bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pharmacological characterization of presynaptic α2‐autoreceptors in rat submaxillary gland and heart atrium
Authors: Limberger Norbert , Trendelenburg Anne‐Ulrike , Starke Klaus 
Published: July 2012

The pharmacological properties of presynaptic α2‐autoreceptors were studied in rat isolated submaxillary glands and atria. Tissue pieces were preincubated with [3H]‐noradrenaline, then superfused with medium containing desipramine, and stimulated electrically. In one series of experiments, pEC30 values of 12 α‐adrenoceptor antagonists were determined, i.e., negative logarithms of concentrations that increased the electrically evoked overflow of tritium by 30%. In another series, pKD values of 9 α‐adrenoceptor antagonists against the release‐inhibiting effect of 5‐bromo‐6‐(2‐imidazolin‐2‐ylamino)‐quinoxaline (UK 14304), and of 3 antagonists against the release‐inhibiting effect of methoxamine, were determined.
In submaxillary glands, the pEC30 values of the antagonists correlated well with their pKD values against UK 14304 (r = 0.93). The same was true for atria (r = 0.92).
In submaxillary glands, the pKD values of 3 antagonists against UK 14304 were very similar to their pKD values against methoxamine, with a maximal difference of 0.4. The same was true for atria where the maximal difference was 0.3.
The pEC30 values obtained in submaxillary glands correlated significantly with those obtained in atria (r = 0.81). The same was true for the pKD values (r = 0.79). However, the pEC30 and pKD values also indicated consistent differences between the two tissues.
It is concluded that the sites of action of the imidazoline UK 14304 (α2‐selective), the phenylethylamine noradrenaline, and the phenylethylamine methoxamine (α1‐selective) are exclusively α2‐adrenoceptors. There is no indication for presynaptic α1‐adrenoceptors or for an effect of UK 14304 mediated by presynaptic imidazoline receptors. The α2‐autoreceptor population in the submaxillary gland differs from that in the atrium.6 Comparison with studies from the literature indicates that the submaxillary autoreceptors are closely similar to the α2D radioligand binding site found in the bovine pineal gland and probably the rat submaxillary gland. The atrial autoreceptors also conform best to this site, but the agreement is more limited; the atrial autoreceptors may represent a type related to, but distinct from, the α2D site, or a mixture of different types.
Modulation of non‐adrenergic non‐cholinergic inhibitory neurotransmission in rat gastric fundus by the α2‐adrenoceptor agonist, UK‐14,304
Authors: Lefebvre R.A. , Smits G.J.M. 
Published: July 2012

The influence of the α2‐adrenoceptor agonist, UK‐14,304, on non‐adrenergic non‐cholinergic (NANC) relaxation induced by electrical field stimulation was investigated in longitudinal muscle strips of the gastric fundus of reserpinized rats.
In tissues where tone was raised by 3 × 10−7 m prostaglandin F2α (PGF2α), the inhibitory effect of 10−6 m UK‐14,304, on the NANC relaxations induced by short train stimulation (40 V, 1 ms, 20 s) was inversely related to the stimulus frequency (1‐4‐16 Hz). UK‐14,304 (10−6 m) did not influence relaxations induced by administration of exogenous nitric oxide (NO, 2 × 10−6 m−10−4 m). The inhibitory effect of UK‐14,304 on the electrically induced relaxations was antagonized by 10−6 m rauwolscine but not by 10−6 m prazosin.
UK‐14,304 (10−6 m) also reduced the amplitude of the sustained NANC relaxation, induced by electrical field stimulation (40 V, 1 ms, 4 Hz) for 5 min. The effect of UK‐14,304 was also antagonized by 10−6 m rauwolscine but not by 10−6 m prazosin. UK‐14,304 (10−6 m) did not reduce the relaxation induced by 3 × 10−9 m. vasoactive intestinal polypeptide (VIP).
These results suggest that the release of the inhibitory NANC neurotransmitter during short train stimulation, thought to be NO, and during sustained stimulation, thought to be VIP, is inhibited by stimulation of presynaptic α2‐adrenoceptors in the rat gastric fundus.
Role of extracellular and intracellular sources of Ca2+ in sarafotoxin S6b‐induced contraction of strips of the rat aorta
Authors: Watanabe Chiaki , Hirano Katsuya , Kanaide Hideo 
Published: July 2012

The effect of sarafotoxin S6b (sarafotoxin), a vasoconstrictor peptide, on cytosolic Ca2+ concentration ([Ca2+]i) and force in rat aortic strips loaded with fura‐2 was determined by front‐surface fluorometry. The objective was to elucidate the role of extracellular and intracellular Ca2+ in the mechanism of action of this peptide.
In the presence of extracellular 1.25 mm Ca2+, sarafotoxin induced a biphasic response consisting of an initial rapid increase in [Ca2+]i followed by a secondary sustained increase. Tension developed slowly but was sustained during the application of sarafotoxin. Diltiazem (10 nm−0.1 mm) partially inhibited both the increases in [Ca2+]i and tension.
In the presence of extracellular Ca2+, the force developed in relation to the increase in [Ca2+]i ([Ca2+]i‐force relationship) observed with sarafotoxin was much greater than that observed upon K+ depolarization. In the presence of diltiazem the sarafotoxin‐induced [Ca2+]i‐force relationship was shifted even further to the left.
In the absence of extracellular Ca2+, sarafotoxin induced a transient increase in [Ca2+]i and a sustained contraction. Extending the incubation time in Ca2+‐free physiological solution, resulted in smaller responses. However, after 60 min in Ca2+‐free solution, sarafotoxin induced a sustained contraction but no change in [Ca2+]i. This residual contraction was inhibited by H‐7, which is known to inhibit protein kinase C.
After treatment with caffeine to reduce intracellular stored Ca2+, sarafotoxin could still elicit increases in [Ca2+]i and in tension, showing that the caffeine‐sensitive intracellular Ca2+ store partially overlaps with the sarafotoxin‐sensitive store.
We conclude that, in addition to those components of contraction dependent on extracellular‐ and on intracellularly stored Ca2+, sarafotoxin can also induce contraction without increasing [Ca2+]i. This component may be partially linked to the activation of protein kinase C and may contribute, in part, to the leftward shift of the [Ca2+]i‐force relationship in the presence of sarafotoxin.
Antiarrhythmic agents act differently on the activation phase of the ACh‐response in guinea‐pig atrial myocytes
Authors: Inomata Norio , Ohno Tomochika , Ishihara Takafumi , Akaike Norio 
Published: July 2012

Anti‐acetylcholine effects of pilsicainide, flecainide, disopyramide and propafenone on the acetylcholine (ACh)‐induced K+ current (IK.ACh) were examined in dissociated guinea‐pig atrial myocytes under whole‐cell voltage clamp by the use of the ‘concentration‐clamp’ technique.
The IK.ACh was activated with a latency of about 100 ms after 1 μm ACh application and desensitized to a steady‐state level. The latent period and the time to peak response were shortened with increasing ACh concentration.
The values of half‐maximal inhibition (IC50) on the peak and steady state responses were 25 and 25 μm for pilsicainide, 1.7 and 2.0 μm for disopyramide, 19 and 2.0 μm for flecainide and 0.7 and 0.2 μm for propafenone, respectively.
Pilsicainide and disopyramide increased the latent period and the time to peak of IK.ACh in a concentration‐dependent manner. Flecainide and propafenone did not change the latent period, but shortened the time to peak and hastened the decay of IK.ACh in a voltage‐independent manner.
The results suggest that the mechanisms underlying the anti‐acetylcholine effect of antiarrhythmic drugs are different among these drugs: i.e., pilsicainide and disopyramide mainly block the muscarinic ACh receptors while flecainide and propafenone inhibit the K+ channel itself as open channel blockers.
Levamisole‐activated single‐channel currents from muscle of the nematode parasite Ascaris suum
Authors: Robertson S.J. , Martin R.J. 
Published: July 2012

The patch‐clamp technique was used to examine levamisole‐activated channels in muscle vesicles from Ascaris suum. Cell‐attached and isolated inside‐out patches were used.
Levamisole (1–90 μm), applied to the extracellular surface, activated channels which had apparent mean open‐times in the range 0.80–2.85 ms and linear I/V relationships with conductances in the range 19–46 pS. Ion‐replacement experiments showed the channels to be cation selective.
The kinetics of the channels were analysed. Generally open‐ and closed‐time distributions were best fitted by two, and three expotentials respectively, indicating the presence of at least two open states and at least three closed states. The distributions of burst‐times were best‐fitted by two exponentials.
Channel open‐ and burst‐times were voltage‐sensitive: at low levamisole concentrations (1–10 μm), they increased with hyperpolarization. At higher concentrations of levamisole (30 μm and 90 μm) flickering channel‐block was observed at hyperpolarized potentials. Using a simple channel‐block model, values for the blocking dissociation constant, KB were determined as 123 μm at −50 mV, 46 μm at −75 mV and 9.4 μm at −100 mV.
At the higher concentration of levamisole (30 μm and 90 μm) long closed‐times separating ‘clusters' of bursts were observed, at both hyperpolarized and depolarized membrane potentials and this was interpreted as desensitization.
Effect of bradykinin and prostaglandins on the release of calcitonin gene‐related peptide‐like immunoreactivity from the rat spinal cord in vitro
Authors: Andreeva L. , Rang H.P. 
Published: July 2012

The release of calcitonin gene‐related peptide‐like immunoreactivity (CGRP‐LI) from the dorsal horn of the rat spinal cord in vitro in response to dorsal root stimulation was measured by radioimmunoassay.
Stimulation of the dorsal roots (3 or 4 roots on each side) at 10 Hz for 5 min evoked a mean release (R1) of 134.3 ± 17.5 (n = 10) fmol CGRP‐LI; the release (R2) evoked by a second stimulation period 30 min later under control conditions was 77 ± 10% (n = 10) of R1. Test compounds were applied to the preparation following release R1, and their effect calculated from the value of R2/R1.
Bradykinin (0.01–10 μm) had no significant effect on the basal release of CGRP‐LI, but at 0.1–10 μm it increased 2–3 fold the release evoked by dorsal root stimulation.
This effect of bradykinin was prevented by indomethacin (10 μm), or by the B2‐receptor antagonist, Hoe140 (1–10 μm). In the presence of Hoe140, bradykinin significantly reduced R2/R1; the explanation for this is not clear.
The B1‐receptor agonist, Des‐Arg9‐bradykinin (10 μm), did not affect CGRP‐LI release nor was the effect of bradykinin blocked by the B1‐receptor antagonist, Des‐Arg9‐Leu8‐bradykinin (10 μm).
Various prostaglandins were found to mimic the effect of bradykinin on CGRP‐LI release. Their approximate order of potency was prostaglandin D2 (PGD2) = PGE1 > PGF2α = PGE2; PGI2 was ineffective at 10 μm.
Forskolin (30 μm) and 3‐isobutyl 1‐methylxanthine (IBMX; 10 μm) also increased the evoked release of CGRP‐LI.
It is concluded that bradykinin acts on B2‐receptors in the spinal cord, causing the formation of prostanoids, which in turn cause an enhancement of neuropeptide release from primary afferent nerve terminals in the dorsal horn. This effect may be secondary to activation of adenylate cyclase. Because B2‐receptors are mainly associated with primary afferent nerve terminals, it is likely that prostanoid production is also a function of these structures. Whether this action of bradykinin has any physiological function in nociceptive transmission remains unclear.
Potentiation of miniature endplate potential frequency by ATP in Xenopus tadpoles
Authors: Fu Wen‐Mei , Yang Shiau‐Hui , Lin‐Shiau Shoei‐Yn 
Published: July 2012

Extracellular application of ATP (1 mm), a substance co‐stored and co‐released with acetylcholine in peripheral nervous systems, potentiated the spontaneous secretion of acetylcholine (ACh) but had no effect on the amplitude and decay time constant of miniature endplate potentials (m.e.p.ps) at neuromuscular synapses in Xenopus tadpoles.
α,β‐Methylene ATP (0.3 mm) and GTP (1 mm) were also effective in increasing m.e.p.p. frequency. On the other hand, ADP, AMP and adenosine (all at 1 mm) decreased m.e.p.p. frequency.
Unlike the transient effect of ATP analogue and GTP on m.e.p.p. frequency, the phorbol ester TPA (2 μm) which is a protein kinase C activator, increased m.e.p.p. frequency consistently and the effects lasted as long as the presence of TPA.
Staurosporine (0.5 μm) and H‐7 (10 μm), which are protein kinase C inhibitors, each decreased the basal level of m.e.p.p. frequency and markedly inhibited the effects of both ATP and TPA.
These results suggest that there is a basal activity of cytosolic protein kinases in the nerve terminals of Xenopus tadpoles and the effect of ATP is probably mediated by the binding of membrane surface purinoceptors which in turn activates cytosolic protein kinases and increases ACh release.
Influence of rhein anthrone on peristaltic reflex of guinea‐pig isolated ileum: involvement of prostaglandins
Authors: Nijs Geert , de Witte Peter , Geboes Karel , Meulemans Ann , Schuurkes Jan , Lemli Joseph 
Published: July 2012

The influence of rhein anthrone on the peristaltic reflex was studied with a modified Trendelenburg technique in a range from 10−8 m to 4 × 10−5 m, on a normal and reversed guinea‐pig ileum segment. Rhein anthrone had no significant effects on longitudinal muscle tension, intraluminal pressure or volume displacement when tested on the normal segment in doses up to 10−5 m. When applied to the mucosal side (reversed segment), rhein anthrone produced a dose‐dependent increase of longitudinal muscle tension (significant from 10−7 m), of intraluminal pressure (significant from 3 × 10−6 m) and of volume displacement (significant from 10−7 m). The data show that rhein anthrone possesses in vitro activity which is dependent on contact with the mucosa.
The action of rhein anthrone on the reversed segment was inhibited by BW755C (a dual inhibitor of cyclo‐oxygenase and lipoxygenase), by indomethacin and by SC19220 (an antagonist of prostaglandin E2 (PGE2) and PGF2α). The effects remaining on longitudinal muscle tension, intraluminal pressure and volume displacement, calculated as percentage (mean ± s.e.mean) of the initial value, were respectively: 13 ± 8; 23 ± 13; 112 ± 5 for BW755C; 66 ± 19; 51 ± 8; 53 ± 8 for indomethacin and 27 ± 12; 13 ± 7; 50 ± 5 for SC19220. It is concluded that arachidonic acid metabolites, especially PGE2 and PGF2α are involved in the effects of rhein anthrone on the reversed segment.
Degradation of acetylcholine in human airways: role of butyrylcholinesterase
Authors: Norel X. , Angrisani M. , Labat C. , Gorenne I. , Dulmet E. , Rossi F. , Brink C. 
Published: July 2012

Neostigmine and BW284C51 induced concentration‐dependent contractions in human isolated bronchial preparations whereas tetraisopropylpyrophosphoramide (iso‐OMPA) was inactive on airway resting tone.
Neostigmine (0.1 μm) or iso‐OMPA (100 μm) increased acetylcholine sensitivity in human isolated bronchial preparations but did not alter methacholine or carbachol concentration‐effect curves.
In the presence of iso‐OMPA (10 μm) the bronchial rings were more sensitive to neostigmine. The pD2 values were, control: 6.05 ± 0.15 and treated: 6.91 ± 0.14.
Neostigmine or iso‐OMPA retarded the degradation of acetylcholine when this substrate was exogenously added to human isolated airways. A marked reduction of acetylcholine degradation was observed in the presence of both inhibitors. Exogenous butyrylcholine degradation was prevented by iso‐OMPA (10 μm) but not by neostigmine (0.1 μm).
These results suggest the presence of butyrylcholinesterase activity in human bronchial muscle and this enzyme may co‐regulate the degradation of acetylcholine in this tissue.
Arterial endothelial barrier dysfunction: actions of homocysteine and the hypoxanthine‐xanthine oxidase free radical generating system
Authors: Berman Rodney S. , Martin William 
Published: July 2012

Endothelial barrier function was assessed by use of an in vitro model in which transfer of trypan blue‐labelled albumin was measured across monolayers of bovine aortic endothelial cells grown on polycarbonate membranes.
Addition of either hypoxanthine (0.2 mm) or xanthine oxidase (20 mu ml−1) alone during a 90 min incubation did not affect albumin transfer across endothelial cell monolayers, but a combination of both increased transfer.
The increase in albumin transfer induced by hypoxanthine and xanthine oxidase was abolished by catalase (3 u ml−1), reduced by allopurinol (4 mm), but unaffected by superoxide dismutase (6000 u ml−1), the hydroxyl radical scavengers, mannitol (15 mm), dimethylthiourea (10 mm) and N‐(2‐mercaptopropionyl)‐glycine (1 mm), the iron chelator, deferoxamine (0.5 mm), ferric chloride (50 μm), an inhibitor of nitric oxide synthase, NG‐nitro‐l‐arginine (30 μm), or the antioxidant, dithiothreitol (3 mm).
Hydrogen peroxide (0.1–30 mm) itself increased albumin transfer across endothelial cell monolayers, exhibiting a biphasic concentration‐response curve. The increase induced by 0.1 mm hydrogen peroxide was abolished in the presence of 0.3 u ml−1 catalase whilst that induced by 10 mm hydrogen peroxide was abolished by 3000 u ml−1 catalase.
Homocysteine (0.5–1.5 mm) did not affect albumin transfer across endothelial monolayers when added alone, but when added in combination with copper sulphate (50 μm), which catalyses its oxidation, a significant increase in albumin transfer was observed.
The increase in albumin transfer induced by the combination of homocysteine (1.5 mm) and copper sulphate was abolished by catalase (1 u ml−1), but was unaffected by superoxide dismutase (6000 u ml−1), mannitol (15 mm), dimethylthiourea (1 mm) or deferoxamine (0.5 mm).
The data suggest that the endothelial barrier dysfunction induced by the combination of hypoxanthine and xanthine oxidase is mediated solely by the action of hydrogen peroxide and not by superoxide anion, hydroxyl radical, peroxynitrite anion or hypochlorous acid. The copper‐catalysed oxidation of homocysteine also induces endothelial barrier dysfunction through the generation of hydrogen peroxide. These findings may have relevance to the endothelial barrier dysfunction associated with ischaemia‐reperfusion injury and the atherogenic actions of homocysteine.
Digoxin activates sarcoplasmic reticulum Ca2+‐release channels: a possible role in cardiac inotropy
Authors: McGarry Stephen J. , Williams Alan J. 
Published: July 2012

The effect of digoxin on rapid 45Ca2+ efflux from cardiac and skeletal sarcoplasmic reticulum (SR) vesicles was investigated. Additionally the interaction of digoxin with single cardiac and skeletal muscle SR Ca2+‐release channels incorporated into planar phospholipid bilayers and held under voltage clamp was determined.
Digoxin (1 nm) increased the initial rate and amount of Ca2+‐induced release of 45Ca2+ from cardiac SR vesicles, passively loaded with 45CaCl2, at an extravesicular [Ca2+] of 0.1 μm. The efflux in the presence and absence of digoxin was inhibited at pm extravesicular Ca2+ and blocked by 5 mm Mg2+.
To elucidate the mechanism of action of digoxin, single‐channel recording was used. Digoxin (1–20 nm) increased single‐channel open probability (Po) when added to the cytosolic but not the luminal face of the cardiac channel in the presence of sub‐maximally activating Ca2+ (0.1 μm−10 μm) with an EC50 of 0.91 nm at 10 μm Ca2+. The mechanisms underlying the action of digoxin appear to be concentration‐dependent. The activation observed at 1 nm digoxin appears to be consistent with the sensitization of the channel to the effects of Ca2+. At higher concentrations the drug appears to interact synergistically with Ca2+ to produce values of Po considerably greater than those seen with Ca2+ as the sole activating ligand.
Digoxin had no effect on single‐channel conductance or the Ca2+/Tris permeability ratio. In channels activated by digoxin the Po was decreased by Mg2+. Single‐channels were characteristically modified to a long lasting open, but reduced, conductance state when 100 nm ryanodine was added to the cytosolic side of the channel.
Activation of the cardiac SR Ca2+‐release channel was observed with similar concentrations of digitoxin, however, higher concentrations of ouabain were required to increase Po. In contrast, a steroid which is not positively inotropic, chlormadinone acetate, had no effect on either cardiac or skeletal SR Ca2+‐release channel activity.
At concentrations up to 1 μm, digoxin had no effect on Ca2+‐induced 45Ca2+ efflux from skeletal muscle SR vesicles nor did it affect skeletal SR Ca2+‐release channel Po, reflecting a difference between the cardiac and skeletal isoforms of the Ca2+‐release channel.
Since activation of the cardiac SR Ca2+‐release channel occurs within the range of concentrations of digoxin encountered therapeutically, it is possible that activation of this channel contributes to the positive inotropic effect observed with this drug. Further, activation of the channel by higher concentrations of digoxin may contribute to the toxic effects seen clinically.
Effects of nifedipine and ryanodine on adrenergic neurogenic contractions of rat vas deferens: evidence for a pulse‐to‐pulse change in Ca2+ sources
Authors: Bültmann Ralph , von Kügelgen Ivar , Starke Klaus 
Published: July 2012

The effects of nifedipine and ryanodine on the adrenergic component of neurogenic contractions of the rat isolated vas deferens were studied in an attempt to identify the sources of Ca2+ mediating the contraction. The tissue was electrically stimulated by single pulses or pairs of widely spaced pulses. The purinergic component of contraction was suppressed by the presence of 300 μm suramin.
In Mg2+‐free medium, nifedipine (0.01–10 μm) reduced the first and, to a greater extent, the second twitch elicited by two pulses 3 s apart. This pattern of inhibition was observed both in the absence of rauwolscine (when twitch 2 was smaller than twitch 1) and in the presence of 0.1 μm rauwolscine (when, due to interruption of prejunctional α2‐adrenoceptor‐mediated autoinhibition, twitch 2 was of similar height to twitch 1). Nifedipine reduced only twitch 2 but not twitch 1 in medium containing 1.2 mm Mg2+.
Single pulses of increasing current strength elicited increasing contraction. Nifedipine reduced contractions by about the same absolute extent at all current strengths, so that the relative contribution of the nifedipine‐sensitive component decreased with increasing current strength.
When the pulse interval in a pair was increased from 5 to 60 s, the inhibition by nifedipine of the second twitch was most marked at an interval of 5 s and declined as the interval increased.
In contrast to nifedipine, 20 μm ryanodine reduced the first twitch of a pair to a greater extent than a second twitch 5 s later, so that twitch 2 became greater than twitch 1. The inhibition by ryanodine of twitch 2 increased with increasing pulse interval.
In vasa deferentia preincubated with [3H]‐noradrenaline, 1 μm nifedipine and 20 μm ryanodine did not change the electrically evoked overflow of tritium, whereas 10 μm nifedipine increased it.
It is concluded that, when the sympathetic axons of the vas deferens are stimulated by a single pulse (or the first pulse of a pair) in Mg2+‐free medium, both Ca2+ mobilization inside the smooth muscle cells and Ca2+ entry contribute to the ensuing adrenergic contraction. The relative contribution of Ca2+ entry is small at maximal stimulus strength but increases with decreasing stimulus strength. When a second pulse follows the first after an appropriate interval, a switch of Ca2+ sources occurs: intracellular Ca2+ mobilization is decreased during twitch 2, whereas Ca2+ entry is increased.