1-Ethyl-2-benzimidazolinone stimulates endothelial K(Ca) channels and nitric oxide formation in rat mesenteric vessels.
Hyperpolarization of most blood vessels occurs by the opening of K(Ca) channels. 1-Ethyl-2-benzimidazolinone (1-EBIO) is a direct activator of K(Ca) channels in epithelial cells and is potentially valuable for studying cellular hyperpolarization. This study reports the effects of 1-EBIO on isolated rat mesenteric beds perfused with normal (4.7 mM), or high (20 or 80 mM) K+ physiological salt solution (PSS) and constricted with an alpha1-adrenoceptor agonist, cirazoline (0.3-1 microM). Arterial perfusion pressures were decreased by 1-EBIO (0.1-30 nmol) in a dose- and endothelium-dependent manner. Infusion of penitrem A (100 nM), a maxi-K+ channel blocker, or apamin (0.5 microM), a small-conductance (SK(Ca)) K+ channel blocker, produced significant increases in cirazoline-mediated tone (mm Hg): 103.3 +/- 8.7 (control) vs. 156.3 +/- 14.3 (penitrem A); or 93.0 +/- 15.8 (control) vs. 114.0 +/- 15.4 (apamin). 1-EBIO relaxations were attenuated by penitrem A, while apamin, dendrotoxin (50 nM; a Kv channel antagonist), or ouabain (100 microM; a sodium pump blocker) failed to alter the responses. I-EBIO-mediated relaxations decreased significantly with increasing extracellular [K+]: relaxations to 30 nmol were 89.3% +/- 3.2% (4.7 mM K+, normal PSS) vs. 59.5% +/- 3.4% and 19.0% +/- 3.9% for 20 and 80 mM K+ PSS, respectively. Nomega-nitro-L-arginine-methyl ester (L-NAME; 100 microM), and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 microM), selective inhibitors of nitric oxide synthase, and nitric oxide-sensitive guanylate cyclase, respectively, abolished 1-EBIO relaxations in vessels perfused with 20 or 80 mM K+ PSS. We conclude that: (1) maxi-K+ and SK(Ca) channels are present in rat mesenteric arterial vessels and actively contribute to vascular tone, (2) vasodilator action of 1-EBIO involves the opening of endothelial maxi-K+ channels and nitric oxide synthesis.
Adeagbo
A S
AS
Department of Physiology, Biophysics and Center for Applied Microcirculatory Research, School of Medicine, Health Sciences Center, University of Louisville, KY 40292, USA. asadea01@gwise.louisville.edu
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology*; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D015220:Calcium Channels; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000187:drug effects / Q000502:physiology; D009599:Nitroprusside / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013152:Splanchnic Circulation / Q000187:drug effects / Q000502:physiology; D014664:Vasodilation / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology
D001562:Benzimidazoles; D002120:Calcium Channel Agonists; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D015221:Potassium Channels; D014665:Vasodilator Agents; D009599:Nitroprusside; D019001:Nitric Oxide Synthase; C102635:1-ethyl-2-benzimidazolinone; D000109:Acetylcholine; D019331:NG-Nitroarginine Methyl Ester