bluuebunny/crossref_metadata_2025_split 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.
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.
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.