A simple model summarising the effect of cholesterol depletion and/or swelling on caveolae configuration, Cav 3 distribution, membrane tension and consequences for <i>I</i>_Cl,swell activation.

<p>A. Under control conditions, caveolae exist in open and closed configurations, Cav 3 is found predominantly in buoyant caveolae-containing membrane fractions (BF; fractions 5,6 of the sucrose gradient, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0008312#pone-0008312-g004" target="_blank">Fig. 4</a>), and the <i>I</i>_Cl,swell channel is inactive. B. MBCD reduces the number of open and closed caveolae in association with translocation of Cav 3 from the BF to non-buoyant fractions (nBF; fractions 7–12), which contain heavy membranes and cytosolic proteins. The <i>I</i>_Cl,swell channel remains inactive. C. By contrast, swelling reduces the number of caveolae in the closed configuration only. We propose that this is through flattening of open caveolae in tandem with sarcolemmal incorporation of closed caveolae. No Cav 3 translocation from BF to nBF is seen during swelling. Membrane tension increases with swelling and this activates <i>I</i>_Cl,swell which abbreviates the action potential. D. In MBCD-treated cells, lack of available membrane reserves (open and closed caveolae) means that swelling increases membrane tension more than in control cells, causing enhanced <i>I</i>_Cl,swell activation, action potential shortening and negative inotropy. Cav 3-containing cholesterol-enriched membranes are shown in red: open caveolae (sarcolemmal red crescents); closed caveloae (intracellular red circles); flattened caveolae (sarcolemmal red lines). A representation of relative Cav 3 band density in BF and nBF, an index of membrane tension, and a representative action potential under each condition is shown to the right.