Role of endothelium-derived vasodilators and K(+) channels in ischemic vasodilation of guinea-pig choroidal arterioles.
OBJECTIVE
To assess the roles of endothelium-derived vasodilators and K(+) channels on metabolic ischemia-induced vasodilation from diameter changes in choroidal arterioles of the guinea-pig.


METHODS
The choroid was isolated from the guinea-pig eye-ball, pinned flat on a silicone rubber plate, and superfused with oxygenated warmed (35 degrees C) Krebs solution. Diameters of choroidal arterioles were measured using video microscopy and a computer program for analysis. Vasodilatory effects were examined after the choroid was exposed to glucose-free/NaCN solutions for 10 minutes. The effects of Nomega-nitro-L-arginine (nitroarginine), indomethacin, and K(+)<?Pub Caret> channel inhibitors (glibenclamide [Glib] and charybdotoxin [ChTX]) on ischemic vasodilation were assessed.


RESULTS
Reversible vasodilation was observed when the choroid was exposed to glucose-free/NaCN (10(-3) M) solutions. Nitroarginine (10( -4) M), Glib (2x10(-5) M) and ChTX (10(-7) M) significantly inhibited glucose-free/NaCN (10(-3) M)-induced vasodilation by 47%, 62%, and 24%, respectively. No significant inhibitory effect was observed with indomethacin (10(-5) M). Simultaneous application of Glib and ChTX reduced vasodilation by 77%. When Glib and ChTX were added together to nitroarginine, dilation was reduced by 86%. With high K(+) ([K]o = 47.2 mM) Krebs solution, ischemia caused a slight vasodilation (11%), which was significantly inhibited by nitroarginine.


CONCLUSIONS
In guinea-pig choroidal arterioles, glucose-free/ NaCN-induced ischemic vasodilation was mainly mediated by NO and K(ATP) channels. A part of NO-mediated vasodilation was induced independent of the opening of K(+) channels.
Tamai
K
K
Nagoya City University Medical School Department of Ophthalmology Japan Nagoya, 467,
Suzuki
H
H
Shirai
S
S
Ogura
Y
Y
D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000378:metabolism; D018999:Charybdotoxin / Q000494:pharmacology; D002829:Choroid / Q000098:blood supply*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D006168:Guinea Pigs; D007511:Ischemia / Q000503:physiopathology*; D008297:Male; D019335:Nitroarginine / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism*; D012966:Sodium Cyanide / Q000494:pharmacology; D014664:Vasodilation; D014665:Vasodilator Agents / Q000378:metabolism*
D004791:Enzyme Inhibitors; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D014665:Vasodilator Agents; D018999:Charybdotoxin; D019335:Nitroarginine; D005947:Glucose; D012966:Sodium Cyanide; D005905:Glyburide