K+-induced hyperpolarization in rat mesenteric artery: identification, localization and role of Na+/K+-ATPases.
1. Mechanisms underlying K(+)-induced hyperpolarizations in the presence and absence of phenylephrine were investigated in endothelium-denuded rat mesenteric arteries (for all mean values, n=4). 2. Myocyte resting membrane potential (m.p.) was -58.8+/-0.8 mV. Application of 5 mM KCl produced similar hyperpolarizations in the absence (17.6+/-0.7 mV) or presence (15.8+/-1.0 mV) of 500 nM ouabain. In the presence of ouabain +30 microM barium, hyperpolarization to 5 mM KCl was essentially abolished. 3. In the presence of 10 microM phenylephrine (m.p. -33.7+/-3 mV), repolarization to 5 mM KCl did not occur in the presence or absence of 4-aminopyridine but was restored (-26.9+/-1.8 mV) on addition of iberiotoxin (100 nM). Under these conditions the K+-induced repolarization was insensitive to barium (30 microM) but abolished by 500 nM ouabain alone. 4. In the presence of phenylephrine + iberiotoxin the hyperpolarization to 5 mM K(+) was inhibited in the additional presence of 300 nM levcromakalim, an action which was reversed by 10 microM glibenclamide. 5. RT-PCR, Western blotting and immunohistochemical techniques collectively showed the presence of alpha(1)-, alpha(2)- and alpha(3)-subunits of Na(+)/K(+)-ATPase in the myocytes. 6. In K(+)-free solution, re-introduction of K(+) (to 4.6 mM) hyperpolarized myocytes by 20.9+/-0.5 mV, an effect unchanged by 500 nM ouabain but abolished by 500 microM ouabain. 7. We conclude that under basal conditions, Na(+)/K(+)-ATPases containing alpha(2)- and/or alpha(3)-subunits are partially responsible for the observed K(+)-induced effects. The opening of myocyte K(+) channels (by levcromakalim or phenylephrine) creates a 'K(+) cloud' around the cells which fully activates Na(+)/K(+)-ATPase and thereby abolishes further responses to [K(+)](o) elevation.
School of Biological Sciences, University of Manchester, Manchester.
A H
AH
Weston
G R
GR
Richards
M P
MP
Burnham
M
M
Félétou
P M
PM
Vanhoutte
G
G
Edwards
D000818:Animals; D015153:Blotting, Western; D004730:Endothelium, Vascular / Q000502:physiology; D005455:Fluorescent Antibody Technique; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D008839:Microelectrodes; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D010656:Phenylephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D020033:Protein Isoforms; D021122:Protein Subunits; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D020033:Protein Isoforms; D021122:Protein Subunits; D014662:Vasoconstrictor Agents; D010656:Phenylephrine; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium