Alterations in connexin expression in the bladder of patients with urge symptoms

To compare the formation of gap junctions between detrusor smooth muscle cells in situ and the distribution of connexin (Cx)40, Cx43 and Cx45 expressions in bladder biopsies from a control group (with bladder tumour) and from patients with urge symptoms, as smooth muscle cells of the human detrusor muscle communicate via gap junctions and express several connexin subtypes, alterations of which may be involved in the causes of lower urinary tract symptoms.

Connexin expression is prominent in myofibroblast-like cells, supposedly involved in afferent signalling pathways of the bladder. Their strategic position directly beneath the urothelium suggests they are a link between urothelial ATP signalling during bladder filling and afferent Adelta-fibre stimulation for co-ordination of bladder tonus and initialization of the micturition reflex. Modification of their coupling characteristics may have profound impact on bladder sensation. Bladder tissue probes of patients undergoing cystectomy or transurethral tumour resection for bladder cancer were used as controls. Tissue samples from patients with severe idiopathic urge symptoms were taken for exclusion diagnostics of interstitial cystitis (IC) and carcinoma in situ. The formation of functional syncytia between detrusor smooth muscle cells were examined in dye-coupling experiments by injecting with Lucifer Yellow. The morphology and structure of gap junctions were assessed by transmission electron microscopy and immunogold labelling of Cx43 and Cx45. The expression of connexin subtypes Cx40, Cx43 and Cx45 was compared by indirect immunofluorescence, and confocal laser scanning microscopy used for semiquantitative analysis.

There was dye coupling between smooth muscle cells of the detrusor in situ. Electron microscopy and immunogold labelling showed very small gap junctional plaques. These findings were confirmed by confocal immunofluorescence. Semiquantitative analyses showed significantly higher Cx43 expression in the detrusor muscle, and a tendency to higher Cx45 expression in the suburothelial layer associated with urge symptoms, whereas Cx40 expression was unaffected.

Smooth muscle cells of the human detrusor muscle are coupled by classical gap junctions, forming limited local functional syncytia. Both Cx43 and Cx45 are expressed at low levels in normal detrusor. Up-regulation of Cx43 in patients with urge incontinence supports the possibility of functional changes in the syncytial properties of detrusor smooth muscle cells in this condition. In addition, the observed increase of Cx45 in the myofibroblast cell layer supports the idea that alterations in sensory signalling are also involved. Comparison with previous reports implies that the pathophysiology of urgency is distinct from that of the unstable bladder and other forms of incontinence.