Altered Caveolar Mediated Purinergic Signaling in Spontaneously Hypertensive Rats with Detrusor Overactivity

Purpose: Loss of bladder smooth muscle caveolae, which are membrane invaginations involved in signaling regulation, is associated with detrusor dysfunction. We investigated whether caveolar loss in bladder smooth muscle from SHR rats contributes to detrusor overactivity by dysregulating caveolar mediated signaling. Materials and Methods: Caveolar density and caveolin-1 protein expression were compared between SHR and WKY rats by ultrastructural and molecular analysis. The functional effects of caveolar depletion achieved by methyl-beta-cyclodextrin on neurogenic and agonist induced contractions, and spontaneous activity in isolated bladder tissue were also compared between the strains. P2X1 receptor and caveolin-1 interaction was investigated by confocal microscopy, co-immunoprecipitation and proximity ligation assay. Results: Bladder smooth muscle caveolar density and caveolin-1 expression were decreased in SHR vs WKY rats. Responses to alpha-beta-methylene adenosine triphosphate at baseline were lower in SHR than in WKY rats. Methyl-beta-cyclodextrin significantly decreased alpha-beta-methylene adenosine triphosphate responses in WKY rats but had less effect in SHR rats. Methyl-beta-cyclodextrin decreased the amplitude of the purinergic component of neurally mediated contractions in each strain but had no effect on the cholinergic component. Bladder spontaneous activity was significantly higher in SHR than in WKY rats. Exposure to methyl-beta-cyclodextrin or P2X1 receptor antagonist significantly increased spontaneous activity in WKY rats but had no effect in SHR rats. P2X1 receptor and caveolin-1 were co-localized and co-precipitated in bladder smooth muscle tissue. Conclusions: Caveolar depletion in WKY bladders results in a functional phenotype analogous to that of overactive SHR bladder. The intrinsically decreased caveolae in SHR rats causes loss of the caveolar mediated regulation of purinergic signaling and augmented spontaneous activity, conditions that may lead to detrusor overactivity.