Microvillus form of focal anchorage in human Chang liver cells rounded by antiporter activation: scanning electron microscopy profiles and evidence of traction origin.

Na+/H+ antiporter activation in human Chang liver cells produces a flat-to-round (FTR) change in cell shape with gross reduction in cell profile area. Scanning electron microscopy (SEM) vividly displays a third phenomenon, viz., the development of focal microvillus anchors. Reduction in cell profile area concomitant with the development of this microvillus form of focal anchorage is quantitated by on-line image analysis during SEM examination. The reduction in profile area is corroborated by spectrophotometric digitization in light microscopy. Transmission electron microscopy (TEM) of rounded cells shows large endocytic channels and endosomes consistent with the observation of internalization of fluoresceinated-dextrans (FDx) of a diverse range of sizes, from 4,400 to 2,000,000 molecular weight, with cell rounding. Concomitant endocytosis of this magnitude indicates massive plasma membrane internalizations which could explain the very considerable profile area reduction and suggest that the microvillus anchors are probably traction processes. Antiporter mediated rounding (AMR) provides a highly reproducible and simple model for the production of anchoring microvilli ('filopodia') whereby they can be further explored.