Fig. 6.

Continuous endocytosis is stimulated by a low Ca²⁺ concentration. A bipolar cell was continuously superfused with salines containing 10 μm ionomycin. Thetiming bars indicate 12 sec applications of 20 μm FM1–43. The cell was superfused first with a saline containing 100 nm Ca²⁺ and then with 30 μm Ca²⁺ as indicated. sis the fluorescence intensity of the surface membrane;v_n is the fluorescence that remains trapped in the cytoplasm and is attributed to endocytosis. The rate of continuous endocytosis C_n was measured asC_n = ρv_n/s Δt. For the two measurements, C_n was 0.33 and 0.22 MEq min⁻¹.