Role of EDHF, PGI2, and Norepinephrine in Hypoxic Vasorelaxation and Vasoconstriction
In the following chapter we will discuss an aspect of peripheral chemoreception, that is oxygen sensing by peripheral blood vessels. The reaction of blood vessels to a lowering of the oxygen partial pressure is not dependent on reaching a threshold value, on the contrary, it is a continuous process. Each slight change in PO2 is complimented by a change in the membrane potential and tone of the vascular smooth muscle cells, and a defined membrane potential and mechanical tension can be correlated with each absolute value of oxygen concentration (activation curve)2,6,7. In principle, the chemoreceptor may be an endothelial cell, a smooth muscle cell, or an autonomic nerve fibre. The oxygen partial pressure measurements as well as the fulfilment of the above requirements for such a measuring system are best made possible by a redox system. Cytoplasmic redox systems have been ubiquitously described. Cell membranous systems until now have not. There are a number of indications that such an O2 system may be found in the outer cell membrane. It could have settled in all three cell species or in one of the three. Since its nature and localization can only be speculated upon, we are reporting on, to begin with, membrane physiological foundations of vascular reactivity when varying the oxygen partial pressure within a specific range.
KeywordsMembrane Potential Oxygen Partial Pressure Oxygen Tension Krebs Solution Membrane Hyperpolarization
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