[The importance of calcium for secretion in excitable and non-excitable cells]

Secretion via exocytosis is a process common to excitable as well as non-excitable cells. The notion that this process is entirely determined by a rise in [Ca]i is no longer tenable in view of recent reports demonstrating secretion at basal or even reduced levels of [Ca]i. It appears appropriate to distinguish between electrically excitable and electrically non-excitable cells. In the former, a rise in [Ca]i is the triggering event for secretion, whereas in the latter, second messengers seem to induce secretion while [Ca]i acts as a modulator of the rate of secretion. Conversely, second messengers may modulate Ca-induced secretion in excitable cells.