THE UPTAKE OF [3H]CHOLINE BY SNAIL (HELIX POMATIA) NERVOUS TISSUE IN VITRO |
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Authors: | N. N. Osborne |
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Affiliation: | Max-Planck-Institut für experimentelle Medizin, Forschungsstelle Neurochemie. 3400 Göttingen, Deutschland |
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Abstract: | Abstract— When suboesophageal ganglia of the snail Helix comalia were incubated at 25°C in a medium containing [3H]choline, tissue: medium ratios of about 14:1 were obtained after 20 min incubation, and only 15°, of the accumulated choline was metabolized to form [3H]acetylcholine. The uptake of [3H]choline showed saturation kinetics and was dependent upon temperature and sodium ions. Kinetic analysis suggested the existence of a high affinity uptake process (Km= 1.7 μM, Vmax= 0.21 nmol/g/min) and a low affinity process (Km= 100 μM, Vmax= 1.2 nmol/g/min). The high affinity uptake differed from the low affinity system in that it was sensitive to various metabolic inhibitors and was competitively inhibited by low concentrations of hemicholinium- and acetylcholine. Neither uptake system was greatly influenced by the absence of calcium, potassium or magnesium ions or by the presence of low concentrations of 5-HT, dopamine. tetrabenazine, chlorpromazine, decamethonium, nalaxone or imipramine. The high affinity uptake process may be important in supplying choline for the biosynthesis of acetylcholine in cholinergic neurons. |
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