/sup 3/H)pirenzepine and (-)-(/sup 3/H)quinuclidinyl benzilate binding to rat cerebral cortical and cardiac muscarinic cholinergic sites. II. Characterization and regulation of antagonist binding to putative muscarinic subtypes

Journal Article · Thu May 01 00:00:00 EDT 1986 · J. Pharmacol. Exp. Ther.; (United States)

OSTI ID:5578981

Watson, M; Roeske, W R; Yamamura, H I

Studies show (/sup 3/H)PZ identified selectively a subpopulation of muscarinic binding sites compared to classical antagonists like (-)-(/sup 3/H)QNB in many central and peripheral tissues. We characterized the binding and regulation of selected antagonists to high-affinity (/sup 3/H)PZ (putative M1) and low-affinity PZ (putative M2) sites in rat cerebral cortex (predominantly M1) and heart (predominantly M2). Saturation isotherms of (/sup 3/H)PZ and (-)-(/sup 3/H)QNB were performed under various conditions. Guanyl-5'-yl-imidodiphosphate (30 microM) showed little effect on Kd (dissociation constant) or total binding capacity (total receptor density) values. Higher ionic strength buffers yielded lower affinity values for (/sup 3/H)PZ and (-)-(/sup 3/H)QNB. Kinetic studies confirmed high affinity Kd values seen in steady-state assays. We conducted inhibition studies of selected muscarinic antagonists including the reportedly cardioselective (putative M2) drug, AF-DX 116 (11-((2-(diethylamino)methyl-1-piperidinyl)-acetyl)-5, 11-dihydro-6H-pyrido(2,3-b)(1,4)-benzodiazepine-6-one), the reportedly M1 selective compound, PZ, and the classical antagonist (-)QNB, using (/sup 3/H)PZ and (-)-(/sup 3/H)QNB-labeled cerebral cortical and cardiac homogenates. Assays were done with and without guanyl-5'-yl-imidophosphate at 25 degrees C in 10 mM Na-K-phosphate, 50 mM Na-K-phosphate and modified Krebs-phosphate buffer. Studies showed antagonists generally had higher affinity in 10 mM Na-K-phosphate buffer, were insensitive to guanyl-5'-yl imidodiphosphate and had Hill values (nH) nearly equal to one. Cardiac PZ/(/sup 3/H)QNB curves were steep.

• Research Organization: Univ. of Arizona Health Sciences Center, Tucson
• OSTI ID: 5578981
• Journal Information: J. Pharmacol. Exp. Ther.; (United States), Journal Name: J. Pharmacol. Exp. Ther.; (United States) Vol. 2; ISSN JPETA
• Country of Publication: United States
• Language: English

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550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
AFFINITY
ALCOHOLS
AMINES
AMMONIUM COMPOUNDS
ANIMALS
AUTONOMIC NERVOUS SYSTEM AGENTS
BIOCHEMICAL REACTION KINETICS
BODY
BRAIN
BUFFERS
CARDIOVASCULAR SYSTEM
CENTRAL NERVOUS SYSTEM
CEREBRAL CORTEX
CEREBRUM
CHOLINE
DRUGS
HEART
HYDROXY COMPOUNDS
IN VITRO
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
LIPOTROPIC FACTORS
MAMMALS
MEMBRANE PROTEINS
MUSCLES
MYOCARDIUM
NERVOUS SYSTEM
ORGANIC COMPOUNDS
ORGANS
PARASYMPATHOLYTICS
PROTEINS
QUATERNARY COMPOUNDS
RATS
REACTION KINETICS
RECEPTORS
RODENTS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
VERTEBRATES