Essential Role of a Ca2+-selective, Store-operated Current (ISOC) in Endothelial Cell Permeability: Determinants of the Vascular Leak Site

Store-operated calcium (SOC) entry is sufficient to disrupt the extra-alveolar, but not the alveolar, endothelial cell barrier. Mechanism(s) underlying such insensitivity to transitions in cytosolic calcium ([Ca2+]i) in microvascular endothelial cells are unknown. Depletion of stored Ca2+ activates a larger SOC entry response in extra-alveolar (pulmonary artery; PAECs) than alveolar (pulmonary microvascular; PMVECs) endothelial cells. In vivo permeation studies revealed that Ca2+ store depletion activates similar nonselective cationic conductances in PAECs and PMVECs, while only PAECs possess the calcium-selective, store-operated Ca2+ entry current, I(SOC). Pretreatment with the type 4 phosphodiesterase inhibitor, rolipram, abolished thapsigargin-activated I(SOC) in PAECs, and revealed I(SOC) in PMVECs. Rolipram pretreatment shifted the thapsigargin-induced fluid leak site from extra-alveolar to alveolar vessels in the intact pulmonary circulation. Thus, our results indicate I(SOC) provides a [Ca2+]i source that is needed to disrupt the endothelial cell barrier, and demonstrate that intracellular events controlling I(SOC) activation coordinate the site-specific vascular response to inflammation.