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P M Vanhoutte

Publications and source records attributed to P M Vanhoutte.

At least 19 recordsLinked to original sources
PubMed2006

Intercellular calcium signaling and nitric oxide feedback during constriction of rabbit renal afferent arterioles.

Vasoconstriction and increase in the intracellular calcium concentration ([Ca(2+)](i)) of vascular smooth muscle cells may cause an increase of endothelial cell [Ca(2+)](i), which, in turn, augments nitric oxide (NO) production and inhibits smooth muscle cell contraction. This hypothesis was tested in microperfused rabbit renal afferent arterioles, using fluorescence imaging microscopy with the calcium-sensitive dye fura-2 and the NO-sensitive dye 4-amino-5-methylamino-2',7'-difluorescein. Both dyes were loaded into smooth muscle and endothelium. Depolarization with 100 mmol/l KCl led to a transient vasoconstriction which was converted into a sustained response by N-nitro-l-arginine methyl ester (l-NAME). Depolarization increased smooth muscle cell [Ca(2+)](i) from 162 +/- 15 nmol/l to a peak of 555 +/- 70 nmol/l (n = 7), and this response was inhibited by 80% by the l-type calcium channel blocker calciseptine. After a delay of 10 s, [Ca(2+)](i) increased in endothelial cells immediately adjacent to reactive smooth muscle cells, and this calcium wave spread in a nonregenerative fashion laterally into the endothelial cell layer with a velocity of 1.2 microm/s. Depolarization with 100 mmol/l KCl led to a significant increase in NO production ([NO](i)) which was inhibited by l-NAME (n = 5). Acetylcholine caused a rapid increase in endothelial [Ca(2+)](i), which did not transfer to the smooth muscle cells. l-NAME treatment did not affect changes in smooth muscle [Ca(2+)](i) after depolarization, but it did increase the calcium sensitivity of the contractile apparatus. We conclude that depolarization increases smooth muscle [Ca(2+)](i) which is transferred to the endothelial cells and stimulates NO production which curtails vasoconstriction by reducing the calcium sensitivity of the contractile apparatus.

Acetylcholine↗
PubMed2002

Characterization of an apamin-sensitive small-conductance Ca(2+)-activated K(+) channel in porcine coronary artery endothelium: relevance to EDHF.

1. The apamin-sensitive small-conductance Ca(2+)-activated K(+) channel (SK(Ca)) was characterized in porcine coronary arteries. 2. In intact arteries, 100 nM substance P and 600 microM 1-ethyl-2-benzimidazolinone (1-EBIO) produced endothelial cell hyperpolarizations (27.8 +/- 0.8 mV and 24.1 +/- 1.0 mV, respectively). Charybdotoxin (100 nM) abolished the 1-EBIO response but substance P continued to induce a hyperpolarization (25.8 +/- 0.3 mV). 3. In freshly-isolated endothelial cells, outside-out patch recordings revealed a unitary K(+) conductance of 6.8 +/- 0.04 pS. The open-probability was increased by Ca(2+) and reduced by apamin (100 nM). Substance P activated an outward current under whole-cell perforated-patch conditions and a component of this current (38%) was inhibited by apamin. A second conductance of 2.7 +/- 0.03 pS inhibited by d-tubocurarine was observed infrequently. 4. Messenger RNA encoding the SK2 and SK3, but not the SK1, subunits of SK(Ca) was detected by RT - PCR in samples of endothelium. Western blotting indicated that SK3 protein was abundant in samples of endothelium compared to whole arteries. SK2 protein was present in whole artery nuclear fractions. 5. Immunofluorescent labelling confirmed that SK3 was highly expressed at the plasmalemma of endothelial cells and was not expressed in smooth muscle. SK2 was restricted to the peri-nuclear regions of both endothelial and smooth muscle cells. 6. In conclusion, the porcine coronary artery endothelium expresses an apamin-sensitive SK(Ca) containing the SK3 subunit. These channels are likely to confer all or part of the apamin-sensitive component of the endothelium-derived hyperpolarizing factor (EDHF) response.

Amino Acid Sequence↗
PubMed2002

K+-induced hyperpolarization in rat mesenteric artery: identification, localization and role of Na+/K+-ATPases.

1. Mechanisms underlying K(+)-induced hyperpolarizations in the presence and absence of phenylephrine were investigated in endothelium-denuded rat mesenteric arteries (for all mean values, n=4). 2. Myocyte resting membrane potential (m.p.) was -58.8+/-0.8 mV. Application of 5 mM KCl produced similar hyperpolarizations in the absence (17.6+/-0.7 mV) or presence (15.8+/-1.0 mV) of 500 nM ouabain. In the presence of ouabain +30 microM barium, hyperpolarization to 5 mM KCl was essentially abolished. 3. In the presence of 10 microM phenylephrine (m.p. -33.7+/-3 mV), repolarization to 5 mM KCl did not occur in the presence or absence of 4-aminopyridine but was restored (-26.9+/-1.8 mV) on addition of iberiotoxin (100 nM). Under these conditions the K+-induced repolarization was insensitive to barium (30 microM) but abolished by 500 nM ouabain alone. 4. In the presence of phenylephrine + iberiotoxin the hyperpolarization to 5 mM K(+) was inhibited in the additional presence of 300 nM levcromakalim, an action which was reversed by 10 microM glibenclamide. 5. RT-PCR, Western blotting and immunohistochemical techniques collectively showed the presence of alpha(1)-, alpha(2)- and alpha(3)-subunits of Na(+)/K(+)-ATPase in the myocytes. 6. In K(+)-free solution, re-introduction of K(+) (to 4.6 mM) hyperpolarized myocytes by 20.9+/-0.5 mV, an effect unchanged by 500 nM ouabain but abolished by 500 microM ouabain. 7. We conclude that under basal conditions, Na(+)/K(+)-ATPases containing alpha(2)- and/or alpha(3)-subunits are partially responsible for the observed K(+)-induced effects. The opening of myocyte K(+) channels (by levcromakalim or phenylephrine) creates a 'K(+) cloud' around the cells which fully activates Na(+)/K(+)-ATPase and thereby abolishes further responses to [K(+)](o) elevation.

Animals↗
PubMed2001

Differential effects of prostacyclin and iloprost in the isolated carotid artery of the guinea-pig.

The effects on membrane potential of prostacyclin and iloprost were compared in smooth muscle cells of the guinea pig carotid artery. Both prostacyclin and iloprost induced hyperpolarization of the smooth muscle cells. In the presence of (3R)-3-(4-fluorophenyl-sulfonamido)-1,2,3,4-tetrahydro-9-carbazolepropanoic acid (Bay U3405), an antagonist of TP receptors, the response to iloprost was unaffected while that to prostacyclin was increased. Iloprost-induced hyperpolarizations were abolished by glibenclamide while those to prostacyclin were either not affected, or converted to either depolarization or to rhythmic electrical activity. The latter effects of prostacyclin were abolished by Bay U3405. After removal of the endothelium, iloprost and prostacyclin produced hyperpolarizations similar to those observed in control blood vessels. However, in the presence of glibenclamide, prostacyclin produced only depolarizations inhibited by Bay U3405. These results suggest that iloprost activates IP receptors and K(ATP) channels in smooth muscle. In contrast, prostacyclin produces additional endothelium-dependent and -independent effects via activation of TP receptors.

Animals↗
PubMed2001

Development of an enzyme-linked immunoassay for the quantification of YKL-40 (cartilage gp-39) in guinea pig serum using hen egg yolk antibodies.

An indirect competition immunoassay for the quantification of YKL-40 (cartilage gp-39, Chondrex) in guinea pig serum has been developed using egg yolk antibodies (IgY). The immune response of hens to YKL-40 was verified by immunoblot analyses. Highly specific antibodies were obtained 30 days after the first injection. The ELISA was developed in 96-well microtiter plates with quadruplicate determinations for each point. The assay was based on the ability of YKL-40 present in serum to displace the binding of antibodies to the coated antigen. An inhibition mixture containing standard YKL-40 or guinea pig serum, diluted 1/5, and primary antibodies, diluted 1/5000, was allowed to equilibrate for 2 h at room temperature and dispensed for 16 h at 4 degrees C in wells coated with 1 microg/ml of YKL-40. Detection was achieved by the addition of rabbit anti-chicken antibodies conjugated to peroxidase followed by tetramethylbenzidine. Specificity was assessed by parallelism between a dilution curve of serum and standard YKL-40. The sensitivity of detection was 10 ng/ml. Intra- and interassay coefficients of variation were both 8.7%. The analytical recovery was 101.5+/-5.4% (mean+/-standard deviation (SD), n=9). The YKL-40 concentration in serum from 12 adult guinea pigs was 330+/-216 ng/ml (mean+/-SD) with a lower value of 164 ng/ml and an upper value of 982 ng/ml. In contrast to the rat, a dilution curve of rabbit serum gave parallelism with the guinea pig standard, suggesting recognition of a similar epitope. Possible applications of the assay in the guinea pig include disease models where YKL-40 is overexpressed and could be used as a marker, i.e. osteoarthritis, rheumatoid arthritis, cancer, liver fibrosis, atherosclerosis and more generally, pathologies with increased tissue remodeling.

Adipokines↗
PubMed2001

Further investigations into the endothelium-dependent hyperpolarizing effects of bradykinin and substance P in porcine coronary artery.

In porcine coronary arteries, smooth muscle hyperpolarizations produced by the nitric oxide donor, NOR-1, and the prostacyclin analogue, iloprost, were compared with those induced by substance P and bradykinin and attributed to the endothelium-derived hyperpolarizing factor (EDHF). In the presence of 300 microM L-nitroarginine and 10 microM indomethacin, iloprost-induced hyperpolarizations were partially inhibited by 10 microM glibenclamide whereas those to NOR-1, substance P and bradykinin were unaffected. Hyperpolarizations produced by maximally-effective concentrations of NOR-1 and NS1619 were identical (to -65 mV). They were significantly less than those generated by either substance P or bradykinin (to approximately -80 mV) and were abolished by iberiotoxin 100 nM, a concentration which had essentially no effect on responses to substance P or bradykinin. Incubation of segments of intact arteries for 16 - 22 h in bicarbonate-buffered Krebs solution had little effect on EDHF responses to substance P or bradykinin. In contrast, after incubation for this period of time in HEPES-buffered Tyrode solution or Krebs containing 10 mM HEPES the EDHF response to substance P was abolished and that to bradykinin was markedly reduced. The residual bradykinin-induced hyperpolarization following incubation in Tyrode solution was inhibited by iberiotoxin and by 10 microM 17-octadecynoic acid. We conclude that substance P activates only the EDHF pathway in the presence of nitric oxide synthase and cyclo-oxygenase inhibitors. Incubation in HEPES-buffered Tyrode solution abolishes the EDHF responses to substance P and bradykinin to reveal an additional hyperpolarizing mechanism, associated with the opening of K(+) channels, activated only by bradykinin.

Animals↗
PubMed2001

Suppression of K(+)-induced hyperpolarization by phenylephrine in rat mesenteric artery: relevance to studies of endothelium-derived hyperpolarizing factor.

In intact mesenteric arteries, increasing [K(+)]o by 5 mM hyperpolarized both endothelial and smooth muscle cells. Subsequent exposure to 10 microM phenylephrine depolarized both cell types which were then repolarized by a 5 mM increase in [K(+)]o. In endothelium-denuded vessels, increasing [K(+)]o by 5 mM hyperpolarized the smooth muscle but K(+) had no effect after depolarization by 10 microM phenylephrine. On subsequent exposure to iberiotoxin plus 4-aminopyridine, the repolarizing action of 5 mM K(+) was restored. In endothelium-intact vessels exposed to phenylephrine, pretreatment with a gap junction inhibitor (gap 27) reduced K(+)-mediated smooth muscle repolarization without affecting the endothelial cell response. It is concluded that phenylephrine-induced efflux of K(+) via smooth muscle K(+) channels produces a local increase in [K(+)]o which impairs repolarization to added K(+). Thus, studies involving vessels precontracted with agonists which increase [K(+)]o maximize the role of gap junctions and minimize any contribution to the EDHF pathway from endothelium-derived K(+).

4-Aminopyridine↗
PubMed2001

Endothelial adrenoceptors.

alpha2 -Adrenergic agonists cause endothelium-dependent relaxation in a number of isolated blood vessels. This effect is explained by the activation of endothelial alpha 2 -adrenoceptors linked to nitric oxide synthase by G i -coupling proteins. The endothelial response to alpha 2 -adrenergic agonists is blunted considerably after regeneration of the endothelium and in atherosclerotic arteries. The relaxation of isolated arteries caused by beta-adrenergic agonists is reduced by removal of the endothelium and, in most cases, by inhibitors of the l -arginine nitric oxide pathway. Likewise, in the intact animal and in the human forearm the vasodilatation to beta 2 -adrenergic agonists is blunted by inhibitors of nitric oxide synthase. Whether these findings reflect the presence of functional beta-adrenoceptors on the endothelium remains controversial. Several beta-adrenergic blockers cause endothelium-dependent relaxation in vitro or augment the production of nitric oxide in vivo. However, these responses cannot be attributed to interactions with endothelial beta-adrenoceptors.

Adrenergic alpha-Agonists↗
PubMed2001

Melatonin potentiates contractile responses to serotonin in isolated porcine coronary arteries.

The present study was designed to determine the effects of melatonin on coronary vasomotor tone. Porcine coronary arteries were suspended in organ chambers for isometric tension recording. Melatonin (10(-10)-10(-5) M) itself caused neither contraction nor relaxation of the tissues. Serotonin (10(-9)-10(-5) M) caused concentration-dependent contractions of coronary arteries, and in the presence of melatonin (10(-7) M) the maximal response to serotonin was increased in rings with but not without endothelium. In contrast, melatonin had no effect on contractions produced by the thromboxane A(2) analog U-46619 (10(-10)-10(-7) M). The melatonin-receptor antagonist S-20928 (10(-6) M) abolished the potentiating effect of melatonin on serotonin-induced contractions in endothelium-intact coronary arteries, as did treatment with 1H-[1, 2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10(-5) M), methylene blue (10(-5) M), or N(G)-nitro-L-arginine (3 x 10(-5) M). In tissues contracted with U-46619, serotonin caused endothelium-dependent relaxations that were inhibited by melatonin (10(-7) M). Melatonin also inhibited coronary artery relaxation induced by sodium nitroprusside (10(-9)-10(-5) M) but not by isoproterenol (10(-9)-10(-5) M). These results support the hypothesis that melatonin, by inhibiting the action of nitric oxide on coronary vascular smooth muscle, selectively potentiates the vasoconstrictor response to serotonin in coronary arteries with endothelium.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed2001

Regulation of murine airway responsiveness by endothelial nitric oxide synthase.

Nitric oxide (NO) is a potent vasodilator, but it can also modulate contractile responses of the airway smooth muscle. Whether or not endothelial (e) NO synthase (NOS) contributes to the regulation of bronchial tone is unknown at present. Experiments were designed to investigate the isoforms of NOS that are expressed in murine airways and to determine whether or not the endogenous release of NO modulates bronchial tone in wild-type mice and in mice with targeted deletion of eNOS [eNOS(-/-)]. The presence of neuronal NOS (nNOS), inducible NOS (iNOS), and eNOS in murine trachea and lung parenchyma was assessed by RT-PCR, immunoblotting, and immunohistochemistry. Airway resistance was measured in conscious unrestrained mice by means of a whole body plethysmography chamber. The three isoforms of NOS were constitutively present in lungs of wild-type mice, whereas only iNOS and nNOS were present in eNOS(-/-) mice. Labeling of nNOS was localized in submucosal airway nerves but was not consistently detected, and iNOS immunoreactivity was observed in tracheal and bronchiolar epithelial cells, whereas eNOS was expressed in endothelial cells. In wild-type mice, treatment with N-nitro-L-arginine methyl ester, but not with aminoguanidine, potentiated the increase in airway resistance produced by inhalation of methacholine. eNOS(-/-) mice were hyperresponsive to inhaled methacholine and markedly less sensitive to N-nitro-L-arginine methyl ester. These results demonstrate that the three NOS isoforms are expressed constitutively in murine lung and that NO derived from eNOS plays a physiological role in controlling bronchial airway reactivity.

Airway Resistance↗
PubMed2000

An endothelium-derived hyperpolarizing factor distinct from NO and prostacyclin is a major endothelium-dependent vasodilator in resistance vessels of wild-type and endothelial NO synthase knockout mice.

In addition to nitric oxide (NO) and prostacyclin (PGI(2)), the endothelium generates the endothelium-derived hyperpolarizing factor (EDHF). We set out to determine whether an EDHF-like response can be detected in wild-type (WT) and endothelial NO synthase knockout mice (eNOS -/-) mice. Vasodilator responses to endothelium-dependent agonists were determined in vivo and in vitro. In vivo, bradykinin induced a pronounced, dose-dependent decrease in mean arterial pressure (MAP) which did not differ between WT and eNOS -/- mice and was unaffected by treatment with N(omega)-nitro-l-arginine methyl ester and diclofenac. In the saline-perfused hindlimb of WT and eNOS -/- mice, marked N(omega)-nitro-l-arginine (l-NA, 300 micromol/liter)- and diclofenac-insensitive vasodilations in response to both bradykinin and acetylcholine (ACh) were observed, which were more pronounced than the agonist-induced vasodilation in the hindlimb of WT in the absence of l-NA. This endothelium-dependent, NO/PGI(2)-independent vasodilatation was sensitive to KCl (40 mM) and to the combination of apamin and charybdotoxin. Gap junction inhibitors (18alpha-glycyrrhetinic acid, octanol, heptanol) and CB-1 cannabinoid-receptor agonists (Delta(9)-tetrahydrocannabinol, HU210) impaired EDHF-mediated vasodilation, whereas inhibition of cytochrome P450 enzymes, soluble guanylyl cyclase, or adenosine receptors had no effect on EDHF-mediated responses. These results demonstrate that in murine resistance vessels the predominant agonist-induced endothelium-dependent vasodilation in vivo and in vitro is not mediated by NO, PGI(2), or a cytochrome P450 metabolite, but by an EDHF-like principle that requires functional gap junctions.

Acetylcholine↗
PubMed2000

Say NO to ET.

The endothelial cells release both relaxing [nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF), prostacyclin] and contracting factors [endoperoxides, thromboxane A(2), superoxide anions, endothelin-1 (ET)]. The production of ET is inhibited by NO. The latter also strongly opposes the direct effects of the former on vascular smooth muscle. With aging and vascular disease, the production of enothelial NO declines, and thus ET can be released, act and contribute to the symptoms.

Animals↗
PubMed2000

3-Morpholinosydnonimine (SIN-1) and K(+) channels in smooth muscle cells of the rabbit and guinea pig carotid arteries.

Experiments were designed to determine the subtype of K(+) channels activated by the nitrovasodilator 3-morpholinosydnonimine (SIN-1) in smooth muscle cells of the rabbit and guinea pig carotid arteries. Membrane potential was recorded in isolated segments with intracellular microelectrode and K(+) currents in freshly dissociated smooth muscle cells, with the patch-clamp technique. In the guinea pig carotid artery, SIN-1 caused a glibenclamide-sensitive hyperpolarization. The nitrovasodilator did not affect the whole-cell K(+) current, but activated a glibenclamide-sensitive K(+) current. In the rabbit carotid artery, SIN-1 induced only an iberiotoxin-sensitive repolarization in phenylephrine-depolarized tissue and in isolated cells, enhanced the activity of an iberiotoxin-sensitive K(+) current. These findings demonstrate that the population of K(+) channels activated by nitric oxide (NO) is species-dependent and support the conclusion that, in the guinea pig carotid artery, in contrast to the rabbit carotid artery, the release of NO cannot account for the responses attributed to endothelium-derived hyperpolarizing factor (EDHF).

Animals↗
PubMed2000

Phenotypic and functional changes in regenerated porcine coronary endothelial cells : increased uptake of modified LDL and reduced production of NO.

Porcine coronary arteries with regenerated endothelium exhibit impaired endothelium-dependent relaxations. Experiments were designed to analyze the structural and functional changes occurring in regenerated endothelial cells. Primary cultures from regenerated endothelium contained giant endothelial cells, with an increased number of cells with diameter >14.5 microm, a reduced ability to proliferate, and signs of apoptosis. The uptake of fluorescent acetylated LDL was increased 2-fold in cultures from regenerated endothelium. The increased uptake of acetylated LDL was confirmed ex vivo in injured coronary arteries. In cultures from regenerated endothelium, cGMP production was decreased under basal conditions and during stimulation with serotonin, bradykinin, and A23187. Thus, during regeneration, there is accelerated senescence of endothelial cells accompanied by increased incorporation of modified LDL and reduction of NO production without decrease in endothelial NO synthase expression. These alterations help to explain the altered endothelium-dependent responses 28 days after balloon injury.

Animals↗
PubMed2000

The impaired renal vasodilator response attributed to endothelium-derived hyperpolarizing factor in streptozotocin--induced diabetic rats is restored by 5-methyltetrahydrofolate.

AIMS/HYPOTHESIS: Endothelial dysfunction contributes to the development of diabetic vascular complications. A better understanding of the pathophysiology of endothelial dysfunction in diabetes could lead to new approaches to prevent microvascular disease. METHODS: Endothelium-dependent and endothelium-independent vasodilator responses were investigated in the renal microcirculation of streptozotocin-induced diabetic rats. We measured renal blood flow changes with an electromagnetic flow probe. In addition, the responses of the different segments of the renal microcirculation were evaluated with videomicroscopy using the hydronephrotic kidney technique. Because endothelial cells release different relaxing factors (nitric oxide, prostacyclin and an unidentified endothelium-derived hyperpolarizing factor), responses to acetylcholine were measured before and after treatment with the nitric oxide synthase inhibitor L-NG-nitroarginine methylester HCI (L-NAME) and the cyclooxygenase inhibitor indomethacin. We evaluated with the effect of 5-methyltetrahydrofolate, the active form of folate, on the responses. RESULTS: The L-NAME- and indomethacin-resistant vasodilation to intra-renal acetylcholine was significantly reduced in the diabetic compared with control rats, suggesting impaired endothelium-derived hyperpolarizing factor-mediated vasodilation. The responses to the nitric oxide donor (Z)-1-[-2-(aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-i um-1,2-diolate (DETA-NONOate) and to the K+-channel opener pinacidil were similar in diabetics and controls, indicating intact endothelium-independent vasodilator mechanisms. The contribution of endothelium-derived hyperpolarizing factor to vasodilation induced by acetylcholine was greatest in the smallest arterioles. In diabetic rats, the response to acetylcholine was increasingly impared as vessel size decreased. Defective vasodilation in diabetic kidneys was rapidly normalized by 5-methyltetrahydrofolate. CONCLUSION-INTERPRETATION: Endothelium-derived hyperpolarizing factor-mediated vasodilation is impaired in the renal microcirculation of diabetic rats, in particular in the smallest arteries. Treatment with folate restores the impaired endothelial function in diabetes.

Acetylcholine↗
PubMed2000

Role of endothelial cell hyperpolarization in EDHF-mediated responses in the guinea-pig carotid artery.

1. Experiments were performed to identify the potassium channels involved in the acetylcholine-induced endothelium-dependent hyperpolarization of the guinea-pig internal carotid artery. Smooth muscle and endothelial cell membrane potentials were recorded in isolated arteries with intracellular microelectrodes. Potassium currents were recorded in freshly-dissociated smooth muscle cells using patch clamp techniques. 2. In single myocytes, iberiotoxin (0.1 microM)-, charybdotoxin (0.1 microM)-, apamin (0.5 microM)- and 4-aminopyridine (5 mM)-sensitive potassium currents were identified indicating the presence of large- and small-conductance calcium-sensitive potassium channels (BK(Ca) and SK(Ca)) as well as voltage-dependent potassium channels (K(V)). Charybdotoxin and iberiotoxin inhibited the same population of BK(Ca) but a conductance specifically sensitive to the combination of charybdotoxin plus apamin could not be detected. 4-aminopyridine (0. 1 - 25 mM) induced a concentration-dependent inhibition of K(V) without affecting the iberiotoxin- or the apamin-sensitive currents. 3. In isolated arteries, both the endothelium-dependent hyperpolarization of smooth muscle and the hyperpolarization of endothelial cells induced by acetylcholine or by substance P were inhibited by 5 mM 4-aminopyridine. 4. These results indicate that in the vascular smooth muscle cells of the guinea-pig carotid artery, a conductance specifically sensitive to the combination of charybdotoxin plus apamin could not be detected, comforting the hypothesis that the combination of these two toxins should act on the endothelial cells. Furthermore, the inhibition by 4-aminopyridine of both smooth muscle and endothelial hyperpolarizations, suggests that in order to observe an endothelium-dependent hyperpolarization of the vascular smooth muscle cells, the activation of endothelial potassium channels is likely to be required.

4-Aminopyridine↗