NO-mediated MaxiK(Ca) channel activation produces relaxation of guinea pig aorta independently of voltage-dependent L-type Ca(2+) channels.
The role of L-type Ca(2+) channels in the relaxation to nitric oxide (NO)-mediated MaxiK(Ca) channel activation was examined in guinea pig aorta. Acetylcholine (ACh) produced an endothelium-dependent relaxation of guinea pig aorta precontracted with noradrenaline (NA), which was abolished by an NO synthase inhibitor, N(G)-nitro-L-arginine (L-NNA). Both endothelium-dependent relaxation by ACh and endothelium-independent relaxation by an NO donor, (+/-)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide (NOR3), were strongly suppressed by a soluble guanylate cyclase (sGC) inhibitor, 1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1-one (ODQ), suggesting that increased intracellular cGMP plays the key role in both responses. ACh- and NOR3-induced relaxations were significantly suppressed by iberiotoxin (IbTX), a selective blocker of MaxiK(Ca) channels. ACh- and NOR3-induced relaxations were greatly attenuated when arteries were precontracted with high KCl instead of NA, supporting the idea that K(+) channel activation mediates the relaxant responses. (6) NOR3-induced relaxations were not affected by a L-type Ca(2+) channel blocker, diltiazem. Furthermore, endothelium-independent relaxation by a K(ATP) channel opener, (+)-7,8-dihydro-6, 6-dimethyl-7-hydroxy-8-(2-oxo-1-piperidinyl)-6H-pyrano[2,3-f] benz-2,1, 3-oxadiazole (NIP-121) was not affected by diltiazem and nicardipine. These findings suggest that blockade of L-type Ca(2+) channels is not a major mechanism responsible for the vascular relaxation due to NO-mediated MaxiK(Ca) channel activation in guinea pig aorta.
Tanaka
Y
Y
Department of Pharmacology, Toho University School of Pharmaceutical Sciences, 2-2-1 Miyama, Chiba 274-8510, Funabashi, Japan. yotanaka@phar.toho-u.ac.jp
Igarashi
T
T
Kaneko
H
H
Yamaki
F
F
Mochizuki
Y
Y
Aida
M
M
Taniguchi
H
H
Tanaka
H
H
Shigenobu
K
K
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology*; D004347:Drug Interactions; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008297:Male; D009569:Nitric Oxide / Q000502:physiology*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009574:Nitro Compounds / Q000494:pharmacology; D019335:Nitroarginine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010069:Oxadiazoles / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism* / Q000502:physiology; D024681:Potassium Channels, Calcium-Activated; D011189:Potassium Chloride / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D051036:Large-Conductance Calcium-Activated Potassium Channels; D020030:Nitric Oxide Donors; D009574:Nitro Compounds; D010069:Oxadiazoles; D010455:Peptides; D010880:Piperidines; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D011810:Quinoxalines; D019335:Nitroarginine; D009569:Nitric Oxide; D011189:Potassium Chloride; C064719:iberiotoxin; C070366:NIP 121; C061872:FK 409; D000109:Acetylcholine; D009638:Norepinephrine