Lipoxin A4 stimulates a cytosolic Ca2+ increase in human bronchial epithelium

Lipoxins are biologically active eicosanoids possessing anti-inflammatory properties. Using a calcium imaging system we investigated the effect of lipoxin A(4) (LXA(4)) on intracellular [Ca2+] ([Ca2+](i)) of human bronchial epithelial cell. Exposure of the cells to LXA(4) produced a dose-dependent increase in [Ca2+](i) followed by a recovery to basal values in primary culture and in 16HBE14o(-) cells. The LXA(4)-induced [Ca2+](i) increase was completely abolished after pre-treatment of the 16HBE14o(-) cells with pertussis toxin (G-protein inhibitor). The [Ca2+](i) response was not affected by the removal of external [Ca2+](i) but completely inhibited by thapsigargin (Ca2+-ATPase inhibitor) treatment. Pretreatment of the bronchial epithelial cells with either MDL hydrochloride (adenylate cyclase inhibitor) or (R-p)-cAMP (CAMP-dependent protein kinase inhibitor) inhibited the Ca2+ response to LXA(4). However, the response was not affected by chelerytrine chloride (protein kinase C inhbitor) or montelukast (cysteinyl leukotriene receptor antagonist). The LXA(4) receptor mRNA was detected, by RT-PCR, in primary culture of human bronchial epithelium and in immortalized 16HBE14o(-)cells. The functional consequences of the effect of LXA(4) on intracellular [Ca2+](i) have been investigated on Cl- secretion, measured using the short-circuit techniques on 16HBE14o(-) monolayers grown on permeable filters. LXA(4) produced a sustained stimulation of the Cl- secretion by 16HBE14o(-) monolayers, which was inhibited by BAPTA-AM, a chelator of intracellular calcium. Taken together our results provided evidence for the stimulation of a [Ca2+](i) increase by LXA(4) through a mechanism involving its specific receptor and protein kinase A activation and resulting in a subsequent Ca2+-dependent Cl- secretion by human airway epithelial cells.