PO2 affinities, heme proteins, and reactive oxygen intermediates involved in intracellular signal cascades for sensing oxygen

The oxygen partial pressure field in different organs ranging from 0 to 100 Torr is likely to be a mirror of oxygen sensitive intracellular signal cascades determining ion channel open probability, metabolic pathway activities and gene expression. High or low PO2 affinities of the particular signal cascade optimize the oxygen sensitive cellular response for adapting organ functions to variations of the oxygen supply conditions. The signal cascades are triggered by an oxygen sensor which is believed to be a heme protein. In some cases reactive oxygen intermediates (ROI) are acting as second messengers revealing these signal cascades as an evolutionary highly conserved principle first described in bacteria.