Extreme deformability of insect cell membranes is governed by phospholipid scrambling.

Organization of dynamic cellular structure is crucial for a variety of cellular functions. In this study, we report that Drosophila and Aedes have highly elastic cell membranes with extremely low membrane tension and high resistance to mechanical stress. In contrast to other eukaryotic cells, phospholipids are symmetrically distributed between the bilayer leaflets of the insect plasma membrane, where phospholipid scramblase (XKR) that disrupts the lipid asymmetry is constitutively active. We also demonstrate that XKR-facilitated phospholipid scrambling promotes the deformability of cell membranes by regulating both actin cortex dynamics and mechanical properties of the phospholipid bilayer. Moreover, XKR-mediated construction of elastic cell membranes is essential for hemocyte circulation in the Drosophila cardiovascular system. Deformation of mammalian cells is also enhanced by the expression of Aedes XKR, and thus phospholipid scrambling may contribute to formation of highly deformable cell membranes in a variety of living eukaryotic cells.

Particle Timing Control and Alignment in Microchannel Flow by Applying Periodic Force Control Using Dielectrophoretic Force.

In this study, a technique for particle streamwise timing, spacing and velocity control (alignment) in microchannel flow by controlling the forces exerted on the particle in space and time, was developed. In the present technique, the timing of particles crossing a certain position in microchannel flow with a specific interval and the particle velocity are controlled by applying acceleration and deceleration forces periodically in the streamwise direction and activating them periodically. The force is produced by a dielectrophoretic force using ladder-type electrodes embedded in the microfluidic device and is turned on and off in a cycle. The timing of particles crossing a certain position can be changed by adjusting the phase of the on-off cycle, i.e., the phase of the voltage signal. In the experiment, timing and velocity were measured at the inlet and outlet of ladder-type regions for Jurkat cells and particles of some variation in size, and probability density functions for the deviation of these values from the equilibrium (aligned) state were evaluated. Further, we will discuss the motion characteristics of the particles numerically and experimentally to understand the mechanism and evaluate the performance of the particle timing control and alignment using the present technique. The results confirm that the particles randomly distributed at the inlet of ladder-type electrode regions are controlled to flow with even spacing at a specific velocity. Moreover, the timing of the particles passing a specific location in the ladder-type electrode region was synchronized with the activated/nonactivated cycle of the applied force and could be specified.

Numerical and experimental study on the development of electric sensor as for measurement of red blood cell deformability in microchannels.

A microsensor that can continuously measure the deformability of a single red blood cell (RBC) in its microchannels using microelectrodes is described in this paper. The time series of the electric resistance is measured using an AC current vs. voltage method as the RBC passes between counter-electrode-type micro-membrane sensors attached to the bottom wall of the microchannel. The RBC is deformed by the shear flow created in the microchannel; the degree of deformation depends on the elastic modulus of the RBC. The resistance distribution, which is unique to the shape of the RBC, is analyzed to obtain the deformability of each cell. First, a numerical simulation of the electric field around the electrodes and RBC is carried out to evaluate the influences of the RBC height position, channel height, distance between the electrodes, electrode width, and RBC shape on the sensor sensitivity. Then, a microsensor was designed and fabricated on the basis of the numerical results. Resistance measurement was carried out using samples of normal RBCs and rigidified (Ca(2+)-A23186 treated) RBCs. Visualization measurement of the cells' behavior was carried out using a high-speed camera, and the results were compared with those obtained above to evaluate the performance of the sensor.