Role of small-conductance Ca2+-dependent K+ channels in in vitro nitric oxide-mediated aortic hyporeactivity to alpha-adrenergic vasoconstriction in rats with cirrhosis.
OBJECTIVE
In vitro studies have shown that cirrhotic aortas are hyporeactive to the contractile effect of vasoconstrictors because upregulated endothelial nitric oxide-synthase (NOS) overproduces nitric oxide (NO). Although stimulation of endothelial small-conductance Ca2+-dependent K+ (SK(Ca)) channels may elicit vasorelaxation in normal arteries, the role of these channels in cirrhosis-induced hyporeactivity is unknown. Thus, the aim of the present study was to investigate the role of endothelial SK(Ca) channels in cirrhosis-induced, NO-mediated, in vitro aortic hyporeactivity to alpha1-adrenergic vasoconstrictors.


METHODS
Isolated thoracic aortas from cirrhotic and normal rats were used. The effects of apamin, a selective SK(Ca) channel blocker, were measured on the vascular reactivity to phenylephrine. In addition, SK(Ca) channel protein expression was studied. The effects of iberiotoxin and charybdotoxin, blockers of other K(Ca) channels, were also studied in cirrhotic aortas.


RESULTS
Apamin suppressed cirrhosis-induced aortic hyporeactivity to phenylephrine in an endothelium-dependent, NOS-inhibitor-sensitive manner. SK(Ca) channel protein was overexpressed in cirrhotic aortic walls. Iberiotoxin abolished cirrhosis-induced aortic hyporeactivity to phenylephrine in an endothelium-dependent but NOS-inhibitor-resistant manner. Charybdotoxin did not induce any significant increase in phenylephrine-elicited contraction.


CONCLUSIONS
In cirrhotic aortas, the overexpression and overactivity of endothelial SK(Ca) channels contributes to in vitro NO-mediated hyporeactivity to the contractile action of alpha1-adrenergic agonists.
Barrière
E
E
Laboratoire d'Hémodynamique Splanchnique et de Biologie Vasculaire, INSERM U-481, Hĵpital Beaujon, Clichy, France.
Tazi
K A
KA
Pessione
F
F
Heller
J
J
Poirel
O
O
Lebrec
D
D
Moreau
R
R
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001011:Aorta / Q000187:drug effects* / Q000502:physiology; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D018999:Charybdotoxin / Q000494:pharmacology; D066298:In Vitro Techniques; D008106:Liver Cirrhosis, Experimental / Q000503:physiopathology*; D008297:Male; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology*; D014661:Vasoconstriction / Q000187:drug effects*
D000316:Adrenergic alpha-Agonists; D015221:Potassium Channels; D018340:Receptors, Adrenergic, alpha-1; D018999:Charybdotoxin; D001030:Apamin; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat; D002118:Calcium