Initiation site of Ca(2+) entry evoked by endoplasmic reticulum Ca(2+) depletion in mouse parotid and pancreatic acinar cells.
OBJECTIVE
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.


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.


CONCLUSIONS
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.
Jo
Hae
H
Yonsei University College of Dentistry, 250 Seongsanno, Seodaemon-gu, Seoul 120-752, Korea.
Byun
Hae Mi
HM
Lee
Syng-Ill
SI
Shin
Dong Min
DM
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008813:Mice, Inbred ICR; D008856:Microscopy, Fluorescence; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010306:Parotid Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology
D015220:Calcium Channels; D019284:Thapsigargin; D002118:Calcium