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The development of analytical methods for determining the cholinergic biomarkers acetylcholine (ACh) and choline (Ch) is important for assessing their role in neurological and cognitive functions. In this review, electrochemical (EC) strategies to detect ACh and Ch are summarized and compared to other analysis methods. Recent research focusing on the development of a versatile nonradiochemical in vitro assay to evaluate Ch transport is also described. The assay coupled to analysis by capillary electrophoresis (CE) with indirect EC detection at an enzyme-modified microelectrode affords exceptional selectivity and sensitivity. Femtomole or lower mass detection limits for ACh (1 fmol) and Ch (100 amol) have been readily achieved, opening up a new range of possible experiments for investigating transport or turnover of Ch and ACh in neurobiological systems. The value of this method is illustrated through the evaluation of the pharmacological efficacy and mode of inhibition of a new class of quaternary ammonium alkyl-substituted catechol-based inhibitors of high-affinity choline transport (CHT). This microanalytical approach is particularly useful when knowledge of endogenous concentrations of Ch or ACh is desired or when the amount of available compounds or the sample size is limited. A brief description of the principles of CE is also provided.

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A direct method for evaluating choline uptake by the high-affinity choline transport system in synaptosomes was developed using capillary electrophoresis (CE) with electrochemical (EC) detection. On-column EC detection of choline and the internal standard, butyrylcholine, was accomplished with a 25 microm platinum electrode modified with the enzymes, choline oxidase and acetylcholinesterase. Choline uptake was evaluated as a function of choline concentration and a KM value of 1.7 microM was determined. The method was also used to evaluate a new class of redox affinity inhibitors of choline transport. In particular, the effectiveness of 3-[(trimethylammonio)methyl]catechol (TMC) as an inhibitor of choline uptake was examined independently and relative to the inhibition of the well-known inhibitor of choline transport, hemicholinium-3. The IC50 and KI for TMC were determined to be 30 microM and 14 microM, respectively. The combination of the selectivity and sensitivity afforded by CEEC provides a relatively straightforward approach for monitoring choline transport in synaptosomes.