Acetylcholine metabolism and choline uptake in cortical slices
article
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 50 μM-[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 K(m) 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 0.84 μM-[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.
Topics
TNO Identifier
228295
ISSN
00223042
Source
Journal of Neurochemistry, 29(3), pp. 477-485.
Pages
477-485
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