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K+ is an endothelium-derived hyperpolarizing factor in rat arteries
G Edwards1, K A Dora, M J Gardener
1Division of Physiology, Pharmacology and Toxicology, School of Biological Sciences, University of Manchester, UK.
Nature
|December 2, 1998
Summary
Endothelium-derived hyperpolarizing factor (EDHF) activity in arteries is due to potassium (K+) efflux through specific channels. This K+ release regulates smooth muscle relaxation and blood flow by affecting ion channels and pumps.
Area of Science:
- Vascular Biology
- Physiology
- Ion Channel Function
Background:
- Arterial smooth muscle relaxation involves an unidentified endothelium-derived hyperpolarizing factor (EDHF), distinct from prostacyclin and nitric oxide.
- Muscarinic agonists like acetylcholine trigger EDHF release in arteries.
Purpose of the Study:
- To identify the molecular nature of EDHF.
- To elucidate the mechanisms by which EDHF induces smooth muscle hyperpolarization and arterial relaxation.
Main Methods:
- Pharmacological inhibition using ouabain (Na+/K+ ATPase blocker) and Ba2+ (inwardly rectifying K+ channel blocker).
- Mimicking EDHF effects with controlled increases in extracellular K+ concentration.
- Investigating the role of charybdotoxin and apamin (K+ channel blockers) on endothelial cell and smooth muscle responses.
- Measuring endothelial cell hyperpolarization and myoendothelial space K+ concentration changes.
Main Results:
- EDHF-induced hyperpolarization and relaxation were inhibited by ouabain plus Ba2+.
- Elevated extracellular K+ mimicked EDHF effects in a manner sensitive to ouabain and Ba2+.
- Acetylcholine-induced endothelial hyperpolarization and increased myoendothelial K+ were abolished by charybdotoxin plus apamin.
- EDHF-induced smooth muscle hyperpolarization was also blocked by these toxins, but direct K+ addition was not.
Conclusions:
- EDHF is identified as potassium (K+) effluxing from endothelial cells via charybdotoxin- and apamin-sensitive K+ channels.
- Increased myoendothelial K+ concentration leads to smooth muscle hyperpolarization and relaxation through Ba2+-sensitive K+ channels and Na+/K+ ATPase.
- Fluctuations in vascular K+ levels are critical regulators of mammalian blood pressure and flow.