title: Partial mitochondrial inhibition causes striatal dopamine release suppression and medium spiny neuron depolarization via H2O2 elevation, not ATP depletion.
abstract: Mitochondrial dysfunction is a potential causal factor in Parkinson's disease. We show here that acute exposure to the mitochondrial complex I inhibitor rotenone (30-100 nM; 30 min) causes concentration-dependent suppression of single-pulse evoked dopamine (DA) release monitored in real time with carbon-fiber microelectrodes in guinea pig striatal slices, with no effect on DA content. Suppression of DA release was prevented by the sulfonylurea glibenclamide, implicating ATP-sensitive K+ (KATP) channels; however, tissue ATP was unaltered. Because KATP channels can be activated by hydrogen peroxide (H2O2), as well as by low ATP, we examined the involvement of rotenone-enhanced H2O2 generation. Confirming an essential role for H2O2, the inhibition of DA release by rotenone was prevented by catalase, a peroxide-scavenging enzyme. Striatal H2O2 generation during rotenone exposure was examined in individual medium spiny neurons using fluorescence imaging with dichlorofluorescein (DCF). An increase in intracellular H2O2 levels followed a similar time course to that of DA release suppression and was accompanied by cell membrane depolarization, decreased input resistance, and increased excitability. Extracellular catalase markedly attenuated the increase in DCF fluorescence and prevented rotenone-induced effects on membrane properties; membrane changes were also largely prevented by flufenamic acid, a blocker of transient receptor potential (TRP) channels. Thus, partial mitochondrial inhibition can cause functional DA denervation via H2O2 and KATP channels, without DA or ATP depletion. Furthermore, amplified H2O2 levels and TRP channel activation in striatal spiny neurons indicate potential sources of damage in these cells. Overall, these novel factors could contribute to parkinsonian motor deficits and neuronal degeneration caused by mitochondrial dysfunction.
authors.affiliation: Department of Physiology and Neuroscience, New York University School of Medicine, New York, New York 10016, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Bao
authors.forename: Marat V
authors.initials: MV
authors.lastname: Avshalumov
authors.forename: Margaret E
authors.initials: ME
authors.lastname: Rice
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000704:Analysis of Variance; D000818:Animals; D002374:Catalase / Q000494:pharmacology; D003342:Corpus Striatum / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D004298:Dopamine / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D005452:Fluoresceins / Q000378:metabolism; D005905:Glyburide / Q000494:pharmacology; D006168:Guinea Pigs; D006861:Hydrogen Peroxide / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D018408:Patch-Clamp Techniques / Q000379:methods; D012402:Rotenone / Q000494:pharmacology*; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D014044:Tolbutamide / Q000494:pharmacology; D014475:Uncoupling Agents
chemical_list: D005452:Fluoresceins; D007004:Hypoglycemic Agents; D026941:Sodium Channel Blockers; D014475:Uncoupling Agents; D012402:Rotenone; D013779:Tetrodotoxin; C037631:2',7'-dichlorofluorescein; D000255:Adenosine Triphosphate; D014044:Tolbutamide; D006861:Hydrogen Peroxide; D002374:Catalase; D005905:Glyburide; D004298:Dopamine