M₃ muscarinic receptors but not M₂ mediate contraction of the porcine detrusor muscle in vitro

Abstract

1. The objective of the study was to determine the role of muscarinic receptor subtypes in mediating contraction of the porcine detrusor smooth muscle in vitro. 2. Strips of pig detrusor muscle were set up in physiological salt solution and the tensions developed by the tissues were recorded. Responses to carbachol were obtained in the absence and presence of a range of muscarinic antagonists (4-DAMP, methoctramine, darifenacin, oxybutynin, tolterodine and pirenzepine). Antagonist affinity values (pKB values) were calculated and compared with those quoted in the literature for these antagonists at each of the muscarinic receptor subtypes. 3. The M3-selective antagonists, 4-DAMP and darifenacin had high affinities (pKB values of 9.4 and 8.6, respectively). Oxybutynin, tolterodine and pirenzepine had affinities of 8.2, 8.1 and 6.8, respectively, whilst the M2-selective agent methoctramine had a relatively low affinity (pKB = 6.1). The rank order of affinities was, therefore, 4-DAMP > darifenacin > oxybutynin > tolterodine > pirenzepine > methoctramine for the pig detrusor. Correlation of the antagonist affinities obtained on the bladder with those published for these antagonists at the five muscarinic receptor subtypes identified the M3(m3)-receptor as the muscarinic subtype mediating detrusor contractile responses in vitro. 4. These data suggest that a small population of M3-muscarinic receptors must mediate direct contractile responses of the pig detrusor muscle to muscarinic receptor stimulation in vitro.

Urothelial/Lamina Propria Spontaneous Activity and the Role of M3 Muscarinic Receptors in Mediating Rate Responses to Stretch and Carbachol

“…However the responses of isolated detrusor strips to muscarinic agonists are mediated via the minor population of M3 receptors (Sellers et al, 2000, Chess-Williams et al, 2001, Fetscher et al, 2002. A similar result was obtained in the urothelium and lamina propria.…”

Non‐adrenergic, non‐cholinergic, non‐purinergic contractions of the urothelium/lamina propria of the pig bladder

“…These responses were frequency-dependent and predominantly (70 -80%) neurogenic in origin as demonstrated by their sensitivity to the neurotoxin tetrodotoxin. Similar neurogenic responses can be observed in the detrusor smooth muscle where the majority of the contraction is mediated via acetylcholine acting on M3 muscarinic receptors (Sellers et al, 2000;Chess-Williams et al, 2001). However, in the urothelial/lamina propria tissue, responses were insensitive to antagonism by atropine even at concentrations up to 10 µM.…”

“…As a positive control, the actions of atropine at the lower concentration of 1 µM were examined on isolated strips of pig detrusor muscle (stimulated under identical conditions), and in these tissues, atropine reduced contractions to electrical stimulation at 5, 10 and 20 Hz. Both the pig detrusor (Sellers et al, 2000) and the urothelium/lamina propria (Moro et al, 2011) contract strongly to muscarinic agonists and these data therefore suggest that the detrusor, but not the urothelium/lamina propria, has a dominant efferent cholinergic innervation capable of inducing contraction.…”

“…The β-adrenoceptor subtype involved is species dependent but responses are mediated via the β3-adrenoceptor subtype in pig (Yamanishi et al, 2002) and human (Igawa et al, 1999;Yamaguchi, 2002;Badawi et al, 2007) detrusor muscle. During bladder emptying, activity in the parasympathetic nerves results in detrusor contraction which is mediated via M3 muscarinic receptors (Sellers et al, 2000;Chess-Williams et al, 2001).…”

Pharmacologic Targets on the Female Urethra

“…2 ) [24,30,54] . Although the M 2 subtype is predominating in number in the urinary bladder [55,56], M 3 receptors are mainly responsible for contraction [57,58] . Four subtypes of muscarinic receptos (M 1 , M 2 , M 3 and M 4 ) have been demonstrated in the rat bladder [59] and M 1 , M 2 and M 3 receptors were shown to cause contraction in the rabbit urethra [60,61] .…”