Discovering The Chemical Identity
Although the phenomenon of EDHF has been observed and reported in scientific literature, to date the chemical identity of the factor(s) has not been determined.
- In some cases, members of a class of arachidonic acid derivatives, the epoxyeicosatrienoic acids (EETs), have been found to mediate the vasodilation. These compounds are formed by epoxidation of any one of four double bonds of the arachidonic acid carbon backbone by cytochrome P450 epoxygenase enzymes.
- In addition, in some cases hydrogen peroxide has been suggested to function as an EDHF in some vascular beds; although the validity of this observation is debated because it may have an inhibitory action on K+ channels, at least, in some vascular beds
- It has been suggested that EDHF is potassium ions (K+) as the activation of endothelial K-Ca+ channels causes an efflux of K+ from endothelial cells towards the extracellular space. An increase in extracellular K+ has been shown to activate a ouabain-sensitive electrogenic Na+–K+-ATPase followed by hyperpolarization and smooth muscle cell relaxation. However the involvement of K+ ions into EDHF-mediated relaxation does not necessarily involve the activation Na+–K+-ATPase channels. It is more likely that K+ ions and gap junctions can be involved in EDHF-mediated relaxation simultaneously, and may also act synergistically
- C-type Natriuretic Peptide (CNP) has been shown to exert a variety of cardiovascular effects including vasodilatation and hyperpolarization of arteries through the opening of KCa+-channels. CNP is widely distributed in the cardiovascular system and it has been found at high concentrations particularly in endothelial Cells. Endothelium-derived CNP has been proposed to acts as an EDHF via specific C-subtype of natriuretic peptide receptor however the evidence in favour of CNP acting as EDHF has yet to be determined
- An alternative explanation for the EDHF phenomenon is that direct intercellular communication via gap junctions allows passive spread of agonist-induced endothelial hyperpolarization through the vessel wall. In some arteries, eicosanoids and K+ ions may themselves initiate a conducted endothelial hyperpolarization, thus suggesting that electrotonic signalling may represent a general mechanism through which the endothelium participates in the regulation of vascular tone.
Read more about this topic: Endothelium-derived Hyperpolarizing Factor
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