POLYMORPHISM OF THE AFFINITY OF MUSCARINIC RECEPTORS IN THE GASTRIC SMOOTH MUSCLES OF GUINEA PIGS

In the experiment of contraction of guinea pig gestric smooth muscle, it was found that pD₂ of acetylcholine for longitudinal and circular smooth muscles from guinea pig gastric fundus and body were 6.5 and 4.0 respectively. ThepA₂ values of atropine for these smooth muscles were approximately 10 and 8.5 respectively. This suggests that there were two kinds of muscarinic receptars of different affinities in the stomach and these receptors played a role in contractile function in longitudinal and circular smooth muscles. Specific ³H-QNB binding tohomogenates of gastric smooth muscles were also studied by using the method described by Yamamura et al. It was also found that high and low affinity bindings in the homogenates of gastric smooth muscles. The KD values of various homogenates of high and low affinity bindings were 1.8 and 18 nmc/L respectively. Since protein modulators with various functions showed different effects of the bindings of two components to labeled ligand, it is therefore concluded that the two components were the binding sites with different affinities.