Association of muscarinic M3 receptors and Kir6.1 with caveolae in human detrusor muscle

Caveolae are 50-100 nm large membrane invaginations that play a role in cellular signaling. The aim of the present study was to assess whether muscarinic M3 receptors and the KATP channel subunit Kir6.1 are associated with human detrusor caveolae, and to pharmacologically assess the relevance of this organization for contractility. Detrusor strips were dissected and used in ultrastructural, biochemical and mechanical studies. Caveolae were manipulated by cholesterol desorption using mβcd (methyl-β-cyclodextrin). Mβcd disrupted caveolae and caused a cholesterol-dependent ~ 3-fold rightward shift of the concentration-response curve for the muscarinic receptor agonist carbachol. The effect of mβcd was inhibited by the KATP blockers glibenclamide, repaglinide and PNU-37883, and it was mimicked by the KATP activator levcromakalim. Immunoelectron microscopy showed muscarinic M3 receptors and Kir6.1 to be enriched in caveolae. In conclusion, pharmacological KATP channel inhibition antagonizes the effect of caveolae disruption on muscarinic contractility in the human detrusor, and the KATP channel subunit Kir6.1 co-localizes with M3 receptors in caveolae.