Hg. Preiksaitis et al., Pharmacological and molecular characterization of muscarinic receptor subtypes in human esophageal smooth muscle, J PHARM EXP, 295(3), 2000, pp. 879-888
Citations number
41
Categorie Soggetti
Pharmacology & Toxicology
Journal title
JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS
Esophageal peristalsis is dependent on activation of muscarinic receptors,
but little is known about the roles of specific receptor subtypes in the hu
man esophagus. We examined muscarinic receptor expression and function in h
uman esophageal smooth muscle obtained from patients undergoing resection f
or cancer. [H-3] Quinuclidinyl benzylate (QNB)-specific binding was similar
in longitudinal muscle (B-max = 106 +/- 22 fmol/mg of protein, K-d = 68 +/
- 9 pM) and circular muscle (B-max = 81 +/- 16 fmol/mg of protein, K-d = 79
+/- 15 pM). Subtype-selective antagonists inhibited [H-3] QNB similarly in
muscle from both layers. Further analysis of antagonist inhibition of [H-3
] QNB binding showed a major site (60-70%) with antagonist affinity profile
consistent with the M2 subtype and a second site that could not be classif
ied. Reverse transcription-polymerase chain reaction and immunoblotting dem
onstrated the presence of all five known muscarinic receptor subtypes, and
immunocytochemistry on acutely isolated smooth muscle cells confirmed the e
xpression of each subtype on the muscle cells. Subtype-selective antagonist
s had similar inhibitory effects on carbachol-evoked contractions in longit
udinal muscle and circular muscle strips with pA(2) values of 9.5 +/- 0.1 a
nd 9.6 +/- 0.2 for 4-diphenylacetoxy-N-methylpiperidine methiodide, 7.1 +/-
0.1 and 7.0 +/- 0.2 for pirenzepine, and 6.2 +/- 0.2 and 6.4 +/- 0.2 for m
ethoctramine, respectively. We conclude that human esophageal smooth muscle
expresses muscarinic receptor subtypes M1 through M5. The antagonist sensi
tivity profile for muscle contraction is consistent with activation of the
M3 subtype.