Caveolin and Cholesterol Control of Mechanosensitive Channels in Muscle

Abstract

In Duchene muscular dystrophy the loss of the cytoskeletal element dystrophin modifies the localization of sarcolemma components and the stress distribution to those components. There is a change in the distribution of caveolae and dysregulation of mechanosensitive ion channels (MSCs) both of which may contribute to the elevated Ca2+ levels present in dystrophic myotubes. Caveolae are curved cholesterol rich membrane structures associated with dystrophin that contain many signaling molecules. We have shown that overexpression of Caveolin-3 in mouse myotubes increases the incidence of MSCs in patches and average MSC current. However, it has no effect on their kinetics of activation. Cholesterol depletion by MβCD produces an even larger increase in MSC incidence and average patch current, and also significantly decreases the relaxation rate of the membrane as observed by membrane capacitance changes. We have used miRNA against TRP channels (TRPC1, TRPC4, TRPC6, TRPV2) that have been reported to mechanosensitive in various systems to try and determine the identity of the channel revealed by cholesterol depletion. Average patch current and immunofluorescence staining has been used to determine the level of knockdown of the individual TRP channel subunits.View Large Image | View Hi-Res Image | Download PowerPoint Slide