Figure 1.

[Ca²⁺]_i response to hyperstimulation with CCK, showing the typical large initial rise followed by a prolonged plateau phase. Removal of external Ca²⁺ during the plateau phase results in a drop in [Ca²⁺]_i back to baseline levels indicating that plasma membrane Ca²⁺ channels remain open throughout the stimulation period. The measurements used to quantify changes in [Ca²⁺]_i as described in the text are indicated.