Rezeptoren der Neurotransmitter, IV. Serotoninrezeptor und Neuraminsäurestoffwechsel der glatten Muskulatur

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Abstract
The 5-hydroxytryptamine (= serotonin) induced contraction of rat stomach fundus preparations was measured quantitatively. Preincubation with enzymes, non-competitive inhibitors, precursors, and nucleotides engaged in sialic-acid metabolism lead to the finding that N-acetyl-neuraminic acid is synthesized by smooth muscle and incorporated into the 5-hydroxytryptamine-receptor. Incorporation experiments with N-[1-14C]acetylneuraminic acid showed that the complete and biologically active 5-hydroxytryptamine-receptor is synthesized from an unknown precursor of the receptor X[long dash]most likely a macromolecular structure at the surface[long dash]and N-acetyl-neuraminic acid. Inhibitors of sialic acid biosynthesis, neuraminidase, and N-acetylneuraminate pyruvate-lyase[long dash]enzymes which either split off or cleave N-acetylneuraminic acid[long dash]diminish the number of active 5-hydroxytryptamine-receptors. Nucleotides, especially CTP, cyclic 3[image],5[image]-AMP, and N-acetyl-D-mannosamine, a precursor of N-acetyl-neuraminic acid, increase the 5-hydroxytryptamine induced contraction of smooth muscle.