The preparation and human muscarinic receptor profiling of oxybutynin and N-desethyloxybutynin enantiomers.

Oxybutynin (1) is a non-selective muscarinic receptor antagonist that is used clinically for the treatment of urinary incontinence. The major metabolite of oxybutynin in humans is desethyloxybutynin (2). We have prepared the enantiomers of 1 and 2 and evaluated their ability to displace N-CT(3)-scopolamine chloride ((3)H-NMS) binding on human cloned muscarinic m1-5 receptors. Compounds 1 and 2 potently displaced (3)H-NMS binding at m1, m3 and m4 receptors, but were less potent at the m2 and m5 subtypes. However, metabolite 2 was more potent than the parent compound 1 in the binding assay. In general the R enantiomers were more potent than their respective S enantiomers. Therefore, we suggest that the cholinergic side effects associated with 2 may be due to its greater apparent potency with m1 and m3 receptors, especially of its R-enantiomer, when compared with parent drug 1.

Fluorescence imaging of electrically stimulated cells.

Designing high-throughput screens for voltage-gated ion channels has been a tremendous challenge for the pharmaceutical industry because channel activity is dependent on the transmembrane voltage gradient, a stimulus unlike ligand binding to G-protein-coupled receptors or ligand-gated ion channels. To achieve an acceptable throughput, assays to screen for voltage-gated ion channel modulators that are employed today rely on pharmacological intervention to activate these channels. These interventions can introduce artifacts. Ideally, a high-throughput screen should not compromise physiological relevance. Hence, a more appropriate method would activate voltage-gated ion channels by altering plasma membrane potential directly, via electrical stimulation, while simultaneously recording the operation of the channel in populations of cells. The authors present preliminary results obtained from a device that is designed to supply precise and reproducible electrical stimuli to populations of cells. Changes in voltage-gated ion channel activity were monitored using a digital fluorescent microscope. The prototype electric field stimulation (EFS) device provided real-time analysis of cellular responsiveness to physiological and pharmacological stimuli. Voltage stimuli applied to SK-N-SH neuroblastoma cells cultured on the EFS device evoked membrane potential changes that were dependent on activation of voltage-gated sodium channels. Data obtained using digital fluorescence microscopy suggests suitability of this system for HTS.