Rough ER degranulation and swelling resolved as lysosomes in Na+/H+ antiporter mediated rounding of human lung fibroblasts.

Na+/H+ antiporter activation by incubation in bicarbonate buffered saline induces long flat anchored human lung fibroblasts in monolayer culture to retract their cytoplasmic processes and become eventually globular in form. Reduction of cell profile area and perimeter in antiporter mediated rounding (AMR) is quantitated by microspectrophotometry and the roundness form factor (PE) calculated from these parameters. Quantitatively, 2 stages of rounding are discernible. Stage I rounding is a simple retraction phenomenon where PE upshifts marginally. Stage II rounding sees the cell transformed into globular refractile form where PE greater than 0.5. Ultrastructural studies show appreciable swelling of rough ER in Stage I rounding. Stage II rounding is accompanied by enhanced swelling of rough ER and degranulation. A dynamic relationship between rough ER (RER) and smooth ER (SER) in different functional states of a cell is novel. Enlarged SER channels appear resolved in later stages as lysosomal bodies suggesting that degranulated ER membranes are lysosomal targets in autophagocytosis.