Diazoxide-induced cardioprotection via DeltaPsim loss depending on timing of application.
Although the role of mitochondrial ATP-sensitive potassium (mitoKATP) channels in cardioprotection is widely accepted, it remains unclear when their opening is critical for protection. We tested the hypothesis that the mitoKATP channel acts as a trigger or mediator of protection against apoptosis through loss of mitochondrial inner membrane potential (DeltaPsim). Exposure of neonatal rat cardiomyocytes to H2O2 (0.5 mmol/L) resulted in apoptosis associated with severe DeltaPsim loss. Pretreatment with diazoxide (20 to 100 micromol/L) prevented H2O2-induced apoptosis and DeltaPsim loss at 2 but not 18 h after exposure, while the latter was prevented by cotreatment with diazoxide. Lack of protection by pretreatment with diazoxide was observed in cardiomyocytes cultured in a medium containing H2O2 for 2 h and then not containing for 16 h. The slopes of the regression lines of the relationship between the proportion of apoptotic cells and DeltaPsim loss (y = -0.89 vs. -0.42) and the proportion of cells with high side scatter signal differed between cardiomyocytes exposed H2O2 for 2 and 18 h. Diazoxide per se caused a transient DeltaPsim loss (within 30 min) with a recovery followed by persistent DeltaPsim loss (after 6 h). Inhibition of the former by 5-hydroxydecanoate (5-HD, 0.5 mmol/L) abolished protection of pretreatment with diazoxide (trigger phase), while that of the latter prevented the protection of cotreatment with diazoxide (mediator phase). Our results suggest that mitoKATP channels act as a trigger and mediator of cardioprotection through a transient or persistent DeltaPsim loss depending on phenotypic consequence in response to oxidants.
Yonemochi
Hidetoshi
H
Department of Cardiovascular Science, Division of Laboratory Medicine, Oita University Faculty of Medicine, 1-1 Idaigaoka, Hasama, Oita, 879-5593, Japan. yenemo@med.oita-u.ac.jp
Ichinose
Masashi
M
Anan
Futoshi
F
Taniguti
Yayoi
Y
Shinohara
Tetsuji
T
Takahashi
Naohiko
N
Nakagawa
Mikiko
M
Saikawa
Tetsunori
T
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002316:Cardiotonic Agents / Q000494:pharmacology*; D003652:Decanoic Acids / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000633:toxicity; D006880:Hydroxy Acids / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008929:Mitochondria, Heart / Q000187:drug effects / Q000502:physiology; D051336:Mitochondrial Membranes / Q000187:drug effects* / Q000502:physiology; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D002316:Cardiotonic Agents; D003652:Decanoic Acids; D006880:Hydroxy Acids; D015221:Potassium Channels; C117780:mitochondrial K(ATP) channel; C052853:5-hydroxydecanoic acid; D006861:Hydrogen Peroxide; D003981:Diazoxide