Oxygen Diffusion: An Enzyme-Controlled Variable Parameter

Previous oxygen microelectrode studies have shown that the oxygen diffusion coefficient (DO2) increases during extracellular PO2 decreases, while intracellular PO2 remained unchanged and thus cell function (spike activity of neurons). Oxygen dependency of complex multicellular organisms requires a stable and adequate oxygen supply to the cells, while toxic concentrations have to be avoided. Oxygen brought to the tissue by convection diffuses through the intercellular and cell membranes, which are potential barriers to diffusion. In gerbil brain cortex, PO2 and DO2 were measured by membrane-covered and by bare gold microelectrodes, as were also spike potentials. Moderate respiratory hypoxia was followed by a primary sharp drop of tissue PO2 that recovered to higher values concomitant with an increase of DO2. A drop in intracellular PO2 recovered immediately. Studies on the abdominal ganglion of aplysia californica showed similar results. Heterogeneity is a feature of both normal oxygen supply to tissue and supply due to a wide range of disturbances in oxygen supply. Oxygen diffusion through membranes is variable thereby ensuring adequate intracellular PO2. Cell-derived glucosamine oxidase seems to regulate the polymerization/depolymerisation ratio of membrane mucopolysaccharides and thus oxygen diffusion. Variability of oxygen diffusion is a decisive parameter for regulating the supply/demand ratio of oxygen supply to the cell; this occurs in highly developed animals as well as in species of a less sophisticated nature. Autoregulation of oxygen diffusion is as important as the distribution/perfusion ratio of the capillary meshwork and as the oxygen extraction ratio in relation to oxygen consumption of the cell. Oxygen diffusion resistance is the cellular protection against luxury oxygen supply (which can result in toxic oxidative species leading to mutagenesis).