Identification of muscarinic receptor subtypes in mouse parotid gland

Abstract

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. [N-methyl-3H]methylscopolamine (NMS) labeled a single class of high-affinity binding sites in membranes from parotid glands with a dissociation constant of 0.67 +/- 0.02 nM and a maximum binding capacity of 176 +/- 15 fmol/mg protein. Competition curves for NMS, atropine, 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) and para-fluoro-hexahydro-sila-difenidol fit best to a one-site binding model, whereas pirenzepine and methoctramine fit best to a two-site binding model, indicating 76-90% M3 receptors. Results from the use of 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 turnover and biphasic effects of carbachol on isoproterenol-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) accumulation was atropine > or = 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.

Telenzepine-sensitive muscarinic receptors on rat pancreatic acinar cells

“…Similar to other systems (29), it appears that the rat pancreatic acinar cell may express both the m1 and m3 receptor subtype. Therefore, it was possible that the two responses to CCh, secretion and zymogen processing, might be regulated by activation of specific receptors.…”

Functional Selectivity of Muscarinic Receptor Antagonists for Inhibition of M3-Mediated Phosphoinositide Responses in Guinea Pig Urinary Bladder and Submandibular Salivary Gland

“…Although it is generally accepted that acetylcholine-in- duced phosphoinositide hydrolysis and contraction are mediated almost exclusively by the M 3 receptor in bladder (Harriss et al, 1995;Chess-Williams et al, 2001), some controversy remains over the potential involvement of "non-M 3 " mACh receptors in cholinergic responses of salivary glands (Laniyonu et al, 1990;Watson et al, 1996). We therefore sought clarification of whether the presence of non-M 3 (in particular, M 1 ) muscarinic receptors could be involved in the phosphoinositide response in submandibular gland, using competition radioligand binding assays with a range of the most selective muscarinic ligands available.…”

Cholinergic Stimulation of Salivary Secretion Studied with M1 and M3 Muscarinic Receptor Single- and Double-Knockout Mice

“…Pharmacological, biochemical, and molecular genetic studies indicate that the M 3 receptor subtype plays a key role in mediating increased salivary flow (Laniyonu et al, 1990;Dai et al, 1991;Caulfield, 1993;Watson et al, 1996;Moriya et al, 1999;Matsui et al, 2000;Bockman et al, 2001;Bymaster et al, 2003). However, pharmacological and biochemical studies suggest that M 1 (Watson and Culp, 1994;Culp et al, 1996;Luo et al, 2001;Tobin et al, 2002) and M 5 mAChRs (Flynn et al, 1997;Meloy et al, 2001;Tobin et al, 2002) may also play a role in muscarinic agonist-mediated salivary secretion.…”