EFFECTS OF 1-METHYL-4-PHENYLPYRIDINIUM ON ISOLATED RAT-BRAIN MITOCHONDRIA - EVIDENCE FOR A PRIMARY INVOLVEMENT OF ENERGY DEPLETION

The effects of 1-methyl-4-phenylpyridinium (MPP(+)) on the oxygen cons umption, ATP production, H2O2 production, and mitochondrial NADH-CoQ(1 ) reductase (complex I) activity of isolated rat brain mitochondria we re investigated. Using glutamate and malate as substrates, concentrati ons of 10-100 mu M MPP(+) had no effect on state 4 (-ADP) respiration but decreased state 3 (+ADP) respiration and ATP production. Incubatin g mitochondria with ADP for 30 min after loading with varying concentr ations of MPP(+) produced a concentration-dependent decrease in H2O2 p roduction. Incubation of mitochondria with ADP for 60 min after loadin g with 100 mu M MPP(+) caused no loss of complex I activity after wash ing of MPP(+) from the mitochondrial membranes. These data are consist ent with MPP(+) initially binding specifically to complex I and inhibi ting both the flow of reducing equivalents and the production of H2O2 by the mitochondrial respiratory chain, without irreversibly damaging complex I. However, mitochondria incubated with H2O2 in the presence o f CU2+ ions showed decreased complex I activity. This study provides a dditional evidence that cellular damage initiated by MPP(+) is due pri marily to energy depletion caused by specific binding to complex I, an y increased damage due to free radical production by mitochondria bein g a secondary effect.