Abstract 9121: Intra-endoplasmic Reticulum Ca2+ Flow Recharges Preferentially to Subcompartments of ER at Caveolin-rich Cell Edges in Endothelial Cells
Subcellular distribution of caveolin-1, a marker protein of caveolae, is polarized especially in migrating or subconfluent endothelial cells (Fig. 1). In response to ATP, IP3 production and Ca2+ release originated at caveolin-1-rich cell edges (CRCE) and then propagated as spatiotemporally organized Ca2+ waves (Fig. 2). Here in this study, we investigated subcellular Ca2+ dynamics in the endoplasmic reticulum (ER) Ca2+ stores by using confocal microscopy and an ER-targeted version of cameleon (D1ER), a GFP-based Ca2+-sensing protein. As expected, FRET imaging using an ER-targeted Ca2+ sensor revealed that the ATP-mediated decrease in local intra-ER Ca2+ concentration ([Ca2+ ]er) at CRCE was more rapid and larger than in other subdomains (Figs. 2, 3). Interestingly, the decreased [Ca2+]er at such CRCE more rapidly returned to the baseline in the presence of normal extracellular Ca2+. Even in the absence of extracellular Ca2+, when maximal ATP stimulation continued to decrease global [Ca2+ ]er, [Ca2+ ]er at CRCE exhibited the opposite incremental recharging. Removal of extracellular Ca2+ or thapsigargin treatment did not affect such local recharging of Ca2+, suggesting no major roles of store-operated Ca2+ entry (SOCE) or reuptake of released Ca2+ into the ER by a Ca2+-ATPase. Thus, we conclude that the local ER Ca2+ store comprises functional subcompartments at CRCE and that an ATP-induced [Ca2+]er decrease at the caveolin-1-rich region is preferentially recharged by intra-ER Ca2+ flow from the other ER subcompartments (Fig. 4).
- © 2011 by American Heart Association, Inc.