Non-uniform distribution of myosin-mediated forces governs red blood cell membrane curvature through tension modulation
Fig 4
Local force density at the RBC dimple.
A local distribution of the pulling force density at the RBC dimple results in a better agreement between the parametric shape of an RBC (Eq 6) and the shape obtained from the simulation. (A) RZ view of the center of an RBC from a confocal Z-stack of an RBC stained for the membrane marker glycophorin A. (B, upper) A schematic depicting a biconcave RBC with a local force at the dimple area (red arrows) and no force in the rim region. Fdimple represents the magnitude of the pulling force density in the dimple region. (B, lower) The applied force density at the dimple as a function of the arclength (Eq. S24 in S1 Text). (C) The simulated shape of the RBC with a local pulling force density in the dimple (solid green line) in comparison with the RBC parametric shape (dotted blue line). (C) The nonmonotonic behavior of the total error when increasing the dimple force density (Fdimple). Three different regimes can be identified based on the shape of the simulated RBC; (i) the spherical shapes where hmax = hmin for the low Fdimple (yellow area), (ii) the biconcave shapes where the dimple forms (hmax > hmin) for the mid-range of Fdimple (purple area), and (iii) the kissing shapes where hmin → 0 for large Fdimple (gray area). The shape error has the lowest value at Fdimple = 3.73 pN/μm2 (ϵtotal ~ 5.62%) when the minimum height of the dimple in the simulated geometry matches closely with the minimum height of the parametric shape. The volume of the simulated RBC at Fdimple = 3.73 pN/μm2 is about 76.78 μm3.