Fig. 16.

The combination of Cd²⁺ and FM1–43 increased membrane permeability to both Cd²⁺and FM1–43. Cells were loaded with fura-2. A, Cd²⁺ does not normally enter a terminal. The cell was superfused alternately with an extracellular saline containing 2 mm Mg²⁺ (no added Ca²⁺) and a saline containing 2 mmCd²⁺. There was little change in the ratio of fura-2 fluorescence produced by 331 and 380 nm light, indicating that Cd²⁺ did not enter. B, Cd²⁺ enters a terminal stained with FM1–43. The cell was superfused with an extracellular saline containing 2 mm Mg²⁺ (no added Ca²⁺). FM1–43 (20 μm) was added to the saline. When Mg²⁺ was replaced by Cd²⁺, fura-2 fluorescence indicted an increase in intracellular, divalent ions. After returning to the Mg²⁺-rich saline, the rate of FM1–43 entry increased.