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Abstract
Caveolae are abundant flask-shaped invaginations of plasma membranes that buffer membrane tension through their deformation. Few quantitative studies on the deformation of caveolae have been reported. Each caveola contains approximately 150 caveolin-1 proteins. In this study, we estimated the extent of caveolar deformation by measuring the density of caveolin-1 projected onto a two-dimensional (2D) plane. The caveolin-1 in a flattened caveola is assumed to have approximately one-quarter of the density of the caveolin-1 in a flask-shaped caveola. The proportion of one-quarter-density caveolin-1 increased after increasing the tension of the plasma membrane through hypo-osmotic treatment. The one-quarter-density caveolin-1 was soluble in detergent and formed a continuous population with the caveolin-1 in the caveolae of cells under isotonic culture. The distinct, dispersed lower-density caveolin-1 was soluble in detergent and increased after the application of tension, suggesting that the hypo-osmotic tension induced the dispersion of caveolin-1 from the caveolae, possibly through flattened caveolar intermediates.
Highlights
The plasma membrane, composed of amphipathic lipid molecules, exhibits two-dimensional fluidic properties that allow for flexible responses against tension without breakage
We did not detect any increase in the population of caveolin-1 corresponding to flattened caveolae after hypo-osmotic treatment, which are expected to have one-quarter the projection density of typical caveolae under isotonic conditions
We used the coordinates of caveolin-1, obtained with stochastic optical reconstruction microscopy (STORM) and photoactivated localization microscopy (PALM), to determine the two-dimensional projection density of caveolin-1 in both hypo-osmotic treated cells and cells under normal isotonic culture conditions; as such, we quantitatively measured the deformation of caveolae
Summary
The plasma membrane, composed of amphipathic lipid molecules, exhibits two-dimensional fluidic properties that allow for flexible responses against tension without breakage. If we set the radius as r and the length of the cylinder as r, the calculated surface area of the cylinder is 2πr × r + 0.5 × 4πr2 = 4πr[2] If this cylinder with its cap is flattened by tension, the diameter projected onto the plane would increase 4-fold because the area of the original projection is πr[2]. 400% area 25% 2D projection density a 200 nm diameter (Fig. 1), and the appearance of one-quarter-density caveolin-1 is expected after the application of tension if caveolin-1 remains in the caveola. We did not detect any increase in the population of caveolin-1 corresponding to flattened caveolae after hypo-osmotic treatment, which are expected to have one-quarter the projection density of typical caveolae under isotonic conditions. Hypo-osmotic tension induced caveolar deformation and dispersion, and the deformed caveolae contained caveolin-1 that is more soluble in detergent
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