Refilling of endothelial calcium stores without bypassing the cytosol

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Abstract
The present study was undertaken to define the route of Ca2+ used for refilling of intracellular Ca2+ stores in endothelial cells. Ca2+ stores, after emptying with bradykinin in Ca2+ free solution and termination of the stimulation with the bradykinin antagonist, Hoe 140, were allowed to refill by addition of Ca2+. Refilling was prevented by 2,5‐di(tert‐butyl)‐1,4‐benzohydroquinone (BuBHQ), an inhibitor of microsomal Ca2+ sequestration. BuBHQ induced large increases in the cytosolic Ca2+ concentration during the refilling phase. This finding is not compatible with a model proposing Ca2+ uptake into the stores directly from the extracellular space but provides evidence for uptake from the cytosolic compartment.