[A study of muscarinic cholinergic receptor subtypes in human detrusor muscle using radioligand binding techniques]

The subtypes of the muscarinic cholinergic receptor in human detrusor muscle were studied using radioligand binding techniques. It was found that there were significant amount of M1, M2 and M3 receptors labeled by 3H-pirenzepine, 3H-AFDX and 3H-4DAMP, respectively, in human detrusor muscle. The rank order of the amount of these receptors was M3 > M1 > or = M2. The amount of M3 receptors was about 10-fold of M1 or M2. In the inhibition experiment of 3H-QNB binding to human detrusor muscle, the Ki values of pirenzepine or AFDX was 50-100 fold of that of 4DAMP and the rank order of Ki values was pirenzepine > AFDX > 4DAMP. The M3 selective drug, 4DAMP showed smallest Ki value among the three drugs studied, indicating that the affinity of M3 receptor was highest among the three muscarinic subtypes. These data suggest that M3 receptors are predominant in human detrusor muscle biochemically.