In the dark-field x-ray image, the strength of the dark-field signal represents the amount of small-angle x-ray scattering. Small-angle x-ray scattering occurs at interfaces between structures of different electron density, e.g., air-tissue interfaces in the lungs or bone-fat interfaces in the spongious bone. This technique has been translated to the use of conventional x-ray sources. Grating-based x-ray dark-field imaging allows detection, quantification, and visualisation of small-angle x-ray scattering, which is not possible with conventional x-ray imaging devices. A grating-based approach has been intensively investigated for its application in biomedical imaging. Similar to visible light, x-rays can not only be interpreted as particles, but also show wave-like properties, such as refraction, that can be utilised for contrast formation. However, even modern computed tomography (CT) imaging exploits only part of the physical interactions between x-rays and matter for contrast formation in x-ray-based images. This might point toward a mechanism where cortical actin controls membrane diffusion in a strong size-dependent manner.The discovery of x radiation marks the birth of diagnostic radiology and its use remains indispensable in daily clinical practice. Our results suggest a stronger interaction of the actin mesh with the larger protein probe compared to the lipid. Complementing Monte Carlo simulations support the analysis of the experimental FCS data. Spot variation FCS was in accordance with a model of fast microscopic diffusion and slower macroscopic diffusion. Moreover, addition of myosin filaments, which contract the actin mesh, allowed switching between fast and slow diffusion in the minimal system. At high actin densities, the effect on the protein probe was ∼3.5-fold stronger compared to the lipid.
A clear correlation of actin density and reduction in mobility was observed for both the lipid and the protein probe. The lateral diffusion of a lipid and a protein probe at varying densities of membrane-bound actin was characterized by fluorescence correlation spectroscopy (FCS). Here, we use a minimal actin cortex to directly study proposed effects of an actin meshwork on the diffusion in a well-defined system. It is assumed that the membrane-associated cytoskeleton modulates lateral diffusion. Diffusion of lipids and proteins within the cell membrane is essential for numerous membrane-dependent processes including signaling and molecular interactions.
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