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The role of phosphatidylinositides in stimulus-secretion coupling in the exocrine pancreas

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Schulz,  Irene
Department of Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Schnefel,  Susanne
Department of Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Thévenod,  Frank
Department of Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Kemmer,  Thomas P.
Department of Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Eckhardt,  Luise
Department of Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Schulz, I., Schnefel, S., Banfić, H., Thévenod, F., Kemmer, T. P., & Eckhardt, L. (1987). The role of phosphatidylinositides in stimulus-secretion coupling in the exocrine pancreas. In Society of General Physiologists Series (pp. 117-131).


Cite as: http://hdl.handle.net/21.11116/0000-0008-0ED6-8
Abstract
Cell activation of different cell types is accompanied by receptor-mediated stimulation of phospholipase C and a consequent breakdown of phosphatidylinositol 4,5-bisphosphate. Evidence suggests that GTP-binding proteins are involved in this signal transduction mechanism, which couples receptors to phospholipase C. Both the hydrolysis products diacylglycerol (DG) and inositol 1,4,5-trisphosphate (IP3) are intracellular messengers for cellular responses such as secretion, as illustrated by the pancreatic acinar cell. IP3 releases Ca2+ from a nonmitochondrial Ca2+ pool likely to be the endoplasmic reticulum (ER). This Ca2+ release leads to a transient rise in the cytosolic free Ca2+ concentration from approximately 100 to approximately 800 nmol/liter, by which enzyme secretion is initiated. For sustained secretion, Ca2+ influx into the cell is necessary to keep the cytosolic free Ca2+ concentration at a slightly elevated level. Activation of protein kinase C by DG and Ca2+ seems to play a major role in the second, sustained phase of secretion. Ca2+ reuptake into the ER and Ca2+ extrusion from the cell are achieved by (Ca2+ + Mg2+)-ATPase in both the ER and the plasma membrane as well as by an Na+/Ca2+ exchange in the latter. In the final step of exocytosis, protein phosphorylation by Ca2+-, DG-, and cAMP-dependent protein kinases is probably involved.