SLOW CELLULAR-DYNAMICS IN MDCK AND R5 CELLS MONITORED BY TIME-LAPSE ATOMIC-FORCE MICROSCOPY

We have examined dynamic events that occur on a time scale of minutes in an epithelial monolayer of MadineDarby Canine Kidney (MDCK) cells a nd in ras-transformed MDCK cells by atomic force microscopy (AFM). Cel ls were imaged under physiological conditions, and time-lapse movies r epresenting similar to 60 s real time per frame were assembled. in nor mal MDCK cells, two types of protrusions in the apical plasma membrane exhibit dynamic behavior. First, smooth bulges formed transiently ove r the time scale of minutes to tens of minutes. Second, spike-like pro trusions appear initially as bulges, extend well above the apical surf ace and, finally, seem to detach. R5, an oncogenic transformant derive d from MDCK cells, grows very flat on g lass. During AFM imaging, thes e cells sometimes round up and detach from the substrate. In light mic roscopic observations of parallel preparations, cells rarely detach, s uggesting that this is an active response of these cells to irritation by the AFM tip. R5 cells often extend processes that are supported by actin stress fibers. During imaging with the AFM, these processes wit hdraw at a rate of 1-5 mu m/min, similar to that observed by light mic roscopy. During the withdrawal, movement of the stress fibers can be c learly seen. In the flat periphery of these cells, the transport of in tracellular particles along cytoskeletal elements was seen. In additio n, we have observed two types of wave-like movements through the cell, which appear to be an organized rearrangement of cytoplasm. One type of wave moves radially out from center of the cell while the other mov es circularly along the cell periphery.