Pharmacological discrimination between muscarinic receptor signal transduction cascades with bethanechol chloride
Program in Neuroscience; Department of Physiology
Animals; Animals, Newborn; Bethanechol; Calcium Channels, L-Type; Calcium Channels, N-Type; Calcium Signaling; Egtazic Acid; Muscarinic Agonists; Oxotremorine; Patch-Clamp Techniques; Pertussis Toxin; Rats; Rats, Sprague-Dawley; Receptor, Muscarinic M2; Receptor, Muscarinic M4; Signal Transduction; Superior Cervical Ganglion
Life Sciences | Medicine and Health Sciences
1. 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. 2. Oxo-M-mediated (10 micro 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 nM), or following pertussis toxin (PTX) pretreatment. 3. 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 nM), an irreversible M(1) receptor antagonist, eliminated this inhibition. Oxo-M (100 micro M) decreased L- and N-type channel activities in cell-attached patches, indicating that a diffusible second messenger is involved. 4. BeCh (100 micro M) also inhibited whole cell currents via the membrane-delimited pathway. Blocking M(4) receptors with 100 nM 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 mM failed to inhibit either peak or long-lasting tail currents following PTX pretreatment. 5. These results indicate that BeCh may be an effective tool for selectively activating M(2) receptor stimulation of the membrane-delimited pathway.
DOI of Published Version
Br J Pharmacol. 2003 Apr;138(7):1259-70. Link to article on publisher's site
British journal of pharmacology
Liu, Liwang and Rittenhouse, Ann R., "Pharmacological discrimination between muscarinic receptor signal transduction cascades with bethanechol chloride" (2003). Open Access Articles. 326.