Figure 3.

Two types of Ca-activated MEND responses in BHK cells, resulting in membrane recycling by different mechanisms. (A) Using standard cytoplasmic solution with 8 mM ATP and 0.2 mM GTP, the activation of Ca influx by NCX1 for 20 s causes an immediate exocytic response followed by a delayed MEND response that amounts to >50% of the cell surface over 2 min. Cycles of large exocytic responses followed by MEND can then be repeated multiple times in the same cell. (B) Using the same cytoplasmic solution as in A, with an additional 1 mM spermidine, large endocytic responses are initiated during Ca transients, rather than after Ca transients, as in A. Over the course of multiple Ca influx episodes, recovery from MEND becomes more pronounced, and MEND responses amounting to >50% of the cell surface can be repeated multiple times with recovery taking place over several minutes.