Ca2+ refilling of the endoplasmic reticulum is largely preserved albeit reduced Ca2+ entry in endothelial cells

• Published in: Cell calcium (Edinburgh) Vol. 41; no. 1; pp. 63 - 76
• Main Authors: Malli, R, Frieden, M, Hunkova, M, Trenker, M, Graier, W.F
• Format: Journal Article
• Language: English
• Published: Netherlands 01.01.2007
• Subjects: Advanced Basic Science; Calcium Channels - drug effects; Calcium Signaling - drug effects; Calcium Signaling - physiology; Cell Line; Cytosol - metabolism; Endoplasmic Reticulum - metabolism; Endothelial Cells - drug effects; Endothelial Cells - metabolism; Enzyme Inhibitors - pharmacology; Humans; Hydroquinones - pharmacology; Inositol 1,4,5-Trisphosphate - metabolism; Inositol 1,4,5-Trisphosphate - pharmacology; Membrane Potentials; Models, Biological; Sarcoplasmic Reticulum Calcium-Transporting ATPases - antagonists & inhibitors; vYC4er; Pericam; ER-targeted venus cameleon 4; Cameleon; Membrane depolarization; free intraluminal ER Ca 2+ concentration; [Ca 2+] er; NCX pm; mitochondrial targeted ratiometric pericam; plasma membrane Na +/Ca 2+ exchanger; BHQ; plasma membrane-Ca 2+ ATPase(s); SOCE; IP 3; [Ca 2+] cyto; inositol 1,4,5-triphosphate; Endoplasmic reticulum Ca 2+ refilling; sarcoplasmic/endoplasmic reticulum Ca 2+ pumps; Mitochondrial Ca 2; [Ca 2+] mito; free mitochondrial Ca 2+ concentration; SERCA; ER; store-operated Ca 2+ entry; 2,5-di- tert-butylhydroquinone; endoplasmic reticulum; RP-mt; PMCA; free cytosolic Ca 2+ concentration
• ISSN: 0143-4160; 1532-1991
• DOI: 10.1016/j.ceca.2006.05.001

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 0.5 mM. 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 IP3 . 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.