Direct interaction of Na‐azide with the K ATP channel

The effects of the metabolic inhibitor sodium azide were tested on excised macropatches from Xenopus oocytes expressing cloned ATP‐sensitive potassium (K ATP ) channels of the Kir6.2/SUR1 type. In inside‐out patches from oocytes expressing Kir6.2ΔC36 (a truncated form of Kir6.2 that expresses in the absence of SUR), intracellular Na‐azide inhibited macroscopic currents with an IC 50 of 11 m M . The inhibitory effect of Na‐azide was mimicked by the same concentration of NaCl, but not by sucrose. Na‐azide and NaCl blocked Kir6.2/SUR1 currents with IC 50 of 36 m M and 19 m M , respectively. Inhibition was abolished in the absence of intracellular Mg 2+ . In contrast, Kir6.2ΔC36 currents were inhibited by Na‐azide both in the presence or absence of intracellular Mg 2+ . Kir6.2/SUR1 currents were less sensitive to 3 m M Na‐azide in the presence of MgATP. This apparent reduction in sensitivity is caused by a small activatory effect of Na‐azide conferred by SUR. We conclude that, in addition to its well‐established inhibitory effect on cellular metabolism, which leads to activation of K ATP channels in intact cells, intracellular Na‐azide has direct effects on the K ATP channel. Inhibition is intrinsic to Kir6.2, is mediated by Na + , and is modulated by SUR. There is also a small, ATP‐dependent, stimulatory effect of Na‐azide mediated by the SUR subunit. The direct effects of 3 m M Na‐azide on K ATP channels are negligible in comparison to the metabolic activation produced by the same Na‐azide concentration.British Journal of Pharmacology (2000) 131 , 1105–1112; doi: 10.1038/sj.bjp.0703680