BK Channels Regulate LPS-induced CCL-2 Release from Human Pulmonary Endothelial Cells.

We recently established a role for the stretch-activated two-pore-domain K+ (K2P) channel TREK-1 in inflammatory cytokine secretion using models of hyperoxia-, mechanical stretch-, and tumor necrosis factor-α (TNF-α)-induced acute lung injury (ALI). We now discovered the expression of large conductance, Ca2+-activated K+ (BK) channels in human pulmonary microvascular endothelial cells and primary human alveolar epithelial cells using semi-quantitative real-time PCR and immunoprecipitation, and investigated their role in inflammatory cytokine secretion using a lipopolysaccharide (LPS)-induced ALI model. As expected, LPS induced interleukin-6 (IL-6) and C-C Motif Chemokine Ligand-2 (CCL-2) secretion from pulmonary endothelial and epithelial cells. BK activation with NS1619 decreased LPS-induced CCL-2 but not IL-6 secretion from endothelial cells and had no effect on epithelial cells, although fluorometric assays revealed that BK activation hyperpolarized the plasma membrane potential (Em) of both cell types. Interestingly, BK inhibition (Paxilline) did not alter cytokine secretion or the Em in either cell type. Furthermore, LPS treatment by itself did not affect the Em or intracellular Ca2+ concentrations. Therefore, we propose BK channel activation as a novel targeted approach to counteract LPS-induced CCL-2 secretion form endothelial cells. This protective effect appears to occur via Em hyperpolarization, but independent of intracellular Ca2+ concentrations.