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Pharmacological discrimination between muscarinic receptor signal transduction cascades with bethanechol chloride
Author(s) -
Liu Liwang,
Rittenhouse Ann R
Publication year - 2003
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0705157
Subject(s) - pertussis toxin , muscarinic acetylcholine receptor , pirenzepine , oxotremorine , muscarinic acetylcholine receptor m1 , biophysics , second messenger system , methoctramine , endocrinology , chemistry , agonist , medicine , receptor , muscarinic acetylcholine receptor m2 , signal transduction , chloride channel , g protein , biology , biochemistry
Muscarinic agonist specificity is limited, making it difficult to match receptor subtypes with signal transduction cascades that mediate ion channel modulation. We have characterized the inhibitory effects of two muscarinic agonists, oxotremorine‐M (Oxo‐M) and bethanechol chloride (BeCh), on Ca 2+ currents in neonatal rat superior cervical ganglion neurons. Oxo‐M‐mediated (10 μ M ) inhibition occurred via two signaling pathways. The first pathway inhibited whole cell peak currents, consisting primarily of N‐type current, but not FPL 64176‐induced, long‐lasting tail currents, comprised entirely of L‐type current. Inhibited currents displayed slowed activation kinetics and voltage dependence, characteristics of membrane‐delimited inhibition. Current inhibition was blocked by the selective M 2 receptor antagonist, methoctramine (METH; 100 n M ), or following pertussis toxin (PTX) pretreatment. Activation of the second pathway inhibited both peak and long‐lasting tail currents. This pathway was voltage‐independent, PTX‐insensitive, but sensitive to internal Ca 2+ chelator concentration. Muscarinic toxin 7 (MT‐7, 100 n M ), an irreversible M 1 receptor antagonist, eliminated this inhibition. Oxo‐M (100 μ M ) decreased L‐ and N‐type channel activities in cell‐attached patches, indicating that a diffusible second messenger is involved. BeCh (100 μ M ) also inhibited whole cell currents via the membrane‐delimited pathway. Blocking M 4 receptors with 100 n M pirenzepine (in the presence of MT‐7) had no effect, while antagonizing M 2 receptors with METH abolished inhibition. Concentrations of BeCh as high as 3 m M failed to inhibit either peak or long‐lasting tail currents following PTX pretreatment. These results indicate that BeCh may be an effective tool for selectively activating M 2 receptor stimulation of the membrane‐delimited pathway.British Journal of Pharmacology (2003) 138 , 1259–1270. doi: 10.1038/sj.bjp.0705157