K(ATP) channel-independent targets of diazoxide and 5-hydroxydecanoate in the heart.
Diazoxide and 5-hydroxydecanoate (5-HD; C10:0) are reputed to target specifically mitochondrial ATP-sensitive K(+) (K(ATP)) channels. Here we describe K(ATP) channel-independent targets of diazoxide and 5-HD in the heart. Using submitochondrial particles isolated from pig heart, we found that diazoxide (10-100 microM) dose-dependently decreased succinate oxidation without affecting NADH oxidation. Pinacidil, a non-selective K(ATP) channel opener, did not inhibit succinate oxidation. However, it selectively inhibited NADH oxidation. These direct inhibitory effects of diazoxide and pinacidil cannot be explained by activation of mitochondrial K(ATP) channels. Furthermore, application of either diazoxide (100 microM) or pinacidil (100 microM) did not decrease mitochondrial membrane potential, assessed using TMRE (tetramethylrhodamine ethyl ester), in isolated guinea-pig ventricular myocytes. We also tested whether 5-HD, a medium-chain fatty acid derivative which blocks diazoxide-induced cardioprotection, was 'activated' via acyl-CoA synthetase (EC 6.2.1.3), an enzyme present both on the outer mitochondrial membrane and in the matrix. Using analytical HPLC and electrospray ionisation mass spectrometry, we showed that 5-HD-CoA (5-hydroxydecanoyl-CoA) is indeed synthesized from 5-HD and CoA via acyl-CoA synthetase. Thus, 5-HD-CoA may be the active form of 5-HD, serving as substrate for (or inhibiting) acyl-CoA dehydrogenase (beta-oxidation) and/or exerting some other cellular action. In conclusion, we have identified K(ATP) channel-independent targets of 5-HD, diazoxide and pinacidil. Our findings question the assumption that sensitivity to diazoxide and 5-HD implies involvement of mitochondrial K(ATP) channels. We propose that pharmacological preconditioning may be related to partial inhibition of respiratory chain complexes.
Hanley
Peter J
PJ
Institut für Normale und Pathologische Physiologie, Universität Marburg, Deutschhausstrasse 2, 35037 Marburg, Germany.
Mickel
Markus
M
Löffler
Monika
M
Brandt
Ulrich
U
Daut
Jürgen
J
D000214:Acyl Coenzyme A / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D003066:Coenzyme A Ligases / Q000378:metabolism; D003652:Decanoic Acids / Q000494:pharmacology*; D003981:Diazoxide / Q000494:pharmacology*; D004579:Electron Transport / Q000187:drug effects; D005420:Flavoproteins / Q000502:physiology; D005453:Fluorescence; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D006880:Hydroxy Acids / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D008929:Mitochondria, Heart / Q000502:physiology; D009206:Myocardium / Q000378:metabolism*; D020110:Pinacidil / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D000098859:Long-Chain-Fatty-Acid-CoA Ligase
C471070:5-hydroxydecanoyl-coenzyme A; D000214:Acyl Coenzyme A; D003652:Decanoic Acids; D005420:Flavoproteins; D006880:Hydroxy Acids; D015221:Potassium Channels; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; C052853:5-hydroxydecanoic acid; D020110:Pinacidil; D000255:Adenosine Triphosphate; D003066:Coenzyme A Ligases; C090799:FAA2 protein, S cerevisiae; D000098859:Long-Chain-Fatty-Acid-CoA Ligase; D003981:Diazoxide