 mm but was reduced at both lower and higher potassium concentrations. The kinetics of uptake were examined under varying potassium concentrations, and at low potassium, only a change in Vmax was observed while at high potassium concentrations, there were changes in both Km and Vmax values.Preincubation and incubation of synaptosomes with 0.1 m‐ouabain, 0.1 mm‐2,4‐dinitrophenol and 1 mm‐KCN caused a reduction in sodium‐dependent uptake. When dextrose was omitted from the preincubation and incubation media there was also a reduction in sodium‐dependent uptake. By contrast, the sodium‐independent uptake was unaffected by the metabolic inhibitors or omission of dextrose, and had a very low Q10. When various incubation temperatures were utilized in uptake experiments, the Q10 for the interval 37‐27°C was 2.7 and the activation energy was 22.7 kcal/mol.Slightly different ionic dependences were observed when animals pretreated with pentobarbital of oentylenetetrazol were utilized as the source of synaptosomes.