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  • Title: The sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA) is the third element in capacitative calcium entry.
    Author: Manjarrés IM, Rodríguez-García A, Alonso MT, García-Sancho J.
    Journal: Cell Calcium; 2010 May; 47(5):412-8. PubMed ID: 20347143.
    Abstract:
    STIM1 and Orai1 are the main players in capacitative calcium entry (CCE). STIM1 senses [Ca(2+)] inside the endoplasmic reticulum (ER) and, when it decreases, opens Orai1, a store-operated calcium channel (SOC) in the plasma membrane that promotes Ca(2+) entry and increases cytosolic Ca(2+). The final destination of the entering Ca(2+) is the ER, which refills very efficiently (capacitatively) with it. We propose here that SERCA is the third element of CCE, to which is tightly coupled to favour rapid Ca(2+) pumping from the high Ca(2+) microdomains, generated at the SOC's mouth, to the ER. We find that, on depletion of the intracellular Ca(2+) stores, SERCA co-localizes with STIM1 at puncta. Adequate coupling of CCE and ER Ca(2+) pumping requires correct proportions of STIM1, Orai1 and SERCA. Overexpression of Orai1 decreased modestly Ca(2+) entry, but produced a dramatic fall of Ca(2+) uptake into ER, which was rescued by STIM1 co-expression or by increasing external Ca(2+). In permeabilized cells, Ca(2+) uptake into the ER was indistinguishable in the Orai1-expressing and in the control cells. We propose that excess Orai1 uncouples SERCA from Ca(2+) entry in the intact cell by disturbing the fine topology of Ca(2+) pumping complexes within the ER-plasma membrane junctions.
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