Abstract 1527: Lipopolysaccharides Up-regulate Kir6.1/SUR2B Channel Expression And Enhance Vascular KATP Channel Activity Through NF-κB And PKA Pathways
Septic shock, characterized by vasodilatation and hyporeactivity to vasoconstrictors, is a major cause of death. Recent studies have shown that an ATP-sensitive K+ (KATP) channel plays a critical role in septic susceptibility. However, the mechanisms underlying KATP channel responses to sepsis are still unclear. Thus, we performed these studies to demonstrate how the vascular KATP channel changes its activity and expression with an exposure to lipopolysaccharides (LPS), a major septic pathogen. In isolated rat mesenteric arterial rings, phenylephrine (PE) induced concentration-dependent vasoconstriction. At the maximum effect, pinacidil, a selective KATP channel opener, relaxed the rings almost completely. The PE response was almost completely lost after a pretreatment with LPS (1μg/ml) overnight. The LPS treatment produced hyperpolarization of acutely dissociated aortic smooth myocytes. Consistently, LPS treatment augmented KATP channel activity via increasing channel density in plasma membranes in these cells. Quantitative PCR analysis showed that LPS stimulated Kir6.1 and SUR2B expressions in a dose-dependent manner. LPS in 0.01 μg/ml raised Kir6.1 mRNA expression by ~1.8-folds (P<0.01, n=8). Stronger effects were seen with higher concentrations (by 2.5 and 3.0-folds with 0.1 and 1 μg/ml LPS, respectively). SUR2B expression also increased dose-dependently, though to a less degree. The LPS-induced expression of Kir6.1 and SUR2B subunits was suppressed by actinomycin D (2 μg/ml) and actidione (2 μg/ml), suggesting both transcriptional and translational mechanisms are involved. The effect of LPS on Kir6.1 and SUR2B expression was diminished by a pretreatment with the selective NF-κB inhibitors dimethyl fumarate (0.1 mM) or pyrrolidine dithiocarbamate (0.1 mM). Furthermore, the specific PKA blockers Rp-cAMP (100 μM) or KT5720 (1 μM) suppressed LPS-induced Kir6.1 and SUR2B expression. These results therefore suggest that KATP channel activity is enhanced with LPS exposure leading to hyperpolarization of vascular smooth muscles and vasodilation, and such an effect involves up-regulation of Kir6.1 and SUR2B expressions, in which NF-κB and PKA-dependent intracellular signaling pathways may play a role.