The calcium loading of secretory granules. A possible key event in stimulus-secretion coupling.
The review focuses on calcium accumulation by secretory organelles. The observation that secretory granules contain variable and often important quantities of calcium (1-200 mM of total calcium) can be interpreted as a maturation index. A progressive loading with calcium would be permitted by a Ca2(+)-transport mechanism on the granular membrane and calcium-binding molecules in the granular core. The saturation of this store by the stimulus-induced calcium transient would permit in mature (calcium-loaded) granules the ionic crisis leading to exocytosis. The inside of secretory organelles being acidic, calcium influx into the granule can be driven by calcium-proton exchange. The calcium-proton exchanger could be a Ca2(+)-ATPase.
Nicaise
G
G
Laboratoire de Physiologie Cellulaire et Comparée, Université de Nice-Sophia Antipolis, Nice, France.
Maggio
K
K
Thirion
S
S
Horoyan
M
M
Keicher
E
E
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000378:metabolism*; D006801:Humans
D002118:Calcium