Recent studies suggest that the degree of mitochondrial dysfunction in cerebral ischemia may be an important determinant of the final extent of tissue injury. Although loss of mitochondrial membrane potential ( m ), one index of mitochondrial dysfunction, has been documented in neurons exposed to ischemic conditions, it is not yet known whether astrocytes, which are relatively resistant to ischemic injury, experience changes in m under similar conditions. To address this, we exposed cortical astrocytes cultured alone or with neurons to oxygen-glucose deprivation (OGD) and monitored m using tetramethylrhodamine ethyl ester. Both neurons and astrocytes exhibited profound loss of m after 45-60 min of OGD. However, although this exposure is lethal to nearly all neurons, it is hours less than that needed to kill astrocytes. Astrocyte m was rescued during OGD by cyclosporin A, a permeability transition pore blocker, and G N-nitro-arginine, a nitric oxide synthase inhibitor. Loss of mitochondrial membrane potential in astrocytes was not accompanied by depolarization of the plasma membrane. Recovery of astrocyte m after reintroduction of O 2 and glucose occurred over a surprisingly long period (Ͼ1 hr), suggesting that OGD caused specific, reversible changes in astrocyte mitochondrial physiology beyond the simple lack of O 2 and glucose. Decreased m was associated with a cyclosporin A-sensitive loss of cytochrome c but not with activation of caspase-3 or caspase-9. Our data suggest that astrocyte mitochondrial depolarization could be a previously unrecognized event early in ischemia and that strategies that target the mitochondrial component of ischemic injury may benefit astrocytes as well as neurons. Key words: tetramethylrhodamine ethyl ester; mitochondrial permeability transition pore; nitric oxide synthase; cyclosporin A; confocal microscopy; cortical cell culturesMitochondrial dysfunction is an early feature in nervous system ischemia. Functional studies on mitochondria isolated from ischemic brain (Sims et al., 1986;Sims, 1991) and metabolic imaging studies of brain during ischemia (Watanabe et al., 1994;Shiino et al., 1998;McCleary et al., 1999;Shadid et al., 1999) indicate that brief periods of ischemia result in transient mitochondrial respiratory defects that normalize rapidly after reperfusion (Schutz et al., 1973;Hillered et al., 1984;Sims et al., 1986). Longer periods of ischemia, however, result in a secondary, irreversible decline in mitochondrial function that occurs minutes to hours later (for review, see Siesjo et al., 1999). Although mitochondrial failure is associated with loss of mitochondrial membrane potential ( m ) in many injury conditions (Green and Reed, 1998), it is not yet known whether impaired mitochondrial respiration during cerebral ischemia is accompanied by loss of m , because of the lack of sensitive and specific probes for m in the intact brain. Suggestive evidence comes from reports by Fujimura et al. (1998), Andreyev et al. (1998), and Perez-Pinzon et al. (1999, who observed releas...

Outside the nervous system, members of the mitochondrial uncoupling protein (UCP) family have been proposed to contribute to control of body temperature and energy metabolism, and regulation of mitochondrial production of reactive oxygen species (ROS). However, the function of brain mitochondrial carrier protein 1 (BMCP1), which is highly expressed in brain, remains to be determined. To study BMCP1 expression and function in the nervous system, a high-af®nity antibody to BMCP1 was generated and used to analyze tissue expression of BMCP1 protein in mouse. BMCP1 protein was highly expressed in heart and kidney, but not liver or lung. In the nervous system, BMCP1 was present in cortex, basal ganglia, substantia nigra, cerebellum, and spinal cord. Both BMCP1 mRNA and protein expression was almost exclusively neuronal. To study the effect of BMCP1 expression on mitochondrial function, neuronal (GT1-1) cell lines with stable overexpression of BMCP1 were generated. Transfected cells had higher State 4 respiration and lower mitochondrial membrane potential (c m ), consistent with greater mitochondrial uncoupling. BMCP1 expression also decreased mitochondrial production of ROS. These data suggest that BMCP1 can modify mitochondrial respiratory ef®ciency and mitochondrial oxidant production, and raise the possibility that BMCP1 might alter the vulnerability of brain to both acute injury and to neurodegenerative conditions.