bluuebunny/crossref_metadata_2025 huggingface dataset:
Voltage‐dependence of Ca2+ agonist effect of YC‐170 on cardiac L‐type Ca2+ channels
Authors: Takeda Youji , Tohse Noritsugu , Nakaya Haruaki , Kanno Morio
Published: July 2012

We investigated the voltage‐dependence of the agonist actions of YC‐170, a dihydropyridine (DHP) derivative, on cardiac L‐type Ca2+ channels in rabbit ventricular cells, using the patch clamp technique. The characteristics of YC‐170 were compared with those of other DHP Ca2+ agonists (Bay K 8644, CGP 28392). Ca2+ channel activities were elicited by depolarizing pulses to 0 mV from a holding potential (HP) of either −80 mV or −40 mV.

YC‐170 (10 μM) increased Ca2+ channel activities when HP was set at −80 mV. However, decreasing HP to −40 mV abolished the agonist action. The agonist effect of Bay K 8644 (1 μM) on Ca2+ channels was elicited to the same extent at either HP. CGP 28392 (10 μm) also increased Ca2+ channel activities at both HPs, but its agonist effect was significantly larger at an HP of −80 mV than at −40 mV.

All of the three DHP Ca2+ agonists prolonged open times of Ca2+ channels, but the prolongation did not correspond to the voltage‐dependence of Ca2+ agonist effects of the three DHPs.

YC‐170 markedly reduced the closed time of the Ca2+ channel when the HP was at −80 mV, but prolonged it at HP of −40 mV. Bay K 8644 reduced closed times at an HP of −80 mV. At an HP of −40 mV, Bay K 8644 slightly reduced closed times. CGP 28392 reduced closed times at an HP of −80 mV and prolonged those at an HP of −40 mV. Thus the voltage‐dependence of the agonist effects of these agents was in good agreement with the voltage‐dependence of changes in closed times of Ca2+ channel.

Two mechanisms may be involved in the agonist action of YC‐170; a prolongation of open times, and a reduction of closed times of Ca2+ channels, i.e. an increase in reopening. The former mechanism is not dependent on HP and the latter mechanism is highly dependent on HP. Thus, the voltage‐dependence of the agonist action may be attributed to the voltage‐dependence of their enhancing effect on reopening of Ca2+ channels.
Action of angiotensin II, 5‐hydroxytryptamine and adenosine triphosphate on ionic currents in single ear artery cells of the rabbit
Authors: Hughes A.D. , Bolton T.B.
Published: July 2012

Angiotensin II, 5‐hydroxytryptamine (5‐HT) and adenosine triphosphate (ATP) evoked a transient inward current in isolated single ear artery cells of rabbit held at −60 mV by whole cell voltage clamp in physiological saline using a KCl‐containing pipette solution. Under these conditions agonist did not activate a calcium‐dependent potassium current.

Responses to each agonist were transient and desensitized rapidly. Inward current at‐60 mV holding potential was not abolished by blockade of voltage‐dependent calcium channels or by buffering intracellular calcium with BAPTA, a calcium chelator, or following depletion of intracellular calcium stores with ryanodine.

The shape of the current‐voltage relationships and the reversal potentials of the current induced by angiotensin II, 5‐HT and ATP were similar under a variety of ionic conditions. Agonist‐induced current was unaffected by replacing intracellular chloride with citrate ions or by replacing intracellular sodium with caesium or extracellular sodium with barium or calcium. Replacement of extracellular sodium with Tris shifted the reversal potential in all cases by around 30 mV negatively.

These data suggest that angiotensin II, 5‐HT and ATP activate similar cationic conductances which are relatively non‐selective allowing mono‐ and divalent cations to cross the smooth muscle cell membrane. These channels may allow the influx of calcium under physiological conditions.
Reduction by NG‐nitro‐L‐arginine methyl ester (L‐NAME) of antigen‐induced nasal airway plasma extravasation in human subjects in vivo
Authors: Dear J.W. , Scadding G.K. , Foreman J.C.
Published: July 2012

In non‐allergic subjects, histamine induced a reduction of minimal nasal cross‐sectional area (Amin) and an increase in albumin release into nasal lavage. The effect of histamine on albumin release was inhibited by pretreatment with NG‐nitro‐L‐arginine methyl ester (L‐NAME), 1 μmol but not by D‐NAME, 1 μmol. L‐NAME, 1 and 10 μmol, did not inhibit the histamine‐induced reduction of Amin. In subjects allergic to grass pollen, antigen challenge induced a reduction in Amin that was not changed by pretreatment with L‐NAME, and an increase in albumin release that was inhibited by L‐NAME, 1 μmol. The data support a role for nitric oxide in mediating plasma extravasation in the nose induced by antigen challenge or histamine.
The in vivo effect of lipopolysaccharide on the spontaneous release of transmitter from motor nerve terminals
Authors: Liu Shing H. , Sheu Tzong J. , Lin Ruey H. , Lin‐Shiau Shoei Y.
Published: July 2012

, Jen Ai Road, 1st Section, Taipei, Taiwan.

The in vivo effect of E. coli lipopolysaccharide (LPS) on the spontaneous release of transmitter was studied in the isolated phrenic nerve‐diaphragm preparation of the mouse

The resting membrane potential was decreased and frequency of miniature endplate potentials (m.e.p.ps) was increased by treatment with LPS

Pretreatment of diaphragms with ouabain markedly increased the frequency of m.e.p.ps in control group but not in the LPS group

When mice were treated with polymyxin B (a LPS neutralizer), pentoxifylline (an inhibitor of tumour necrosis factor‐α formation) and NG‐nitro‐L‐arginine (an inhibitor of nitric oxide (NO) synthase) the effects of LPS were reversed

These results suggest that LPS increases the spontaneous transmitter release through, at least in part, the pathways of tumour necrosis factor‐α and NO followed by an inhibition of the Na+‐pump activity in the endplate area.
Mechanism of inhibition of the sodium current by bepridil in guinea‐pig isolated ventricular cells
Authors: Nawada Takahiro , Tanaka Yasunori , Hisatome Ichiro , Sasaki Norihito , Ohtahara Akira , Kotake Hiroshi , Mashiba Hiroto , Sato Ryoichi
Published: July 2012

Effects of bepridil, a sodium‐, calcium‐, and potassium‐antagonistic agent, on the Na+ current were studied by the whole cell voltage clamp technique (tip resistance = 0.5 MOhm, [Na]i and [Na]o 10 mmol T−1 at 20°C)

Bepridil produced tonic block (K drest = 295.44 μmol 1−1, Kdi = 1.41 μmol −1; n = 4)

Bepridil (100 μmol 1−1) shifted the inactivation curve in the hyperpolarization direction by 13.4 ±2.7 mV (n = 4) without change in the slope factor

In the presence of 50 μmol 1−1 bepridil, bepridil showed use‐dependent block at 2 Hz, whereas changes in pulse duration did not significantly effect this use‐dependent block (81% ±2% at 10 ms, 84% ±3% at 30 ms, 86% ±3% at 100 ms; n = 4)

After removal of fast inactivation of the Na+ current by 3 mmol 1−1 tosylchloramide sodium, bepridil (50 μmol 1−1) still showed use‐dependent block which was independent of the holding potential

The recovery time constant from the bepridil‐induced use‐dependent block was 0.48 s at holding potential of −100 mV and 0.51 s at holding potential of −140 mV

These results indicate that bepridil could bind to the receptor in the sodium channel through the hydrophobic and the hydrophilic pathway and leave the receptor through the hydrophobic pathway in the lipid bilayer. The binding and dissociation kinetics of this drug were shown to be fast, and the accumulation of the drug in the sodium channel appeared to be small. Bepridil is presumed to be safe in terms of adverse effects that result from drug‐accumulation in the sodium channel.
The effect of folate on the methotrexate/indomethacin interaction in a murine cancer cell line
Authors: Hollingsworth S.J. , Anderson E.M. , Bennett A.
Published: July 2012

The effect of folate on the interaction between methotrexate (a folate analogue) and indomethacin has been examined in murine NC carcinoma cells

Conditioning of NC cells to a physiological (20 nM) folate concentration after culture in a high folate concentration increased the response to methotrexate. The sensitivity of these conditioned cells to methotrexate related inversely to the folate concentration

At 20 nM and 2 μm folate, indomethacin 1 μg ml−1 potentiated the cytotoxicity of methotrexate 4 and 8 ng ml−1 (both P<0.03)

When NC cells were incubated with [3H]‐methotrexate at 20 nM and 2 μm folate, there was a trend for increased tritium accumulation with indomethacin 0.36 μg ml−1 (1 μm; P<0.01)

We conclude that the folate concentration can affect the sensitivity of NC cells to methotrexate, although the degree of potentiation of cytotoxicity by indomethacin remains similar.
Phosphoramidon inhibition of the in vivo conversion of big endothelin‐1 to endothelin‐1 in the human forearm
Authors: Plumpton Christopher , Haynes William G. , Webb David J. , Davenport Anthony P.
Published: July 2012

The vasoconstrictor peptide, endothelin‐1 (ET‐1) and a biologically inactive C‐terminal fragment (CTF) are generated from an intermediate big ET‐1 by a putative ET converting enzyme, sensitive to phosphoramidon. We have developed a procedure using selective solid‐phase extraction and specific radioimmunoassays to measure the levels of immunoreactive (IR) big ET‐1 and the products of conversion (ET‐1 and CTF) in human plasma. These techniques have been used to determine the levels of the three peptides in venous plasma following local infusions of ET‐1 and big ET‐1, both alone and together with phosphoramidon

Infusion of ET‐1 into the brachial artery (5 pmol min−1) significantly increased (P<0.05) IR ET levels from a basal level of 2.3 pM to 55.2 pM in plasma from the infused arm after 60 min of infusion. This corresponded with a marked decrease in forearm blood flow from a basal level of 2.6 ml dl−1 min−1 to 1.7 ml dl−1 min−1. The levels of IR big ET‐1 and CTF were unchanged. Co‐infusion of phosphoramidon (30 nmol min−1) with ET‐1 had no significant effect on the plasma IR levels of ET, big ET‐1, CTF, or blood flow

Big ET‐1 (50 pmol min−1) significantly increased (P < 0.05) venous concentrations of all three IR peptides after 60 min compared to basal (ET: from 2.2 to 7.7 pM, big ET‐1: from 0 to 386.0 pM, CTF: from 0.2 to 37.0 pM). Forearm blood flow decreased significantly (P < 0.05) from a basal level of 3.0 ml dl−1 min−1 to 1.6 ml dl−1 min−1

When phosphoramidon was co‐infused with big ET‐1, both the rise in IR ET and associated vasoconstriction were abolished. However, IR CTF was still detected, suggesting that either some conversion by phosphoramidon‐insensitive enzyme(s) was occurring, and/or that CTF was being protected from further degradation by phosphoramidon

These data show that in the human forearm the activity of a phosphoramidon‐sensitive ET converting enzyme is at least in part responsible for the vasoconstrictor properties of exogenous big ET‐1. Furthermore, because measurable levels of newly synthesized ET‐1 are likely to be rapidly reduced in the blood/plasma through receptor binding, assay of IR big ET‐1 and CTF may be a more sensitive measure of ET‐1 generation in disease.
Effects of 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase inhibitors on mitochondrial respiration in ischaemic dog hearts
Authors: Satoh Kumi , Yamato Atsuko , Nakai Tohru , Hoshi Katsuji , Ichihara Kazuo
Published: July 2012

Effects of 3‐hydroxy‐3‐methylglutaryl coenzyme A (HMG‐CoA) reductase inhibitors, pravastatin and simvastatin, on the myocardial level of coenzyme Q10, and on mitochrondrial respiration were examined in dogs

Either vehicle (control), pravastatin (4 mg kg−1day−1), or simvastatin (2 mg kg−1day−1) was administered orally for 3 weeks. First, the myocardial tissue level of coenzyme Q10 was determined in the 3 groups. Second, ischaemia was induced by ligating the left anterior descending coronary artery (LAD) in anaesthetized open chest dogs, pretreated with the inhibitors. After 30 min of ischaemia, nonischaemic and ischaemic myocardium were removed from the left circumflex and LAD regions, respectively, and immediately used for isolation of mitochondria. The mitochondrial respiration was determined by polarography, with glutamate and succinate used as substrates

Simvastatin significantly decreased the myocardial level of coenzyme Q10, but pravastatin did not

Ischaemia decreased the mitochondrial respiratory control index (RCI) in both groups. Significant differences in RCI between nonischaemic and ischaemic myocardium were observed in the control and simvastatin‐treated groups

Only in the simvastatin‐treated group did ischaemia significantly decrease the ADP/O ratio, determined with succinate

The present results indicate that simvastatin but not pravastatin may cause worsening of the myocardial mitochondrial respiration during ischaemia, probably because of reduction of the myocardial coenzyme Q10 level.
Antinociceptive activity of the tachykinin NK1 receptor antagonist, CP‐99,994, in conscious gerbils
Authors: Rupniak N.M.J. , Webb J.K. , Williams A.R. , Carlson E. , Boyce S. , Hill R.G.
Published: July 2012

The ability of CP‐99,994, and its less active enantiomer, CP‐100,263, to inhibit spontaneous behaviours and hyperalgesia induced by central infusion of the NK1 receptor agonist, GR73632 or intraplantar injection of formalin was investigated in rats and gerbils

GR73632 (3 pmol, i.c.v.)‐induced foot tapping in gerbils was dose‐dependently inhibited by CP‐99,994 (0.1‐1 mg kg−1, s.c), but not by CP‐100,263 (10 mg kg−1, s.c.) using pretreatment times up to 60 min. The centrally active dose‐range for CP‐99,994 was increased to 1 −10 mg kg−1 s.c. with a higher challenge dose of GR73632 (30 pmol, i.e.v.)

In gerbils, intrathecal (i.t.) injection of GR73632 (30 pmol) elicited behaviours (licking, foot tapping or flinching and face washing) which closely resembled, but which was less specifically localized than, behaviours seen in animals injected with formalin (0.1–5%) into one hindpaw

In rats, CP‐100,263, but not CP‐99,994 (up to 30 mg kg−1), inhibited the early phase response to intraplantar injection of 5% formalin (ID50= 13.9 mg kg−1. The late phase was inhibited by both compounds (ID50 values 36.3 and 20.9 mg kg−1, respectively). In gerbils, there was marginal evidence for enantioselective inhibition of the early phase induced by formalin (2%). The ID50 values were 6.2 mg kg−1 for CP‐99,994 and 13.4 mg kg−1 for CP‐100,263

Intrathecal injection of GR73632 (30 pmol) caused thermal hyperalgesia in gerbils which was inhibited enantioselectively by s.c. administration of CP‐99,994 (ID50 = 2.46 mg kg−1, but not by CP‐100,263 (30 mg kg−1)

In gerbils, intraplantar injection of formalin (0.1%) caused thermal hyperalgesia which was inhibited by CP‐99,994 (ID50= 1.1 mg kg−1, s.c). There was a nonsignificant trend for an anti‐algesic effect of CP‐100,236 (estimated ID50 = 8.2 mg kg−1, s.c)

These findings support the proposal that NKi receptor antagonists may be useful in the clinical management of pain and reinforce the need to dissociate specific and nonspecific antinociceptive effects of available compounds.
Induction of calcium‐independent nitric oxide synthase by allergen challenge in sensitized rat lung in vivo
Authors: Yeadon Michael , Price Robert
Published: July 2012

There is some evidence that nitric oxide synthase (NOS) is induced in the lungs of patients with allergic asthma, but the mechanism of this is not understood. The aim of the present study was to investigate whether the levels of NOS in rat lung could be altered by exposure of the animals to aerosols of allergen (ovalbumin). Brown‐Norway rats were actively sensitized to ovalbumin, raising a mixed IgE/IgG antibody response. The levels of total and calcium‐independent NOS in lung tissue homogenates were elevated at 6 h and 24 h after allergen exposure in sensitized rats but not in unsensitized rats. The induction was not due to contaminating lipopolysaccharide in the challenge solution. The allergen‐induced increase in calcium‐independent lung NOS was inhibited by pretreatment of the animals with the corticosteroid betamethasone (3 mg kg−1 i.p., 1 h prior to and 6 h after allergen). These results show that allergen challenge induces calcium‐independent NOS in the lungs of sensitized rats, a process inhibited by an anti‐inflammatory corticosteroid.
SPECIAL REPORT Evidence that endogenous nitric oxide modulates plasma fibrinogen levels in the rat
Authors: Kawabata Atsufumi
Published: July 2012

This study investigated the effect of prolonged inhibition of nitric oxide (NO) synthase on plasma fibrinogen levels and platelet count in the rats. NG‐nitro‐L‐arginine methyl ester (L‐NAME), when administered orally twice a day, at 10 − 100 mg kg−1, for 7 consecutive days, 14 times in all, significantly elevated fibrinogen levels and systolic blood pressure in a dose‐dependent manner. The same dose range of L‐NAME failed to alter platelet count and plasma protein concentrations. The increase in fibrinogen levels produced by chronic treatment with L‐NAME at 30 mg kg−1 was reversed by L‐arginine at 500 − 1500 mg kg−1 in a dose‐dependent manner. These findings suggest that endogenous NO tonically acts to reduce plasma fibrinogen levels in rats under physiological conditions.
Intracerebroventricular responses to neuropeptide γ in the conscious rat: characterization of its receptor with selective antagonists
Authors: Picard Pierre , Couture Réjean
Published: July 2012

The cardiovascular and behavioural effects elicited by the intracerebroventricular (i.c.v.) administration of neuropeptide γ (NPγ) in the conscious rat were assessed before and 5 min after i.c.v. pretreatment with antagonists selective for NK1 (RP 67,580), NK2 (SR 48,968) and NK3 (R 820) receptors. In addition, the central effects of NPγ before and after desensitization of the NK1 and NK2 receptors with high doses of substance P (SP) and neurokinin A (NKA) were compared.

Intracerebroventricular injection of NPγ (10–780 pmol) evoked dose‐ and time‐dependent increases in mean arterial blood pressure (MAP), heart rate (HR), face washing, head scratching, grooming and wet‐dog shake behaviours. Similar injection of vehicle or 1 pmol NPγ had no significant effect on those parameters.

The cardiovascular and behavioural responses elicited by NPγ (25 pmol) were significantly and dose‐dependently reduced by pretreatment with 650 pmol and 6.5 nmol of SR 48,968. No inhibition of NPγ responses was observed when 6.5 nmol of RP 67,580 was used in a similar study. Moreover, the prior co‐administration of SR 48,968 (6.5 nmol) and RP 67,580 (6.5 nmol) with or without R 820 (6.5 nmol) did not reduce further the central effects of NPγ and significant residual responses (30–50%) remained.

No tachyphylaxis to NPγ‐induced cardiovascular and behavioural changes was observed when two consecutive injections of 25 pmol NPγ were given 24 h apart.

Simultaneous NK1 and NK2 receptor desensitization reduced significantly central effects mediated by 25 pmol NPγ. However, significant residual responses persisted as seen after pretreatment with SR 48,968.

The results suggest that the central effects of NPγ are mediated partly by NK2 receptors and by another putative tachykinin receptor subtype (NPγ receptor?) that appears to be different from NK1 and NK3 receptors.
Functional characterization of adenosine receptors in the nucleus tractus solitarius mediating hypotensive responses in the rat
Authors: White Paul J. , Rose'Meyer Roselyn B. , Hope Wendy
Published: July 2012

The aim of this study was to characterize adenosine receptors located in the nucleus tractus solitarius (NTS) that mediate decreases in blood pressure in the anaesthetized rat. To determine the adenosine receptor subtype involved, a range of selective agonists and antagonists were studied and their relative potencies evaluated.

The rank order of agonist potency in inducing decreases in diastolic blood pressure was N6‐ cyclopentyladenosine (CPA)> N6‐cyclohexyladenosine (CHA)> N‐ethyl‐carboxamidoadenosine (NECA)≥ 2‐phenylaminoadenosine (CV1808)> 2‐p‐(carboxyethyl) phenethylamino‐5′ N‐ethylcarboxamidoadenosine (CGS 21680)> N6−(2−(4‐aminophenyl)ethyl)‐adenosine (APNEA).

The hypotensive action of CPA following microinjection into the NTS was antagonized by i.v. infusions (50 μg kg−1 min−1) of adenosine receptor antagonists, 8‐cyclopentyl‐1,3 dipropylxanthine (DPCPX), 8‐phenyltheophylline (8‐PT), 8‐(p‐sulphophenyl)theophylline (8‐SPT), and 1,3‐dipropyl‐8‐N‐(2‐(diethylamino)ethyl)‐N methyl‐4‐(2,3,6,7‐tetrahydro‐2,6‐dioxo) benzenesulphonamidexanthine (PD 115199). The antagonist potency order was DPCPXPD1151998‐PT. Intravenous infusion of 8‐SPT had no effect on blood pressure responses to microinjection of CPA into the NTS.

The results suggest that adenosine A1 receptors in the NTS mediate hypotensive responses in the anaesthetized rat preparation.
δ‐ and μ‐opioid receptor mobilization of intracellular calcium in SH‐SY5Y human neuroblastoma cells
Authors: Connor Mark , Henderson Graeme
Published: July 2012

In this study we have investigated δ and μ opioid receptor‐mediated elevation of intracellular Ca2+ concentration ([Ca2+]i) in the human neuroblastoma cell line, SH‐SY5Y.

The Ca2+‐sensitive dye, fura‐2, was used to measure [Ca2+]i in confluent monolayers of SH‐SY5Y cells. Neither the δ‐opioid agonist, DPDPE ([D‐Pen2,5]‐enkephalin) nor the μ‐opioid agonist, DAMGO (Tyr‐D‐Ala‐Gly‐N‐Me‐Phe‐Gly‐ol enkephalin) elevated [Ca2+]i when applied alone. However, when either DPDPE or DAMGO was applied in the presence of the cholinoceptor agonist, carbachol (100 nM‐1 mM) they evoked an elevation of [Ca2+]i above that caused by carbachol alone.

In the presence of 1 μm or 100 μm carbachol, DPDPE elevated [Ca2+]i with an EC50 of 10 nM. The elevation of [Ca2+]i was independent of the concentration of carbachol. The EC50 for DAMGO elevating [Ca2+]i in the presence of 1 μm and 100 μm carbachol was 270 nM and 145 nM respectively.

The δ‐receptor antagonist, naltrindole (30 nM), blocked the elevations of [Ca2+]i by DPDPE (100 nM) without affecting those caused by DAMGO while the μ‐receptor antagonist, CTAP (D‐Phe‐Cys‐Tyr‐D‐Trp‐Arg‐Pen‐Thr‐NH2) (100 nM‐1 μm) blocked the elevations of [Ca2+]i caused by DAMGO (1 μm) without affecting those caused by DPDPE.

Block of carbachol activation of muscarinic receptors with atropine (10 μm) abolished the elevation of [Ca2+]i by the opioids. The nicotinic receptor antagonist, mecamylamine (10 μm), did not affect the elevations of [Ca2+]i caused by opioids in the presence of carbachol.

Muscarinic receptor activation, not a rise in [Ca2+]i, was required to reveal the opioid response. The Ca2+ channel activator, maitotoxin (3 ng ml−1), also elevated [Ca2+]i but subsequent application of opioid in the presence of maitotoxin caused no further changes in [Ca2+]i.

The elevations of [Ca2+]i by DPDPE and DAMGO were abolished by pretreatment of the cells with pertussis toxin (200 ng ml−1, 16 h). This treatment did not significantly affect the response of the cells to carbachol.

The opioids appeared to elevate [Ca2+]i by mobilizing Ca2+ from intracellular stores. Both DPDPE and DAMGO continued to elevate [Ca2+]i when applied in nominally Ca2+ ‐free external buffer or when applied in a buffer containing a cocktail of Ca2+ entry inhibitors. Thapsigargin (100 nM), an agent which discharges intracellular Ca2+ stores, also blocked the opioid elevations of [Ca2+]i.

δ and μ Opioids did not appear to mobilize intracellular Ca2+ by modulating the activity of protein kinases. The application of H‐89 (10 μm), an inhibitor of protein kinase A, H‐7 (100 μm), an inhibitor of protein kinase C, protein kinase A and cyclic GMP‐dependent protein kinase, or Bis I, an inhibitor of protein kinase C, did not alter the opioid mobilization of [Ca2+]i.

Thus, in SH‐SY5Y cells, opioids can mobilize Ca2+ from intracellular stores but they require ongoing muscarinic receptor activation. Opioids do not elevate [Ca2+]i when applied alone.
Comparison of the effects of hydroxocobalamin and oxyhaemoglobin on responses to NO, EDRF and the nitrergic transmitter
Authors: La Mylinh , Li Chun Guang , Rand Michael J.
Published: July 2012

The effects of ranges of concentrations of oxyhaemoglobin (0.01–30 μm) and hydroxocobalamin (1–100 μm) were compared for their abilities to reduce relaxant responses to EDRF released by acetylcholine in endothelium‐intact rat aortic rings, the nitergic transmitter in rat anococcygeus muscles, and NO in aqueous solution in both tissues (aortic rings were denuded of endothelium).

The concentrations of oxyhaemoglobin producing 50% reduction of responses to EDRF and NO in rat aorta correspond closely, the IC50 values being 0.13 ± 0.02 μm and 0.11 ± 0.02 μm respectively.

Oxyhaemoglobin was equally effective in inhibiting responses to NO in anococcygeus muscles and in aortic rings with an IC50 of 0.14 ± 0.05 μm. However, responses to the nitrergic transmitter were considerably less sensitive to inhibtion by oxyhaemoglobin, the IC50 being 19.7 ± 5.1 μm.

The IC50 values for hydroxocobalamin in inhibiting responses to EDRF and NO in aorta were 3.4 ± 0.2 μm and 8.4 ± 0.63 μm, respectively, but it was less effective against responses to NO in anococcygeus muscles the IC50 being 46 ± 9.6 μm. However, even in the highest concentration used (100 μm), it did not reduce responses to the nitrergic transmitter.

The findings are compatible with the views that EDRF is NO, but suggest that the nitergic transmitter in the rat anococcygeus muscle does not behave like free NO.
Protective effect of platelet activating factor antagonists on cultured endothelial cell lysis induced by elastase or activated neutrophils
Authors: Renesto Patricia , Vicart Patrick , Paulin Denise , Chignard Michel
Published: July 2012

The mechanism(s) responsible for injury of endothelial cells induced by human leukocyte elastase (HLE) was investigated in an immortalized venous human endothelial cell line (IVEC).

First, the proteinase concentrations and incubation delays necessary to trigger a significant IVEC cytotoxicity were determined by chromium assays. Thus, exposure of IVEC for 6 h to 10 μ ml−1 HLE resulted in 22 ± 2.8% lysis and 36.4 ± 5.4% detachment (mean ± s.e. mean; n = 4; P < 0.05).

WEB 2086, a specific platelet‐activating factor (PAF) receptor antagonist, induced a significant concentration‐dependent decrease of such a lysis (39.6 ± 7.7% protection at 100 μ n = 4). This potential role for PAF was confirmed with two other antagonists of this lipid mediator, i.e., BN 52021 and RP 48740.

Finally, we demonstrated that pretreatment of IVEC with WEB 2086 protected significantly against cell lysis induced by stimulated human neutrophils, an experimental model in which HLE participates.
Altered thermoregulatory responses to clonidine in streptozotocin‐diabetic rats
Authors: O'Donnell J.M. , Banyasz T. , Kovacs T.
Published: July 2012

The effects of streptozotocin (STZ) treatment on α2‐adrenoceptor regulation of body temperature were studied by monitoring the response of colonic temperature to administration of clonidine.

A dose‐dependent fall in colonic temperature occurred in control rats given clonidine challenge (0.05‐2.0 mg kg−1, s.c.); this response was inhibited by prior administration of either yohimbine or idazoxan (2 mg kg−1, s.c.) but not by the peripherally‐acting α2‐adrenoceptor antagonist L‐659,066 (10 mg kg−1, s.c.).

In rats treated with STZ (65 mg kg−1, i.v.) administration of clonidine elicited a dose‐independent hyperthermia (circa 1°C.); this effect was unaltered by prior administration of yohimbine or idazoxan.

Naloxone (5 mg kg−1, s.c.) elicited a small fall in temperature(< 1°C.) in both control and STZ‐treated rats; naloxone pretreatment did not alter the temperature response to clonidine in either group.

Nicotinic acid (10 mg kg−1, s.c.) caused a similar small elevation in temperature in both groups.

Administration of replacement insulin to STZ‐treated rats maintained weight gain and low blood glucose while the thermoregulatory response to clonidine slowly reverted to normal.

These results show that altered central temperature control is an element of the generalised abnormality of α2 receptor function induced by STZ.
Properties of the inhibitory junction potential in smooth muscle of the guinea‐pig gastric fundus
Authors: Ohno Naotomo , Xue Lin , Yamamoto Yoshimichi , Suzuki Hikaru
Published: July 2012

In circular smooth muscle of the guinea‐pig gastric fundus, transmural nerve stimulation evoked a cholinergic excitatory junction potential (e.j.p.), and blockade of the e.j.p. by atropine revealed a non‐adreriergic non‐cholinergic (NANC) inhibitory junction potential (i.j.p.).

The amplitude of the e.j.p. was increased by apamin, suramin or NGnitro‐L‐arginine (L‐NOARG), with no significant change in the membrane potential.

The i.j.p. consisted of two components (fast and slow); apamin inhibited the former, nitroarginine inhibited the latter, and suramin inhibited both components.

Apamin inhibited the hyperpolarization produced by adenosine 5′‐triphosphate (ATP) but not by vasoactive intestinal polypeptide (VIP). Suramin inhibited the hyperpolarization produced by VIP but not by ATP. The sodium nitroprusside (SNP)‐induced hyperpolarization was not blocked by apamin or suramin. L‐NOARG or tetrodotoxin did not inhibit the hyperpolarization produced by ATP, VIP or SNP.

The data did not support the hypothesis that ATP, VIP or nitric oxide (NO) is the main transmitter responsible for generation of the NANC i.j.p. in the fundus.

Actions of L‐NOARG suggest that endogenous NO may be involved in junctional transmission, mainly as an inhibitory modulator of cholinergic transmission.
Characterization of inositol hexakisphosphate (InsP6)3‐mediated priming in human neutrophils: lack of extracellular [3H]‐InsP6 receptors
Authors: Kitchen E. , Condliffe A.M. , Rossi A.G. , Haslett C. , Chilvers E.R.
Published: July 2012

Inositol hexakisphosphate (InsP6) is a ubiquitous and abundant cytosolic inositol phosphate that has been reported to prime human neutrophils for enhanced agonist‐stimulated superoxide anion generation. This led to the proposal that the release of InsP6 from necrotic cells may augment the functional responsiveness of neutrophils at an inflammatory focus. The aim of this study was to examine whether the functional effects of InsP6 in neutrophils are receptor‐mediated and establish the magnitude of this priming effect relative to other better characterized priming agents.

Analysis of [3H]‐InsP6 binding to human neutrophil membranes in 20 mM Tris, 20 mM NaCl, 100 mM KC1, 5 mM EDTA (pH 7.7) buffer using 0.1 mg ml−1 membrane protein and 2.5 nM [3H]‐InsP6 (90 min, 4°C), demonstrated specific low affinity [3H]‐InsP6 binding that was non‐saturable up to a radioligand concentration of 10 nM.

[3H]‐InsP6 displacement by InsP6 gave a Hill coefficient of 0.55 and best fitted a two‐site logistic model (53% KD 150 nM, 47% KD 5 μm). [3H]‐InsP6 binding also displayed low (3 fold) selectivity for InsP6 over Ins(1,3,4,5,6)P5.

The specific [3H]‐InsP6 binding displayed a pH optimum of 8, was abolished by pre‐boiling the membranes, and was enhanced by Ca2+, Mg2+ and Na+.

In incubations with intact neutrophils, where high levels of specific [3H]‐LTB4 binding was observed, no [3H]‐InsP6 binding could be identified.

Preincubation of neutrophils with 100 μm InsP6 had no effect on resting cell morphology, but caused a minor and transient (maximal at 30 s) enhancement of (0.1 nM) fMLP‐induced shape change (% cells shape changed: fMLP 53±3%, fMLP+InsP6 66±4%). Similarly, InsP6 (100 μm, 30 s) had no effect on basal superoxide anion generation and, compared to lipopolysaccharide (LPS, 100 ng ml−1, 60 min), tumour necrosis factor‐α (TNFα, 200 u ml−1, 30 min) or platelet‐activating factor (PAF, 100 nM, 5 min) caused only a small enhancement of 100 nM fMLP‐stimulated superoxide anion generation (fold‐increase in superoxide anion generation over fMLP alone: InsP6 1.8±0.3, LPS 6.8±0.6, TNFα 5.2±0.7, PAF 5.8±0.6).

While these data support the presence of a specific, albeit low affinity, [3H]‐InsP6 binding site in human neutrophil membrane preparations, the lack of binding to intact cells implies that the functional effects of InsP6 (ie. enhanced fMLP‐stimulated superoxide anion generation and shape change) are not receptor‐mediated.
Endothelin receptors in human coronary artery and aorta
Authors: Bacon C.R. , Davenport A.P.
Published: July 2012

ETA and ETB‐selective and non‐selective ligands were used to define the endothelin receptors in the media (vascular smooth muscle layer) of human aorta and coronary artery. Saturation experiments with iodinated endothelin‐1 (ET‐1), endothelin‐2 and sarafotoxin 6b (S6b) identified high affinity binding sites in aorta (KD [125I]‐ET‐1 0.33±0.02nM (n=9), KD [125I]‐ET‐2 1.04±0.23 nM (n=5), KD [125I]‐S6b 0.15±0.01 nM (n=9 ±s.e.mean)) and coronary artery (KD [125I]‐ET‐1 0.43±0.10nM, KD [125I]‐ET‐2 0.71±0.17 nM, KD [125I]‐S6b 0.27±0.03 nM (n=3 ±s.e.mean)). Hill coefficients (nH) approached unity in each case.

No specific binding was detectable with [125I]‐ET‐3 (4 pM‐4 nM) in aorta. Unlabelled ET‐3 competed monophasically with [125I]‐ET‐1 in aorta (KD 8.21±1.62 nM, compared to unlabelled ET‐1 KD, 0.60±0.20 nM) (n= 3 ±s.e.mean). In coronary artery, the KD and Bmax values calculated from [125I]‐ET‐3 saturation experiments were 2.13±1.39nM and 20.6±12.9 fmol mg−1 protein, respectively (n=3 ±s.e.mean).

ETA antagonists competed monophasically for [125I]‐ET‐1 (100 pM) binding sites with nanomolar or subnanomolar affinity in the aorta (KD BQ123, 0.47±0.13nM; KD FR139317, 0.40±0.10nM; KD PD151242, 2.09±0.48 nM) and coronary artery (KD FR139317, 0.41±0.13 nM; KD PD151242, 3.60±0.74nM) (n=3 ±s.e.mean). However, two site fits were preferred on analysis of competition experiments with ETB‐selective agonists versus [125I]‐ET‐1 in coronary artery (BQ3020: KDETA 0.96±0.14)μm, KD ETB 1.34±1.08nM and sarafotoxin 6c: KD ETA 1.15±0.14 μm, KD ETB 1.77±0.72nM) (n=3 ±s.e.mean). The selectivity of the agonists for ETB receptors (700 fold) was lower than reported in other species.

Sarafotoxin 6b (2 pM‐2 μm) completely inhibited [125I]‐ET‐1 (100 pM) binding in aorta (KD 1.36±0.22nM) (n=3 ±s.e.mean). The non‐peptide compounds Ro462005 and bosentan, competed with [125I]‐ET‐1 binding in coronary artery with KD values of 0.19±0.04 μm and 2.94±0.95 nM, respectively (n=3 ±s.e.mean).

Inhibition of [125I]‐ET‐2 and [125I]‐S6b binding by FR139317 was similar to the inhibition of [125I]‐ET‐1 binding in both arteries, being monophasic with KD values in the same range.

ETA receptors in coronary artery media were detected by [125I]‐PD151242 (KD 0.23±0.04 nM, Bmax 10.1±1.2 fmol mg−1 protein) (n=3 ±s.e.mean). [125I]‐BQ3020, an ETB‐selective radioligand, indicated the presence of a smaller population of ETB receptors in this tissue (KD 0.60±0.31 nM, Bmax 4.5±2.1 fmol mg−1 protein) (n=3 ±s.e.mean).

Autoradiography with [125I]‐PD151242 and [125I]‐BQ3020 confirmed the predominance of ETA receptors in the media of both arteries.

The results of this study indicate that ETA receptors predominate in the vascular smooth muscle of human cardiac arteries, with a small and variable population of ETB receptors detectable in the coronary artery.
Full sensitivity of P2times2 purinoceptor to ATP revealed by changing extracellular pH
Authors: King Brian F. , Ziganshina Lilia E. , Pintor Jesus , Burnstock Geoffrey
Published: July 2012

A full pharmacological characterization was carried out on a recombinant ATP‐gated ion channel (P2times2 purinoceptor) expressed in Xenopus oocytes. This slowly‐desensitizing neuronal P2times2 purinoceptor, activated by ATP (EC50 = 4.6 ± 1 μm at pH 7.4; n 4), showed the agonist potency order: ATP ≥ 2‐ MeSATP = ATPγS ≥ ATPαS < < Bz‐ATP. The receptor affinity for ATP was enhanced 5–10 fold by acidifying the bathing solution (to pH 6.5) but was diminished 4–5 fold in an alkaline solution (pH 8.0). The maximum activity of P2times2 purinoceptors and the activity order of a series of nucleotides were unaltered by changing extracellular pH. Interestingly, ATP sensitivity at a recombinant P2Y1, purinoceptor remained unaltered with changing extracellular pH. These results indicate that acidotic conditions in the synaptic cleft could strengthen purinergic transmission at neuronal P2times2 purinoceptors.
Angiotensin II‐activated Ca2+ entry‐induced release of Ca2+ from intracellular stores in rat portal vein myocytes
Authors: Morel J.L. , Macrez‐Leprêtre N. , Mironneau J.
Published: July 2012

. The action of angiotensin II (AII) was studied in single myocytes from rat portal vein in which the cytoplasmic Ca2+ concentration was estimated by emission from dyes Fura‐2 or Indo‐1 and the Ca2+ channel current was measured with the whole‐cell mode of the patch‐clamp technique.

. Most of the AII‐evoked increases in [Ca2+]i were reduced by about 60% after pretreatment with ryanodine and caffeine to deplete intracellular Ca2+ stores. However, in some cells the AII‐induced Ca2+ responses were of small amplitude and resembled those obtained in the presence of ryanodine and caffeine. Both types of Ca2+ responses induced by AII were selectively inhibited by losartan, suggesting that the AII effects resulted from activation of the angiotensin AT1 receptors.

. The concentration‐response curve to AII had an EC50 value close to 1 nM for the increase in [Ca2+]i obtained after depletion of intracellular Ca2+ stores. This value was increased to around 18 nM in experiments where the intracellular Ca2+ stores were not depleted.

. AII‐evoked Ca2+ responses were abolished in the absence of external Ca2+ and in the presence of 1 μm oxodipine to block L‐type Ca2+ channels.

. Intracellular applications of the InsP3 receptor antagonist, heparin or an anti‐PdtIns antibody did not modify AII‐induced Ca2+ responses.

. Our results show that AII releases Ca2+ from intracellular stores without involving InsP3 but through a Ca2+ release mechanism activated by Ca2+ influx through L‐type Ca2+ channels.
Effects of dexamethasone and SB 209670 on the regional haemodynamic responses to lipopolysaccharide in conscious rats
Authors: Gardiner S.M. , Kemp P.A. , March J.E. , Bennett T.
Published: July 2012

. Male (350–450 g) Long Evans rats were chronically instrumented to permit regional haemodynamics to be monitored in the conscious state. In the first experiment, either saline (0.4 ml h−1) or dexamethasone (3 mg kg−1, 125 μg kg−1 h−1) was infused continuously for 24 h, before co‐infusion of lipopolysaccharide of (LPS, 150 μg kg−1 h−1) for 24 h. Dexamethasone prevented the delayed (5–24 h) fall in mean arterial blood pressure (MAP) and the renal and hindquarters vasodilatation seen with LPS infusion alone, but not the initial (about 2 h) fall in MAP or renal vasodilatation. However, at this dose, dexamethasone itself caused a significant rise in MAP and regional vasoconstrictions.

. In the second experiment, dexamethasone at a lower dose (12.5 μg kg−1 h−1) had only slight pressor and vasoconstrictor effects. However, in its presence, infusion of LPS caused a substantial and progressive rise in MAP (maximum at 8 h, + 32±3 mmHg) together with persistent mesenteric and hindquarters vasoconstriction and a transient renal vasodilatation.

. In the third experiment, the non‐selective endothelin antagonist, SB 209670 (600 μg kg−1 h−1), blocked the slight pressor and regional vasoconstrictor effects of the lower dose of dexamethasone. Furthermore, in the presence of dexamethasone and SB 209670, infusion of LPS caused marked, but transient hypotension (nadir at 5 h, —24±2 mmHg) and renal and mesenteric vasodilatation.

. At the end of all experimental protocols, sequential administration of the AT1‐receptor antagonist, losartan, followed by the V1‐receptor antagonist, (+)‐(CH2)5‐0‐Me‐Tyr, vasopressin, caused effects indicating a variable involvement of angiotensin and vasopressin in the maintenance of cardiovascular status.

. Collectively, the results indicate that, in the conscious rat, dexamethasone interacts with vasoconstrictor and vasodilator mechanisms, and hence its influence on the haemodynamic responses to LPS cannot be attributed, simply, to inhibition of the activity of inducible nitric oxide synthase and/or cyclo‐oxygenase‐2.
Endothelin‐1‐induced potentiation of human airway smooth muscle proliferation: an ETA receptor‐mediated phenomenon
Authors: Panettieri Reynold A. , Goldie Roy G. , Rigby Paul J. , Eszterhas Andrew J. , Hay Douglas W.P.
Published: July 2012

. In this study the mitogenic effects in human cultured tracheal smooth muscle cells of endothelin‐1 (ET‐1), ET‐3, and sarafotoxin S6c (S6c), the ETB receptor‐selective agonist, were explored either alone or in combination with the potent mitogen, epidermal growth factor (EGF).

. In confluent, growth‐arrested human airway smooth, neither ET‐1 (0.01 nM‐1μm) nor ET‐3 (0.001 nM‐1 μm) or S6c (0.01 nM‐1 μm) induced cell proliferation, as assessed by [3H]‐thymidine incorporation. In contrast, EGF (1.6 pM − 16 nM) produced concentration‐dependent stimulation of DNA synthesis (EC50 of about 0.06 nM). The maximum increase of about 60 fold above control, elicited by 16nM EGF, was similar to that obtained with 10% foetal bovine serum (FBS). EGF (0.16‐16 nM) also produced a concentration‐dependent increase in cell counts, whereas ET‐1 (1 − 100 nM) was without effect on this index of mitogenesis.

. ET‐1 (1–100 nM) potentiated EGF‐induced proliferation of human tracheal smooth muscle cells. For example, ET‐1 (100 nM), which alone was without significant effect, increased by 3.0 to 3.5 fold the mitogenic influence of EGF (0.16 nM). The potentiating effect of ET‐1 on EGF‐induced proliferation was antagonized by BQ‐123 (3 μm), the ETA receptor antagonist, but was unaffected by the ETB receptor antagonist BQ‐788 (10 μm).

. Neither ET‐3 (1 − 100 nM) nor S6c (1 − 100 nM) influenced the mitogenic effects of EGF (0.16‐1.6 nM).

. [125I]‐ET‐1 binding studies revealed that on average the ratio of ETA to ETB receptors in human cultured tracheal smooth muscle cells was 35:65 (±3; n=4), confirming the predominance of the ETB receptor subtype in human airway smooth muscle.

. These data indicate that ET‐1 alone does not induce significant human airway smooth muscle cell proliferation. However, it potently potentiated mitogenesis induced by EGF, apparently via an ETA receptor‐mediated mechanism. These findings suggest that ET‐1, a mediator detected in increased amounts in patients with acute asthma, may potentiate the proliferative effects of mitogens and contribute to the airway smooth muscle hyperplasia associated with chronic severe asthma.
Effect of cyclosporin A and analogues on cytosolic calcium and vasoconstriction: possible lack of relationship to immunosuppressive activity
Authors: Russo A. Lo , Passaquin A.‐C. , André P. , Skutella M. , Rüegg U.T.
Published: July 2012

The full therapeutic potential of the main immunosuppressive drug, cyclosporin A (CsA), is limited because of its side effects, namely nephrotoxicity and hypertension. Several lines of evidence suggest that the origin of both side effects could be CsA‐induced vasoconstriction. However, the underlying molecular mechanisms are not well understood.

Diameter measurements of rat isolated mesenteric arteries showed an increase in noradrenaline‐ and [Arg]8vasopressin‐induced vasoconstriction when arteries were pretreated with CsA.

Measurements in cultured vascular smooth muscle cells (VSMC) of either cytosolic calcium concentration or of 45Ca2+ efflux showed that CsA potentiated the calcium influx to several vasoconstrictor hormones: [Arg]8vasopressin, angiotensin II, endothelin‐1 and 5‐hydroxytryptamine. On the other hand, 45Ca2+ efflux in response to thapsigargin, which depletes calcium from intracellular pools, was not potentiated by CsA. 45Ca2+ uptake was not altered by CsA or by any of the analogues tested.

Time‐course studies in cultured VSMC showed that maximal CsA‐induced Ca2+ potentiation occurred after ca. 20 h and this effect was reversed over approximately the next 20 h.

To investigate the possible role played by the known intracellular targets of CsA, namely cyclophilin and calcineurin, CsA derivatives with variable potencies with respect to their immunosuppressive activity, were tested on the calcium influx to [Arg]8vasopressin. Derivatives devoid of immunosuppressive activity (cyclosporin H, PSC‐833) potentiated calcium signalling, while the potent immunosuppressant, FK520, a close derivative of FK506, and MeVal4CsA, an antagonist of the immunosuppressive effect of CsA did not. The latter compound was unable to reverse the calcium potentiating effect of CsA.

Our results show that CsA increases the calcium influx to vasoconstrictor hormones in smooth muscle cells, which presumably increases vasoconstriction. Loading of the intracellular calcium pools appears not to be involved. Experiments with derivatives of CsA and FK520 suggest that interactions with cyclophilins and calcineurin are not the mechanism involved. This indicates, for the first time, that the immunosuppressive activity can be dissociated from the calcium potentiating effect of CsA in vascular smooth muscle.
Effects of calcium antagonists on endothelin‐1‐induced myocardial ischaemia and oedema in the rat
Authors: Filep János G. , Skrobik Yoanna , Fournier Alain , Földes‐Filep Éva
Published: July 2012

The effects of the calcium channel blockers, verapamil and nifedipine on myocardial ischaemia and oedema evoked by endothelin‐1 (ET‐1) or IRL 1620, an ETB receptor‐selective agonist were studied in anaesthetized and conscious rats.

Bolus injection of ET‐1 (1 nmol kg−1, i.v.) or IRL 1620 (1 nmol kg−1, i.v.) to conscious chronically catheterized rats evoked a transient depressor response followed by a prolonged pressor effect. Corresponding to changes in blood pressure, a transient tachycardia and a sustained bradycardia were observed. Pretreatment of the animals with verapamil (1 mg kg−1, i.v.) or nifedipine (200 μg kg−1, i.v.) produced on average 5 mmHg decrease in mean arterial blood pressure. Both verapamil and nifedipine inhibited by 63 and 44% the pressor actions of ET‐1 or IRL 1620 (1 nmol kg−1), respectively, and the accompanying bradycardia. Both verapamil and nifedipine potentiated the magnitude of the depressor action of ET‐1 and IRL 1620 without affecting the accompanying tachycardia. Decreasing mean arterial blood pressure with hydralazine (0.2‐0.3 μmol kg−1, i.v.) to levels comparable to those observed after verapamil or nifedipine had no significant effects on the haemodynamic responses to ET‐1 or IRL‐1620.

Intravenous bolus injection of ET‐1 or IRL 1620 (0.1–2 nmol kg−1) into anaesthetized rats produced dose‐dependent ST segment elevation of the electrocardiogram without causing arrhythmias. ST segment elevation developed within 30–50 s and persisted for at least 10–20 min following injection of the peptides.

Pretreatment of the animals with verapamil (1 mg kg−1, i.v.) or nifedipine (200 μg kg−1, i.v.) inhibited on average by 79 and 76% the ST segment elevation elicited by ET‐1 (1 nmol kg−1), respectively. Verapamil and nifedipine also attenuated IRL 1620 (1 nmol kg−1)‐induced ST segment elevation on average by 71 and 74%, respectively. In contrast, no significant inhibition was observed with hydralazine (0.2‐0.3 μmol kg−1).

Both ET‐1 and, to a lesser extent, IRL 1620 (0.1–2 nmol kg−1) evoked albumin accumulation in cardiac tissues in a dose‐dependent fashion as measured by the local extravascular accumulation of Evans blue dye in conscious rats. ET‐1 and IRL 1620 (1 nmol kg−1) enhanced albumin extravasation by 109 and 82%, and 34 and 44% in the left ventricle and right atrium, respectively. ET‐1 or IRL 1620‐induced albumin extravasation was completely prevented by verapamil (1 mg kg−1) or nifedipine (200 μg kg−1) in these vascular beds. In contrast, hydralazine (0.2‐0.3 μmol kg−1) failed to modify the effects of ET‐1 or IRL 1620 on albumin extravasation.

These results show that verapamil and nifedipine are highly effective in protecting the myocardium against the pro‐ischaemic and microvascular permeability enhancing effects of ET‐1 and suggest that ETA and constrictor ETB (tentatively termed ETB2) receptors mediating these actions of ET‐1 are coupled to calcium influx through dihydropyridine‐sensitive calcium channels.