Identification of muscarinic receptor subtypes in mouse parotid
gland.
Watson, Eileen L., Peter W. Abel, Dennis Dijulio, W. Zeng, M. Makoid,
Kerry L. Jacobson, Lincoln T. Potter, and Frank J. Dowd.
Departments of Oral Biology and Pharmacology, University of
Washington, Seattle, WA 98195; Department of Pharmacology, Creighton
University School of Medicine, and Department of Pharmaceutical
Sciences, Creighton University School of Pharmacy and Allied Health,
Omaha, NE; Department of Molecular and Cellular Pharmacology,
University of Miami, Miami, FL
APStracts 3:0074C, 1996.
Immunoprecipitation of muscarinic receptors from mouse parotid
membranes by specific subtype antisera showed that M3 and M1
receptors represented 75% and 15% of the total number of precipitable
receptors, respectively. [3H]N-methyl-scopolamine (NMS) labeled a
single class of high affinity binding sites in membranes from parotid
glands with a Kd of 0.67 0.02 nM; Bmax was 176 15 fmol/mg protein.
Competition curves for NMS, atropine, 4-diphenylacetoxy-N
-methylpiperidine methiodide (4-DAMP) and para-fluro
-hexahydrosiladifenidol (p-F-HHSiD) fit best to a one-site binding
model, while pirenzepine (P) and methoctramine fit best to a two-site
binding model indicating 76-90% M3 receptors. Results using
pirenzepine indicated that the second mouse parotid receptor subtype,
unlike that of the submandibular gland, has atypical characteristics
for an M1 receptor. The rank order of potency of muscarinic
antagonists in inhibiting phosphoinositide (PI) turnover, and
biphasic effects of carbachol on isoproterenol-stimulated cAMP
accumulation was atropine > 4-DAMP >> pirenzepine > AF-DX 116. A
specific M1 antagonist, m1-toxin, had no effect on carbachol
augmentation or inhibition of isoproterenol responses. Results
suggest that M3 receptors couple to both augmentation and inhibition
of stimulated cAMP levels.
Received 19 September 1995; accepted in final form 12 February
1996.
APS Manuscript Number C561-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 20 March 96