CREATINE KINASE AND BRAIN ENERGETICS

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DESCRIPTION (Investigator's Abstract): The long-range goal of this research program is to understand the physiology of ATP metabolism or energy production and utilization in the mature and the developing brain. A second goal is to understand the role of adaptations in ATP metabolism in maintaining brain cell viability in states of energy deficit (hypoxia) and high energy demand (seizures). The primary hypothesis for this proposal is that the activity of creatine kinase (CK), which catalyzes the phosphoryl transfer between PC and ATP, also is central in closely coupling ATP synthesis to the large and rapid changes in energy demand characteristic of the mature brain. A second hypothesis is that activity of the CK isoforms, specifically the mitochondrial CK, is critical for maintaining cellular energy under conditions of decreased energy availability. Thus, adaptations to a decrease in CK catalyzed reaction rates are expected to maintain close regulation of ATP during seizures but not hypoxia. The present proposal combines in vivo 31P-nuclear magnetic resonance spectroscopy with in vitro measures of enzymes and metabolites involved in ATP metabolism. Three conditions, in which brain CK activity is 20-30 percent of the activity in normal adult cortex, are used; immaturity, feeding an analogue of creatine, and cerebral white matter. The studies comparing gray and white matter use volume localized NMR spectroscopic techniques. In the other in vivo NMR studies, non-localized spectra with high signal-to-noise will be acquired frequently to provide close comparisons of cellular energy, pH, EEG, and EKG. The expectation is that the conditions in which the CK-catalyzed reaction rate is low will be associated with larger energy losses during hypoxia than seen in the mature brain where phosphocreatine (PC) losses are 30-50 percent and ATP is stable. In contrast, the physiology of ATP metabolism in the presence of rapid or slow CK catalyzed reaction rates is expected to maintain stable brain ATP and a small loss in PC during seizures. The results of these NMR studies will provide an understanding of the in vivo regulation of brain ATP while the in vitro studies will provide an initial understanding of the molecular and cellular bases for these metabolic properties. This understanding will allow more rational use of non-invasive clinical metabolic brain monitoring.The results also will provide a clearer understanding of the pathogenesis of brain cellular injury during the critical clinical conditions of hypoxia and seizures.