Uptake of neurotransmitters and precursors by clonal lines of astrocytoma and neuroblastoma: III. Transport of choline

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Abstract
Clonal lines of glial, neuronal, and nonneural origin accumulate choline via a high-affinity carrier-mediated transport system withK m in the range of 10–14 μM. These cell lines also accumulate choline by a second system that is not saturable at 10 mM choline, and that may represent diffusion. The transport of choline in glial cells differs from that seen in neuronal cells with respect to its Na+ requirement. The omission of Na+ from the incubation medium reduces high-affinity choline transport in neuronal cells and enhances it in glial cells. Kinetic analysis of the data indicates that reversible cholinesterase inhibitors and hemicholinium-3 (HC-3) inhibit the high-affinity transport system for choline. On the other hand, the diffusional or low-affinity component of choline transport in either cell type appears to have no Na+ requirement and is unaffected by either cholinesterase inhibitors or 10−4 M HC-3. The neuronal-glial differences in the Na+ requirement of choline transport may be related to the coupling of transport to choline metabolism, which differs in the two cell types. The presence of a high-affinity transport system for choline in clonal glial lines used as models of normal glia suggest that glia may modulate the availability of choline for acetylcholine synthesis at cholinergic synapses.