Induced interphase cell retraction: its reversal and EGF potentiation.

Human epidermoid A431 carcinoma cells retract into globular shapes upon activation with epidermal growth factor (EGF) but not normal cells. We find that normal anchor-dependent cultured cells will retract from attachment on incubation in saline with pH upshifting. There is significant potentiation of that phenomenon by EGF prepulsing as seen in (a) dose- and time-response experiments quantitated by measuring profile area and perimeter of cells (b) 22Na+-uptake studies and (c) pHi measurements. EGF action by itself produces quantitatively significant retractions, although only to a very small degree. Blocking Na+/H+ exchanges using (a) trifluoperazine (150 microM), (b) amiloride (2 mM) and (c) Na+-omission could block the cell retractions. Retracted cells can be reversed in low [Na+]o during which rapid 22Na+-efflux is observed. A dose-response ouabain (1 mM) sensitive relationship exists between [Na+]o and retardation of the reversal phenomenon. Ouabain however does not prevent reversal in low [Na+]o, nor even in combination with high [Na+]o given the presence of Ca2+. Retraction into spherical shapes would maximize volume-holding for a given surface area, however they are quantitatively more bulgy than cells rounded by trypsinization.