title: Ca2+ refilling of the endoplasmic reticulum is largely preserved albeit reduced Ca2+ entry in endothelial cells.
abstract: In this study the relationship between the efficiency of endoplasmic reticulum (ER) Ca2+ refilling and the extent of Ca2+ entry was investigated in endothelial cells. ER and mitochondrial Ca2+ concentration were measured using genetically encoded Ca2+ sensors, while the amount of entering Ca2+ was controlled by varying either the extracellular Ca2+ or the electrical driving force for Ca2+ by changing the plasma membrane potential. In the absence of an agonist, ER Ca2+ replenishment was fully accomplished even if the Ca2+ concentration applied was reduced from 2 to 0.5mM. A similar strong efficiency of ER Ca2+ refilling was obtained under condition of plasma membrane depolarization. However, in the presence of histamine, ER Ca2+ refilling depended on mitochondrial Ca2+ transport and was more susceptible to membrane depolarization. Store-operated Ca2+ entry (SOCE), was strongly reduced under low Ca2+ and depolarizing conditions but increased if ER Ca2+ uptake was blocked or if ER Ca2+ was released continuously by IP(3). A correlation of the kinetics of ER Ca2+refilling with cytosolic Ca2+ signals revealed that termination of SOCE is a rapid event that is not delayed compared to ER refilling. Our data indicate that ER refilling occurs in priority to, and independently from the cytosolic Ca2+ elevation upon Ca2+ entry and that this important process is widely achieved even under conditions of diminished Ca2+entry.
authors.affiliation: Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Molecular and Cellular Physiology Research Unit (MCPRU), Medical University Graz, Harrachgasse 21/III, A-8010 Graz, Austria.
authors.forename: R
authors.initials: R
authors.lastname: Malli
authors.affiliation: Department of Cell Physiology and Metabolism, University of Geneva, Medical Center, 1211 Geneva 4, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Frieden
authors.affiliation: Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Molecular and Cellular Physiology Research Unit (MCPRU), Medical University Graz, Harrachgasse 21/III, A-8010 Graz, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Hunkova
authors.affiliation: Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Molecular and Cellular Physiology Research Unit (MCPRU), Medical University Graz, Harrachgasse 21/III, A-8010 Graz, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Trenker
authors.affiliation: Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Molecular and Cellular Physiology Research Unit (MCPRU), Medical University Graz, Harrachgasse 21/III, A-8010 Graz, Austria.
authors.forename: W F
authors.initials: WF
authors.lastname: Graier
mesh_terms: D015220:Calcium Channels / Q000187:drug effects; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006873:Hydroquinones / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism / Q000494:pharmacology; D008564:Membrane Potentials; D008954:Models, Biological; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000037:antagonists & inhibitors
chemical_list: D015220:Calcium Channels; D004791:Enzyme Inhibitors; D006873:Hydroquinones; C019359:2,5-di-tert-butylhydroquinone; D015544:Inositol 1,4,5-Trisphosphate; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases