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In a study from Sydney, authors present data on the expression of M2 and M3 receptors in human detrusor and bladder mucosa, comparing patients with idiopathic detrusor overactivity with controls. It was found that M3 muscarinic receptor RNA expression was reduced in mucosa from patients with detrusor overactivity, leading to a proposal that mucosal M3 receptors might have an important role in the aetiology of this condition. OBJECTIVE To examine the expression of muscarinic M2 and M3 receptors in human bladder detrusor and mucosa, from controls and patients with idiopathic detrusor overactivity (IDO), as antimuscarinic agents are the primary pharmacological treatment for IDO. PATIENTS AND METHODS Biopsies from the bladder body were collected at cystoscopy from 20 women with urodynamically confirmed refractory IDO (age range 25–86 years); biopsies were also collected from 30 asymptomatic female controls (age range 32–87 years). Samples were collected into RNA extraction medium and dissected into mucosa (urothelium plus lamina propria) and detrusor. RNA was extracted and the expression of M2 and M3 receptor mRNA determined by quantitative competitive reverse transcription-polymerase chain reaction. Results were normalized to β-actin expression in the same sample. RESULTS Expression of M3 receptor mRNA, in mucosa of IDO patients (median 0.057 pg M3/100 ng total RNA; interquartile range 0.03–0.13, 12 samples), was four times ( P = 0.039, Mann–Whitney) lower than from the control (median 0.22 pg M3/100 ng total RNA; 0.13–0.51, 11 samples). The expression of muscarinic M3 receptor mRNA was higher (14–35 times) in detrusor (control median 3.17; 26 samples) than in mucosa and did not change in IDO (median 2.03; 14 samples). M2 expression was not significantly different with region or with IDO. CONCLUSIONS These data show that M3 muscarinic receptor mRNA expression was significantly less in mucosa from IDO patients than from age-matched controls. The role of mucosal M3 receptors is unknown at present and elucidation of this role might provide a greater understanding of the aetiology of IDO. [ABSTRACT FROM AUTHOR]

We investigated muscarinic receptors in the detrusor and mucosa of the human bladder body. Radioligand-binding studies with[3H]QNB were conducted using specimens collected from patients (36-77 years) with normal bladder function, undergoing surgery. For RT-PCR, biopsies of normal bladder were obtained from patients (30-88 years) undergoing check cystoscopy.Binding of[3H]QNB in detrusor (n=20) was of high affinity (KD 77.1 (55.2-99.0)?pM) and capacity (Bmax 181±7?fmol?mg?protein-1). Similar values were obtained in mucosa (n=6) (KD 100.5 (41.2-159.9)?pM; Bmax 145±9?fmol?mg?protein-1).Competition-binding experiments in detrusor membranes with muscarinic receptor antagonists including trospium, darifenacin, 4-DAMP, methoctramine, AQ-RA 741, AF-DX 116 and pirenzepine indicated a receptor population of 71%M2, 22%M3 and 7%M1. In the mucosa, 75%of sites were M2 receptors, with 25%M3/M5.Using RT-PCR, expression of M1, M2, M3 and M5 mRNA was demonstrated in both detrusor and mucosa.The presence of a high density of mainly M2 muscarinic receptors in the mucosa appears to be a novel finding and raises the question of their physiological significance and the source of their endogenous ligand.There was a negative correlation of receptor number (Bmax) with age in detrusor muscle from male patients (P=0.02). Quantitative competitive RT-PCR demonstrated a selective age-related decrease in mRNA for muscarinic M3 but not M2 receptors, in both male (P<0.0001) and female (P=0.019) detrusor. These findings correspond with reports of decreased detrusor contractility with ageing.British Journal of Pharmacology (2005) 144, 1089-1099. doi:10.1038/sj.bjp.0706147 [ABSTRACT FROM AUTHOR]

Summary 1. The present study compared the binding and functional characteristics of tachykinin NK[sub 2] receptors in human detrusor muscle with those in human colon circular muscle. 2. In radioligand binding studies, similar K[sub D] values were observed for tachykinin NK[sub 2] receptor radioligands [[sup 125] I]-neurokinin (NK) A, [[sup 125] I]-[Lys[sup 5] ,Tyr(I[sub 2] )[sup 7] ,MeLeu[sup 9] ,Nle[sup 10,] ]NKA(4–10) and [[sup 3] H]-SR48968 in both human colon circular muscle (0.28–1.1 nmol/L) and human bladder detrusor (0.49–0.91 nmol/L), suggesting binding was primarily to tachykinin NK[sub 2] receptors. Receptor capacity (B[sub max] ) was greater in colon compared with detrusor muscle. 3. In functional studies of isolated smooth muscle contraction, there was an excellent positive correlation between human bladder detrusor and colon circular muscle with respect to in vitro contractile potency (r = 0.97) and maximum responses (r = 0.98) to tachykinins, selective tachykinin receptor ligands and l-Ala-substituted NKA(4–10) analogues. 4. Species differences between the human and rat tachykinin NK[sub 2] receptors were apparent as observed by a low correlation for potency (r = 0.77) and efficacy (r = 0.32) of l-Ala-substituted analogues in isolated smooth muscle contractile studies. 5. Minor differences observed in the affinity and potency of NK[sub 2] receptor agonists between colon and bladder are dependent on the tissue of interest, the receptor–effector coupling and the presence of other tachykinin receptors. Overall, the NK[sub 2] receptors of human colon and urinary bladder smooth muscle appear pharmacologically identical. [ABSTRACT FROM AUTHOR]

Abstract: The urinary bladder purinergic system is reported to change with age and with bladder dysfunction. Here, we examined the expression of purinergic P2X1 receptors in detrusor and mucosa (urothelium+lamina propria) from male control bladder and investigated age-related P2X1 receptor mRNA expression in control and obstructed detrusor. Biopsy specimens were obtained at cystoscopy from control patients (n =46, age range 30–86years) and patients diagnosed with outlet obstruction (n =29, 46–88years). Calponin expression (measured by RT-PCR) was similar in control and obstructed detrusor and did not change with age. Quantitative competitive RT-PCR was used to measure P2X1 receptor and GAPDH mRNA in control and obstructed detrusor. P2X1 receptor mRNA expression was 9-fold (p <0.0001) higher in the detrusor than in the mucosa. Expression of mRNA for the internal control GAPDH remained stable with age and across control and obstructed detrusor. No difference in P2X1 receptor expression was observed between control and obstructed detrusor (p =0.35). However, an age-related decrease in P2X1 mRNA expression was observed in control (n =27; p =0.0054; Spearman coefficient r =−0.520) but not obstructed detrusor (n =19; p =0.093; r =−0.396). Downregulation of P2X1 mRNA expression might occur as a result of an increased component of neural ATP release in the aging bladder. [Copyright &y& Elsevier]