Relationships between Acetylcholine Release and Membrane Phosphatidylcholine Turnover in Brain and in Cultured Cholinergic Neurons
Cholinergic neurons derive their choline from the circulation (choline crosses the blood-brain-barrier via a facilitated diffusion mechanism, Pardridge et al., 1979) or from its synthesis in situ (Blusztajn and Wurtman, 1981). Within cholinergic neurons choline can undergo two transformations: it may be acetylated by choline acetyltransferase (CAT) to form the neurotransmitter acetylcholine (ACh), or it may be incorporated into choline phospholipids (Ch-PL), PtdCho, sphingomyelin, or plasmalogens via the CDP-choline (Kennedy and Weiss, 1956) or base-exchange (Porcellati et al., 1971; Abdel-Latif and Smith, 1972) pathways. We hypothesize that a dynamic equilibrium exists between choline’s reversible fluxes into and out of ACh and Ch-PL, and that these fluxes are well regulated in order to maintain both adequate ACh synthesis and the functional integrity of membranes (Ch-PL are the major lipid components of all biological membranes). This chapter describes the relationships between choline, ACh, and Ch-PL in the nervous system, and discusses evidence derived from experiments on brain slices, synaptosomes, and cultured cells.
KeywordsCholinergic Neuron Choline Kinase Free Choline Fatty Acyl Composition Choline Phospholipid
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