Abstract— The uptake of (14C)choline was studied in cortical slices from rat brain after their incubation in a Krebs‐Henseleit medium containing either 4.7 mm‐KCl (low K), 25 mm‐KCl (high K) or 25 mm‐KCl without calcium (Ca free, high K). With 0.84 μm‐(14C)choline in the medium the uptake per gram of tissue was 0.62 nmol after incubation in low K medium, 1.13 nmol after incubation in high K medium and 0.78 nmol after incubation in a Ca free, high K medium. The differences caused by potassium were greater in fraction P2 than in fractions P1 and S2. With 17 and 50μm‐(14C)choline in the medium greater amounts of (14C)choline were taken up, but the effect of potassium on the uptake almost disappeared. The amount of radioactive material in fraction P2 followed Michaelis‐Menten kinetics with Km values of 2.1 and 2.3 μm after incubation in low and high K medium, respectively. Hemicholinium‐3 only slightly inhibited choline uptake from a medium with 0.84μm‐(14C)choline, but it abolished the extra‐uptake induced by high K medium. The radioactivity in the slices consisted mainly of unchanged choline and little ACh was formed after incubation in low K medium, but after incubation in high K medium 50% of the choline taken up was converted into ACh. The hemicholinium‐3 sensitive uptake of choline, the conversion of choline into ACh and the synthesis of total ACh, were stimulated about 7–8‐fold by potassium. It is concluded that in cortical slices from rat brain all choline used for the synthesis of ACh is supplied by the high‐affinity uptake system, of which the activity is geared to the rate of ACh synthesis.
Journal of Neurochemistry – Wiley
Published: Sep 1, 1977
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