Figure 1. Optical recording of spontaneous massive endocytosis in an isolated cardiac muscle cell.

To follow the changes that take place in the cell membrane during massive endocytosis, a Na/Ca exchanger (NCX1) is fused with a pH-sensitive green protein (green circle; Lariccia et al., 2011) and overexpressed in cardiac muscle cells (unpublished data courtesy of Donald Hilgemann). The fluorescence is bright when the green protein is on the external membrane of the cell, where the pH is 7.8 (top left, 1), but it gradually declines during endocytosis as the NCX1 is progressively internalized into vesicles, where the pH is 6.5 (middle, 2). The fluorescence can be increased again by using ammonium chloride (NH₄Cl) to increase the pH inside the vesicles (right, 3). This shows that massive endocytosis can be activated during routine cell isolation procedures.

D HILGEMANN, UTSW