title: Partial agonistic effects of pilocarpine on Ca(2+) responses and salivary secretion in the submandibular glands of live animals.
abstract: What is the central question of this study? Pilocarpine stimulates salivary secretion via muscarinic ACh receptors (mAChRs), although the Ca(2+) -mobilizing effect of pilocarpine in salivary gland cells is extremely small. Therefore, we examined the effect of pilocarpine on Ca(2+) responses in submandibular gland cells and on secretion in vitro and in vivo. What is the main finding and its importance? Pilocarpine induces small Ca(2+) responses and reduces the effects of other mAChR agonists on Ca(2+) responses via its partial agonistic effects. These effects of pilocarpine on Ca(2+) responses in the submandibular gland were further established in vivo with a novel Ca(2+) imaging system and a genetically encoded Ca(2+) indicator. Pilocarpine stimulates salivary secretion via muscarinic ACh receptors (mAChRs), although the effect of pilocarpine on Ca(2+) responses in dispersed salivary gland cells is extremely small. Here, we demonstrate the effect of pilocarpine on Ca(2+) responses and salivary secretion in the rat submandibular gland (SMG). In fura-2-loaded SMG cells, the maximal effect of pilocarpine on [Ca(2+) ]i elevation was 16% of that of carbachol, and pilocarpine attenuated carbachol- and bethanechol (Bet)-induced [Ca(2+) ]i increases, indicating that pilocarpine acts as a partial agonist for mAChR-mediated Ca(2+) responses. The partial agonistic effect of pilocarpine on Ca(2+) dynamics in the SMG was also confirmed in live animals using the genetically encoded Ca(2+) indicator, YC-Nano50. Administration of pilocarpine (3 mg kg(-1) , i.p.) elicited a small increase in [Ca(2+) ]i in the SMG. Quantitative analyses demonstrated that resting [Ca(2+) ]i was ∼37 nm, which was increased by pilocarpine (3 mg kg(-1) ) and Bet (10 mg kg(-1) ) to 44 and 69 nm, respectively. The inhibitory effects of pilocarpine on Bet-induced Ca(2+) responses were also elucidated in vivo. We further examined real-time changes in pilocarpine-induced SMG salivary secretion and showed that pilocarpine induced an extremely weak secretory response and reduced Bet-induced secretion. Unlike Ca(2+) responses, pilocarpine failed to reduce the effect of Bet on SMG blood flow. Our results demonstrate that pilocarpine acts as a partial agonist of mAChRs to induce weak salivary secretion that is correlated with small increases in [Ca(2+) ]i . Furthermore, pilocarpine exhibits an antagonistic effect on mAChR-induced Ca(2+) responses and salivary secretion.
authors.affiliation: Department of Pharmacology, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido, 061-0293, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Nezu
authors.affiliation: Department of Pharmacology, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido, 061-0293, Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Morita
authors.affiliation: Department of Pharmacology, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido, 061-0293, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Tojyo
authors.affiliation: The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka, 567-0047, Japan.
authors.forename: Takeharu
authors.initials: T
authors.lastname: Nagai
authors.affiliation: Department of Pharmacology, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido, 061-0293, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Tanimura
mesh_terms: D000818:Animals; D018723:Bethanechol / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects*; D002217:Carbachol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D054333:Drug Partial Agonism; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology*; D010862:Pilocarpine / Q000494:pharmacology*; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism; D012463:Saliva / Q000378:metabolism*; D012472:Salivation / Q000187:drug effects*; D013363:Submandibular Gland / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors
chemical_list: D018721:Muscarinic Agonists; D011976:Receptors, Muscarinic; D018723:Bethanechol; D010862:Pilocarpine; D002217:Carbachol; D002118:Calcium