• muscarinic;
  • quantitative competitive RT-PCR;
  • bladder;
  • urothelium;
  • overactive bladder

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.


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.


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.


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.


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.