Relaxation by bradykinin in porcine ciliary artery. Role of nitric oxide and K(+)-channels.
OBJECTIVE
To assess the effects of K(+)-channel blockers on bradykinin-induced relaxations in porcine ciliary artery.


METHODS
Vascular isometric forces were measured with a myograph system. Ciliary vascular rings were precontracted with thromboxane A2 analog (U 46619, 10(-7) M) to assess dose-dependent (10(-10)-3 x 10(-6) M) bradykinin-induced relaxation after addition of one of the following: the nitric oxide (NO) synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 10(-4) M) or inactive enantiomer (D-NAME, 10(-4) M); the nonspecific K(+)-channel blocker tetra-ethylammonium (TEA, 10(-2) M); or the ATP-sensitive K(+)-channel blocker glibenclamide (10(-5) M). The effect of TEA on relaxations to the NO donor, sodium nitroprusside (SNP, 10(-10)-10(-4) M) was investigated. The membrane potential of vascular smooth muscle cells (VSMC) was recorded after exposure to bradykinin (2.5 x 10(-7) M).


RESULTS
Endothelium-dependent relaxations to bradykinin (maximal [max], 99% +/- 3%) were strongly inhibited by L-NAME (max, 39% +/- 4%, P < 0.01) and partially by TEA (max, 62% +/- 3%, P < 0.01) or glibenclamide (max, 77% +/- 4%, P < 0.01). Administration of glibenclamide plus L-NAME further suppressed bradykinin-induced relaxation (max, 23% +/- 6%; P < 0.01), whereas TEA and L-NAME (max, 6% +/- 2%; P < 0.01) abolished the relaxation. SNP relaxations were unaffected by TEA. Bradykinin had no effect on the membrane potential of VSMC.


CONCLUSIONS
In porcine ciliary artery, the endothelium-dependent relaxations to bradykinin are primarily mediated by NO and involve K(+)-channels. As only relaxations to bradykinin, but not those mediated by SNP, were inhibited by TEA, this implies that K(+)-channel blockers most likely affect the bradykinin-evoked NO production or release by the endothelium.
Zhu
P
P
Laboratory of Ocular Pharmacology and Physiology, University Eye Hospital, Basel, Switzerland.
Bény
J L
JL
Flammer
J
J
Lüscher
T F
TF
Haefliger
I O
IO
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000818:Animals; D001158:Arteries; D001920:Bradykinin / Q000494:pharmacology*; D002924:Ciliary Body / Q000098:blood supply*; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D013552:Swine; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013928:Thromboxane A2 / Q000031:analogs & derivatives / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D004791:Enzyme Inhibitors; D015221:Potassium Channels; D011450:Prostaglandin Endoperoxides, Synthetic; D013757:Tetraethylammonium Compounds; D014662:Vasoconstrictor Agents; D009569:Nitric Oxide; D013928:Thromboxane A2; D019789:Tetraethylammonium; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D001920:Bradykinin; D005905:Glyburide; D019331:NG-Nitroarginine Methyl Ester