EFFECT OF CHOLINE ON THE RATES OF SYNTHESIS and OF RELEASE OF ACETYLCHOLINE IN THE ELECTRIC ORGAN OF TORPEDO

Abstract— Slices of electric organ of Torpedo marmorata were chopped and incubated in a saline-urea-sucrose medium. This preparation of minced tissue exhibited a relative enrichment in ACh and nerve endings, which was attributed to a loss of electroplaque cytoplasm. Electron microscopic controls showed nerve endings of normal morphology, some of them forming 'chaplets' separated from electro-plaques. Miniature endplate potentials were recorded on sealed fragments also present in this preparation. ACh levels remained unchanged during incubation periods as long as 19 h. The time course of the incorporation of 1-¹⁴C]acetate of 2-¹⁴C]pyruvate into ACh pools was studied. These incorporations were similarly affected by the choline added to the medium. In the presence of increasing choline concentrations (up to 10^-4 m ), the incorporation of ¹⁴C]acetate or ¹⁴C]pyruvate into ACh increased. They both diminished when choline was added above 10^-4M. The ACh content of the tissue was not affected by added choline. From the constancy of ACh levels in the presence of various choline concentrations and from the steady state of our preparation, we can conclude that the release of transmitter varied in parallel to the incorporation rate of the precursor of the acetyl moiety of ACh. This fact was also found using the efflux of ¹⁴C]acetate as an evaluation of ACh release. The values of release calculated by this method were in good agreement with those determined from the incorporations of acetate and pyruvate into ACh. It is suggested that the primary action of choline is on its high affinity carrier system. This triggers a secondary action on the ACh release mechanisms.