5-Hydroxydecanoate and coenzyme A are inhibitors of native sarcolemmal KATP channels in inside-out patches

Background5-Hydroxydecanoate (5-HD) inhibits preconditioning, and it is assumed to be a selective inhibitor of mitochondrial ATP-sensitive K+ (mitoKATP) channels. However, 5-HD is a substrate for mitochondrial outer membrane acyl-CoA synthetase, which catalyzes the reaction: 5‑HD + CoA + ATP → 5-HD-CoA (5-hydroxydecanoyl-CoA) + AMP + pyrophosphate. We aimed to determine whether the reactants or principal product of this reaction modulate sarcolemmal KATP (sarcKATP) channel activity.MethodsSingle sarcKATP channel currents were measured in inside-out patches excised from rat ventricular myocytes. In addition, sarcKATP channel activity was recorded in whole-cell configuration or in giant inside-out patches excised from oocytes expressing Kir6.2/SUR2A.Results5-HD inhibited (IC50 ∼ 30 μM) KATP channel activity, albeit only in the presence of (non-inhibitory) concentrations of ATP. Similarly, when the inhibitory effect of 0.2 mM ATP was reversed by 1 μM oleoyl-CoA, subsequent application of 5-HD blocked channel activity, but no effect was seen in the absence of ATP. Furthermore, we found that 1 μM coenzyme A (CoA) inhibited sarcKATP channels. Using giant inside-out patches, which are weakly sensitive to “contaminating” CoA, we found that Kir6.2/SUR2A channels were insensitive to 5-HD-CoA. In intact myocytes, 5-HD failed to reverse sarcKATP channel activation by either metabolic inhibition or rilmakalim.General significanceSarcKATP channels are inhibited by 5-HD (provided that ATP is present) and CoA but insensitive to 5-HD-CoA. 5-HD is equally potent at “directly” inhibiting sarcKATP and mitoKATP channels. However, in intact cells, 5-HD fails to inhibit sarcKATP channels, suggesting that mitochondria are the preconditioning-relevant targets of 5-HD.