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K ATP channel‐independent targets of diazoxide and 5‐hydroxydecanoate in the heart
Author(s) -
Hanley Peter J.,
Mickel Markus,
Löffler Monika,
Brandt Ulrich,
Daut Jürgen
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2002.023960
Subject(s) - diazoxide , pinacidil , chemistry , mitochondrion , biochemistry , biophysics , pharmacology , endocrinology , biology , glibenclamide , insulin , diabetes mellitus
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 μ m ) 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 μ m ) or pinacidil (100 μ m ) 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 (β‐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 reelated to partial inhibition of respiratory chain complexes.