Antiport-mediated cell retraction: viable rounding and distinctive endocytosis.

Cells that are detached through Na+/H+ antiport-mediated cell retraction (the flat-to-round or FTR change) are as viable as trypsinized cells despite unusually high trypan blue dye inclusion. Even high molecular weight dextran and carbon particles are easily loaded following the FTR change. ECM of confluent cultures of human keloid fibroblasts and Chang liver epitheloid cells stained directly by fluorescein-conjugated monoclonal anti-fibronectin is dramatically reduced or removed upon cell rounding. At the ultrastructural level, distinctive channels and vacuoles filled with extracellular material are seen, resolved at later stages as peripheral granular patches which too disappear when the rounded cells are reflattened in round-to-flat (RTF) change. Antiport-mediated endocytosis (AME) could explain the drastic reduction in cell area concomitant with cell rounding and detachment. AME provides a new way of loading cells with impermeant macromolecules.