Fig. 5.

Optical signals detected in control and Ca²⁺-free bathing solution. In Ca²⁺-free Ringer’s solution, CaCl₂ was replaced by MgCl₂. The recording was made 15 min after the replacement of Ca²⁺ with Mg²⁺. Similarly, the recovery experiment was made 15 min after replacement of the Ca²⁺-free Ringer’s solution with normal Ringer’s solution. Note that the slow signal was eliminated in the Ca²⁺-free Ringer’s solution.