STIMULUS-SECRETION COUPLING IN EXCITABLE CELLS - A CENTRAL ROLE FOR CALCIUM

Secretion of vesicular contents by exocytosis is a common feature of n euroendocrine secretory cells such as adrenal chromaffin cells and PC 1 2 cells. Although it is clear that in these cells an elevation in in tracellular calcium concentration, [Ca2+]i, is the triggering event th at induces secretion, recent studies using video-imaging, patch-clamp and flash photolysis techniques have all indicated that the Ca2+ signa l that triggers secretion is in fact very complex, with the subcellula r distribution of Ca2+ being of particular importance along with the m agnitude of the rise. It has become evident that Ca2+ signals with dif ferent spatial profiles can be triggered in the same cell by a given s timulus, depending upon the nature of the Ca2+ signalling pathway acti vated, and that this ability to be able to vary the method of delivery of Ca2+ into the cell is important physiologically, because it provid es a means of obtaining differential activation of Ca2+-dependent proc esses.