bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variability in spontaneous subcellular calcium release in guinea‐pig ileum smooth muscle cells
Authors: Gordienko D. V. , Bolton T. B. , Cannell M. B. 
Published: September 2004

Spontaneous, localized transient increases in [Ca2+]i (‘Ca2+ sparks’) were observed in about 40 % of fluo‐3‐loaded myocytes examined using laser scanning confocal microscopy. Ca2+ sparks persisted after application of Cd2+ (200 μM), but were abolished by ryanodine (30 μM) or thapsigargin (0.1 μM), suggesting that they arise from the spontaneous activation of ryanodine receptors (RyR) in the sarcoplasmic reticulum (SR).
Ca2+ sparks occurred much more frequently at certain sites (or ‘frequent discharge sites’, FDSs) within any confocal plane of the cell and line‐scan imaging revealed a wide variation in their spatial size, amplitude and time course. Some spontaneous local transients were very similar to ‘Ca2+ sparks’ observed in heart, i.e. lasting ≈200 ms with a peak fluorescence ratio of 1.75 ± 0.23 (mean ± s.d., n= 33). Other events were faster and smaller, lasting only ≈40 ms with a peak normalized fluorescence of 1.36 ± 0.09 (mean ± s.d., n= 28).
Spontaneous Ca2+ waves with a wide range of propagation velocities (between 30 and 260 μm s−1) were also observed. In about 60 % of records (n= 33), Ca2+ sparks could be detected at the sites of wave initiation. Waves of elevated [Ca2+]i propagated with non‐constant velocity and in some cases terminated. These observations could be explained by heterogeneity in the distribution of subcellular release sites as well as variability in the contribution of each release site to the wave.
Spontaneous [Ca2+]i transients in single dispersed visceral smooth muscle cells have a wide spectrum of behaviour that is likely to be the result of spatio‐temporal recruitment of smaller local events, probably via a calcium‐induced calcium release (CICR) mechanism. The spatial non‐uniformity of SR and RyR distribution within the cell may account for the existence of ‘frequent discharge sites’ firing the majority of the smooth muscle Ca2+ sparks and the wide variation in the Ca2+ wave propagation velocities observed.
Ca2+ sparks activate K+ and Cl− channels, resulting in spontaneous transient currents in guinea‐pig tracheal myocytes
Authors: ZhuGe Ronghua , Sims Stephen M. , Tuft Richard A. , Fogarty Kevin E. , Walsh John V. 
Published: September 2004

Local changes in cytosolic [Ca2+] were imaged with a wide‐field, high‐speed, digital imaging system while membrane currents were simultaneously recorded using whole‐cell, perforated patch recording in freshly dissociated guinea‐pig tracheal myocytes.
Depending on membrane potential, Ca2+ sparks triggered ‘spontaneous’ transient inward currents (STICs), ‘spontaneous’ transient outward currents (STOCs) and biphasic currents in which the outward phase always preceded the inward (STOICs). The outward currents resulted from the opening of large‐conductance Ca2+‐activated K+ (BK) channels and the inward currents from Ca2+‐activated Cl− (ClCa) channels.
A single Ca2+ spark elicited both phases of a STOIC, and sparks originating from the same site triggered STOCs, STICs and STOICs, depending on membrane potential.
STOCs had a shorter time to peak (TTP) than Ca2+ sparks and a much shorter half‐time of decay. In contrast, STICs had a somewhat longer TTP than sparks but the same half‐time of decay. Thus, the STIC, not the STOC, more closely reflected the time course of cytosolic Ca2+ elevation during a Ca2+ spark.
These findings suggest that ClCa channels and BK channels may be organized spatially in quite different ways in relation to points of Ca2+ release from intracellular Ca2+ stores. The results also suggest that Ca2+ sparks may have functions in smooth muscle not previously suggested, such as a stabilizing effect on membrane potential and hence on the contractile state of the cell, or as activators of voltage‐gated Ca2+ channels due to depolarization mediated by STICs.
Albumin elicits calcium signals from astrocytes in brain slices from neonatal rat cortex
Authors: Nadal Angel , Sul Jai‐Yoon , Valdeolmillos Miguel , McNaughton Peter A. 
Published: September 2004

Albumin causes calcium signals and mitosis in cultured astrocytes, but it has not been established whether astrocytes in intact brain also respond to albumin. The effect of albumin on intracellular calcium concentration ([Ca2+]i) in single cells was therefore studied in acutely isolated cortical brain slices from the neonatal rat.
Physiological concentrations of albumin from plasma and from serum produced an increase in [Ca2+]i in a subpopulation of cortical cells. Trains of transient elevations in [Ca2+]i (Ca2+ spikes) were seen in 41 % of these cells.
The cells responding to albumin are identified as astrocytes because the neurone‐specific agonist NMDA caused much smaller and slower responses in these cells. On the other hand NMDA‐responsive cells, which are probably neurones, exhibited only small and slow responses to albumin. The residual responses of astrocytes to NMDA and neurones to albumin are likely to be due to crosstalk with adjacent neurones and astrocytes, respectively.
Methanol extraction of albumin removes a polar lipid and abolishes the ability of albumin to increase intracellular calcium.
Astrocyte calcium signalling caused by albumin may have important physiological consequences when the blood‐brain barrier breaks down and allows albumin to enter the CNS.
Identification and characterization of a monocarboxylate transporter (MCT1) in pig and human colon: its potential to transport l‐lactate as well as butyrate
Authors: Ritzhaupt Armin , Wood I. Stuart , Ellis Antony , Hosie Ken B. , Shirazi‐Beechey Soraya P. 
Published: September 2004

Oligonucleotide primers based on the human heart monocarboxylate transporter (MCT1) cDNA sequence were used to isolate a 544 bp cDNA product from human colonic RNA by reverse transcription‐polymerase chain reaction (RT‐PCR). The sequence of the RT‐PCR product was identical to that of human heart MCT1. Northern blot analysis using the RT‐PCR product indicated the presence of a single transcript of 3.3 kb in mRNA isolated from both human and pig colonic tissues. Western blot analysis using an antibody to human MCT1 identified a specific protein with an apparent molecular mass of 40 kDa in purified and well‐characterized human and pig colonic lumenal membrane vesicles (LMV).
Properties of the colonic lumenal membrane l‐lactate transporter were studied by the uptake of L‐[U‐14C]lactate into human and pig colonic LMV. l‐lactate uptake was stimulated in the presence of an outward‐directed anion gradient at an extravesicular pH of 5.5. Transport of l‐lactate into anion‐loaded colonic LMV appeared to be via a proton‐activated, anion exchange mechanism.
l‐lactate uptake was inhibited by pyruvate, butyrate, propionate and acetate, but not by Cl− and SO42−. The uptake of l‐lactate was inhibited by phloretin, mercurials and α‐cyano‐4‐hydroxycinnamic acid (4‐CHC), but not by the stilbene anion exchange inhibitors, 4,4′‐diisothiocyanostilbene‐2,2′‐disulphonic acid (DIDS) and 4‐acetamido‐4′‐isothiocyanostilbene‐2,2′‐disulphonic acid (SITS).
The results indicate the presence of a MCT1 protein on the lumenal membrane of the colon that is involved in the transport of l‐lactate as well as butyrate across the colonic lumenal membrane. Western blot analysis showed that the abundance of this protein decreases in lumenal membrane fractions isolated from colonic carcinomas compared with that detected in the normal healthy colonic tissue.
Kainate induces an intracellular Na+‐activated K+ current in cultured embryonic rat hippocampal neurones
Authors: Liu Qi‐Ying , Schaffner Anne E. , Barker Jeffery L. 
Published: September 2004

In embryonic rat hippocampal neurones cultured for < 3 days, kainate induced an inward current at negative potentials that recovered to baseline levels immediately upon termination of agonist application. However, in neurones cultured for longer, the kainate‐induced current was often followed by a long‐lasting inward current that slowly recovered to baseline levels. The amplitude of the delayed current (Idelay) triggered by kainate was positively related both to the duration of application at constant agonist concentration and to concentration at constant application duration.
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delay could last for several minutes and was accompanied by a conductance increase, which closely paralleled current amplitude. Depression of the kainate‐induced current response at receptor level with CNQX or at ionic level with Na+‐free solution eliminated Idelay. However, when applied during Idelay neither CNQX nor Na+‐free solution had any effect on Idelay. Li+ effected the same response as Na+ in mediating kainate‐induced Idelay.
GABA‐activated Cl− current, which was associated with the same amount of inwardly directed charge flow at the same potential as that induced by kainate, did not trigger a long‐lasting delayed current.
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delay depended on the existence of extracellular K+ and its amplitude increased with the increase in K+ concentration. Neither applying Cl−‐ or Ca2+‐free solutions nor increasing intracellular Ca2+ buffering speed and capacity altered Idelay. Exposure to the specific KCa channel blockers apamin and charybdotoxin also failed to alter Idelay. However, Idelay could be blocked by Cs+, Ba2+ and high concentrations of 4‐aminopyridine (4‐AP) and TEA.
Inside‐out excised patch‐clamp recordings revealed that low density or highly clustered Na+‐activated K+ channels were expressed in the cell bodies of cultured embryonic rat hippocampal neurones. These could be the elementary channels underlying Idelay.
Functional expression of the Ile693Thr Na+ channel mutation associated with paramyotonia congenita in a human cell line
Authors: Plassart‐Schiess Emmanuelle , Lhuillier Loïc , George Alfred L. , Fontaine Bertrand , Tabti Nacira 
Published: September 2004

The Ile693Thr mutation of the skeletal muscle Na+ channel α‐subunit is associated with an unusual phenotype of paramyotonia congenita characterized by cold‐induced muscle weakness but no stiffness. This mutation occurs in the S4‐S5 linker of domain II, a region that has not been previously implicated in paramyotonia congenita.
The Ile693Thr mutation was introduced into the human skeletal muscle Na+ gene for functional expression in human embryonic kidney (HEK) cells. The currents expressed were recorded with the whole‐cell voltage‐clamp technique.
In comparison with wild‐type currents, Ile693Thr mutant currents showed a clear shift of about −9 mV in the voltage dependence of activation.
In contrast to other mutations of the Na+ channel known to cause paramyotonia congenita, the Ile693Thr mutation did not induce any significant change in the kinetics, nor in the voltage dependence, of fast inactivation.
In conclusion, this study provides further evidence of the involvement of the S4‐S5 linker in the voltage dependence of Na+ channel activation. The negative shift in the voltage dependence found in this mutation must be associated to other defects, plausibly an impairment of the slow inactivation, to account for the long periods of muscle weakness experienced by the patients.
Facilitation of the presynaptic calcium current at an auditory synapse in rat brainstem
Authors: Cuttle Matthew F. , Tsujimoto Tetsuhiro , Forsythe Ian D. , Takahashi Tomoyuki 
Published: September 2004

The presynaptic calcium current (IpCa) was recorded from the calyx of Held in rat brainstem slices using the whole‐cell patch clamp technique.
Tetanic activation of IpCa by 1 ms depolarizing voltage steps markedly enhanced the amplitude of IpCa. Using a paired pulse protocol, the second (test) response was facilitated with inter‐pulse intervals of less than 100 ms. The facilitation was greater at shorter intervals and was maximal (about 20 %) at intervals of 5–10 ms.
When the test pulse duration was extended, the facilitation was revealed as an increased rate of IpCa activation. From the current‐voltage relationship measured at 1 ms from onset, facilitation could be described by a shift in the half‐activation voltage of about −4 mV.
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pCa facilitation was not attenuated when guanosine‐5′‐O‐(3‐thiotriphosphate) (GTPγS) or guanosine‐5′‐O‐(2‐thiodiphosphate) (GDPβS) was included in the patch pipette, suggesting that G‐proteins are not involved in this phenomenon.
On reducing [Ca2+]o, the magnitude of facilitation diminished proportionally to the amplitude of IpCa. Replacement of [Ca2+]o by Ba2+ or Na+, or buffering of [Ca2+]i with EGTA or BAPTA attenuated IpCa facilitation.
We conclude that repetitive presynaptic activity can facilitate the presynaptic Ca2+ current through a Ca2+‐dependent mechanism. This mechanism would be complementary to the action of residual Ca2+ on the exocytotic machinery in producing activity‐dependent facilitation of synaptic responses.
Functional and molecular expression of volume‐regulated chloride channels in canine vascular smooth muscle cells
Authors: Yamazaki Jun , Duan Dayue , Janiak Robert , Kuenzli Karri , Horowitz Burton , Hume Joseph R. 
Published: September 2004

We examined the possibility of functional and molecular expression of volume‐regulated Cl− channels in vascular smooth muscle using the whole‐cell patch‐clamp technique and quantitative reverse transcriptase‐polymerase chain reaction (RT‐PCR) on cells from canine pulmonary and renal arteries.
Decreasing external osmolarity induced cell swelling, which was accompanied by activation of Cl−‐dependent outward‐rectifying membrane currents with an anion permeability sequence of SCN− > I− > Br− > Cl− > aspartate−. These currents were sensitive to block by DIDS, extracellular ATP and the antioestrogen compound tamoxifen.
Experiments were performed to determine whether the molecular form of the volume‐regulated chloride channel (ClC‐3) is expressed in pulmonary and renal arteries. Quantitative RT‐PCR confirmed expression of ClC‐3 in both types of smooth muscle. ClC‐3 expression was 76.4 % of β‐actin in renal artery and 48.0 % of β‐actin in pulmonary artery.
We conclude that volume‐regulated Cl− channels are expressed in vascular smooth muscle cells and exhibit functional properties similar to those found in other types of cells, presumably contributing to the regulation of cell volume, electrical activity and, possibly, myogenic tone.
Facilitatory effect of Ca2+ on the noradrenaline‐evoked cation current in rabbit portal vein smooth muscle cells
Authors: Helliwell R. M. , Large W. A. 
Published: September 2004

The facilitatory effect of external calcium ions (Ca2+o) on the α1 ‐adrenoceptor‐activated non‐selective cation current (Icat) was investigated in rabbit portal vein cells using noise and voltage‐jump relaxation analysis of the whole‐cell macroscopic current.
Micromolar concentrations of Ca2+o potentiated the peak amplitude of Icat at a holding potential (Vh) of −50 mV. The effective [Ca2+]o which produced a 50 % potentiation (EC50) was 3 μm.
From noise analysis the estimated single channel conductance (γ) was approximately 23 pS with [Ca2+]o between 3 and 100 μm, whereas in < 10 nm or 1 μm Ca2+oγ was approximately 10 pS.
The spectral density function of Icat at negative potentials could be described by the sum of two Lorentzians in every [Ca2+]o examined. The time constant of the lower frequency Lorentzian component (τ1) was about 11 ms in < 10 nm Ca2+o and was about 45 ms in micromolar concentrations of Ca2+o (1–100 μm). In contrast, the time constant of the higher frequency component (τ2) was similar in < 10 nm Ca2+o and 100 μm Ca2+o (between 1 and 2 ms).
The lower frequency Lorentzian component was responsible for about half the total current variance in < 10 nm Ca2+o whereas in micromolar concentrations of Ca2+o it was responsible for most of the measured current variance.
In voltage‐jump experiments, on stepping the voltage from −50 to +50 mV the instantaneous current was followed by an exponential decline of Icat. Stepping back to −30 mV produced an exponential inward relaxation (Irelax,‐30 mV) leading to an increase in the steady‐state amplitude of Icat in micromolar concentrations of Ca2+o, but this relaxation was not observed in < 10 nm Ca2+o. The relative amplitude of Irelax,‐30 mV increased in an [Ca2+]o ‐dependent manner (EC50 was 2 μm) although the time constant of this relaxation (τrelax,‐30 mV) remained unchanged (about 60 ms between 2 and 100 μm Ca2+o).
The data suggest that Ca2+o produces marked changes in the kinetics and single channel conductance of cation channels, which may account for the facilitatory effect of micromolar concentrations of Ca2+o on the peak amplitude of Icat.
Glycinergic synaptic inputs to bipolar cells in the salamander retina
Authors: Maple Bruce R. , Wu Samuel M. 
Published: September 2004

Glycine activated strychnine‐sensitive chloride conductances at both the dendrites and the axonal telodendria of most bipolar cells in the salamander retina.
The chloride equilibrium potential of bipolar cells was found to be negative to ‐50 mV, indicating that glycinergic synapses on bipolar cells are inhibitory.
Some bipolar cells exhibited discrete, strychnine‐sensitive, chloride‐mediated inhibitory postsynaptic currents (IPSCs). These were elicited by focal application of glutamate at the inner plexiform layer (IPL). Glycinergic synapses were localized using simultaneous focal application of calcium to retinal slices bathed in calcium‐free media. Both dendritic and telodendritic glycinergic IPSCs were observed.
The decay of the telodendritic IPSCs was well fitted by a single exponential with a time constant of 17.7 ± 8.7 ms. Similar kinetics were observed for dendritic IPSCs in some cells, but in one class of on‐centre bipolar cell the decay of the dendritic IPSCs was better fitted by a sum of two exponentials with time constants 9.9 ± 4.3 and 51.3 ± 24.3 ms.
The dendritic IPSCs were best driven by application of glutamate at the distal IPL (the off sublamina), while the telodendritic IPSCs were driven best by application near the telodendria. These results suggest that bipolar cell dendrites receive inhibitory glycinergic inputs from interplexiform cells that are excited by off‐centre bipolar cells, whereas bipolar cell telodendria receive glycinergic amacrine cell inputs that are antagonistic to the photoreceptor inputs.
Both inputs could be elicited in the presence of tetrodotoxin (TTX), but the dendritic IPSCs were sometimes abolished by TTX, suggesting that sodium‐dependent spikes play an important role in the transmission of interplexiform cell signals to the outer plexiform layer.
Differential roles for NMDA and non‐NMDA receptor subtypes in baroreceptor afferent integration in the nucleus of the solitary tract of the rat
Authors: Zhang Jing , Mifflin Steven W. 
Published: September 2004

Microinjection studies have established that both NMDA and non‐NMDA excitatory amino acid (EAA) receptor subtypes are involved in the integration of baroreceptor afferent inputs within the nucleus of the solitary tract (NTS). The present study was undertaken to determine which EAA receptor subtypes are involved in baroreceptor afferent integration by second and higher order NTS neurones.
Experiments utilizing intracellular recordings or extracellular recordings with microiontophoresis were performed in pentobarbitone‐anaesthetized, paralysed and artificially ventilated rats to determine the ionotropic EAA receptor subtypes involved in baroreceptor afferent integration in the NTS. NTS neurones were classified according to their responses to aortic depressor nerve (ADN) stimulation: monosynaptic neurones (MSNs), polysynaptic neurones (PSNs) and ADN‐non‐evoked neurones (NENs).
In the extracellular studies, the ADN‐evoked discharge of most MSNs was selectively reduced by microiontophoretic application of the non‐NMDA receptor antagonists 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX; n= 8, P < 0.05) or 1,2,3,4‐tetrahydro‐6‐nitro‐2,3‐dioxo‐benzo(f)quinoxaline‐7‐sulphonamide (NBQX; n= 9, P < 0.01), but not by the NMDA antagonist dl‐2‐amino‐5‐phosphonopentanoic acid (AP‐5; n= 6, P= 0.28). ADN‐evoked responses of PSNs were attenuated by microiontophoretic application of AP‐5 (n= 12, P < 0.001), CNQX (n= 13, P < 0.001) or NBQX (n= 11, P < 0.001). All EAA antagonists inhibited the spontaneous discharge of MSNs/PSNs and NENs (P < 0.01 for each group).
In the intracellular studies, ADN stimulation evoked faster rising and shorter duration excitatory postsynaptic potentials (EPSPs) in MSNs (n= 16) than in PSNs (n= 15) (P < 0.05 for each comparison).
Our results demonstrate that synaptic inputs from ADN to MSNs have faster rise times and shorter durations than those to PSNs, suggesting that baroreceptor inputs to MSNs and PSNs are mediated by different synaptic mechanisms. These more rapid synaptic events are selectively mediated by non‐NMDA receptors. In addition, synaptic integration of ADN inputs by PSNs is mediated by both NMDA and non‐NMDA receptors. Finally, the ADN‐evoked discharge of some MSNs and PSNs is not attenuated by ionotropic EAA antagonists, suggesting that another receptor or transmitter system may mediate synaptic excitation in these neurones.
Inhibition of oxidative metabolism increases persistent sodium current in rat CA1 hippocampal neurons
Authors: Hammarström A. K. M. , Gage P. W. 
Published: September 2004

Whole‐cell patch‐clamp recordings from freshly dissociated rat CA1 neurons revealed a large transient Na+ current (INa,T) and a smaller, inactivation‐resistant persistent Na+ current (INa,P). Both currents could be blocked with TTX.
The average current densities of INa,T and INa,P in thirty cells were 111.0 ± 9.62 and 0.87 ± 0.13 pA pF−1, respectively.
Inhibiting oxidative phosphorylation by adding 5 mM sodium cyanide to the pipette solution significantly increased the amplitude of INa,P but had no significant effect on the amplitude of INa,T.
Exposing CA1 neurons to hypoxia for more than 7 min caused an increase in the amplitude of INa,P. There was also a delayed decrease in the amplitude of INa,T.
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Na,P was more sensitive to the Na+ channel blockers TTX and lidocaine than INa,T. The IC50 for the effect of TTX on INa,P was 9.1 ± 1.2 nM whereas the IC50 for INa,T was 37.1 ± 1.2 nM, approximately 4‐fold higher. Lidocaine (lignocaine; 1 μM) reduced INa,P to 0.24 ± 0.15 of control (n= 4) whereas INa,T was essentially unaffected (0.99 ± 0.11, n= 4).
These results show that INa,P is increased when oxidative metabolism is blocked in CA1 neurons. The persistent influx of Na+ through non‐inactivating Na+ channels can be blocked by concentrations of Na+ channel blockers that do not affect INa,T.
Calcium current activated by potassium ions in voltage‐clamped rat hippocampal pyramidal neurones
Authors: Deák Ferenc , Nagy Gábor , Várnai Péter , Madarász Emília , Spät András 
Published: September 2004

Neuronal activity results in local elevation of extracellular K+ concentration ([K+]o).
Using the patch‐clamp technique in the whole‐cell configuration, we investigated whether extracellular K+ activates non‐voltage‐operated Ca2+ channels in pyramidal cells cultured from rat embryonic hippocampi.
K+ (12 mM) reversibly activated a sustained inward current at a holding potential of ‐100 mV. Membrane conductance and variance of noise were significantly increased by K+. This current could be observed at membrane potentials negative to +60 mV.
Inhibitors of inward rectifier K+ channels and hyperpolarization‐induced cation current reduced the current only at potentials negative to ‐50 mV.
The K+‐induced current was activated in Na+‐free but not in Ca2+‐free medium, did not depend on cytosolic [Cl−], and was blocked by Cd2+ but not by organic channel inhibitors.
Half‐maximal activation of the current (at ‐100 mV) was attained at [K+]o≈ 20 mM.
The current is similar to Igl, a K+‐induced Ca2+ current described in glomerulosa cells. It was also present in pyramidal cells from prefrontal cortex but not in hippocampal bipolar and glial cells.
Activation of K+‐induced Ca2+ current may elevate cytoplasmic [Ca2+] at [K+]o levels which are insufficent to activate voltage‐dependent Ca2+ channels.