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The present study was designed to examine whether in the human artery, synthetic peroxisome proliferator-activated receptor (PPAR)-gamma agonists restore vasorelaxation as well as hyperpolarization via ATP-sensitive K+ channels impaired by the high concentration of D-glucose and whether the restoration may be mediated by the antioxidant capacity of these agents. The isometric force and membrane potential of human omental arteries without endothelium were recorded. The production rate of superoxide was evaluated using a superoxide-generating system with xanthine-xanthine oxidase in the absence of smooth muscle cells. Glibenclamide abolished vasorelaxation and hyperpolarization in response to levcromakalim. Addition of D-glucose (20 mM) but not L-glucose (20 mM) reduced this vasorelaxation and hyperpolarization. Synthetic PPAR-gamma agonists (troglitazone and rosiglitazone) and/or an inhibitor of superoxide generation (4,5-dihydroxy-1,3-benzene-disulfonic acid, Tiron), but not a PPAR-alpha agonist (fenofibrate), restored vasorelaxation and hyperpolarization in response to levcromakalim in arteries treated with D-glucose. Troglitazone and rosiglitazone, but not fenofibrate, decreased the production rate of superoxide without affecting uric acid generation. These findings suggest that synthetic PPAR-gamma agonists recover the function of ATP-sensitive K+ channels reduced by the high concentration of glucose in human vascular smooth muscle cells and that the effect of these agonists may be mediated in part by their antioxidant capacity.

Objective: The present study was designed to examine in the human omental artery whether high concentrations of D-glucose inhibit the activity of ATP-sensitive K+ channels in the vascular smooth muscle and whether this inhibitory effect is mediated by the production of superoxide., Methods and Results: Human omental arteries without endothelium were suspended for isometric force recording. Changes in membrane potentials were recorded and production of superoxide was evaluated. Glibenclamide abolished vasorelaxation and hyperpolarization in response to levcromakalim. D-glucose (10 to 20 mmol/L) but not l-glucose (20 mmol/L) reduced these vasorelaxation and hyperpolarization. Tiron and diphenyleneiodonium, but not catalase, restored vasorelaxation and hyperpolarization in response to levcromakalim in arteries treated with D-glucose. Calphostin C and Gö6976 simultaneously recovered these vasorelaxation and hyperpolarization in arteries treated with D-glucose. Phorbol 12-myristate 13 acetate (PMA) inhibited the vasorelaxation and hyperpolarization, which are recovered by calphostin C as well as Gö6976. D-glucose and PMA, but not l-glucose, significantly increased superoxide production from the arteries, whereas such increased production was reversed by Tiron., Conclusions: These results suggest that in the human visceral artery, acute hyperglycemia modulates vasodilation mediated by ATP-sensitive K+ channels via the production of superoxide possibly mediated by the activation of protein kinase C.

Background: Carbon dioxide is an important vasodilator of cerebral blood vessels. Cerebral vasodilation mediated by adenosine triphosphate (ATP)-sensitive K+ channels has not been demonstrated in precapillary microvessel levels. Therefore, the current study was designed to examine whether ATP-sensitive K+ channels play a role in vasodilation induced by mild hypercapnia in precapillary arterioles of the rat cerebral cortex., Methods: Brain slices from rat cerebral cortex were prepared and superfused with artificial cerebrospinal fluid, including normal (Pco2 = 40 mmHg; pH = 7.4), hypercapnic (Pco2 = 50 mmHg; pH = 7.3), and hypercapnic normal pH (Pco2 = 50 mmHg; pH = 7.4) solutions. The ID of a cerebral parenchymal arteriole (5-9.5 microm) was monitored using computerized videomicroscopy., Results: During contraction to prostaglandin F2alpha (5 x 10(-7) m), hypercapnia, but not hypercapnia under normal pH, induced marked vasodilation, which was completely abolished by the selective ATP-sensitive K+ channel antagonist glibenclamide (5 x 10(-6) m). However, the selective Ca2+-dependent K+ channel antagonist iberiotoxin (10(-7) m) as well as the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (10(-4) m) did not alter vasodilation. A selective ATP-sensitive K+ channel opener, levcromakalim (3 x 10(-8) to 3 x 10(-7) m), induced vasodilation, whereas this vasodilation was abolished by glibenclamide., Conclusion: These results suggest that in parenchymal microvessels of the rat cerebral cortex, decreased pH corresponding with hypercapnia, but not hypercapnia itself, contributes to cerebral vasodilation produced by carbon dioxide and that ATP-sensitive K+ channels play a major role in vasodilator responses produced by mild hypercapnia.

Unlabelled: Hypoxia induces vasodilation, partly via the activation of K(+) channels. Lidocaine impairs vasorelaxation mediated by a K(+) channel opener, suggesting that this antiarrhythmic drug may inhibit hypoxia-induced vasodilation mediated by K(+) channels. We designed the current study to determine whether, in the carotid artery, K(+) channels contribute to vasorelaxation in response to hypoxia and whether lidocaine modulates vasorelaxation induced by K(+) channels via pathophysiological and pharmacological stimuli. Rings of rat common carotid artery without endothelium were suspended for isometric force recording. During contraction to phenylephrine, hypoxia-induced vasorelaxation or concentration-response to an adenosine triphosphate-sensitive K(+) channel opener was obtained changing control gas to hypoxic gas and the cumulative addition of levcromakalim, respectively. Hypoxia-induced vasorelaxation was significantly reduced by glibenclamide (5 micro M) but not by iberiotoxin (0.1 micro M), apamin (0.1 micro M), BaCl(2) (10 micro M), or 4-aminopyridine (1 mM). Levcromakalim-induced vasorelaxation was completely abolished by glibenclamide. Lidocaine (10-100 micro M) concentration-dependently inhibited this vasodilation, whereas it did not affect hypoxia-induced vasodilation. These results suggest that adenosine triphosphate-sensitive K(+) channels play a role in hypoxia-induced vasodilation in the rat carotid artery and that lidocaine differentially modulates vasodilation via these channels activated by pathophysiological and pharmacological stimuli., Implications: In rat carotid artery, levcromakalim produced vasorelaxation mediated by adenosine triphosphate (ATP)-sensitive K(+) channels, whereas hypoxia induced it partly via these channels. Lidocaine inhibited vasorelaxation induced by an ATP-sensitive K(+) channel opener but not by hypoxia, indicating the differential mechanisms of modulatory effects of this antiarrhythmic drug on vasodilation via ATP-sensitive K(+) channels activated by pathophysiological and pharmacological stimuli.

Unlabelled: The modification of vasodilation through adenosine triphosphate (ATP)-sensitive K(+) channels induced by antiarrhythmic drugs has not been studied in chronic hypertension. We designed the present study to examine whether mexiletine modulates vasorelaxation via these channels in hypertensive rat aortas. Normotensive and hypertensive rat aortas without endothelium were suspended for isometric force recording. Mexiletine (3 x 10(-5) M) increased vasorelaxation induced by levcromakalim (10(-8)-10(-5) M) in normotensive, but not hypertensive, rat aortas. Mexiletine (10(-5) to 3 x 10(-5) M) also augmented vasorelaxation to sodium nitroprusside (10(-10)-10(-5) M) only in normotensive rat aortas, whereas mexiletine (3 x 10(-5) M) did not affect this vasodilation in aortas treated with an ATP-sensitive K(+) channel antagonist glibenclamide (10(-5) M). A nitric oxide scavenger (carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide; 10(-3) M) abolished augmented vasorelaxation to sodium nitroprusside induced by mexiletine (3 x 10(-5) M) in normotensive rat aortas, whereas a soluble guanylate cyclase inhibitor (1H-[1,2,4]oxadiazolo [4,3,-a]quinoxaline-1-one; 10(-5) M) failed to alter this augmentation of vasorelaxation. These results suggest that mexiletine induces augmentation of vasodilation via ATP-sensitive K(+) channels activated by the opener as well as a nitric oxide donor only in normotensive rat aortas. The vasodilator effects of mexiletine are partly caused by the soluble guanylate cyclase-independent action of nitric oxide on these channels., Implications: Mexiletine induces augmentation of vasodilation mediated by adenosine triphosphate (ATP)-sensitive K(+) channels activated by the opener as well as a nitric oxide donor in normotensive, but not hypertensive, rat aortas, partly by the soluble guanylate cyclase-independent action of nitric oxide on ATP-sensitive K(+) channels of vascular smooth muscle cells.

Background: The effect of ketamine on vasodilation mediated by adenosine triphosphate (ATP)-sensitive K(+) channels has not been studied. The present study was designed to determine whether ketamine might stereoselectively affect vasorelaxation induced by an ATP-sensitive K(+) channel opener in the isolated rat aorta., Methods: Rings of the rat aorta with or without endothelium were suspended for isometric force recording. During contraction to phenylephrine (3 x 10(-7) M), vasorelaxation in response to an ATP-sensitive K(+) channel opener levcromakalim (10(-8) to 10(-5) M) or a nitric oxide donor sodium nitroprusside (10(-10) to 10(-5) M) was obtained. Glibenclamide (10(-5) M), S(+) ketamine (10(-4) M), or ketamine racemate (10(-5) to 10(-4) M) was applied 15 min before addition of phenylephrine., Results: Vasorelaxation induced by levcromakalim was completely abolished by an ATP-sensitive K(+) channel antagonist glibenclamide (10(-5) M) in the aorta with or without endothelium. Ketamine racemate (3 x 10(-5) to 10(-4) M) significantly inhibited this vasorelaxation in a concentration-dependent fashion, whereas S(+) ketamine did not affect the relaxation. However, the highest concentration of ketamine racemate and S(+) ketamine used in the present study did not alter vasorelaxation in response to sodium nitroprusside in the aorta without endothelium., Conclusion: In the isolated rat aorta, clinically relevant concentrations of ketamine racemate can inhibit relaxation induced by an ATP-sensitive K(+) channel opener, whereas S(+) ketamine did not produce any inhibitory effect on this vasorelaxation. These results suggest that ketamine stereoselectively alters vasodilation ATP-sensitive K(+) channels in the conduit artery.

Unlabelled: Studies in cardiac myocytes have shown that cibenzoline reduces adenosine triphosphate (ATP)-sensitive K(+) currents, suggesting that this class Ia antiarrhythmic drug may modify the activity of ATP-sensitive K(+) channels in these preparations. The effects of class Ia antiarrhythmic drugs on vasodilation mediated by ion channels have not been studied. Therefore, we designed this study to examine whether cibenzoline may produce changes in vasorelaxation in response to a selective ATP-sensitive K(+) channel opener, levcromakalim, in the isolated rat carotid artery. Rings of rat carotid arteries without endothelium were suspended for isometric force recording. Concentration-response curves were obtained in a cumulative fashion. During submaximal contraction to phenylephrine (3 x 10(-7) M), vasorelaxation in response to levcromakalim (10(-8) to 10(-5) M) or 1-hydroxy-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl-1-triazene (NOC-7; 10(-10) to 10(-5) M) was obtained. During contraction to phenylephrine, levcromakalim induced concentration-dependent vasorelaxation. A selective ATP-sensitive K(+) channel antagonist, glibenclamide (5 x 10(-6) M), completely abolished vasorelaxation in response to levcromakalim, whereas a selective Ca(2+)-dependent K(+) channel antagonist, iberiotoxin (5 x 10(-8) M), did not affect the relaxation. Cibenzoline (10(-6) to 10(-5) M) significantly reduced vasorelaxation to levcromakalim in a concentration-dependent fashion. In contrast, cibenzoline (10(-5) M) did not alter vasorelaxation to a nitric oxide donor, NOC-7. These results suggest that from the clinically relevant concentrations, a novel class Ia antiarrhythmic drug, cibenzoline, impairs carotid vasodilation mediated by ATP-sensitive K(+) channels., Implications: In isolated rat carotid artery, cibenzoline (10(-6) to 10(-5) M) reduced vasorelaxation to levcromakalim in a concentration-dependent fashion. These results suggest that from the clinically relevant concentrations, a novel class Ia antiarrhythmic drug, cibenzoline, impairs carotid vasodilation mediated by adenosine triphosphate-sensitive K(+) channels.

Background: The previous study by the authors showed that the class Ib antiarrhythmic drug lidocaine impairs but mexiletine augments vasorelaxation mediated by adenosine triphosphate-sensitive K+ channels. Lidocaine and mexiletine have different values of the negative logarithm of the drug-proton dissociation constant, indicating that the ion channel-blocking effects of these drugs under different pH levels may vary. However, the role of pH in the effects of lidocaine and mexiletine on vasodilation mediated by K+ channels has not been studied. Therefore, the current study was designed to examine whether the inhibition and augmentation of vasorelaxation in response to an adenosine triphosphate-sensitive K+ channel opener, levcromakalim, by the clinically relevant concentrations of lidocaine or mexiletine are modified by mild alkalinization or acidification in the isolated rat aorta., Methods: Rings of the rat aorta without endothelium were suspended for isometric force recording. Three types of modified Krebs-Ringer solutions (pH 7.2, 7.4, and 7.6) were prepared by changing the composition of NaCl and NaHCO3. During contractions in response to phenylephrine (3 x 10(-7) M), relaxations in response to levcromakalim (10(-8) to 10(-5) M) were obtained. Lidocaine (10(-5) to 10(-4) M), mexiletine (10(-5) to 10(-4) M), or glibenclamide (10(-5) M) was applied 15 min before addition of phenylephrine., Results: Relaxations in response to levcromakalim, which are abolished by the selective adenosine triphosphate-sensitive K+ channel antagonist glibenclamide (10(-5) M), were not different among the three pH groups. In the normal Krebs-Ringer solution of pH 7.4, lidocaine significantly reduced these relaxations in a concentration-dependent fashion. Alkalinization of pH 7.6 augmented the inhibitory effect of lidocaine on these relaxations, whereas acidification of pH 7.2 substantially abolished this effect. In contrast, mexiletine pH independently augmented relaxations in response to levcromakalim. Glibenclamide (10(-5) M) abolished these relaxations in arteries treated with mexiletine (10(-4) M) in any pH group., Conclusions: These results suggest that even under conditions of such mild alkalosis or acidosis, vasorelaxation via adenosine triphosphate-sensitive K+ channels is dependent on pH in the presence of clinically relevant concentrations of lidocaine but not mexiletine.

Hydrogen peroxide and peroxynitrite induce relaxations via ATP-sensitive K+ channels, indicating that oxygen-derived free radicals may activate these channels. Levels of free radicals are increased throughout the arterial wall in animal models of atherosclerosis, and therefore, vasorelaxation via ATP-sensitive K+ channels may be augmented in chronic hypertension. The present study was designed to determine whether relaxations to an ATP-sensitive K+ channel opener, levcromakalim, are increased in the aorta from spontaneously hypertensive rats (SHR) and whether free radical scavengers reduce these relaxations. Rings of aortas without endothelium taken from age-matched Wistar-Kyoto rats (WKY) and SHR were suspended for isometric force recording. Relaxations to levcromakalim (10(-8) to 10(-5) M), which are abolished by glibenclamide (10(-5) M), were augmented in the aorta from SHR, compared to those in the aorta from WKY. In the aorta from SHR, catalase (1200 U/ml), but neither superoxide dismutase (150 U/ml) nor deferoxamine (10(-4) M), reduced relaxations to levcromakalim, whereas in the aorta from WKY, the free radical scavengers did not affect these relaxations. These results suggest that in chronic hypertension, vasorelaxation to an ATP-sensitive K+ channel opener is augmented and that hydrogen peroxide produced in smooth muscle cells may partly contribute to these relaxations.