Biochimica Et Biophysica Acta I.53 the Effect of Hemicholinium-3 on the in Vw0 Formation of Cerebral Phosphatidylcholine*

The effect of hemicholinium-3 on the incorporation of [Me-%]choline into the phospholipids of the subcellular fractions of the canine caudate nucleus was studied. A correlation between the amount of hemicholinium-3 administered and increased choline incorporation into phospholipids was obtained. The analysis of the labeled phospholipids revealed that 93% of the radioactivity was in phosphatidylcholine and the remainder in lysophosphatidyl choline and sphingomyelin + choline plasmalogens. The specific radioactivity of phosphatidylcholine (countslmin per ,ug phosphorus) determined after its isolation by thin-layer chromatography, increased markedly as a result of the administration of hemicholinium. An unequal time-dependence in the labeling of the phosphatidylcholine in the subcellular fraction containing nerve endings, mitochondria and lysosomes, as opposed to the phosphatidylcholine of the microsomal fraction was also noted, particularly after the administration of hemicholinium and choline in a weight ratio of 500. Discontinuous density gradient centrifugation of the fraction containing the nerve endings, the mitochondria and the lysosomes showed that phosphatidylcholine formation was most affected by hemicholinium in the fraction containing the “heavy” nerve endings, followed by the fraction containing the mitochondria + lysosomes. It is suggested that hemicholinium acts by accelerating the intracellular rate of movement of choline from the water-soluble into the lipid pool of the caudate nucleus where, by virtue of its presencelQ, it subsequently also stimulates the incorporation of choline into membrane phosphatidylcholine.