TY - JOUR
T1 - A minority of muscarinic receptors mediate rabbit tracheal smooth muscle contraction.
AU - Mahesh, V. K.
AU - Nunan, L. M.
AU - Halonen, M.
AU - Yamamura, H. I.
AU - Palmer, J. D.
AU - Bloom, J. W.
PY - 1992/3
Y1 - 1992/3
N2 - To enhance our understanding of cholinergic mechanisms and muscarinic receptors in bronchoconstriction, we have characterized the muscarinic receptor subtypes in rabbit tracheal smooth muscle using radioligand binding and functional assays. The Kd for [3H]quinuclidinyl benzilate ([3H](-)QNB) binding determined from saturation isotherms was 12.6 x/divided by 1.1 pM (geometric mean x/divided by SEM), and the Bmax was 269 +/- 7 fmol/mg protein (arithmetic mean +/- SEM). Competitive inhibition studies with the muscarinic antagonists pirenzepine (PZ), 11[[2-[(diethylamino)-methyl]1-piperidinyl]acetyl]-5,11-dihydro-6H- pyrido[2,3-b][1,4]benzodiazepine-6-one (AF-DX116), 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP), and hexahydrosiladifenidol (HHSiD) demonstrated heterogeneity of muscarinic receptor subtypes in rabbit tracheal smooth muscle. PZ bound with low affinity to a single receptor site, indicative of an absence of M1 receptors. AF-DX116 (M2 selective) bound with high affinity to approximately 83% of muscarinic binding sites, and 4-DAMP and HHSiD (M3 antagonists) bound with high affinity to approximately 24 and 28% of muscarinic binding sites, respectively. Additionally, direct binding studies with [3H]4-DAMP demonstrated high-affinity binding with 23% of muscarinic binding sites. Thus, the majority of muscarinic receptors in rabbit tracheal smooth muscle bound with high affinity to an M2-selective antagonist, and the remaining receptor sites bound with high affinity to M3 antagonists. The inhibitory effects of atropine, PZ, AF-DX116, and 4-DAMP on methacholine-induced contraction of rabbit tracheal rings were compared. 4-DAMP was a potent inhibitor of methacholine-induced contraction, but PZ and AF-DX116 demonstrated low potency.(ABSTRACT TRUNCATED AT 250 WORDS)
AB - To enhance our understanding of cholinergic mechanisms and muscarinic receptors in bronchoconstriction, we have characterized the muscarinic receptor subtypes in rabbit tracheal smooth muscle using radioligand binding and functional assays. The Kd for [3H]quinuclidinyl benzilate ([3H](-)QNB) binding determined from saturation isotherms was 12.6 x/divided by 1.1 pM (geometric mean x/divided by SEM), and the Bmax was 269 +/- 7 fmol/mg protein (arithmetic mean +/- SEM). Competitive inhibition studies with the muscarinic antagonists pirenzepine (PZ), 11[[2-[(diethylamino)-methyl]1-piperidinyl]acetyl]-5,11-dihydro-6H- pyrido[2,3-b][1,4]benzodiazepine-6-one (AF-DX116), 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP), and hexahydrosiladifenidol (HHSiD) demonstrated heterogeneity of muscarinic receptor subtypes in rabbit tracheal smooth muscle. PZ bound with low affinity to a single receptor site, indicative of an absence of M1 receptors. AF-DX116 (M2 selective) bound with high affinity to approximately 83% of muscarinic binding sites, and 4-DAMP and HHSiD (M3 antagonists) bound with high affinity to approximately 24 and 28% of muscarinic binding sites, respectively. Additionally, direct binding studies with [3H]4-DAMP demonstrated high-affinity binding with 23% of muscarinic binding sites. Thus, the majority of muscarinic receptors in rabbit tracheal smooth muscle bound with high affinity to an M2-selective antagonist, and the remaining receptor sites bound with high affinity to M3 antagonists. The inhibitory effects of atropine, PZ, AF-DX116, and 4-DAMP on methacholine-induced contraction of rabbit tracheal rings were compared. 4-DAMP was a potent inhibitor of methacholine-induced contraction, but PZ and AF-DX116 demonstrated low potency.(ABSTRACT TRUNCATED AT 250 WORDS)
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U2 - 10.1165/ajrcmb/6.3.279
DO - 10.1165/ajrcmb/6.3.279
M3 - Article
C2 - 1540392
AN - SCOPUS:0026831458
SN - 1044-1549
VL - 6
SP - 279
EP - 286
JO - American journal of respiratory cell and molecular biology
JF - American journal of respiratory cell and molecular biology
IS - 3
ER -