MECHANISMS AND MEANING OF CELLULAR OXYGEN SENSING IN THE ORGANISM

Oxygen sensors in the body induce various cell activities to avoid any mismatch between oxygen demand and oxygen supply and to maintain an o ptimal level of oxygen partial pressure (P-o2) in Various organs. Oxyg en sensing seems to be a well conserved process among procaryontic and eucaryontic cells. The molecular mechanism of oxygen sensing is unkno wn, but it has been suggested that a hemeprotein is involved that does not participate in the mitochondrial energy production. As examplifie d on the carotid body and on erythropoietin producing HepG2 cells, a c ytochrome b was described for the NAD(P)H oxidase of neutrophiles migh t be an attractive candidate for this hemeprotein. It is hypothesised that hydrogen peroxide (H2O2) produced by this cytochrome b in direct correlation with cellular P-o2, serves as a second messenger to regula te potassium channels or gene expression. One might forsee, that this new concept of oxygen sensing could have an impact on all processes in physiology and pathophysiology which are dealing with reactive oxygen intermediates.