Figure 3.

(a) Time-course of single-cell volume response to membrane perforation and subsequent osmolality changes. Representative traces are shown, each representing a single-cell experiment. Volume changes are relative to initial volume of the cell in PS before membrane permeabilization. The vertical dotted lines indicate: change of external solution from PS to ILS (1); plasma membrane permeabilization with digitonin (5 μg/ml, 2 min, denoted by the thick horizontal bar) (2); change of external osmolality from isotonic 316 mOsm to (in mOsm): 158 (▾), 516 (■), 616 (○), and 716 (▴) (3); return to isotonic conditions (4). Below are examples of light microscopic side-view images of two different cells taken sequentially at the time points corresponding to vertical lines 1, 3, and 4 as described above. Images were taken via a 20× phase contrast objective (Nikon, LWD, NA 0.4). At 4, the two cells were exposed to hypertonic (716 mOsm) or hypotonic (158 mOsm0 solutions. The scale bar below corresponds to 20 μm. (b) Volume of intact cells (■) and of cytoplasmic gel (●) plotted against reciprocal osmolality. The data points are the average (± SE) from 5 to 50 independent experiments. The two straight lines represent a least-square linear regression fitted to the data points in the entire osmolality range tested for intact cells, whereas for permeabilized cells the data point of lowest osmolality was excluded. Corresponding slopes were: 212 ± 9 mOsm and 782 ± 24 mOsm and intercepts 0.26 ± 0.03 and −0.65 ± 0.07.