Cells require a continuous supply of energy, as adenosine triphosphate, for survival and function.
Restrictions in availability of substrates for oxidative phosphorylation, such as oxygen, or failure the regulatory mechanisms leads to disruption of cellular and tissue function. The regulation of, and interactions among, metabolic pathways is being examined at all levels of organization, from isolated mitochondria to tissue in vivo . Particular interest is in the oxygen dependence of energy metabolism, with the related problems of oxygen delivery to tissue, oxygen sensing by tissue, and hypoxia induced cellular injury. A new optical technique, oxygen dependent quenching of phosphorescence, is being developed for noninvasive measurement of oxygen. This method provides quantitative oxygen measurements with high spatial and temporal resolution both in vitro and in vivo .