1.Initiation Site of Ca2+ Entry Evoked by Endoplasmic Reticulum Ca2+ Depletion in Mouse Parotid and Pancreatic Acinar Cells.
Hae JO ; Hae Mi BYUN ; Syng Ill LEE ; Dong Min SHIN
Yonsei Medical Journal 2007;48(3):526-530
PURPOSE: In non-excitable cells, which include parotid and pancreatic acinar cells, Ca(2+) entry is triggered via a mechanism known as capacitative Ca(2+) entry, or store-operated Ca(2+) entry. This process is initiated by the perception of the filling state of endoplasmic reticulum (ER) and the depletion of internal Ca(2+) stores, which acts as an important factor triggering Ca(2+) entry. However, both the mechanism of store-mediated Ca(2+) entry and the molecular identity of store-operated Ca(2+) channel (SOCC) remain uncertain. MATERIALS AND METHODS: In the present study we investigated the Ca(2+) entry initiation site evoked by depletion of ER to identify the localization of SOCC in mouse parotid and pancreatic acinar cells with microfluorometeric imaging system. RESULTS: Treatment with thapsigargin (Tg), an inhibitor of sarco/endoplasmic reticulum Ca(2+)-ATPase, in an extracellular Ca(2+) free state, and subsequent exposure to a high external calcium state evoked Ca(2+) entry, while treatment with lanthanum, a non-specific blocker of plasma Ca(2+) channel, completely blocked Tg-induced Ca(2+) entry. Microfluorometric imaging showed that Tg-induced Ca(2+) entry started at a basal membrane, not a apical membrane. CONCLUSION: These results suggest that Ca2+ entry by depletion of the ER initiates at the basal pole in polarized exocrine cells and may help to characterize the nature of SOCC.
Animals
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Calcium/*metabolism
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Calcium Channels/drug effects/metabolism
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Cells, Cultured
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Endoplasmic Reticulum/drug effects/*metabolism
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Mice
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Mice, Inbred ICR
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Microscopy, Fluorescence
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Pancreas/cytology/drug effects/*metabolism
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Parotid Gland/cytology/drug effects/*metabolism
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Thapsigargin/pharmacology
2.Expression of Ca2+-dependent Synaptotagmin Isoforms in Mouse and Rat Parotid Acinar Cells.
Hae JO ; Hae Mi BYUN ; Jong Hoon KIM ; Min Seuk KIM ; Seung Hyeoi KIM ; Jeong Hee HONG ; Jeong Taeg SEO ; Syng Ill LEE ; Dong Min SHIN ; Heung Kyu SON
Yonsei Medical Journal 2006;47(1):70-77
Synaptotagmin is a Ca2+ sensing protein, which triggers a fusion of synaptic vesicles in neuronal transmission. Little is known regarding the expression of Ca2+ - dependent synaptotagmin isoforms and their contribution to the release of secretory vesicles in mouse and rat parotid acinar cells. We investigated a type of Ca2+ - dependent synaptotagmin and Ca2+ signaling in both rat and mouse parotid acinar cells using RT-PCR, microfluorometry, and amylase assay. Mouse parotid acinar cells exhibited much more sensitive amylase release in response to muscarinic stimulation than did rat parotid acinar cells. However, transient [Ca2+]i increases and Ca2+ influx in response to muscarinic stimulation in both cells were identical, suggesting that the expression or activity of the Ca2+ sensing proteins is different. Seven Ca2+ - dependent synaptotagmins, from 1 to 7, were expressed in the mouse parotid acinar cells. However, in the rat parotid acinar cells, only synaptotagmins 1, 3, 4 and 7 were expressed. These results indicate that the expression of Ca2+ - dependent synaptotagmins may contribute to the release of secretory vesicles in parotid acinar cells.
Synaptotagmins/*metabolism
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Signal Transduction
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Rats
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Protein Isoforms/metabolism
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Parotid Gland/cytology/*metabolism
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Muscarinic Agonists/pharmacology
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Mice
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Exocytosis/drug effects/physiology
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Carbachol/pharmacology
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Calcium/metabolism/*physiology
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Animals
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Amylases/secretion