Fig. 13.

Endocytosis was delayed until after Ca²⁺ influx stopped. The timing of endocytosis was measured with 18 sec applications of 20 μm FM1–43 combined with 6 sec pulses of high Ca²⁺ and K⁺ saline. The first applications of FM1–43 and high Ca²⁺ and K⁺ saline ended together and were immediately followed by a pulse of 20 μm FM4–64 in a saline containing 100 nmCa²⁺. The FM4–64 quenched the fluorescence of FM1–43 in the surface membrane (see Fig. 3) but not in vesicles trapped in the cytoplasm. T_n measured (as shown in Fig. 10) with FM1–43 was 0.004 MEq and indicated that little endocytosis occurred during superfusion with the high Ca²⁺ and K⁺ saline.T_n measured with FM4–64 was 0.05 MEq and indicated that significant endocytosis occurred after return to the control saline. The second application of FM1–43 measured the total amount of endocytosis; T_n = 0.07 MEq.