Choline acetyltransferase in cerebral arteries: modulator of amino acid uptake?

The possibility exists that synthesis of acetylcholine in cerebral blood vessels does not reflect the presence of cholinergic nerves, but is the property of some other cell type. Therefore, the hypothesis that acetylcholine synthesis in cerebral arteries modulates amino acid transport was tested. Choline acetyltransferase activity in rabbit cerebral arteries was inhibited by (2-benzoylethyl) trimethylammonium chloride. Furthermore, the product formed in this assay was degraded by added acetylcholinesterase, confirming the authenticity of measurements of choline acetyltransferase. Rabbit pial arteries (basilar and middle cerebral) accumulated alpha-aminoisobutyric acid to a greater extent than peripheral arteries. Ouabain (10(-5) M) blocked this accumulation, suggesting that it is analogous to the A-system for amino acid transport. (2-benzoylethyl) Trimethylammonium chloride showed a concentration dependent inhibition of alpha-aminoisobutyric acid accumulation in cerebral arteries, but was without effect on peripheral arteries. Atropine and physostigmine in concentrations as high as 10(-6) M had no significant effects on alpha-aminoisobutyric acid accumulation. An association between choline acetyltransferase activity and amino acid uptake is apparent in the cerebral vasculature, suggesting that synthesis of acetylcholine may be involved in modulation of the blood-cerebrospinal fluid barrier. This finding underscores the uncertainty of assuming that acetylcholine synthesis necessarily indicates the presence of cholinergic nerves.