Super-resolution visualization of caveolae deformation in response to osmotic stress [Signal Transduction]

Caveolae are protein dense plasma membrane domains structurally composed of caveolin -1 or -3 along with other proteins. Our previous studies have shown that caveolae enhance calcium signals generated through the Gαq/phospholipase Cβ signaling pathway, and that subjecting cells to hypo-osmotic stress reverses this enhancement. In this study, we have used super-resolution fluorescence microscopy supplemented by fluorescence correlation studies to determine the structural factors that underlie this behavior. We find similar and significant populations of Gαq and one of its receptors, bradykinin type 2 receptor (β2R), as well as Gαi and its coupled 2-adrenergic receptor (βAR), localize to caveolae domains. While mild osmotic stress deforms caveolae altering interactions between caveolae and these proteins, it does not affect the general structure and the localization of caveolae components remain largely unchanged. Additionally, in contrast to calcium signals mediated through Gαq-B2R, osmotic stress does not affect cAMP signals mediated through Gαi and βAR. Structurally, we find that mild osmotic stress corresponding roughly to a pressure of 3.82 N/m2 increases the domain diameter by ~30% and increases the fluorescence intensity in the center of the domain mouth suggesting a flattening of the invagination. Approximate calculations show that caveolae in muscle tissue have the strength to handle the stress of muscle movement.

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