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Signaling Bias and Antagonism of Pilocarpine for M3 Muscarinic Acetylcholine Receptor
Author(s) -
Pronin Alexey N.,
Wang Kelly,
Slepak Vladlen Z.
Publication year - 2018
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2018.32.1_supplement.555.7
Subject(s) - pilocarpine , muscarinic acetylcholine receptor , chemistry , muscarinic acetylcholine receptor m3 , carbachol , pirenzepine , agonist , muscarinic acetylcholine receptor m1 , muscarinic acetylcholine receptor m2 , muscarinic agonist , endocrinology , muscarinic antagonist , medicine , pharmacology , receptor , biochemistry , biology , neuroscience , epilepsy
Pilocarpine is a prototypical drug used to treat glaucoma and dry mouth since the 19 th century and classified as either a full or partial muscarinic agonist. Here, we report several unexpected results pertaining to its interaction with its main therapeutic target ‐ muscarinic M3 receptor (M3R). We found that pilocarpine was 1,000 times less potent in stimulating mouse eye pupil constriction than muscarinic agonists oxotremorin‐M (Oxo‐M) or carbachol (CCh), even though all three ligands have similar K d values for M3R. In contrast to CCh or Oxo‐M, pilocarpine does not induce Ca 2+ mobilization via endogenous M3R in HEK293T or mouse insulinoma MIN6 cells. Pilocarpine also fails to stimulate insulin secretion, and instead, antagonizes insulinotropic effect of Oxo‐M and CCh‐induced Ca 2+ upregulation. However, in HEK293T or CHO‐K1 cells overexpressing M3R, pilocarpine induces Ca 2+ transients like those recorded with another Gq‐coupled muscarinic receptor, M1R. Stimulation of cells overexpressing M1R or M3R with CCh resulted in a similar reduction in PIP2. In contrast to CCh, pilocarpine stimulated PIP2 hydrolysis only in cells overexpressing M1R, but not M3R. Moreover, pilocarpine blocked CCh‐stimulated PIP2 hydrolysis in M3R‐overexpressing cells, thus, it acted as an antagonist. Pilocarpine activates ERK1/2 in MIN6 cells. The stimulatory effect on ERK1/2 was blocked by the Src family kinase inhibitor PP2, indicating that the action of pilocarpine on endogenous M3R is biased toward b‐arrestin. Taken together, our findings show that pilocarpine can act as either an agonist or antagonist of M3R, depending on the cell type, expression level and signaling pathway downstream of this receptor. Support or Funding Information This work was supported by the National Institutes of Health Grants RO1DK105427 and RO1DK111538 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .