Critical role for small and large conductance calcium-dependent potassium channels in endotoxemia and TNF toxicity.

Sepsis-associated vasodilation and shock are centrally orchestrated by NO. Nevertheless, inhibition of NO synthesis may not be the target of choice for the treatment of septic shock because it increases morbidity and mortality. Potential other therapeutic targets include soluble guanulate cyclase (sGC) and K+ channels. In this study, we investigated the protective effect of the sGC inhibitor methylene blue (MB) and various K+ channel inhibitors on LPS- and TNF-induced mortality in mice. In TNF-induced shock, the importance of SK channels was underscored by the ability of a single treatment with the small-conductance calcium-activated SK channel inhibitor apamin to provide significant protection. The only other K+ channel inhibitor that can add survival benefit to the apamin treatment was iberiotoxin, stressing the importance of large-conductance calcium-activated BK channels as well. Although MB can protect against TNF-induced shock and mortality, it cannot prevent LPS-induced mortality. Treatment with the nonspecific K+ channel inhibitor tetraethylammonium or with inhibitors specific for adenosine triphosphate (ATP)-sensitive KATP channels (glibenclamide), BK channels (iberiotoxin), or SK channels (apamin) could not protect either. However, when we combined MB treatment with a single dose of apamin and iberiotoxin, mice were completely protected against LPS-induced death for at least 2 days. In conclusion, the protective effect of MB in combination with apamin and iberiotoxin indicates an important role for SK and BK channels, rather than KATP channels, during endotoxemia. Our results point to SK and BK channels as potential targets in septic shock treatment to be modulated preferentially together with sGC.