Mitochondrial ATP-sensitive potassium channel: a novel site for neuroprotection.
OBJECTIVE
It has been shown that bradykinin (BK) protects retinal neurons against glutamate excitotoxicity, but it was not clear how BK inhibits glutamate excitotoxicity. The purpose of this study was to investigate the effect of opening the mitochondrial adenosine triphosphate (ATP)-sensitive potassium (Mit K (ATP)) channel on glutamate excitotoxicity and the protective effect of BK using cultured retinal neurons.


METHODS
Primary cultures were obtained from the retina of fetal rats (gestation days 17-19). Glutamate neurotoxicity was assessed by 10-minute exposure to 1 mM glutamate followed by 1-hour incubation in glutamate-free medium, using the trypan blue exclusion method. BK, diazoxide (the opener of the Mit K (ATP) channel), 5HD, and glibenclamide (blockers of the Mit K (ATP) channel) were applied simultaneously with glutamate. Mitochondrial membrane potential was measured as the ratio of 590:527 nm fluorescence of JC-1.


RESULTS
Cell viability was markedly reduced by 10-minute exposure to 1 mM glutamate followed by 1-hour incubation in glutamate-free medium, and glutamate induced mitochondrial depolarization of retinal neurons. BK and diazoxide protected retinal neurons against glutamate excitotoxicity and inhibited glutamate-induced mitochondrial depolarization. These actions of BK and diazoxide were inhibited by the coapplication of 5HD and glibenclamide. Furthermore, diazoxide inhibited the sodium nitroprusside (SNP, NO donor) toxicity, but did not inhibit the 3-morpholinosydnonimine (SIN-1, NO, and superoxide donor) toxicity.


CONCLUSIONS
These results suggest that BK and diazoxide protect retinal neurons against glutamate excitotoxicity by opening the Mit K (ATP) channel. It is suggested that opening of the Mit K (ATP) channel inhibited glutamate-induced generation of superoxide.
Yamauchi
Tomofusa
T
Department of Ophthalmology and Visual Sciences, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
Kashii
Satoshi
S
Yasuyoshi
Hiroki
H
Zhang
Shen
S
Honda
Yoshihito
Y
Akaike
Akinori
A
D000818:Animals; D001920:Bradykinin / Q000494:pharmacology*; D018929:Cell Culture Techniques; D002470:Cell Survival / Q000187:drug effects; D019610:Cytoprotection; D003652:Decanoic Acids / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology*; D018698:Glutamic Acid / Q000633:toxicity*; D005905:Glyburide / Q000494:pharmacology; D006880:Hydroxy Acids / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008928:Mitochondria / Q000502:physiology; D008981:Molsidomine / Q000031:analogs & derivatives* / Q000633:toxicity; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D018696:Neuroprotective Agents / Q000494:pharmacology*; D009599:Nitroprusside / Q000633:toxicity; D015221:Potassium Channels; D051381:Rats; D017208:Rats, Wistar; D012160:Retina / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism
D003652:Decanoic Acids; D006880:Hydroxy Acids; D008565:Membrane Proteins; D018696:Neuroprotective Agents; D015221:Potassium Channels; C117780:mitochondrial K(ATP) channel; D009599:Nitroprusside; D018698:Glutamic Acid; C002385:linsidomine; C052853:5-hydroxydecanoic acid; D008981:Molsidomine; D003981:Diazoxide; D001920:Bradykinin; D005905:Glyburide