Swift transformation and locomotion of polymorphonuclear leukocytes and microglia as observed by VEC-DIC microscopy (video microscopy)

The detailed assembly used by us for video-enhanced contrast-differential interference contrast (VEC-DIC) microscopy (video microscopy) is first described. Employing such video microscopy, we then examined the morphological changes occurring during locomotion and activation processes of polymorphonuclear leukocytes (PMNL) and microglia at an almost electron microscopic magnification. Upon contacting the substratum, PMNL transformed into a polarized ameboid shape and crawled extending pseudopodia, as has been well documented previously. The PMNL sometimes displayed a peculiar locomotion as if they were stepping on "tiny legs", or sliding on a treadmill of cell membrane. Cultured microglia were observed to exist in 4 forms; ramified, reactive, villous, and ameboid. Microglia in the reactive form pivoted, circled and crawled on the astroglial cell layer using their transparent lamellipodia with no morphological changes in their cell body. Unlike PMNL, reactive microglia exhibited no agitated movements of their intracellular organelles, including granules and cytosol, during locomotion. Lamellipodia on the undersurface of the cell body touching the cell layer adhesively, appeared to serve as the locomotive apparatus. When activated, both floating PMNL and microglia of villous form assumed an ameboid shape within a few seconds. Microglia occasionally swam in the medium waving their lamellipodia towards a target object (e.g. zymosan A particles), remodelling to an amorphous ameboid form and covering up the target. We attempt to discuss such swift morphological changes from the standpoint of thermodynamic potential of Gibbs free energy which is stored within the cells.