REGIONAL AND SUBCELLULAR DISTRIBUTION OF CHOLINE ACETYLTRANSFERASE IN THE BRAIN OF RATS¹

Abstract

Homogenates of corpus striatum, cerebral cortex and hypothalamus excised from rat brain were fractionated on discontinuous Ficoll and sucrose density gradients, and the distribution of choline acetyltransferase (ChAc) in the mitochondria1 and synaptosomal fractions was determined. In the hypothalamic and cortical regions the fractions enriched in synaptosomes showed much higher activity of ChAc than those containing mainly mitochondria. On the other hand, the corpus striaturn showed an equal distribution of ChAc activity in those two fractions. The localization of ChAc was also studied in the postnuclear supernatants obtained from three brain regions, using continuous sucrose density gradients. The distribution of ChAc was compared to that of monoamine oxidase (MAO), potassium and protein. When the pellets obtained from the fractions collected from the gradient were suspended in sucrose, the peak of ChAc activity was close to that of M A 0 in all three brain regions. When 0.1 mM EDTA +1% butanol was used in order to liberate the occluded form of ChAc, the maximum liberation occurred in lighter fractions, resulting in a shift of the activity peak toward the top of the gradient. This was found with fractions from hypothalamic and cortical regions. In the striatum, the liberated ChAc remained in the same fractions as the occluded enzyme. The results indicate that ChAc is liberated only in those fractions where it is present in synaptosomes. In agreement with the results on the discontinuous gradients this occurs in particles of lower density than mitochondria in cortex and hypothalamus, but in particles of similar density to mitochondria in the corpus striatum, indicating regional differences in the distribution of ChAc in the brain. K+ containing particles centrifuged in less dense fractions than those containing ChAc, indicating that synaptosomes are heterogeneous with respect to these two marker substances. MORPHINE has been shown to affect the activity of choline acetyltransferase (EC 2.3.1.6., ChAc) in the rat brain (DATTA et al., 1971). Changes in the enzymatic activity were traced on the conformational alterations of the ChAc molecule under the influence of morphine (DATTA and WAJDA, 1972). In these studies ChAc was measured in the corpus striatum, in which the activity of the enzyme is several-fold higher than in other brain regions, indicating the cholinergic nature of the striatum. In order to investigate morphine effects in neural tissue of lower specific activity, we attempted to concentrate the enzyme prior to assay by preparing fractions enriched in synaptosomal particles.Early studies on the subcellular distribution of ChAc in the brain indicate that the bulk of the enzyme is present in nerve-terminals (HEBB and WHITTAKER, 1958; GRAY

Transport and Metabolism of Radiolabeled Choline in Hepatocellular Carcinoma

“…Upregulated choline (Cho) uptake, relative to benign lesions and normal tissue, has been used as a diagnostic marker for cancer. , It has been suggested that carcinogenesis is associated with the upregulation of choline kinase (ChoK) activity, resulting in increased levels of phosphocholine (PC). ,− Furthermore, it is also known that rapidly proliferating tumors contain large amounts of phospholipids, particularly phosphatidylcholine (PtdCho). , In our previous tracer comparison study, well-differentiated HCC lesions (the early stage of HCC) were distinguished visually and by standardized uptake value (SUV) on PET/CT imaging with radiolabeled Cho as the tracer despite observable Cho uptake at the surrounding hepatic tissue. Longer half-life 18 F-labeled Cho derivative [ 18 F]fluorocholine (FCH) has also been applied to HCC in a proof of concept study .…”