Characteristics of Muscarinic Receptor Subtypes in Guinea Pig Gallbladder Smooth Muscle

Lee, Jong Kyun; Rhee, Poong Lyul; Kang, Tong Mook; Kim, Jae Jun; Koh, Kwang Cheol; Paik, Seung Woon; Rhee, Jong Chul

Abstract

BACKGROUND AND AIMS: Acetylcholine (Ach) is the most irnportant rnediator in vagal-induced and cholecystokinin-induced gallbladder contraction. There are several rnuscarinic receptor subtypes characterized by pharmacologic study. The majority of smooth muscles from many species exhibit heterogenous populations of muscarinic receptors and different subtypes activate different signal transduction pathways. Therefore, it is important and essential to characterize the muscarinic receptor subtypes for understanding the mechanism of muscle contraction in a certain tissue. The aim of the present study was to characterize the muscarinic receptor subtypes in guinea pig gallbladder smooth muscle using relatively selective receptor subtype antagonists.
METHODS
Gallbladder muscle strips were prepared and mounted in an organ bath. Isometric contractions were recorded on a polygraph. 50% inhibitory concentrations (Icqp) and pA (-log KB) values of pirenze-pine, methoctramine, and 4-DAMP (M1, M2, and M3 antagonist, respectively) were compared on Ach-induced gallbladder muscle contraction.
RESULTS
Icsp of pirenzepine, methoctramine, and 4-DAMP on 1pM Ach-induced contraction were 7.8 > 10 'M, 2.'7 x 10 M, and 3,7 x 10"" M, respectively. pA, values of pirenzepine, methoctramine, and 4-DAMP were 6.8, 5.0 and 11.4, respectively.
CONCLUSIONS
M3 subtype may play the most important role in Ach-induced contraction of guinea pig gallbladder muscle.