Cholinergic stimulation of salivary secretion studied with M1 and M3 muscarinic receptor single- and double-knockout mice.
Identification of the specific muscarinic acetylcholine receptor (mAChR) subtypes mediating stimulation of salivary secretion is of considerable clinical interest. Recent pharmacological and molecular genetic studies have yielded somewhat confusing and partially contradictory results regarding the involvement of individual mAChRs in this activity. In the present study, we re-examined the roles of M(1) and M(3) mAChRs in muscarinic agonist-mediated stimulation of salivary secretion by using M(1) and M(3) receptor single-knockout (KO) mice and newly generated M(1)/M(3) receptor double-KO mice. When applied at a low dose (1 mg/kg, s.c.), the muscarinic agonist pilocarpine showed significantly reduced secretory activity in both M(1) and M(3) receptor single-KO mice. However, when applied at higher doses, pilocarpine induced only modestly reduced (5 mg/kg, s.c.) or unchanged (15 mg/kg, s.c.) salivation responses, respectively, in M(1) and M(3) receptor single-KO mice, indicating that the presence of either M(1) or M(3) receptors is sufficient to mediate robust salivary output. Quantitative reverse transcriptase-polymerase chain reaction studies with salivary gland tissue showed that the inactivation of the M(1) or M(3) mAChR genes did not lead to significantly altered mRNA levels of the remaining mAChR subtypes. Strikingly, the sialagogue activity of pilocarpine was abolished in M(1)/M(3) receptor double-KO mice. However, salivary glands from M(1)/M(3) receptor double-KO mice remained responsive to stimulation by the beta-adrenergic receptor agonist, (S)-isoproterenol. Taken together these studies support the concept that a mixture of M(1) and M(3) receptors mediates cholinergic stimulation of salivary flow.
Gautam
Dinesh
D
Molecular Signaling Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892-0810, USA.
Heard
Thomas S
TS
Cui
Yinghong
Y
Miller
Georgina
G
Bloodworth
Lanh
L
Wess
Jürgen
J
D000818:Animals; D001665:Binding Sites; D004305:Dose-Response Relationship, Drug; D015870:Gene Expression; D051379:Mice; D018345:Mice, Knockout; D018721:Muscarinic Agonists / Q000494:pharmacology*; D019832:N-Methylscopolamine / Q000378:metabolism; D010862:Pilocarpine / Q000494:pharmacology*; D016133:Polymerase Chain Reaction; D043643:Receptor, Muscarinic M1 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D043587:Receptor, Muscarinic M3 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D011950:Receptors, Cholinergic / Q000378:metabolism; D012469:Salivary Glands / Q000187:drug effects / Q000378:metabolism*; D012472:Salivation / Q000187:drug effects*; D013997:Time Factors; D014316:Tritium
D018721:Muscarinic Agonists; D043643:Receptor, Muscarinic M1; D043587:Receptor, Muscarinic M3; D011950:Receptors, Cholinergic; D010862:Pilocarpine; D014316:Tritium; D019832:N-Methylscopolamine