SUMMARY In order to understand the role of metabolic regulation in environmental stress tolerance, a comprehensive analysis of demand-side effects (i.e. changes in energy demands for basal maintenance) and supply-side effects (i.e. metabolic capacity to provide ATP to cover the energy demand) of environmental stressors is required. We have studied the effects of temperature (12, 20 and 28°C) and exposure to a trace metal, cadmium (50 μg l–1), on the cellular energy budget of a model marine poikilotherm, Crassostrea virginica (eastern oysters), using oxygen demand for ATP turnover, protein synthesis, mitochondrial proton leak and non-mitochondrial respiration in isolated gill and hepatopancreas cells as demand-side endpoints and mitochondrial oxidation capacity, abundance and fractional volume as supply-side endpoints. Cadmium exposure and high acclimation temperatures resulted in a strong increase of oxygen demand in gill and hepatopancreas cells of oysters. Cd-induced increases in cellular energy demand were significant at 12 and 20°C but not at 28°C,possibly indicating a metabolic capacity limitation at the highest temperature. Elevated cellular demand in cells from Cd-exposed oysters was associated with a 2–6-fold increase in protein synthesis and, at cold acclimation temperatures, with a 1.5-fold elevated mitochondrial proton leak. Cellular aerobic capacity, as indicated by mitochondrial oxidation capacity,abundance and volume, did not increase in parallel to compensate for the elevated energy demand. Mitochondrial oxidation capacity was reduced in 28°C-acclimated oysters, and mitochondrial abundance decreased in Cd-exposed oysters, with a stronger decrease (by 20–24%) in warm-acclimated oysters compared with cold-acclimated ones (by 8–13%). These data provide a mechanistic basis for synergism between temperature and cadmium stress on metabolism of marine poikilotherms. Exposure to combined temperature and cadmium stress may result in a strong energy deficiency due to the elevated energy demand on one hand and a reduced mitochondrial capacity to cover this demand on the other hand, which may have important implications for surviving seasonally and/or globally elevated temperatures in polluted estuaries.

Mitochondrial dysfunctions contribute to neurodegeneration, the locations of which vary among neurodegenerative diseases. To begin to understand what mechanisms may underlie higher vulnerability of the spinal cord motor neurons in amyotrophic lateral sclerosis, compared with brain mitochondria, we studied three major functions of rat brain mitochondria (BM) and spinal cord mitochondria (SCM) mitochondria: oxidative phosphorylation, Ca 2ϩ sequestration, and production of reactive oxygen species (ROS), using a new metabolic paradigm (Panov et al., J. Biol. Chem. 284: 14448 -14456, 2009). We present data that SCM share some unique metabolic properties of the BM. However, SCM also have several distinctions from the BM: 1) With the exception of succinate, SCM show significantly lower rates of respiration with all substrates studied; 2) immunoblotting analysis showed that this may be due to 30 -40% lower contents of respiratory enzymes and porin; 3) compared with BM, SCM sequestered 40 -50% less Ca 2ϩ , and the total tissue calcium content was 8 times higher in the spinal cord; 4) normalization for mitochondria from 1 g of tissue showed that BM can sequester several times more Ca 2ϩ than was available in the brain tissue, whereas SCM had the capacity to sequester only 10 -20% of the total tissue Ca 2ϩ ; and 5) with succinate and succinate-containing substrate mixtures, SCM showed significantly higher state 4 respiration than BM and generated more ROS associated with the reverse electron transport. We conclude that SCM have an intrinsically higher risk of oxidative damage and overload with calcium than BM, and thus spinal cord may be more vulnerable under some pathologic conditions. (250) oxidative phosphorylation; permeability transition; reactive oxygen species MITOCHONDRIAL DYSFUNCTIONS play important roles in pathogenesis of degenerative diseases of the central nervous system (4,14). Although many neurodegenerative diseases are systemic, such as Huntington's disease (15), amyotrophic lateral sclerosis (ALS) (2), and Friedrich's ataxia (8), neurodegeneration predominantly occurs at specific locations within the central nervous system in each of these diseases. An important question in neurodegenerative diseases is what determines localization of neuronal death? There is evidence that, during systemic intoxication with rotenone, or in transgenic mice bearing mutated human G93A SOD1 gene, the pathological changes occur in brain and spinal cord mitochondria, but not in liver mitochondria (10, 32). It was also shown that various brain regions differ in their sensitivity to the deleterious effects of oxygen deprivation (22, 41). Thus, differences in the tissue-specific and regional properties of mitochondria may contribute to selectivity of neurodegeneration.Regarding ALS, one of the major questions is, "Why are motor neurons in the spinal cord more vulnerable than neurons in brain?" Because mitochondrial dysfunctions play important roles in pathogenesis of ALS (2, 24), the above question can be restated as, "What featu...