Yonsei Med J.  2007 Jun;48(3):526-530. 10.3349/ymj.2007.48.3.526.

Initiation Site of Ca2+ Entry Evoked by Endoplasmic Reticulum Ca2+ Depletion in Mouse Parotid and Pancreatic Acinar Cells

• Jo H
• Byun HM
• Lee SI
• Shin DM

• KMID: 724110
• DOI: http://doi.org/10.3349/ymj.2007.48.3.526

Abstract

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.

Keyword

Parotid; Ca2+ signaling; store-operated calcium channel

MeSH Terms

Animals
Calcium/*metabolism
Calcium Channels/drug effects/metabolism
Cells, Cultured
Endoplasmic Reticulum/drug effects/*metabolism
Mice
Mice, Inbred ICR
Microscopy, Fluorescence
Pancreas/cytology/drug effects/*metabolism
Parotid Gland/cytology/drug effects/*metabolism
Thapsigargin/pharmacology

Figure

• 

  Fig. 1 Measurement of thapsigargin-induced [Ca2+]i increases. A (a) and B (a): parotid and pancreatic acinar mouse cell responses, respectively, after depletion of internal Ca2+ stores with 1µM thapsigargin (Tg) in nominally Ca2+-free media. Cells were stimulated with 1mM carbachol, and then thapsigargin-induced [Ca2+]i increases were measured by exposure to external 7.5mM Ca2+. A (b) and B (b): parotid and pancreatic acinar mouse cell responses, respectively, after the cells were treated with 1mM lanthanum before exposure to external high Ca2+. Each result was the Trepresentative of 5 independent experiments.

• 

  Fig. 2 Measurement of the initiation site of Tg-induced [Ca22+]i increases. (A) and (B) parotid and pancreatic acinar mouse cell responses, respectively. Initiation site of Tg- induced [Ca2+]i increases were imaged with fura2 fluorescence. (C) and (D) The cells were treated with 1mM lanthanum before exposure to external high Ca2+. In each transmission image, red and black circles shows apical and basal pole, respectively. Each result was the representative of 5 independent experiments.

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