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The endoplasmic reticulum as one continuous Ca 2+ pool: visualization of rapid Ca 2+ movements and equilibration
Author(s) -
Park Myoung Kyu,
Petersen Ole H.,
Tepikin Alexei V.
Publication year - 2000
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/19.21.5729
Subject(s) - endoplasmic reticulum , library science , biology , computer science , microbiology and biotechnology
We investigated whether the endoplasmic reticulum (ER) is a functionally connected Ca 2+ store or is composed of separate subunits by monitoring movements of Ca 2+ and small fluorescent probes in the ER lumen of pancreatic acinar cells, using confocal microscopy, local bleaching and uncaging. We observed rapid movements and equilibration of Ca 2+ and the probes. The bulk of the ER at the base was not connected to the granules in the apical part, but diffusion into small apical ER extensions occurred. The connectivity of the ER Ca 2+ store was robust, since even supramaximal acetylcholine (ACh) stimulation for 30 min did not result in functional fragmentation. ACh could elicit a uniform decrease in the ER Ca 2+ concentration throughout the cell, but repetitive cytosolic Ca 2+ spikes, induced by a low ACh concentration, hardly reduced the ER Ca 2+ level. We conclude that the ER is a functionally continuous unit, which enables efficient Ca 2+ liberation. Ca 2+ released from the apical ER terminals is quickly replenished from the bulk of the rough ER at the base.