State-dependent Inhibition of the Mitochondrial KATPChannel by Glyburide and 5-Hydroxydecanoate*

The mitochondrial KATPchannel (mitoKATP) is hypothesized to be the receptor for the cardioprotective effects of K+channel openers (KCO) and for the blocking of cardioprotection by glyburide and 5-hydroxydecanoate (5-HD). Studies on glyburide have indicated that this drug is inactive in isolated mitochondria. No studies of the effects of 5-HD on isolated mitochondria have been reported. This paper examines the effects of glyburide and 5-HD on K+flux in isolated, respiring mitochondria. We show that mitoKATPis completely insensitive to glyburide and 5-HD under the experimental conditions in which the open state of the channel is induced by the absence of ATP and Mg2+. On the other hand, mitoKATPbecame highly sensitive to glyburide and 5-HD when the open state was induced by Mg2+, ATP, and a physiological opener, such as GTP, or a pharmacological opener, such as diazoxide. In these open states, glyburide (K½ values 1–6 μm) and 5-HD (K½ values 45–75 μm) inhibited specific, mitoKATP-mediated K+flux in both heart and liver mitochondria from rat. These results are consistent with a role for mitoKATPin cardioprotection and show that different open states of mitoKATP, although catalyzing identical K+fluxes, exhibit very different susceptibilities to channel inhibitors.