Osmotic Stress Reduces Ca2+ Signals through Deformation of Caveolae

Caveolae are membrane invaginations that can sequester various signaling proteins. Caveolae have been shown to provide mechanical strength to cells by flattening to accommodate increased volume when cells are subjected to hypo-osmotic stress. We have previously found that caveolin, the main structural component of caveolae, specifically binds G alpha(q) and stabilizes its activation state resulting in an enhanced Ca2+ signal upon activation. Here, we show that osmotic stress caused by decreasing the osmolarity in half reversibly changes the configuration of caveolae without releasing a significant portion of caveolin molecules. This change in configuration due to flattening leads to a loss in Cav1-G alpha(q) association. This loss in G alpha(q)/Cav1 association due to osmotic stress results in a significant reduction of G alpha(q)/phospholipase C alpha(q)-mediated Ca2+ signals. This reduced Ca2+ response is also seen when caveolae are reduced by treatment with siRNA(Cav1) or by dissolving them by methyl-beta-cyclodextran. No change in Ca2+ release with osmotic swelling can be seen when growth factor pathways are activated. Taken together, these results connect the mechanical deformation of caveolae to G alpha(q)-mediated Ca2+ signals.