5-Hydroxydecanoate and coenzyme A are inhibitors of native sarcolemmal KATP channels in inside-out patches.
BACKGROUND
5-Hydroxydecanoate (5-HD) inhibits preconditioning, and it is assumed to be a selective inhibitor of mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channels. However, 5-HD is a substrate for mitochondrial outer membrane acyl-CoA synthetase, which catalyzes the reaction: 5HD + 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 K(ATP) (sarcK(ATP)) channel activity.


METHODS
Single sarcK(ATP) channel currents were measured in inside-out patches excised from rat ventricular myocytes. In addition, sarcK(ATP) channel activity was recorded in whole-cell configuration or in giant inside-out patches excised from oocytes expressing Kir6.2/SUR2A.


RESULTS
5-HD inhibited (IC(50) approximately 30 microM) K(ATP) 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 microM 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 microM coenzyme A (CoA) inhibited sarcK(ATP) 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 sarcK(ATP) channel activation by either metabolic inhibition or rilmakalim.


CONCLUSIONS
SarcK(ATP) 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 sarcK(ATP) and mitoK(ATP) channels. However, in intact cells, 5-HD fails to inhibit sarcK(ATP) channels, suggesting that mitochondria are the preconditioning-relevant targets of 5-HD.
Li
Xiantao
X
Institut für Normale und Pathologische Physiologie, Philipps-Universität Marburg, Deutschhausstrasse 2, 35037 Marburg, Germany.
Rapedius
Markus
M
Baukrowitz
Thomas
T
Liu
Gong Xin
GX
Srivastava
D K
DK
Daut
Jürgen
J
Hanley
Peter J
PJ
D000106:Acetate-CoA Ligase / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D003065:Coenzyme A / Q000494:pharmacology*; D003652:Decanoic Acids / Q000494:pharmacology*; D006352:Heart Ventricles / Q000187:drug effects; D006880:Hydroxy Acids / Q000494:pharmacology*; D054086:KATP Channels / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D032342:Muscle Cells / Q000187:drug effects / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects / Q000502:physiology; D051381:Rats; D012508:Sarcolemma / Q000502:physiology*; D000099161:Kcnj11 Channel
D000106:Acetate-CoA Ligase; D003065:Coenzyme A; D003652:Decanoic Acids; D006880:Hydroxy Acids; D054086:KATP Channels; D024661:Potassium Channels, Inwardly Rectifying; D000099161:Kcnj11 Channel; C052853:5-hydroxydecanoic acid