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Partial agonistic effects of pilocarpine on Ca 2+ responses and salivary secretion in the submandibular glands of live animals
Author(s) -
Nezu Akihiro,
Morita Takao,
Tojyo Yosuke,
Nagai Takeharu,
Tanimura Akihiko
Publication year - 2015
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/ep085110
Subject(s) - pilocarpine , muscarinic acetylcholine receptor , submandibular gland , carbachol , medicine , endocrinology , chemistry , secretion , in vivo , salivary gland , muscarinic agonist , receptor , biology , neuroscience , microbiology and biotechnology , epilepsy
New FindingsWhat 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 n m , which was increased by pilocarpine (3 mg kg −1 ) and Bet (10 mg kg −1 ) to 44 and 69 n m , 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.