bluuebunny/crossref_metadata_2025_split huggingface dataset:
Endogenous peptidergic modulation of perisynaptic Schwann cells at the frog neuromuscular junction
Authors: Bourque Marie‐Josée , Robitaille Richard 
Published: September 2004

Although peptides are important modulators of synapses, their action on synapse‐glia interactions remain unclear. The amphibian neuromuscular junction (NMJ) was used to examine the effects of substance P (SP) on perisynaptic Schwann cells (PSCs), glial cells at the frog NMJ, by monitoring changes in intracellular Ca2+.
SP induced Ca2+ responses that were mimicked by the neurokinin 1 receptor (NK‐1) agonist septide and with a shorter delay by the SP fragment, SP(6–11). SP and SP(6–11) responses were blocked by NK‐1 antagonists SR140333 and LY303870.
Ca2+ responses remained unchanged when extracellular Ca2+ was removed but were blocked after pertussis toxin (PTX) treatment, indicating that the receptors were linked to internal stores of Ca2+ via a PTX‐sensitive G‐protein.
The slowly hydrolysable NK‐1 agonist [Sar9, Met(O2)11]‐SP only induced Ca2+ responses when applied for a long period of time and not during brief, local applications, suggesting the involvement of SP hydrolysis. Acetylcholinesterase (AChE) may not be involved in SP degradation since Ca2+ responses evoked by SP were unchanged in the presence of the cholinesterase inhibitor neostigmine.
Ca2+ responses induced by muscarine and nerve stimulations were almost abolished when preceded by SP applications, while those induced by ATP were significantly reduced. The rundown of the nerve‐evoked Ca2+ responses in PSCs was attenuated in the presence of SR140333.
These results indicate that endogenous SP is involved in the regulation of PSC activity and that SP is an important modulator of glial cell Ca2+ signalling and synapse‐glia communication.
Spontaneous electrical rhythmicity in cultured interstitial cells of Cajal from the murine small intestine
Authors: Koh Sang Don , Sanders Kenton M. , Ward Sean M. 
Published: September 2004

Interstitial cells of Cajal (ICC) are pacemaker cells in the small bowel, and therefore this cell type must express the mechanism responsible for slow wave activity. Isolated ICC were cultured for 1–3 days from the murine small intestine and identified with c‐Kit‐like immunoreactivity (c‐Kit‐LI).
Electrical recordings were obtained from cultured ICC with the whole‐cell patch clamp technique. ICC were rhythmically active, producing regular slow wave depolarizations with waveforms and properties similar to slow waves in intact tissues.
Spontaneous activity of c‐Kit‐LI cells was inhibited by reduced extracellular Na+, gadolinium, and reduced extracellular Ca2+. The activity was not affected by nisoldipine. Voltage clamp studies showed rhythmic inward currents that were probably responsible for the slow wave activity. The current‐voltage relationship showed that the spontaneous currents reversed at about +17 mV. These observations are consistent with the involvement of a non‐selective cation current in the generation of slow waves, but do not rule out contributions from other conductances or transporters.
A Ba2+‐sensitive inwardly rectifying K+ current in c‐Kit‐LI cells that may be involved in slow wave repolarization and maintenance of a negative potential between slow waves was also found. Similar pharmacology was observed in studies of intact murine intestinal muscles.
Cultured ICC may be a useful model for studying the properties and pharmacology of some of the ionic conductances involved in spontaneous rhythmicity in the gastrointestinal tract.
Neuroeffector transmission in arterioles of the guinea‐pig choroid
Authors: Hashitani H. , Windle A. , Suzuki H. 
Published: September 2004

Using conventional microelectrode techniques, membrane potentials were recorded from smooth muscle cells of guinea‐pig choroidal arterioles.
Transmural stimulation initiated excitatory junction potentials (EJPs) which were abolished by either guanethidine or α,β‐methylene‐ATP but not by phentolamine, indicating that they resulted from activation of purinoceptors.
Trains of stimuli evoked EJPs which were followed by a slow depolarization, an inhibitory junction potential (IJP) or a biphasic membrane potential change which consisted of an IJP and a subsequent slow depolarization.
Slow depolarizations were abolished by either phentolamine or guanethidine, indicating that they resulted from activation of α‐adrenoceptors.
IJPs were abolished by atropine but not by guanethidine, and were reduced by 50 % by apamin with the residual response being abolished by charybdotoxin, indicating that they resulted from the activation of muscarinic receptors which open two sets of Ca2+‐activated K+ channels.
Most responses were followed by slow hyperpolarizations. These were almost abolished by L‐nitroarginine, an effect which was partly overcome by L‐arginine, and were abolished by glibenclamide, indicating that they resulted from the release of NO and activation of ATP‐sensitive K+ channels.
Immunohistochemical analysis showed that arterioles were densely innervated by adrenergic nerve fibres. A population of fibres, likely to be cholinergic, was also identified. Furthermore, populations of nerve fibres immunoreactive to antibodies against either nitric oxide synthase (NOS) or substance P (SP) were also identified.
These findings indicate that choroidal arterioles of the guinea‐pig are innervated by at least three different populations of nerves, adrenergic nerves which evoke excitatory responses, cholinergic nerves which evoke inhibitory responses and a population of nerves which cause the release of NO.
Tetrodotoxin‐resistant impulses in single nociceptor nerve terminals in guinea‐pig cornea
Authors: Brock James A. , McLachlan Elspeth M. , Belmonte Carlos 
Published: September 2004

Extracellular recording techniques have been used to study nerve impulses in single sensory nerve terminals in guinea‐pig cornea isolated in vitro.
Nerve impulses occurred spontaneously and were evoked by electrical stimulation of the ciliary nerves.
The nerve impulses were identified as originating in polymodal receptors, mechano‐receptors or ‘cold’ receptors. All three types are believed to be nociceptors.
Tetrodotoxin (TTX, 1 μm) blocked nerve impulses evoked by electrical stimulation of the ciliary nerves. However, ongoing and/or naturally evoked nerve impulses persisted in the presence of TTX in all three types of receptors. Lignocaine (lidocaine; 1 mm) blocked all electrical activity.
TTX‐resistant sodium channels therefore play a major role in generating the action potentials that signal pain to the brain.
Ionotropic and metabotropic activation of a neuronal chloride channel by serotonin and dopamine in the leech Hirudo medicinalis
Authors: Ali Declan W. , Catarsi Stefano , Drapeau Pierre 
Published: September 2004

Cl− channels on the pressure‐sensitive (P) neuron in the leech are directly activated by synaptic release of serotonin (5‐HT) and are indirectly stimulated by the cAMP second messenger pathway, suggesting an unusual dual regulation of the channels. We have investigated the mode of action of 5‐HT and dopamine (DA) on a Cl− channel in adult P cells in culture by recording from cell‐attached patches.
5‐HT increased Cl− channel activity only when included in the recording pipette and not when applied in the bath.
Pipette or, more effectively, bath application of DA led to an increase in Cl− channel activity. This effect was blocked by the potent and specific dopaminergic (DA1) receptor blocker, SCH‐23390.
The stimulation by DA, but not by 5‐HT, was also blocked by the cAMP‐dependent protein kinase A (PKA) inhibitor Rp‐cAMP and was mimicked by the membrane‐permeant cAMP analogue dibutyryl cAMP (db‐cAMP).
Our results show that 5‐HT directly gates a Cl− channel that is also activated by DA via the cAMP pathway. This study demonstrates that a ligand‐gated channel can be independently operated by another transmitter acting via a second messenger pathway.
Chloride and non‐selective cation channels in unstimulated trout red blood cells
Authors: Egée Stéphane , Mignen Olivier , Harvey Brian J. , Thomas Serge 
Published: September 2004

The cell‐attached and excised inside‐out configurations of the patch‐clamp technique were used to demonstrate the presence of two different types of ion channels in the membrane of trout red blood cells under isotonic and normoxic conditions, in the absence of hormonal stimulation. The large majority (93 %) of successful membrane seals allowed observation of at least one channel type.
In the cell‐attached mode with Ringer solution in the bath and Ringer solution, 145 mM KCl or 145 NaCl in the pipette, a channel of intermediate conductance (15‐25 pS at clamped voltage, Vp= 0 mV) was present in 85 % of cells. The single channel activity reversed between 5 and 7 mV positive to the spontaneous membrane potential. A small conductance channel of 5‐6 pS and +5 mV reversal potential was also present in 62 % of cells.
After excision into the inside‐out configuration (with 145 mM KCl or NaCl, pCa 8 in the bath, 145 mM KCl or NaCl, pCa 3 in the pipette) the intermediate conductance channel was present in 439 out of 452 successful seals. This channel was spontaneously active in 90 % of patches and in the other 10 % of patches the channel was activated by suction. The current‐voltage relationship showed slight inward rectification. The channel conductance was in the range 15‐20 pS between ‐60 and 0 mV and increased to 25‐30 pS between 0 and 60 mV, with a reversal potential close to zero. Substitution of K+ for Na+ in the pipette or in the bath did not significantly change the single channel conductance. Dilution of the bathing solution KCl concentration shifted the reversal potential towards the Nernst equilibrium for cations. Substitution of N‐methyl‐D‐glucamine (NMDG) for K+ or Na+ in the bath almost abolished the outward current whilst the divalent cation Ca2+ permeated the channel with a higher permeability than K+ and Na+. Inhibition of channel openings was obtained with flufenamic acid, quinine, gadolinium or barium. Taken together these data demonstrate that the intermediate conductance channel belongs to a class of non‐selective cation (NSC) channels.
In excised patches, under the same control conditions, the conductance of the small conductance non‐rectifying channel was 8·6 ± 0·8 pS (n= 12) between ‐60 and +60 mV and the reversal potential was close to 0 mV. This channel could be blocked by 5‐nitro‐2‐(3‐phenylpropylamino)‐benzoate (NPPB) but not by flufenamic acid, DIDS, barium or gadolinium. Selectivity and substitution experiments made it possible to identify this channel as a non‐rectifying small conductance chloride (SCC) channel.
Validation of the [1,2‐13C]acetate recovery factor for correction of [U‐13C]palmitate oxidation rates in humans
Authors: Schrauwen Patrick , van Aggel‐Leijssen Dorien P. C. , van Marken Lichtenbelt Wouter D. , van Baak Marleen A. , Gijsen Annemie P. , Wagenmakers Anton J. M. 
Published: September 2004

The validity of estimations of plasma fatty acid oxidation using tracers has often been questioned. The appearance of isotopic markers in breath CO2 is delayed and incomplete. Recently suggestions have been made that substantial amounts of tracer are incorporated into products of the tricarboxylic acid cycle (e.g. glucose, glutamine and glutamate) and that an acetate correction factor can be used to correct for tracer fixation. In the present study we investigated whether the appearance of 13CO2 during a separate infusion of [1,2‐13C]acetate could be used for correction of [U‐13C]palmitate oxidation rates in studies lasting <2 h and we quantified the appearance of tracer in the glutamine, glutamate and glucose pools of the body.
An infusion of either [1,2‐13C]acetate (0.104 μmol min−1 kg−1) or [U‐13C]palmitate (0.013 μmol min−1 kg−1) was given to eight male subjects and continued for 2 h at rest. In six subjects the infusion of [1,2‐13C]acetate was repeated to determine reproducibility of the acetate recovery.
Fractional recovery in breath from [1,2‐13C]acetate gradually increased during the infusion period at rest from 14.1 ± 0.6 % at 60 min to 26.5 ± 0.5 % at 120 min after the start of the infusion. Intersubject coefficient of variance was 8.3 ± 0.6 % and intrasubject coefficient of variance of the acetate recovery tests was 4.0 ± 1.5 %. After 2 h of [1,2‐13C]acetate infusion, 12.4 ± 0.8 and 10.3 ± 0.9 % of infused 13C was incorporated in the glutamine and glutamate pools, respectively.
In conclusion, the [1,2‐13C]acetate recovery factor can be used for correcting the rate of [U‐13C]palmitate oxidation in infusing studies of 2 h in resting conditions. Failure to use this recovery factor leads to a substantial underestimation of the rate of plasma free fatty acid oxidation. The extent of label fixation could largely be explained by accumulation of tracer carbon in glutamine and glutamate, and the accumulation in glucose is negligible.
Potentiation of transmitter release by protein kinase C in goldfish retinal bipolar cells
Authors: Minami Naotoshi , Berglund Ken , Sakaba Takeshi , Kohmoto Hiromi , Tachibana Masao 
Published: September 2004

We examined whether transmitter release could be modified by the activation of protein kinase C (PKC) of retinal bipolar cells. A bipolar cell with a large axon terminal was isolated from the goldfish retina. The presynaptic Ca2+ current was measured under whole‐cell voltage clamp, and the released transmitter (probably glutamate) was detected electrophysiologically by using the response of NMDA receptors of catfish horizontal cells as a reporter.
Transmitter release was potentiated by a PKC activator, phorbol 12‐myristate 13‐acetate (PMA), but not by an ineffective phorbol ester, 4α‐phorbol 12,13‐didecanoate. A PKC inhibitor, bisindolylmaleimide I, did not affect the transmitter release by itself but blocked the PMA‐induced potentiation of transmitter release. These results suggest that the actions of PMA were mediated via the activation of PKC.
Introduction of 5 mm EGTA into the presynaptic terminals of bipolar cells revealed two separate components of transmitter release. A rapid component was triggered immediately after depolarization while a slow component appeared with a delay. Application of PMA selectively potentiated the slow component without affecting the Ca2+ dependence of exocytosis.
We suggest that the activation of PKC may modify the recruitment process of synaptic vesicles in retinal bipolar cells.
Developmental profile and synaptic origin of early network oscillations in the CA1 region of rat neonatal hippocampus
Authors: Garaschuk Olga , Hanse Eric , Konnerth Arthur 
Published: September 2004

By applying fura‐2‐based fluorometric calcium imaging to neonatal rat hippocampal slices we identified a developmentally regulated spontaneous neuronal activity in the CA1 region of the hippocampus. The activity consisted of bursts of intracellular Ca2+ transients recurring synchronously at a slow rate of 0.4–2 min−1 in the entire population of pyramidal neurones and interneurones.
These early network oscillations (ENOs) were present during a restricted period of postnatal development. Thus, they were not detected at the day of birth (P0), at P1–P4 they consisted of bursts of large (up to 1.5 μm) Ca2+ transients, gradually transforming into regularly occurring, smaller Ca2+ transients during the subsequent week. Beyond P15–P16 no ENOs were detected.
The ENOs were blocked by tetrodotoxin (TTX) and by a reduction in temperature from 33–35°C to 20–22°C. By combining fluorometric imaging with whole‐cell current‐clamp recordings, we found that each ENO‐related Ca2+ transient was associated with a high‐frequency (up to 100 Hz) train of action potentials riding on a depolarizing wave.
Recordings in the voltage‐clamp mode revealed barrages of synaptic currents that were strictly correlated with the ENO‐associated Ca2+ transients in neighbouring pyramidal neurones. Perfusing the cells with an intracellular solution that allowed for a discrimination between GABAA and glutamate receptor‐mediated currents showed that these barrages of synaptic currents were predominantly of GABAergic origin.
The ENOs were totally blocked by the GABAA receptor antagonist bicuculline and they were also substantially reduced by the glutamatergic antagonists d,l‐2‐amino‐5‐phosphonovaleric acid (d,l‐APV) and 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX).
Synaptic stimulation and application of the GABAA receptor agonist muscimol mimicked the spontaneous Ca2+ transients in pyramidal neurones. The efficacy of muscimol in evoking Ca2+ transients decreased during development in parallel with the gradual disappearance of the ENOs.
The developmental decrease in the amplitude of ENO‐associated Ca2+ transients occurred in parallel with the transformation of the excitatory synaptic transmission in the hippocampus from the immature GABAergic to the mature glutamatergic form. Thus, at the beginning of the first postnatal week single‐shock synaptic stimulation produced Ca2+ transients that were completely blocked by bicuculline. At the end of the second postnatal week the same type of evoked synaptic stimulation produced a Ca2+ transient that was little affected by bicuculline but was abolished by the combined application of d,l‐APV and CNQX.
These results demonstrate the presence of periodic and spontaneous Ca2+ transients in the majority of pyramidal cells and interneurones of the neonatal CA1 hippocampal network. These ENOs exhibit a highly region‐specific developmental profile and may control the activity‐dependent wiring of the synaptic connectivity during early postnatal development.
Synaptic currents at individual connections among stellate cells in rat cerebellar slices
Authors: Kondo Satoru , Marty Alain 
Published: September 2004

Unitary inhibitory synaptic connections among stellate cells were studied in rat cerebellar slices. Presynaptic action potentials and inhibitory postsynaptic currents (IPSCs) were simultaneously recorded by loose cell‐attached and tight‐seal whole‐cell recording, respectively.
Several types of synaptic connections were distinguished on the basis of the shape of the amplitude distribution of successfully evoked currents. For simple synapses, which presumably arise at single release sites, these histograms could be fitted to a single Gaussian (5 cases). In four additional cases a small amplitude component (< 50 pA) was superimposed to a single Gaussian peak. The small events had slow rise times and widely distributed amplitudes. Finally eleven histograms showed two or more Gaussian components and were classified as complex connections.
Failure rates ranged from 0.06 to 0.85 for unitary connections (n= 20) and from 0.59 to 0.78 for simple synapses (n= 5).
Coefficient of variation values derived from Gaussian fits to simple synapse histograms ranged between 0.20 and 0.38 (n= 5).
In simple synapses peak current amplitudes were positively correlated to both current rise time and decay half‐width.
Intervals between presynaptic action potentials were widely distributed. During stationary periods there was no correlation between interspike interval and amplitude size, success rate or latency. In some experiments, episodes with shorter interspike intervals were observed. During these periods, amplitude and success rate decreased, and the latency increased. Thus, IPSC characteristics depend on the mean frequency of presynaptic spikes, but not on random fluctuations of interspike intervals during stationary periods.
Differential oxygen sensitivity of the K+‐Cl− cotransporter in normal and sickle human red blood cells
Authors: Gibson J. S. , Speake P. F. , Ellory J. C. 
Published: September 2004

K+ influx and efflux were measured in normal (HbA) and sickle (HbS) red blood cells to investigate the interaction of swelling, H+ ions and urea with O2 (0 to 150 mmHg O2) in the presence of ouabain and bumetanide (both 100 μM).
In HbA cells, K+‐Cl− cotransport was O2 dependent. At low oxygen tensions (PO2s) the transporter was inactive and refractory to low pH, swelling or urea.
Cl−‐independent K+ influxes in sickle cells were elevated at low PO2s, as previously reported. Cl−‐dependent K+ influxes were large at both high and low PO2s, whether stimulated by swelling, H+ ions or urea. In the absence of O2, Cl−‐dependent K+ influxes were similar in magnitude to those measured at high PO2s. The minimum for Cl−‐dependent K+ influx was observed at PO2s of about 40‐70 mmHg.
K+ efflux from HbS cells was stimulated by the addition of urea (500 mM). The rate constants were of similar magnitude whether measured at high PO2 or in the absence of O2, and were predominantly Cl− dependent under both conditions.
In HbS red blood cells, reduction of extracellular Ca2+, addition of 1 mM Mg2+ or nitrendipine (10 μM) to the saline had no effect. Inhibitors of K+‐Cl− cotransport, [(dihydroindenyl)oxy] alkanoic acid (DIOA; 100 μM) or calyculin A (0·1 μM), inhibited influxes by a similar magnitude to Cl− substitution.
Results are significant for the pathophysiology of sickle cell disease. Low pH and urea are able to stimulate KCl loss from sickle cells, leading to cellular dehydration, even in regions of low PO2.
The chronic effect of vascular endothelial growth factor on individually perfused frog mesenteric microvessels
Authors: Bates D. O. 
Published: September 2004

Hydraulic conductivity (Lp) of the wall of perfused microvessels has previously been shown to be chronically increased 24 h after a 10 min perfusion with vascular endothelial growth factor (VEGF). In order to investigate this further, Lp and the effective oncotic pressure difference (σΔΠ) acting across the vessel walls was measured before exposure to VEGF and 24 h later after the mesentery had been replaced in the abdominal cavity.
Acute 10 min perfusion with VEGF did not chronically change σΔΠ despite chronically increasing Lp 6.8 ± 1.2‐fold. This suggests that pathways formed 24 h after perfusion with VEGF which increase hydraulic conductivity of the capillary walls have the same reflection coefficient as those present before VEGF.
Acute 10 min perfusion with VEGF significantly increased the diameter of vessels after 24 h by 48 ± 13 %. To determine whether this was due to changes in the compliance of the vessel wall, the distensibility of microvessels was measured before and 24 h after perfusion with VEGF. The distensibility was increased 45 ± 15 % by VEGF but this was not great enough to account for the increase in diameter.
The chronic increase in Lp could be attenuated by inhibition of nitric oxide synthase with l‐NAME. In addition, the chronic increase in permeability was correlated with the acute response to VEGF (r= 0.71, P < 0.01) suggesting that the acute and chronic changes may be related.
These results show that VEGF chronically increases Lp without affecting the oncotic reflection coefficient. This may be due to reduced pore path length, or increased small pore numbers, which are properties of fenestrated capillaries. They also show that VEGF increases microvascular distensibility and diameter.