Abstract 1527: Lipopolysaccharides Up-regulate Kir6.1/SUR2B Channel Expression And Enhance Vascular K ATP Channel Activity Through NF-κB And PKA Pathways

Abstract

Septic shock, characterized by vasodilatation and hyporeactivity to vasoconstrictors, is a major cause of death. Recent studies have shown that an ATP-sensitive K + (K ATP ) channel plays a critical role in septic susceptibility. However, the mechanisms underlying K ATP channel responses to sepsis are still unclear. Thus, we performed these studies to demonstrate how the vascular K ATP 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 K ATP 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 K ATP 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 K ATP 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.