Potassium and potassium clouds in endothelium-dependent hyperpolarizations.
A small increase in extracellular K(+) acts as a local, physiological regulator of blood flow to certain vascular beds. The K(+) derives from active tissues such as contracting skeletal muscle and brain and increases blood supply to these organs by the activation of Na(+)/K(+)-ATPases and/or inwardly-rectifying K(+) channels on the vascular myocytes. K(+) liberated from the vascular endothelium also acts as an endothelium-derived hyperpolarizing and relaxing factor within blood vessels. The K(+) effluxes from endothelial cell intermediate- and small-conductance, Ca(2+)-sensitive K(+) channels which open in response to stretch and local hormones. In many vessels, endothelium-derived hyperpolarizing factor (EDHF) seems identical to the K(+) derived from endothelial cells; it activates Na(+)/K(+)-ATPases (particularly those containing alpha2 and alpha3 subunits) and inward rectifiers (particularly Kir2.1) located on the vascular myocytes. Vasospastic agents generate "potassium clouds" around vascular smooth muscle cells via the efflux of this ion through large conductance, Ca(2+)-sensitive K(+) channels on the myocytes. These potassium clouds can reduce the hyperpolarizing actions of endothelium-derived K(+) by effectively saturating the Na(+)/K(+)-ATPases and inward rectifiers on the muscle cells and they may be of clinical significance in vasospastic conditions.
Edwards
Gillian
G
Division of Physiology, Pharmacology & Toxicology, School of Biological Sciences, G38 Stopford Building, University of Manchester, Manchester M13 9PT, UK.
Weston
Arthur H
AH
D000818:Animals; D001685:Biological Factors / Q000502:physiology*; D004730:Endothelium, Vascular / Q000502:physiology*; D006801:Humans; D008564:Membrane Potentials / Q000502:physiology; D011188:Potassium / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology
D001685:Biological Factors; D015221:Potassium Channels; C067410:endothelium-dependent hyperpolarization factor; D011188:Potassium