Choline Uptake in Nerve Cultures and in Synaptosomal Preparation is Regulated by the Endogenous Pool of Choline

Choline and Cholinergic Neurons

“…When synaptosomes (50,63,75) or preparations of chick ciliary muscle (62) were incubated in the presence of 0.5 to 5.0 puM labeled choline, a major fraction of the transported label could be recovered as ACh. In neuronal cultures (72,76) and in photoreceptor cells (74), the choline label is recovered predominantly as PCh and phospholipids, and not as ACh. The association between choline's transport and its acetylation observed in some preparations has been interpreted as reflecting direct (77) or kinetic (62,78) coupling; other observers, noting that the ACh synthesized intrasynaptosomally derives primarily from a preexisting choline pool (79) and that ACh synthesis can be inhibited without affecting choline transport, have concluded that high-affinity choline uptake need not be a selective source for the ACh precursor (80) and that choline's uptake is independent of its acetylation.…”

“…Such transactivation can be explained by a mechanism in which attachment of its ligand to the carrier molecule facilitates the carrier's passage across the membrane. Indeed, the higher the extrasynaptosomal concentration of choline, the greater the efflux of synaptosomal choline into the medium (76,81). Preparations of choline carrier incorporated into liposomes also exhibit transactivation (82).…”

“…Similarly, intracellular choline concentrations must be considered: not all of the synaptosomes prepared from mammalian brain are cholinergic, so that 1.5 nmole of choline per milligram of protein may be an over-or underestimation of the real choline concentration in cholinergic synaptosomes. Loading synaptosomes with exogenous choline stimulates their choline influx (76,81). Such transactivation can be explained by a mechanism in which attachment of its ligand to the carrier molecule facilitates the carrier's passage across the membrane.…”

The metabolic fate of [3H-methyl]choline in cultured human neuroblastoma cell lines, LA-N-1 and LA-N-2

“…As enumerated by Richardson et al (1989), the principle watersoluble compound into which labeled Cho is incorporated is PCho, as shown with NS-20 neuroblastoma cells (Lanks et al, 1974); neuroblastoma X glioma hybrid cells, NG108-15 (Blusztajn et al, 1986); dissociated neurons of chick brain and rat brain synaptosomes (Massarelli and Wong, 1981;Wong et al, 1983); and cultures of septal slices of neonatal rats (Keller et al, 1987) in vivo, which may be a possible precursor for AcCho synthesis.…”

Neurobiology of Acetylcholine

“…Since Massarelli and Wong (1981) suggested that CK activity may be coupled to the transport of choline in neuronal membranes, we investigated the subcellular distribution of CK activity in rat striatum (Reinhardt and Wecker, 1983).…”