In the last 10-15 years, our laboratory has been investigating mechanisms of nerve cell injury or survival during conditions of O2 limitation, acute or chronic. In particular, we have focused our recent efforts on the role that membrane proteins (e.g. voltage-sensitive Na+ and KATP) play during graded hypoxia in inducing neuronal damage or preventing and delaying it. Based on preliminary data that we have recently gathered and as a result of new collaborations within the Center Grant, we have formulated hypotheses aimed at understanding the cellular and molecular mechanisms underlying the role of ionic fluxes and energy metabolism in neuronal injury during O2 and energy deprivation. Our general hypothesis is that the neuronal plasma membrane Na-dependent exchangers and their regulation are of paramount importance in determining the vulnerability to neuronal injury not only during acute but also during chronic O2 limitation. The following are our specific hypotheses: l) Na+ influx into neocortical neurons is critical for inducing hypoxic depolarization and injury during graded O2 glucose limitation and during recovery; decreasing Na+ influx protects neurons and this protection is, in part, related to presentation of high energy metabolites; 2) this Na+ influx is mediated via Na+-dependent plasma membrane exchangers (e.g. Na/H and Na/Ca; 3) neocortical neurons obtained from animals chronically exposed to low O2 postnatally are more vulnerable to acute graded O2/glucose limitation than naive neurons and that this is due to an increase in Na+ influx via up-regulated expression of exchangers and 4) the increased vulnerability in exposed neocortical neurons to O2/glucose deprivation is the result of a faster depletion of high energy metabolites caused by an increased Na+ load. Using techniques and approaches that are operative in our laboratories such as electrophysiologic, molecular biologic techniques and magnetic resonance spectroscopy, we will be able to address all 4 hypotheses. Although we realize that neuronal responsiveness to low O2 is very complex, our long term objectives are to intervene with this system In order to prolong neuronal survival or prevent nerve cell injury. We believe that these current studies are critical steps in the overall understanding of neuronal response and adaptation to short and long term stress.
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