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 M-3 receptors and the K-ATP 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 m beta cd (methyl-beta-cyclodextrin). M beta cd disrupted caveolae and caused a cholesterol-dependent similar to 3-fold rightward shift of the concentration-response curve for the muscarinic receptor agonist carbachol. The effect of m beta cd was inhibited by the K-ATP blockers glibenclamide, repaglinide and PNU-37883, and it was mimicked by the K-ATP activator levcromakalim. Immunoelectron microscopy showed muscarinic M-3 receptors and Kir6.1 to be enriched in caveolae. In conclusion, pharmacological K-ATP channel inhibition antagonizes the effect of caveolae disruption on muscarinic contractility in the human detrusor, and the K-ATP channel subunit Kir6.1 co-localizes with M3 receptors in caveolae. (C) 2012 Elsevier B. V. All rights reserved.