Activation of BKCa channels by nitric oxide prevents coronary artery endothelial dysfunction in ouabain-induced hypertensive rats.
OBJECTIVE
Chronic-ouabain administration to rats induces hypertension and increases the endothelial modulation of vasoconstrictor responses. The aim of this study was to analyze whether ouabain-treatment affects the mechanisms involved in endothelium-dependent relaxation of coronary arteries.


METHODS
Coronary arteries from control and ouabain-treated rats (approximately 8.0 microg/day, 5 weeks) were used. Vascular reactivity was analyzed by isometric tension recording and membrane currents were measured using the whole-cell configuration of the patch-clamp technique.


RESULTS
In 5-hydroxytryptamine (5-HT) precontracted arteries, acetylcholine (ACh, 1 nmol/l-10 micromol/l) induced a similar relaxant response in coronary arteries from both groups that was abolished by the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (100 micromol/l). However, when arteries were contracted with high KCl (60 mmol/l) or preincubated with the large-conductance Ca2+-activated K+ (BKCa) channels-blocker iberiotoxin (0.1 micromol/l), the relaxation elicited by ACh was more reduced in ouabain-treated than control rats. After iberiotoxin preincubation, the relaxant response of the nitric-oxide donor, DEA-NO (10 nmol/l-100 micromol/l) was significantly inhibited in ouabain-treated coronary arteries but not in control vessels. The soluble guanylyl cyclase activator BAY 41-2272 (10 nmol/l-30 micromol/l) induced relaxant responses that were inhibited by iberiotoxin. In coronary-artery myocytes isolated from ouabain-treated rats DEA-NO (1 micromol/l) markedly increased the amplitude of the iberiotoxin-sensitive current in the whole range of test potentials, compared with nontreated rats.


CONCLUSIONS
Our results indicate that chronic ouabain treatment increases activation of BKCa currents by nitric oxide and this effect might contribute to preserve the endothelial function in coronary arteries in this hypertension model.
Briones
Ana M
AM
Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain.
Padilha
Alessandra S
AS
Cogolludo
Angel L
AL
Alonso
Maria J
MJ
Vassallo
Dalton V
DV
Pérez-Vizcaino
Francisco
F
Salaices
Mercedes
M
D000818:Animals; D003331:Coronary Vessels / Q000503:physiopathology*; D004730:Endothelium, Vascular / Q000503:physiopathology*; D006834:Hydrazines / Q000494:pharmacology; D006973:Hypertension / Q000139:chemically induced / Q000503:physiopathology*; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D008297:Male; D009569:Nitric Oxide / Q000502:physiology*; D010042:Ouabain / Q000633:toxicity*; D015221:Potassium Channels / Q000502:physiology*; D011720:Pyrazoles / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014664:Vasodilation
C423582:3-(4-Amino-5-cyclopropylpyrimidine-2-yl)-1-(2-fluorobenzyl)-1H-pyrazolo(3,4-b)pyridine; D006834:Hydrazines; C494842:Kcnma1 protein, rat; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D015221:Potassium Channels; D011720:Pyrazoles; D011725:Pyridines; D009569:Nitric Oxide; D010042:Ouabain; C084012:1,1-diethyl-2-hydroxy-2-nitrosohydrazine