M₂ mediated contractions of human bladder from organ donors is associated with an increase in urothelial muscarinic receptors

Abstract

Aims: Previous studies have shown increased density of M 2 receptors in hypertrophied rat bladders that possess an M 2 contractile phenotype. The aim of the current study is to determine whether human bladders with an M 2 contractile phenotype also have a greater density of bladder M 2 receptors. Materials and Methods: Human bladders were obtained from 24 di¡erent organ transplant donors. Darifenacin and methoctramine a⁄nity was determined by the rightward shift of cumulative carbachol concentration contractile response curves for each bladder. Radioligand binding and immunoprecipitation was used to quantify M 2 and M 3 subtypes in isolated detrusor muscle and urothelium. In addition, pig bladder muscle and urothelial receptors were quanti¢ed for comparison. Results: In the human urothelium total, M 2 and M 3 muscarinic receptor density is signi¢cantly negatively correlated with the a⁄nity of darifenacin for inhibition of contraction of the detrusor muscle. In the detrusor muscle there is no correlation between receptor density and darifenacin a⁄nity for inhibition of contraction. Muscarinic receptor density is greater in the muscle than in the urothelium in human bladders whereas in the pig bladder the density is greater in the urothelium than in the muscle. Conclusions: The greater density of urothelial muscarinic receptors in human bladders with lower darifenacin a⁄nity, indicative of a greater contribution of M 2 receptors to the contractile response, points towards a possible role of the urothelium in controlling M 2 mediated contractile phenotype. In comparison between human and pig bladders, the distribution of muscarinic receptor subtypes in the muscle and urothelium are quite di¡erent.

M2 muscarinic receptors inhibit cell proliferation and migration in urothelial bladder cancer cells

“…[4][5][6][7] Among them, the muscarinic acetylcholine receptors (mAChRs), expressed both in detrusor muscle and in urothelial cells, are strongly involved in the biology of the normal human bladder. 8,9 Specifically, the M2 and M3 receptors have been identified as the most abundant receptor subtypes, with M2 receptors mainly expressed in umbrella cells and in the bladder mucosa, 10 and in a higher proportion (3:1) respect to M3 in the detrusor muscle. 8,11 The main function of these receptors is the control of both contraction of detrusor cells and the release of substances such as ATP and NO on urothelium, thus affecting detrusor functions.…”

“…8,9 Specifically, the M2 and M3 receptors have been identified as the most abundant receptor subtypes, with M2 receptors mainly expressed in umbrella cells and in the bladder mucosa, 10 and in a higher proportion (3:1) respect to M3 in the detrusor muscle. 8,11 The main function of these receptors is the control of both contraction of detrusor cells and the release of substances such as ATP and NO on urothelium, thus affecting detrusor functions. 8,12,13 The expression of muscarinic receptors in bladder is decreased in urothelial and suburothelial cells of patients affected by overactive human bladder.…”

“…8,11 The main function of these receptors is the control of both contraction of detrusor cells and the release of substances such as ATP and NO on urothelium, thus affecting detrusor functions. 8,12,13 The expression of muscarinic receptors in bladder is decreased in urothelial and suburothelial cells of patients affected by overactive human bladder. 14,15 Functional alterations of mAChRs have also been detected in diabetic patients and with aging 16,17 Although the activity of mAChRs has been investigated in normal bladder and in some pathological conditions, the role of these receptors in bladder cancer has been poorly investigated.…”

The Use of Occupation Isoboles for Analysis of a Response Mediated by Two Receptors: M2and M3Muscarinic Receptor Subtype-Induced Mouse Stomach Contractions

“…The M 1 , M 3 , and M 5 subtypes predominantly couple to G q , whereas the M 2 and M 4 subtypes predominantly couple to G i (Caulfield, 1993;Caulfield and Birdsall, 1998). It has been proposed that the M 2 receptor aids in contraction by inhibiting the increased cAMP generated in response to ␤-adrenergic receptor-stimulated smooth muscle relaxation (Ehlert and Thomas, 1995;Ehlert et al, 2007).In the urinary bladder, although cholinergic contractions are predominantly M 3 receptor mediated, the M 2 subtype contributes to contraction in rats (Braverman and Ruggieri, 2003;Gevaert et al, 2006) and humans (Pontari et al, 2004;Braverman et al, 2007). In addition, the M 2 receptor mediates esophageal muscle contraction and contributes to lower esophageal sphincter contraction after induction of esophagitis (Biancani et al, 1992).…”

“…In the urinary bladder, although cholinergic contractions are predominantly M 3 receptor mediated, the M 2 subtype contributes to contraction in rats (Braverman and Ruggieri, 2003;Gevaert et al, 2006) and humans (Pontari et al, 2004;Braverman et al, 2007). In addition, the M 2 receptor mediates esophageal muscle contraction and contributes to lower esophageal sphincter contraction after induction of esophagitis (Biancani et al, 1992).…”