MCC-134, a single pharmacophore, opens surface ATP-sensitive potassium channels, blocks mitochondrial ATP-sensitive potassium channels, and suppresses preconditioning.
BACKGROUND
MCC-134 (1-[4-(H-imidazol-1-yl)benzoyl]-N-methylcyclobutane-carbothioamide), a newly developed analog of aprikalim, opens surface smooth muscle-type ATP-sensitive potassium (K(ATP)) channels but inhibits pancreatic K(ATP) channels. However, the effects of MCC-134 on cardiac surface K(ATP) channels and mitochondrial K(ATP) (mitoK(ATP)) channels are unknown. A mixed agonist/blocker with differential effects on the two channel types would help to clarify the role of K(ATP) channels in cardioprotection.


RESULTS
To index mitoK(ATP) channels, we measured mitochondrial flavoprotein fluorescence in rabbit ventricular myocytes. MCC-134 alone had little effect on basal flavoprotein fluorescence. However, MCC-134 inhibited diazoxide-induced flavoprotein oxidation in a dose-dependent manner (EC(50)=27 micro mol/L). When ATP was included in the pipette solution, MCC-134 slowly activated surface K(ATP) currents with some delay (>10 minutes). These results indicate that MCC-134 is a mitoK(ATP) channel inhibitor and a surface K(ATP) channel opener in native cardiac cells. In cell-pelleting ischemia assays, coapplication of MCC-134 with diazoxide abolished the cardioprotective effect of diazoxide, whereas MCC-134 alone did not alter cell death. These results were reproducible in both rabbit and mouse myocytes. MCC-134 also attenuated the effect of ischemic preconditioning against myocardial infarction in mice, consistent with the results of cell-pelleting ischemia assays.


CONCLUSIONS
A single drug, MCC-134, opens surface K(ATP) channels but blocks mitoK(ATP) channels; the fact that this drug inhibits preconditioning reaffirms the primacy of mitoK(ATP) rather than surface K(ATP), channels in the mechanism of cardioprotection.
Sasaki
Norihito
N
Laboratory of the Institute of Molecular Cardiobiology, Johns Hopkins University, Baltimore, MD 21205, USA.
Murata
Mitsushige
M
Guo
Yiru
Y
Jo
Su-Hyun
SH
Ohler
Andreas
A
Akao
Masaharu
M
O'Rourke
Brian
B
Xiao
Rui-Ping
RP
Bolli
Roberto
R
Marbán
Eduardo
E
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002316:Cardiotonic Agents / Q000037:antagonists & inhibitors; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D003981:Diazoxide / Q000037:antagonists & inhibitors; D004553:Electric Conductivity; D005260:Female; D005420:Flavoproteins / Q000737:chemistry; D005453:Fluorescence; D006321:Heart / Q000187:drug effects / Q000502:physiology; D007093:Imidazoles / Q000494:pharmacology*; D019157:Ischemic Preconditioning, Myocardial; D008297:Male; D051379:Mice; D008929:Mitochondria, Heart / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D009203:Myocardial Infarction / Q000473:pathology / Q000628:therapy*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D015221:Potassium Channels / Q000819:agonists* / Q000502:physiology; D011817:Rabbits; D013854:Thioamides / Q000494:pharmacology*
D002316:Cardiotonic Agents; D005420:Flavoproteins; D007093:Imidazoles; C403079:MCC 134; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D013854:Thioamides; D000255:Adenosine Triphosphate; D003981:Diazoxide