Primary Oxygen Sensors

Wilson DF, Mokashi A, Chugh D, Vinogradov S, Osanai S, et al. 1994. The primary oxygen sensor of the cat carotid body is cytochrome of the mitochondrial respiratory chain. FEBS Lett 351 370-374. 

The initial sensors and subsequent signal transduction systems of hypoxic vasoconstriction (HPV) remain an area of intense investigation (21,22). At the cellular level, pulmonary artery smooth muscle (PASM) contraction depends on an increase in cytosolic calcium from the extracellular space as well as release from intracellular stores, and membrane depolarization due to closure of K+ channels. Many argue that the mitochondria is a primary oxygen sensor such that electron transport chain inhibitors can specifically inhibit HPV and/or prevent the hypoxia-specific response. Reactive oxygen species are also implicated in HPV. Two different models are proposed one describes an increase in mitochondrial ROS mediated via increased intracellular calcium release, and the second describes a decrease in mitochondrial ROS mediated via inhibition of the Kv channel (Figure 8.2). 

It is clear that the NEB cell primary O2 sensor is NADPH oxidase, while in the other 02-sensing cells (notably, the pulmonary vasculature and carotid body) it is not. However, one controversial mechanism that has been implicated in a variety of O2-sensitive tissues (86), including pulmonary arteriolar smooth muscle cells (87), is modulation of mitochondrial production of reactive oxygen species. However, in H146 cells at least, mitochondrial involvement is at best hmited since inhibition of the mitochondrial respiratory chain by myxothiazol as well as p cells (cells genetically manipulated to be free of mitochondria) does not demonstrate significant perturbation in their acute hypoxic response (Fig. 9a-d). 

Microbial sensors offer effective tools for mlcrobioassay. They require a much shorter time and less experience as compared with conventional mlcrobioassay methods. A novel primary screening test for a mutagen has been proposed by Suzuki et al. (107). Living cells of the Rec and the Rec strains were Immobilized in different membrane matrices and attached to oxygen electrodes. The bacterial respiratory activity of the Rec strain was electrochemically compared with that of the Rec strain. 

Only a limited number of biochemical analytes have an intrinsic optical absorption that can be measured with sufficient selectivity directly by spectroscopic methods. Other species, particularly hydrogen, oxygen, carbon dioxide, and glucose, which are of primary interest in diagnostic applications, are not susceptible to direct photometry. Therefore, indicator-mediated sensors have been developed using specific reagents that are properly immobilized on the surface of an optical sensor. 

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