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Stimulation of exocytosis without a calcium signal
Author(s) -
Hille Bertil,
Billiard Julia,
Babcock Donner F.,
Nguyen Toan,
Koh DukSu
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.00023.x
Subject(s) - exocytosis , secretion , munc 18 , stimulation , biology , degranulation , microbiology and biotechnology , intracellular , cell type , neuroscience , phosphorylation , cell , vesicle , endocrinology , biochemistry , synaptic vesicle , receptor , membrane
More than 30 years ago, Douglas (Douglas & Rubin, 1961; Douglas, 1968) proposed that intracellular Ca 2+ controls stimulus‐secretion coupling in endocrine cells, and Katz & Miledi (1967; Katz, 1969) proposed that intracellular Ca 2+ ions control the rapid release of neurotransmitters from synapses. These related hypotheses have been amply confirmed in subsequent years and for students of excitable cells, they dominate our teaching and research. Calcium controls regulated exocytosis. On the other hand, many studies of epithelial and blood cell biology emphasize Ca 2+ ‐independent regulation of secretion of mucin, exocytotic delivery of transporters and degranulation. The evidence seems good. Are these contrasting conclusions somehow mistaken, or are the dominant factors controlling exocytosis actually different in different cell types? In this essay, we try to reconcile these ideas and consider classes of questions to ask and hypotheses to test in seeking a more integrated understanding of excitation‐secretion coupling. Our review is conceptual and narrowly selective of a few examples rather than referring to a broader range of useful studies in the extensive literature. The examples are taken from mammals and are documented principally by citing other reviews and two of our own studies. The evidence shows that protein phosphorylation by kinases potentiates Ca 2+ ‐dependent exocytosis and often suffices to induce exocytosis by itself. Apparently, protein phosphorylation is the physiological trigger in a significant number of examples of regulated exocytosis. We conclude that although sharing many common properties, secretory processes in different cells are specialized and distinct from each other.