K+ currents underlying the action of endothelium-derived hyperpolarizing factor in guinea-pig, rat and human blood vessels.
Membrane currents attributed to endothelium-derived hyperpolarizing factor (EDHF) were recorded in short segments of submucosal arterioles of guinea-pigs using single microelectrode voltage clamp. The functional responses of arterioles and human subcutaneous, rat hepatic and guinea-pig coronary arteries were also assessed as changes in membrane potential recorded simultaneously with contractile activity. The current-voltage (I-V) relationship for the conductance due to EDHF displayed outward rectification with little voltage dependence. Components of the current were blocked by charybdotoxin (30-60 nM) and apamin (0.25-0.50 microM), which also blocked hyperpolarization and prevented EDHF-induced relaxation. The EDHF-induced current was insensitive to Ba2+ (20-100 microM) and/or ouabain (1 microM to 1 mM). In human subcutaneous arteries and guinea-pig coronary arteries and submucosal arterioles, the EDHF-induced responses were insensitive to Ba2+ and/or ouabain. Increasing [K+]o to 11-21 mM evoked depolarization under conditions in which EDHF evoked hyperpolarization. Responses to ACh, sympathetic nerve stimulation and action potentials were indistinguishable between dye-labelled smooth muscle and endothelial cells in arterioles. Action potentials in identified endothelial cells were always associated with constriction of the arterioles. 18beta-Glycyrrhetinic acid (30 microM) and carbenoxolone (100 microM) depolarized endothelial cells by 31 +/- 6 mV (n = 7 animals) and 33 +/- 4 mV (n = 5), respectively, inhibited action potentials in smooth muscle and endothelial cells and reduced the ACh-induced hyperpolarization of endothelial cells by 56 and 58 %, respectively. Thus, activation of outwardly rectifying K+ channels underlies the hyperpolarization and relaxation due to EDHF. These channels have properties similar to those of intermediate conductance (IKCa) and small conductance (SKCa) Ca2+-activated K+ channels. Strong electrical coupling between endothelial and smooth muscle cells implies that these two layers function as a single electrical syncytium. The non-specific effects of glycyrrhetinic acid precludes its use as an indicator of the involvement of gap junctions in EDHF-attributed responses. These conclusions are likely to apply to a variety of blood vessels including those of humans.
Department of Physiology, Monash University, Melbourne, Victoria 3800, Australia. h.coleman@med.monash.edu.au
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D000818:Animals; D001158:Arteries / Q000378:metabolism*; D001160:Arterioles / Q000378:metabolism; D001464:Barium / Q000494:pharmacology; D001685:Biological Factors / Q000502:physiology*; D003331:Coronary Vessels / Q000378:metabolism; D004553:Electric Conductivity; D004594:Electrophysiology; D004730:Endothelium, Vascular / Q000502:physiology; D005260:Female; D006034:Glycyrrhetinic Acid / Q000494:pharmacology; D006168:Guinea Pigs; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats
D001685:Biological Factors; D015221:Potassium Channels; C067410:endothelium-dependent hyperpolarization factor; D001464:Barium; D010042:Ouabain; D011189:Potassium Chloride; D006034:Glycyrrhetinic Acid