Role of Ca2+-activated K+ channels on adrenergic responses of human saphenous vein.
BACKGROUND
We studied the participation of K(+) channels on the adrenergic responses in human saphenous veins as well as the intervention of dihydropyridine-sensitive Ca(2+) channels on modulation of adrenergic responses by K(+) channels blockade.


METHODS
Saphenous vein rings were obtained from 40 patients undergoing coronary artery bypass surgery. The vein rings were suspended in organ bath chambers for isometric recording of tension.


RESULTS
Iberiotoxin (10(-7) mol/L), an inhibitor of large conductance Ca(2+)-activated K(+) channels, and charybdotoxin (10(-7) mol/L), an inhibitor of both large and intermediate conductance Ca(2+)-activated K(+) channels, enhanced the contractions elicited by electrical field stimulation and produced a leftward shift of the concentration-response curve to norepinephrine. In contrast, the inhibitor of small conductance Ca(2+)-activated K(+) channels apamin (10(-6) mol/L) did not modify the contractile response to electrical field stimulation or norepinephrine. In the presence of the dihydropyridine Ca(2+)-channel blocker nifedipine (10(-6) mol/L), iberiotoxin and charybdotoxin failed to enhance the contractile responses to electrical field stimulation and norepinephrine.


CONCLUSIONS
The results suggest that large conductance Ca(2+)-activated K(+) channels are activated by stimulation with norepinephrine to counteract the adrenergic-induced contractions of human saphenous vein. Thus, inhibition of these channels increases significantly the contraction, an effect that appears to be mediated by an increase in Ca(2+) entry through L-type voltage-dependent Ca(2+) channels.
Mauricio
Maria D
MD
Department of Physiology, School of Medicine, University of Valencia, Avenida Blasco Ibañez 17, 46010 Valencia, Spain.
Serna
Eva
E
Cortina
Belen
B
Novella
Susana
S
Segarra
Gloria
G
Aldasoro
Martín
M
Martínez-León
Juan B
JB
Vila
Jose M
JM
D002121:Calcium Channel Blockers; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D009129:Muscle Tonus / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D009543:Nifedipine; D009638:Norepinephrine / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology*; D012501:Saphenous Vein / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology*
D002121:Calcium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D009543:Nifedipine; D009638:Norepinephrine