Mechanisms underlying potentiation of murine airway smooth muscle contraction by activation of postjunctional M2 muscarinic receptors

Ghosh, Srijit (2026) Mechanisms underlying potentiation of murine airway smooth muscle contraction by activation of postjunctional M2 muscarinic receptors. Doctoral thesis, Dundalk Institute of Technology.

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Abstract

Postjunctional M2 muscarinic receptors (M2Rs) on airway smooth muscle (ASM) outnumber M3 receptors (M3Rs) by approximately 4:1 in most species, yet M3Rs are classically considered the primary mediators of acetylcholine (ACh)-induced bronchoconstriction. Recent research, however, suggests that M2R stimulation can markedly potentiate ASM contractility. The present study investigated the cellular and ionic mechanisms underlying M2R-dependent potentiation of nerve-evoked contractions of murine ASM using pharmacological and electrophysiological approaches. In contrast to the role of M3Rs, which drive IP3-dependent Ca2+ release from sarcoplasmic reticulum (SR), we demonstrated that M2R-mediated contractions were abolished by the L-type Ca2+ channels (LTCC) blocker nifedipine indicating that M2R activation enhanced cholinergic contractions predominantly through Ca2+ influx via LTCCs. Further analysis revealed that M2R-LTCC pathway was facilitated by inhibition of Kv7 channels and SR Ca2+-ATPase (SERCA) activity, along with activation of Ano1 Ca2+-activated Cl⁻ channels. Potassium channel subtypes Kv7.4 and Kv7.5 were prominently expressed in ASM and M2R activation suppressed Kv7.4 and Kv7.5 currents via depletion of PIP2 and downregulation of cAMP/PKA, respectively. Inhibition of SERCA pumps with thapsigargin mimicked and potentiated M2R-mediated responses. These effects were also abolished by nifedipine, indicating that M2R activation likely inhibited SERCA activity, reducing subplasmalemmal Ca2+ buffering of Ca2+ entry via LTCC. Inhibition of Ano1 with Ani9 suppressed M2R responses, indicating an important role for these channels in M2R-dependent contractions. Collectively, these findings provide first comprehensive evidence that M2R activation enhances ASM excitability through a coordinated mechanism involving the inhibition of Kv7 channels and SERCA pumps, as well as the activation of LTCCs and Ano1. This integrated pathway sustains depolarisation and Ca2+ influx, contributing to airway hyperresponsiveness. The study identifies Kv7.4/7.5 and SERCA2 as potential therapeutic targets and establishes a mechanistic framework linking M2R signalling to cholinergic airway contraction, offering new avenues for intervention in asthma and chronic obstructive pulmonary disease (COPD).

Item Type:	Thesis (Doctoral)
Additional Information:	Smooth Muscle Research Centre, DkIT.
Subjects:	Science
Research Centres:	UNSPECIFIED
Depositing User:	Sean McGreal
Date Deposited:	16 Apr 2026 11:34
Last Modified:	16 Apr 2026 11:40
License:	Creative Commons: Attribution-Noncommercial-Share Alike 4.0
URI:	https://eprints.dkit.ie/id/eprint/1047

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