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Review
. 1999 Oct 1;520 Pt 1(Pt 1):23-31.
doi: 10.1111/j.1469-7793.1999.00023.x.

Stimulation of exocytosis without a calcium signal

B Hille  1 , J Billiard, D F Babcock, T Nguyen, D S Koh
Affiliations
Review

Stimulation of exocytosis without a calcium signal

B Hille et al. J Physiol. .

Abstract

More than 30 years ago, Douglas (Douglas & Rubin, 1961; Douglas, 1968) proposed that intracellular Ca2+ controls stimulus-secretion coupling in endocrine cells, and Katz & Miledi (1967; Katz, 1969) proposed that intracellular Ca2+ 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 Ca2+-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 Ca2+-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.

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Figures

Figure 1
Figure 1. Kinetic pools of vesicles in the regulated secretory pathway of an excitable cell
Steps of vesicle traffic towards exocytosis are defined by kinetic analysis of responses to Ca2+ steps and evoked Ca2+ rises in endocrine cells and synapses. Exocytosis (step k1) is triggered by binding of n Ca2+ ions. The small readily releasable pool (RRP) of vesicles is formed by priming (step k2) of docked vesicles. Docked vesicles are formed (step k3) by mobilization and transport from deeper intracellular pools.
Figure 2
Figure 2. Forskolin-stimulated exocytosis in an epithelial cell
Subconfluent dog pancreatic duct epithelial cells were loaded with 1 μm indo-1 AM for 30 min, then 70 mm dopamine-containing saline solution for 40 min at room temperature. A carbon fibre electrode polarized to +600 mV lightly touched a cell to detect oxidation of quantally released exogenous dopamine upon exocytosis. A, amperometric currents during application of 5 μm thapsigargin (open bar) and 20 μm forskolin (filled bar). Currents > 24 pA have been truncated. B, rate of exocytosis plotted as number of events per minute. C, [Ca2+]i measured with indo-1 ratio photometry. Data are from a single cell.
Figure 3
Figure 3. Releasing hormone and kinase-stimulated exocytosis in pituitary cells
Cells were cultured following enzymatic dispersal from the anterior pituitary of a castrated male rat. The number of cells secreting luteinizing hormone (LH) in 1 h was counted using a reverse haemolytic plaque assay with antibodies against LH and normalized to the mean number of cells secreting in response to the natural releasing hormone GnRH. Note that this assay does not report the amount of LH secreted, rather the number of cells secreting above a certain threshold amount. A, similar stimulation of LH secretion by 50 nM GnRH, 100 nM phorbol myristate acetate (PMA), and both together (both); and no stimulation by 1 μm 4α-phorbol-12,13-didecanoate (4α-Ph). B, greater sensitivity of PMA-induced secretion vs. GnRH-induced secretion to block by the PKC inhibitor bisindolylmaleimide I (BIS, 100 and 500 nM). C, greater sensitivity of GnRH-induced secretion vs. PMA-induced secretion to block by 100 μm extracellular Cd2+ or intracellular BAPTA (loading in 10 μm BAPTA-AM solution for 15 min). (After Billiard et al. 1997.)
Figure 4
Figure 4. Possible sites of action of protein kinases on the secretory pathway
Kinases may act indirectly by augmenting the Ca2+ signal in the cytoplasm (A), directly on the conventional Ca2+-sensitive pathway (B-D) or directly on populations of vesicles that are not Ca2+ sensitive (E).
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References

    1. Almers W, Neher E. Gradual and stepwise changes in the membrane capacitance of rat peritoneal mast cells. The Journal of Physiology. 1987;386:205–217. - PMC - PubMed
    1. Ammala C, Eliasson L, Bokvist K, Berggren PO, Honkanen RE, Sjøholm A, Rorsman P. Activation of protein kinases and inhibition of protein phosphatases play a central role in the regulation of exocytosis in mouse pancreatic beta cells. Proceedings of the National Academy of Sciences of the USA. 1994;91:4343–4347. - PMC - PubMed
    1. Avery J, Jahn R, Edwardson JM. Reconstitution of regulated exocytosis in cell-free systems: a critical appraisal. Annual Review of Physiology. 1999;61:777–807. - PubMed
    1. Billiard J, Koh D-S, Babcock DF, Hille B. Protein kinase C as a signal for exocytosis. Proceedings of the National Academy of Sciences of the USA. 1997;94:12192–12197. - PMC - PubMed
    1. Brown D, Katsura T, Gustafson CE. Cellular mechanisms of aquaporin trafficking. American Journal of Physiology. 1998;275:F328–331. - PubMed

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