Background Unstable bladder is one of the common clinical dysfunctions of the lower urinary tract.Gap junctions (GJs)are the plaques of aqueous channels that facilitate electrical and metabolic communication between the intracellular compartments of adjacent cells,exchange of nutrients and ions between connected cells and transfer of electrical signals.In the present study we investigated the quantitative alterations of the GJ in the rat detrusor muscle and its functional changes related to the developing of unstable bladder (USB).Methods Thirteen female Wistar rats (study group) with obstructive unstable bladder as determined by urodynamic study and 10 sham-operated rats (control group) were sacrificed at 6 weeks after surgery.Cystometric investigation,and the content and distribution of the GJ protein connexin 43 (Cx43) in the detrusors which were taken from the bladder of the rats were studied by Western blot and laser confocal microscopy with a double label immunohistochemistry technique.Results The expression of Cx43 was found adjacent to the detrusor with the laser confocal microscopy.The Cx43 expression increased markedly in the study group (pixel density 29.5+13.9,staining size (17.9±8.8) μm2) compared with the control group (pixel density 14.2,.2.2,staining size (5.7±3.1) μm2,P＜0.05).Westem blot analysis demonstrated that Cx43 in the study group (the average gray level was 31.066) was significantly higher than in the control group (the average gray level was 11.701,P＜0.01).Conclusion The increase of GJ leading to a intercellular excitatory communication is one of the important mechanisms related to developing unstable bladder.