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A H Weston

Publications and source records attributed to A H Weston.

At least 19 recordsLinked to original sources
PubMed2004

Functional evidence of a role for two-pore domain potassium channels in rat mesenteric and pulmonary arteries.

1. Experiments were performed to elucidate the mechanism by which alterations of extracellular pH (pH(o)) change membrane potential (E(M)) in rat mesenteric and pulmonary arteries. 2. Changing pH(o) from 7.4 to 6.4 or 8.4 produced a depolarisation or hyperpolarisation, respectively, in mesenteric and pulmonary arteries. Anandamide (10 microm) or bupivacaine (100 microm) reversed the hyperpolarisation associated with alkaline pH(o), shifting the E(M) of both vessels to levels comparable to that at pH 6.4. In pulmonary arteries, clofilium (100 microm) caused a significant reversal of hyperpolarisation seen at pH 8.4 but was without effect at pH 7.4. 3. K(+) channel blockade by 4-aminopyridine (4-AP) (5 mm), tetraethylammonium (TEA) (10 mm), Ba(2+) (30 microm) and glibenclamide (10 microm) depolarised the pulmonary artery. However, shifts in E(M) with changes in pH(o) remained and were sensitive to anandamide (10 microm), bupivacaine (100 microm) or Zn(2+) (200 microm). 4. Anandamide (0.3-60 microm) or bupivacaine (0.3-300 microm) caused a concentration-dependent increase in basal tone in pulmonary arteries. 5. RT-PCR demonstrated the expression of TASK-1, TASK-2, THIK-1, TRAAK, TREK-1, TWIK-1 and TWIK-2 in mesenteric arteries and TASK-1, TASK-2, THIK-1, TREK-2 and TWIK-2 in pulmonary arteries. TASK-1, TASK-2, TREK-1 and TWIK-2 protein was demonstrated in both arteries by immunostaining. 6. These experiments provide evidence for the presence of two-pore domain K(+) channels in rat mesenteric and pulmonary arteries. Collectively, they strongly suggest that modulation of TASK-1 channels is most likely to have mediated the pH-induced changes in membrane potential observed in these vessels, and that blockade of these channels by anandamide or bupivacaine generates a small increase in pulmonary artery tone.

Animals↗
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

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↗
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

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↗
PubMed2000

Role of gap junctions and EETs in endothelium-dependent hyperpolarization of porcine coronary artery.

1. The effects of endothelium-derived hyperpolarizing factor (EDHF: elicited using substance P or bradykinin) were compared with those of 11,12-EET in pig coronary artery. Smooth muscle cells were usually impaled with microelectrodes through the adventitial surface. 2. Substance P (100 nM) and 11,12-EET (11,12-epoxyeicosatrienoic acid; 3 microM) hyperpolarized endothelial cells in intact arteries. These actions were unaffected by 100 nM iberiotoxin but were abolished by charybdotoxin plus apamin (each 100 nM). 3. Substance P (100 nM) and bradykinin (30 nM) hyperpolarized intact artery smooth muscle; Substance P had no effect after endothelium removal. 11,12-EET hyperpolarized de-endothelialized vessels by 12.6+/-0.3 mV, an effect abolished by 100 nM iberiotoxin. 4. 11,12-EET hyperpolarized intact arteries by 18.6+/-0.8 mV, an action reduced by iberiotoxin, which was ineffective against substance P. Hyperpolarizations to 11, 12-EET and substance P were partially inhibited by 100 nM charybdotoxin and abolished by further addition of 100 nM apamin. 5. 30 microM barium plus 500 nM ouabain depolarized intact artery smooth muscle but responses to substance P and bradykinin were unchanged. 500 microM gap 27 markedly reduced hyperpolarizations to substance P and bradykinin which were abolished in the additional presence of barium plus ouabain. 6. Substance P-induced hyperpolarizations of smooth muscle cells immediately below the internal elastic lamina were unaffected by gap 27, even in the presence of barium plus ouabain. 7. In pig coronary artery, 11,12-EET is not EDHF. Smooth muscle hyperpolarizations attributed to 'EDHF' are initiated by endothelial cell hyperpolarization involving charybdotoxin- (but not iberiotoxin) and apamin-sensitive K(+) channels. This may spread electrotonically via myoendothelial gap junctions but the involvement of an unknown endothelial factor cannot be excluded.

8,11,14-Eicosatrienoic Acid↗
PubMed1999

Further investigation of endothelium-derived hyperpolarizing factor (EDHF) in rat hepatic artery: studies using 1-EBIO and ouabain.

1. The characteristics of endothelium-dependent hyperpolarization in rat hepatic artery have been further investigated in the presence of inhibitors of cyclo-oxygenase and nitric oxide synthase. 2. Using sharp micro-electrodes, the smooth muscle hyperpolarization induced by acetylcholine, KCl or 1-ethyl-2-benzimidazolinone (1-EBIO) in intact hepatic arteries was abolished by 30 micronM barium plus 500 nM ouabain. 3. In vessels without endothelium, the smooth muscle hyperpolarization induced by KCl was not reduced by 30 micronM barium alone. However, in the presence of barium the effects of KCl were partially inhibited by 100 nM ouabain and essentially abolished by 500 nM ouabain. 4. Using sharp micro-electrodes, the hyperpolarization of both the smooth muscle and the endothelium induced by 1-EBIO or by acetylcholine was unaffected by 100 nM iberiotoxin. However, in the presence of 100 nM charybdotoxin, the effects of 1-EBIO were abolished whereas those of acetylcholine were only partially reduced. The hyperpolarization induced by levcromakalim was unaffected by either charybdotoxin or iberiotoxin. 5 Under whole-cell patch-clamp recording conditions, 1-EBIO induced a voltage-insensitive, charybdotoxin-sensitive K+ current in cultured endothelial cells but was without effect on K+ currents in smooth muscle cells isolated from hepatic arteries. 6 It is concluded that the endothelium-dependent hyperpolarization of smooth muscle induced by either acetylcholine or by 1-EBIO in rat hepatic artery is initially associated with the opening of endothelial calcium-sensitive K+-channels insensitive to iberiotoxin. The resulting accumulation of K+ in the myoendothelial space activates an isoform of Na+/K+-ATPase which is sensitive to low concentrations of ouabain.

Acetylcholine↗
PubMed1999

Role of gap junctions in the responses to EDHF in rat and guinea-pig small arteries.

1. In guinea-pig internal carotid arteries with an intact endothelium, acetylcholine (10 microM) and levcromakalim (10 microM) each hyperpolarized the smooth muscle whereas a 5 mM elevation of extracellular K(+) was without effect. 2. Incubation of the carotid artery with the gap junction inhibitors carbenoxolone (100 microM) or gap 27 (500 microM) essentially abolished the hyperpolarization to acetylcholine but it was without effect on that to levcromakalim. Carbenoxolone had no effect on the acetylcholine-induced endothelial cell hyperpolarization but inhibited the smooth muscle hyperpolarization induced by the endothelial cell K(+) channel opener, 1-ethyl-2-benzimidazolinone (600 microM). 3. In rat hepatic and mesenteric arteries with endothelium, carbenoxolone (100 or 500 microM) depolarized the smooth muscle but did not modify hyperpolarizations induced by KCl or levcromakalim. In the mesenteric (but not the hepatic) artery, the acetylcholine-induced hyperpolarization was inhibited by carbenoxolone. 4. Phenylephrine (1 microM) depolarized the smooth muscle cells of intact hepatic and mesenteric arteries, an effect enhanced by carbenoxolone. Gap 27 did not have a depolarizing action. In the presence of phenylephrine, acetylcholine-induced hyperpolarization of both hepatic and mesenteric artery myocytes was partially inhibited by each of the gap junction inhibitors. 5. Collectively, the data suggest that gap junctions play some role in the EDHF (endothelium-derived hyperpolarizing factor) response in rat hepatic and mesenteric arteries. However, in the guinea-pig internal carotid artery, electrotonic propagation of endothelial cell hyperpolarizations via gap junctions may be the sole mechanism underlying the response previously attributed to EDHF.

Acetylcholine↗
PubMed1998

K+ is an endothelium-derived hyperpolarizing factor in rat arteries.

In arteries, muscarinic agonists such as acetylcholine release an unidentified, endothelium-derived hyperpolarizing factor (EDHF) which is neither prostacyclin nor nitric oxide. Here we show that EDHF-induced hyperpolarization of smooth muscle and relaxation of small resistance arteries are inhibited by ouabain plus Ba2+; ouabain is a blocker of Na+/K+ ATPase and Ba2+ blocks inwardly rectifying K+ channels. Small increases in the amount of extracellular K+ mimic these effects of EDHF in a ouabain- and Ba2+-sensitive, but endothelium-independent, manner. Acetylcholine hyperpolarizes endothelial cells and increases the K+ concentration in the myoendothelial space; these effects are abolished by charbdotoxin plus apamin. Hyperpolarization of smooth muscle by EDHF is also abolished by this toxin combination, but these toxins do not affect the hyperpolarizaiton of smooth muscle by added K+. These data show that EDHF is K+ that effluxes through charybdotoxin- and apamin-sensitive K+ channels on endothelial cells. The resulting increase in myoendothelial K+ concentration hyperpolarizes and relaxes adjacent smooth-muscle cells by activating Ba2+-sensitive K+ channels and Na+/K+ ATPase. These results show that fluctuations in K+ levels originating within the blood vessel itself are important in regulating mammalian blood pressure and flow.

Acetylcholine↗
PubMed1998

Endothelium-derived hyperpolarizing factor--a critical appraisal.

Endothelium-derived hyperpolarizing factor is defined as that substance which produces vascular smooth muscle hyperpolarization which cannot be explained by nitric oxide or by a cyclo-oxygenase product such as prostacyclin. The possibility that the factor is an epoxyeicosatrienoic acid or a cannabinoid agonist such as anandamide continues to be investigated, but definitive evidence in favour of either is lacking. The sensitivity of EDHF-mediated responses to charybdotoxin, to apamin or to mixtures of these two toxins may indicate the opening of more than one smooth muscle K-channel, but the possibility that these are located on the vascular endothelium is discussed.

Animals↗
PubMed1997

Involvement of voltage-dependent potassium channels in the EDHF-mediated relaxation of rat hepatic artery.

1. In the rat hepatic artery, the acetylcholine-induced relaxation mediated by endothelium-derived hyperpolarizing factor (EDHF) is abolished by a combination of apamin and charybdotoxin, inhibitors of small (SKCa) and large (BKCa) conductance calcium-sensitive potassium (K)-channels, respectively, but not by each toxin alone. The selective BKCa inhibitor iberiotoxin cannot replace charybdotoxin in this combination. Since delayed rectifier K-channels (KV) represent another target for charybdotoxin, we explored the possible involvement of KV in EDHF-mediated relaxation in this artery. 2. The KV inhibitors, agitoxin-2 (0.3 microM), kaliotoxin (0.3 microM), beta-dendrotoxin (0.3 microM), dofetilide (1 microM) and terikalant (10 microM), each in combination with apamin (0.3 microM) had no effect on the EDHF-mediated relaxation induced by acetylcholine in the presence of N omega-nitro-L-arginine (0.3 mM) and indomethacin (10 microM), inhibitors of nitric oxide (NO) synthase and cyclo-oxygenase, respectively (n = 2-3). Although the KV inhibitor margatoxin (0.3 microM) was also without effect (n = 5), the combination of margatoxin and apamin produced a small inhibition of the response (pEC50 and Emax values were 7.5 +/- 0.0 and 95 +/- 1% in the absence and 7.0 +/- 0.1 and 81 +/- 6% in the presence of margatoxin plus apamin, respectively; n = 6; P < 0.05). 3. Ciclazindol (10 microM) partially inhibited the EDHF-mediated relaxation by shifting the acetylcholine-concentration-response curve 12 fold to the right (n = 6; P < 0.05) and abolished the response when combined with apamin (0.3 microM; n = 6). This combination did not inhibit acetylcholine-induced relaxations mediated by endothelium-derived NO (n = 5). 4. A 4-aminopyridine-sensitive delayed rectifier current (IK(V)) was identified in freshly-isolated single smooth muscle cells from rat hepatic artery. None of the cells displayed a rapidly-activating and -inactivating A-type current. Neither charybdotoxin (0.3 microM; n = 3) nor ciclazindol (10 microM; n = 5), alone or in combination with apamin (0.3 microM; n = 4-5), had an effect on IK(V). A tenfold higher concentration of ciclazindol (0.1 mM, n = 4) markedly inhibited IK(V), but this effect was not increased in the additional presence of apamin (0.3 microM; n = 2). 5. By use of membranes prepared from rat brain cortex. [125I]-charybdotoxin binding was consistent with an interaction at a single site with a KD of approximately 25 pM. [125I]-charybdotoxin binding was unaffected by iberiotoxin (0.1 microM, n = 6), but was increased by apamin in a concentration-dependent manner (Emax 43 +/- 10%, P < 0.05 and pEC50 7.1 +/- 0.2; n = 7-8). Agitoxin-2 (10 nM) displaced [125I]-charybdotoxin binding by 91 +/- 3% (n = 6) and prevented the effect of apamin (1 microM; n = 6). 6. It is concluded that the EDHF-mediated relaxation in the rat hepatic artery is not mediated by the opening of either KV or BKCa. Instead, the target K-channels for EDHF seem to be structurally related to both KV and BKCa. The possibility that a subtype of SKCa may be the target for EDHF is discussed.

4-Aminopyridine↗
PubMed1997

Studies on the effects of anandamide in rat hepatic artery.

1. The effects of anandamide on K+ currents and membrane potential have been examined in freshly-isolated smooth muscle cells from rat hepatic artery and the results compared with the effects of this arachidonic acid derivative on tension and membrane potential changes in segments of whole artery. 2. In the presence of 0.3 mM L-NOARG and 10 microM indomethacin, anandamide (0.1-100 microM) and endothelium-derived hyperpolarizing factor (EDHF; liberated by acetylcholine, 0.01-10 microM) each relaxed endothelium-intact segments of hepatic artery precontracted with phenylephrine. These effects of anandamide, but not those of EDHF, were antagonized by the cannabinoid receptor antagonist, SR141716A (3 microM). 3. The relaxant effects of anandamide were unaffected by a toxin combination (apamin plus charybdotoxin, each 0.3 microM) which abolishes EDHF relaxations and were essentially unchanged in endothelium-denuded arteries. The relaxant effects of anandamide in endothelium-intact arteries were significantly reduced in a physiological salt solution containing 30 mM KCl and abolished when the K+ concentration was raised to 60 mM. 4. Anandamide (10 microM), acetylcholine (1 microM, via release of EDHF) and levcromakalim (10 microM) each markedly hyperpolarized the membrane potential of the smooth muscle cells of endothelium-intact arteries. However, when the endothelium was removed, the hyperpolarizing effects of both anandamide (10 microM) and acetylcholine were essentially abolished whereas those of levcromakalim (10 microM) were unaffected. 5. Under voltage-clamp conditions, anandamide (10 microM) abolished spontaneous transient outward currents (STOCs) in freshly-isolated single hepatic artery cells held at 0 mV but had no effect on the holding current at this potential. In current-clamp mode, the spontaneous hyperpolarizing potentials which corresponded to the STOCs were abolished with no significant change in basal membrane potential. 6. Anandamide (10 microM) abolished the iberiotoxin-sensitive K+ current (IBK(Ca)) produced by caffeine and the corresponding hyperpolarizations generated by this xanthine derivative in current-clamp mode. In contrast, anandamide had no effect on IBK(Ca) generated on exposure to NS1619 (30 microM). 7. It was concluded that anandamide is not EDHF in the rat hepatic artery. Anandamide-induced hyperpolarization is exerted indirectly and requires the presence of the endothelium. Anandamide also acts on the smooth muscle cells to inhibit processes which require functional intracellular calcium stores. This direct action seems more important than membrane hyperpolarization in relaxing phenylephrine-contracted vessels.

Animals↗
PubMed1996

Modulation of membrane currents and mechanical activity by niflumic acid in rat vascular smooth muscle.

The effects of niflumic acid on whole-cell membrane currents and mechanical activity were examined in the rat portal vein. In freshly dispersed portal vein cells clamped at -60 mV in caesium (Cs+)-containing solutions, niflumic acid (1-100 microM) inhibited calcium (Ca2+)-activated chloride currents (IC1(Ca)) induced by caffeine (10 mM) and by noradrenaline (10 microM). In a potassium (K+)-containing solution and at a holding potential of - 10 mV, niflumic acid (10-100 microM) induced an outward K+ current (IK(ATP)) which was sensitive to glibenclamide (10-30 microM). At concentrations < 30 microM and at a holding potential of -2 mV, niflumic acid had no effect on the magnitude of the caffeine- or noradrenaline-stimulated current (IBK(Ca)) carried by the large conductance, Ca(2+)-sensitive K+ channel (BKCa). However, at a concentration of 100 microM, niflumic acid significantly inhibited IBK(Ca)) evoked by caffeine (10 mM) but not by NS1619 (1-(2'-hydroxy-5'-trifluoromethylphenyl)-5-trifluoromethyl-2(3 H) benzimidazolone; 20 microM). In Cs(+)-containing solutions, niflumic acid (10-100 microM) did not inhibit voltage-sensitive Ca2+ currents. In intact portal veins, niflumic acid (1-300 microM) inhibited spontaneous mechanical activity, an action which was partially antagonised by glibenclamide (1-10 microM), and contractions produced by noradrenaline (10 microM), an effect which was glibenclamide-insensitive. It is concluded that inhibition of ICl(Ca) and stimulation of IK(ATP) both contribute to the mechano-inhibitory actions of niflumic acid in the rat portal vein.

Adrenergic alpha-Agonists↗