Evidence for a receptor-activated Ca2+ entry pathway independent from Ca2+ store depletion in endothelial cells

Ca2+ entry in endothelial cells is a key signaling event as it prolongs the Ca2+ signal activated by a receptor agonist, and thus allows an adequate production of a variety of compounds. The possible routes that lead to Ca2+ entry in non-excitable cells include the receptor-activated Ca2+ entry (RACE), which requires the presence of an agonist to be activated, and the store-operated Ca2+ entry (SOCE) pathway, whose activation requires the depletion of the ER Ca2+ store. However, the relative importance of these two influx pathways during physiological stimulation is not known. In the present study we experimentally differentiated these two types of influxes and determined under which circumstances they are activated. We show that La3+ (at 10 mu M) is a discriminating compound that efficiently blocks SOCE but is almost without effect on histamine-induced Ca2+ entry (RACE). In line with this, histamine does not induce massive store depletion when performed in the presence of extracellular Ca2+. In addition, inhibition of mitochondrial respiration significantly reduces SOCE but modestly affects RACE. Thus, agonist-induced Ca2+ entry is insensitive to La3+, and only modestly affected by mitochondrial depolarization. These data shows that agonist relies almost exclusively on RACE for sustained Ca2+ signaling in endothelial cells. (c) 2007 Elsevier Ltd. All rights reserved.