A STUDY ON THE AFFINITIES OF VARIOUS MUSCARINIC ANTAGONISTS TO THE HUMAN DETRUSOR MUSCLE

The affinities of various muscarinic antagonists to human detrusor muscle were determined using radioligand binding techiniques. Saturation experiments with 3H-QNB revealed that there were significant amount of muscarinic cholinergic receptors in human detrusor muscle. Displacement of 3H-QNB binding by various muscarinic subtype selective drugs was studied in the inhibition experiment. Pirenzepine, AFDX-116 and 4-DAMP inhibited the 3H-QNB binding to human detrusor muscle with the Ki values (nM) (mean±S. D., n=6) of 243±62.5, 59.7±15.3 and 2.69±0.96, respectively. These data indicate that M3-selective drug possesses the highest affinity to human detrusor muscle. The Ki values of oxybutynin and tiquizium bromide were similar to those of 4-DAMP, suggesting that these two drugs have strong affinities to human detrusor muscle.