Fig. 5. A study of effects of extracellular pHext on the simulated cell. In all figures, the red filled region is the original outline of the cell. The final position of the cell in all three cases is shown after the same amount of simulation time has elapsed (
1 sec of real time). Bottom, pHext=7.6. This is the case of normal motility. At the front, pH reaches the value of >6.15, so that both the storage of elastic energy, cytoskeletal assembly and adhesion are strong at the leading edge. Middle, pHext=6.75. At this pH motility is impaired. At the front, pH drops to less than 6.15, but both the storage of elastic energy and adhesion are still strong at the leading edge. However, the cytoskeletal assembly is attenuated significantly. The cell body moves forward, but the leading edge is nearly stationary. Top, at pHext=6.35 this motility ceases. At the front the pH decreases to less than 6.1, so that all of the protrusion-supporting processes – adhesion, storage of elastic energy and cytoskeletal assembly – are inhibited. The contraction of the lamellipod takes place transiently owing to the elastic energy stored prior to the change in extracellular pH. This contraction moves the cell body forward slightly, at the same time pulling the leading edge backward significantly. The adhesion of the cell body is now greater than the adhesion of the lamellipod.
