bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lambert‐Eaton syndrome antibodies inhibit acetylcholine release and P/Q‐type Ca2+ channels in electric ray nerve endings
Authors: Satoh Yasushi , Hirashima Naohide , Tokumaru Hiroshi , Takahashi Masanori P. , Ang Jin K , Viglione Michael P. , Kim Yong I. , Kirino Yutaka 
Published: September 2004

The types of voltage‐dependent calcium channels (VDCCs) present in the cholinergic terminals isolated from the electric organ of the ray, Narke japonica, were characterized on the basis of their pharmacological sensitivity to specific antagonists. Inhibition of these channel types by autoantibodies from patients with the Lambert‐Eaton syndrome (LES) was then studied to determine the specificity of the pathogenic IgG.
In normal untreated synaptosomal preparations, maximal doses of N‐ and P and/or Q‐type Ca2+ channel antagonists, ω‐conotoxin GVIA and ω‐agatoxin IVA, inhibited depolarization‐evoked ACh release by 47 % and 43 %, respectively. Calciseptine, an L‐type VDCC antagonist, caused a 20 % reduction in the release. This indicates that the exocytotic release process is predominantly mediated by N‐ and P/Q‐type VDCCs.
LES IgG or sera caused an inhibition of ACh release by 39‐45 % in comparison with the control antibody‐treated preparations. The ionomycin‐induced ACh release, however, was not altered by the antibodies. Additionally, the same LES antibodies inhibited whole‐cell calcium currents (ICa) in bovine adrenal chromaffin cells. Thus, the pathogenic antibodies exert their action on VDCCs present in the synaptosomes.
The efficacy of three Ca2+ channel antagonists in blocking ACh release was determined in preparations pretreated with LES IgG. ω‐Agatoxin IVA produced only an additional 3‐5 % reduction in release beyond that obtained with LES antibodies. Despite the pretreatment with LES IgG, ω‐conotoxin GVIA and calciseptine inhibited the release to nearly their control levels.
These results indicate that LES antibodies mainly downregulate P/Q‐type Ca2+ channels which contribute to presynaptic transmitter release from the cholinergic nerve terminals of electric organ.
The present findings are consistent with the hypothesis that P/Q‐type VDCCs at the neuromuscular junction are the target of LES antibodies and that their inhibition by the antibodies produces the characteristic neuromuscular defect in this disease.
Chemosensitivity of rat medullary raphe neurones in primary tissue culture
Authors: Wang Wengang , Pizzonia John H. , Richerson George B. 
Published: September 2004

The medullary raphe, within the ventromedial medulla (VMM), contains putative central respiratory chemoreceptors. To study the mechanisms of chemosensitivity in the raphe, rat VMM neurones were maintained in primary dissociated tissue culture, and studied using perforated patch‐clamp recordings. Baseline electrophysiological properties were similar to raphe neurones in brain slices and in vivo.
Neurones were exposed to changes in CO2 from 5 % to 3 or 9 % while maintaining a constant [NaHCO3]. Fifty‐one per cent of neurones (n= 210) did not change their firing rate by more than 20 % in response to hypercapnic acidosis. However, 22 % of neurones responded to 9 % CO2 with an increase in firing rate (‘stimulated’), and 27 % of neurones responded with a decrease in firing rate (‘inhibited’).
Chemosensitivity has often been considered an all‐or‐none property. Instead, a method was developed to quantify the degree of chemosensitivity. Stimulated neurones had a mean increase in firing rate to 298 ± 215 % of control when pH decreased from 7.40 to 7.19. Inhibited neurones had a mean increase in firing rate to 232 ± 265 % of control when pH increased from 7.38 to 7.57.
Neurones were also exposed to isocapnic acidosis. All CO2‐stimulated neurones tested (n= 15) were also stimulated by isocapnic acidosis, and all CO2‐inhibited neurones tested (n= 19) were inhibited by isocapnic acidosis. Neurones with no response to hypercapnic acidosis also had no response to isocapnic acidosis (n= 12). Thus, the effects of CO2 on these neurones were mediated in part via changes in pH.
In stimulated neurones, acidosis induced a small increase in the after‐hyperpolarization level of 1.38 ± 1.15 mV per −0.2 pH units, which was dependent on the level of tonic depolarizing current injection. In voltage clamp mode at a holding potential near resting potential, there were small and inconsistent changes in whole‐cell conductance and holding current in both stimulated and inhibited neurones. These results suggest that pH modulates a conductance in stimulated neurones that is activated during repetitive firing, with a reversal potential close to resting potential.
The two subtypes of chemosensitive VMM neurones could be distinguished by characteristics other than their response to acidosis. Stimulated neurones had a large multipolar soma, whereas inhibited neurones had a small fusiform soma. Stimulated neurones were more likely than inhibited neurones to fire with the highly regular pattern typical of serotonergic raphe neurones in vivo.
Within the medullary raphe, chemosensitivity is a specialization of two distinct neuronal phenotypes. The response of these neurones to physiologically relevant changes in pH is of the magnitude that suggests that this chemosensitivity plays a functional role. Elucidating their mechanisms in vitro may help to define the cellular mechanisms of central chemoreception in vivo.
T‐type Ca2+ current as a trigger for Ca2+ release from the sarcoplasmic reticulum in guinea‐pig ventricular myocytes
Authors: Sipido Karin R. , Carmeliet Edward , van de Werf F. 
Published: September 2004

We have investigated whether Ca2+ entry through T‐type Ca2+ channels participates in triggering Ca2+ release from the sarcoplasmic reticulum (SR) in single guinea‐pig ventricular myocytes (whole‐cell voltage clamp, K5fura‐2 as [Ca2+]i indicator; all monovalent cations replaced by impermeant ions to record uncontaminated Ca2+ currents; T= 23 or 36 °C).
T‐type Ca2+ currents were elicited from a holding potential of ‐90 mV during steps to ‐50 to ‐20 mV. For steps to ‐50 mV, very small [Ca2+]i transients could be recorded with high loading of the SR (peak Δ[Ca2+]i, 67 ± 41 nM; n= 9).
For steps to ‐40, ‐30 and ‐20 mV, we compared the amplitude of Ca2+ release for a holding potential of ‐50 mV with L‐type Ca2+ current only to Ca2+ release for a holding potential of ‐90 mV with both T‐ and L‐type Ca2+ current. Significantly more Ca2+ release was observed with T‐type current present, and both the T‐type current and the additional Ca2+ release were suppressed by 50 μM NiCl2.
Ca2+ influx through T‐type Ca2+ channels triggered less Ca2+ release than a comparable Ca2+ influx through L‐type Ca2+ channels.
Rapid block of T‐type Ca2+ current during the action potential (50 μM NiCl2 during steady‐state stimulation at 1 or 2 Hz) did not immediately reduce Ca2+ release, although a small decrease was observed after longer application.
We conclude that T‐type Ca2+ current can trigger Ca2+ release from the SR albeit less efficiently than L‐type Ca2+ current. T‐type current is most likely to provide only a small contribution to the trigger for Ca2+ release in normal conditions. These results support the hypothesis that L‐type Ca2+ channels have a privileged role in excitation‐contraction coupling.
Absorptive apical amiloride‐sensitive Na+ conductance in human endometrial epithelium
Authors: Matthews C. Jane , McEwan Gordon T. A. , Redfern Christopher P. F. , Thomas Eric J. , Hirst Barry H. 
Published: September 2004

Human endometrial epithelial cells cultured on porous tissue culture supports formed tight, polarized epithelial monolayers with features characteristic of tight epithelia. Endometrial epithelial layers generated significant transepithelial electrical resistance (750 Ω cm2) and potential difference (15.3 mV), with an inward short‐circuit current (Isc; 20.5 μA cm−2).
The Isc was linearly proportional to the external Na+ concentration and was abolished in the absence of Na+. The Isc was sensitive to apical amiloride. Net 22Na+ flux was in the absorptive apical to basolateral direction and fully accounted for the inward Isc. In addition, apical to basolateral and net 22Na+ transport were reduced in the presence of amiloride.
The Isc was also sensitive to addition of ouabain and Ba2+ to the basal solution, consistent with a role for basolateral Na+−K+‐ATPase and K+ channels in generation of the current.
These data demonstrate that human endometrial epithelial cells in primary culture produce tight, functional monolayers on permeable supports. We provide the first evidence that human endometrial epithelial cells have an inward Isc accounted for by an amiloride‐sensitive Na+ conductance. The Na+‐absorptive function of the endometrium may provide an appropriate environment for sperm function and embryo growth.
Sodium pump evokes high density pump currents in rat midbrain dopamine neurons
Authors: Shen Ke‐Zhong , Johnson Steven W. 
Published: September 2004

Patch pipettes contained various concentrations of Na+ ([Na+]pip) in order to record strophanthidin‐sensitive currents under voltage clamp in dopamine neurons in slices of rat substantia nigra and ventral tegmental area.
When [Na+]pip was 40 mm and the external K+ concentration ([K+]o) was 2.5 mm, strophanthidin (10 μm) evoked 461 ± 121 pA of inward current. This effect was concentration dependent, with an EC50 of 7.1 ± 2.6 μm. At potentials of −60 to −120 mV, strophanthidin‐induced currents were not associated with significant changes in chord conductance.
Strophanthidin (10 μm) evoked 234 ± 43 pA of inward current when [Na+]pip was 0.6 mm, and 513 ± 77 pA when [Na+]pip was 80 mm. Despite higher pump currents with greater [Na+]pip, the strophanthidin EC50 was not significantly different for any of six different [Na+]pip.
Sodium pump currents were half‐maximal when the [Na+]pip was about 1.3 mm. Maximum pump current was estimated at 830 pA (29 μA cm−2) at concentrations of intracellular Na+ that were assumed to be saturating (50–100 mm).
Strophanthidin currents were smaller in a reduced [K+]o (EC50= 0.2 mm).
These data show that intracellular Na+ loading evokes relatively large pump currents. Our results are consistent with the physiological role of the sodium pump in burst firing in midbrain dopamine neurons
Prejunctional effects of the nicotinic ACh receptor agonist dimethylphenylpiperazinium at the rat neuromuscular junction
Authors: Singh Shila , Prior Chris 
Published: September 2004

We have studied the effects of the nicotinic acetylcholine (ACh) receptor agonist dimethylphenylpiperazinium (DMPP) on the evoked release of ACh from motor terminals in the rat isolated hemidiaphragm using an electrophysiological approach.
DMPP (1–4 μM) had no effect on the rate of spontaneous quantal ACh release but increased the number of quanta of ACh released per impulse during 50 Hz stimulation. The DMPP‐induced increase in evoked ACh release was dependent on the frequency of stimulation, being absent when it was reduced to 0.5 Hz, but was not Ca2+ dependent, being unaffected at 50 Hz by a 4‐fold decrease in the extracellular Ca2+ concentration.
The facilitation of evoked ACh release at 50 Hz by 2 μM DMPP was abolished by 10 μM of the calmodulin antagonist W7 (N‐(6‐aminohexyl)‐5‐chloro‐1‐naphthalenesulphonamide hydrochloride) and, in the presence of W7, 2 μM DMPP depressed evoked ACh release at 0.5 Hz. The ability of the nicotinic ACh receptor antagonist vecuronium (1 μM) to depress evoked ACh release at 50 Hz was also abolished by 10 μM W7.
The present findings demonstrate, using an electrophysiological technique, that DMPP can produce changes in the evoked ACh release from rat motor nerve terminals that are consistent with the existence of facilitatory nicotinic ACh receptors on the motor nerve endings. Further, they indicate a role for calmodulin‐dependent systems in this facilitatory effect of the compound.
Characterization of cell volume‐sensitive chloride currents in freshly prepared and cultured pancreatic acinar cells from early postnatal rats
Authors: Schmid Andreas , Blum Robert , Krause Elmar 
Published: September 2004

In freshly prepared and cultured exocrine pancreatic acinar cells from 5‐ to 7‐day‐old rats a chloride‐selective membrane conductance could be activated by intracellular application of GTPγS (40–100 μM), by application of positive pressure (5 cmH2O) to the pipette interior or by challenging the cells with a hyposmolar bath solution. Hyperosmolar bath solutions inhibited the cell volume‐sensitive chloride currents.
The anion permeability sequence of the cell volume‐sensitive chloride conductance was I− > Cl−≈ Br− > F− > methanesulphonate− > glutamate−. I− had a higher permeability but lower conductance than Cl−. The permeability ratio for Pglutamate/PCl was 0.12.
The cell volume‐sensitive chloride conductance showed outward rectification. Membrane depolarization to high positive voltages (≥+60 mV) caused a time‐dependent decay in outward currents.
DIDS (4,4′‐diisothiocyanatostilbene‐2,2′‐disulphonic acid) and SITS (4‐acetamido‐4′‐isothiocyanatostilbene‐2,2′‐disulphonic acid) reversibly inhibited the cell volume‐sensitive chloride current in a voltage‐dependent manner. NPPB (5‐nitro‐2‐(3‐phenylpropylamino)‐benzoic acid), quinidine, quinine and tamoxifen caused voltage‐independent current inhibition.
Combined fura‐2 and whole‐cell current measurements showed that activation of the cell volume‐sensitive chloride current does not involve cytosolic Ca2+ signals. Furthermore, there is no evidence that Ca2+‐activated chloride currents play a significant role in cultured pancreatic acinar cells from 5‐ to 7‐day‐old rats.
Polymerase chain reaction followed by DNA sequence analysis indicated the presence of mRNA homologous to the ClC‐3 chloride channel in pancreatic tissue from 5‐day‐old rats.
Interaction of the Na+‐K+ pump and Na+‐Ca2+ exchange via [Na+]i in a restricted space of guinea‐pig ventricular cells
Authors: Fujioka Yasutada , Matsuoka Satoshi , Ban Toshihiko , Noma Akinori 
Published: September 2004

The whole‐cell Na+‐K+ pump current (INa‐K) and Na+‐Ca2+ exchange current (INa‐Ca) were recorded in guinea‐pig ventricular myocytes to study the interaction between the two Na+ transport mechanisms.
I
Na‐K was isolated as an external K+‐induced current, and INa‐Ca as an external Ca2+‐ induced or Ni2+‐sensitive current. The experimental protocol used for one ion carrier did not affect the other.
The amplitude of INa‐K decreased to 54 ± 17 % of the initial peak during continuous application of K+ with 20 mM Na+ in the pipette. The outward INa‐Ca, which was intermittently activated by brief applications of Ca2+, decreased during activation of INa‐K, and recovered after cessation of INa‐K activation. These findings revealed a dynamic interaction between INa‐K and INa‐Ca via a depletion of Na+ under the sarcolemma.
To estimate changes in Na+ concentration ([Na+]i) under the sarcolemma, the reversal potential (Vrev) of INa‐Ca was measured. Unexpectedly, Vrev hardly changed during activation of INa‐K. However, when INa‐Ca was blocked by Ni2+ at the same time that INa‐K was activated, Vrev changed markedly, maximally by +100 mV, immediately after the removal of Ni2+ and K+.
Subsarcolemmal [Na+]i was calculated from the Vrev of INa‐Ca on the assumption that the subsarcolemmal Ca2+ concentration ([Ca2+]i) was fixed with EGTA, and mean [Na+]i was calculated from both the time integral of INa‐K and the cell volume. The subsarcolemmal [Na+]i was about seven times greater than the mean [Na+]i.
The interaction between the Na+‐K+ pump and Na+‐Ca2+ exchange was well simulated by a diffusion model, in which Na+ diffusion was restricted to one‐seventh (14 %) of the total cell volume.
Acid/base transport across the leech giant glial cell membrane at low external bicarbonate concentration
Authors: Deitmer Joachim W. , Schneider Hans‐Peter 
Published: September 2004

We have studied acid/base transport across the cell membrane of the giant neuropile glial cell in the leech (Hirudo medicinalis) central nervous system induced by changing the external pH (pHo), using double‐barrelled, pH‐sensitive microelectrodes. In the presence of 5 % CO2 and 24 mm HCO3−, the intracellular pH (pHi) rapidly changes due to a potent, reversible Na+‐HCO3− cotransport across the glial membrane. We have now investigated the transport mechanism which leads to pHi changes in the nominal absence of CO2/HCO3−, where the HCO3− concentration is expected to be below 1 mm.
The intracellular pH increased and then decreased when pHo was altered from 7.4 to 7.8 and then 7.0 with a rate of increase of +0.026 ± 0.008 and a rate of decrease of −0.028 ± 0.009 pH units min−1 (± s.d., n= 49), indicating an acid/base flux rate of 0.64 and 0.71 mm min−1 across the glial membrane, respectively.
In the absence of external sodium (Na+replaced by N‐methyl‐D‐glucamine), pHi slowly decreased, and the rate of alkali and acid loading was reduced to 19 and 28 %, respectively, (n= 12). Amiloride (2 mm), which inhibits Na+‐H+ exchange, had no effect on the alkali/acid loading (n= 6).
The alkali and acid loading were not impaired after the removal of external chloride (Cl−o, replaced by gluconate; n= 11), but were significantly reduced by the anion transport inhibitor 4,4′‐diisothiocyanatostilbene‐2,2′‐disulphonic acid (DIDS, 0.5 mm) to 23 and 16 %, respectively, of the control (P < 0.001; n= 5).
Alkali and acid loading were affected differently by manipulating the availability of residual HCO3−. After adding the membrane‐permeable carbonic anhydrase inhibitor ethoxyzolamide (EZA, 2 μm) to the saline, the acid loading, but not the alkali loading, was significantly reduced (by 25 %, P < 0.01), while lowering the residual CO2/HCO3− concentration in the saline by O2 bubbling significantly reduced the alkali loading (by 59 %, P < 0.02), but not the acid loading.
Changing the membrane holding potential in voltage‐clamped glial cells or raising the external K+ concentration to 30 mm had no significant effect on acid/base loading.
It is concluded that a residual HCO3− concentration of less than 1 mm in nominally CO2/HCO3−‐free salines and HCO3− produced endogenously in the glial cells support alkali and acid loading across the glial cell membrane, presumably by activation of the reversible Na+‐HCO3− cotransporter. The results suggest a very high selectivity and affinity of this cotransporter for HCO3−; they imply that HCO3−‐dependent processes may not be negligible even in the nominal absence of CO2/HCO3−, when the HCO3− concentration is expected to be in the submillimolar range.
Analysis of the periodicity of synaptic events in neurones in the superior cervical ganglion of anaesthetized rats
Authors: McLachlan Elspeth M. , Häbler Heinz‐Joachim , Jamieson John , Davies Philip J. 
Published: September 2004

The patterns of on‐going synaptic events recorded intracellularly in neurones of superior cervical ganglia (SCG)of anaesthetized female rats were analysed by constructing inter‐event interval histograms, autocorrelograms, ln‐survivor curves and histograms triggered by the arterial pulse wave and by the intercostal EMG.
In 11/12 cells with on‐going frequencies > 0.5 Hz, one or two inputs were strong (i.e. always suprathreshold). In five cells, action potentials also arose from synaptic potentials with amplitudes close to threshold.
Synaptic events in 5/11 neurones tested were phase‐related to the arterial pressure wave (i.e. had cardiac rhythmicity, CR).
Synaptic events in 9/10 neurones tested (including all with CR) were phase‐related to the intercostal EMG and/or their autocorrelograms showed peaks at multiples of the respiratory interval (i.e. had respiratory rhythmicity, RR).
The intervals between all synaptic events were exponentially distributed in 8/12 neurones although intervals between single strong events showed peaks related to the respiratory cycle. Bursts occurred only by chance.
Event patterns could be simulated by combining events from several respiration‐modulated inputs with their timing distributed over nearly half the cycle. From the simulations, the mean number of active preganglionic inputs was estimated to be ≈6 with mean discharge frequency ≈0.4 Hz.
We conclude that, in the spontaneously breathing anaesthetized rat, most preganglionic neurones to the SCG fire with relatively low probability in relation to the respiratory cycle. Rhythms in a postganglionic neurone reflect the activity of its suprathreshold preganglionic inputs.
Properties and glial origin of osmotic‐dependent release of taurine from the rat supraoptic nucleus
Authors: Deleuze Charlotte , Duvoid Anne , Hussy Nicolas 
Published: September 2004

Taurine, prominently concentrated in glial cells in the supraoptic nucleus (SON), is probably involved in the inhibition of SON vasopressin neurones by peripheral hypotonic stimulus, via activation of neuronal glycine receptors. We report here the properties and origin of the osmolarity‐dependent release of preloaded [3H]taurine from isolated whole SO nuclei.
Hyposmotic medium induced a rapid, reversible and dose‐dependent increase in taurine release. Release showed a high sensitivity to osmotic change, with a significant enhancement with less than a 5 % decrease in osmolarity. Hyperosmotic stimulus decreased basal release.
Evoked release was independent of extracellular Ca2+ and Na+, and was blocked by the Cl− channel blockers DIDS (4,4′‐diisothiocyanatostilbene‐2,2′‐disulphonic acid) and DPC (N‐phenylanthranilic acid), suggesting a diffusion process through volume‐sensitive Cl− channels.
Evoked release was transient for large osmotic reductions (≥ 15 %), probably reflecting regulatory volume decrease (RVD). However, it was sustained for smaller changes, suggesting that taurine release induced by physiological variations in osmolarity is not linked to RVD.
Basal and evoked release were strongly inhibited by an incubation of the tissue with the glia‐specific toxin fluorocitrate, but were unaffected by a neurotoxic treatment with NMDA, demonstrating the glial origin of the release of taurine in the SON.
The high osmosensitivity of taurine release suggests an important role in the osmoregulation of the SON function. These results strengthen the notion of an implication of taurine and glial cells in the regulation of the whole‐body fluid balance through the modulation of vasopressin release.
Role of protein kinase C in the induction of homosynaptic long‐term depression by brief low frequency stimulation in the dentate gyrus of the rat hippocampus in vitro
Authors: Wang Y. , Wu J. , Rowan M. J. , Anwyl R. 
Published: September 2004

Enhancement of the induction of long‐term depression (LTD) of excitatory postsynaptic currents (EPSCs) by a priming stimulus was investigated in the medial perforant pathway of the dentate gyrus of the hippocampus in vitro.
In control, LTD could be induced by a conditioning low frequency stimulation (LFS) consisting of sixty, although not thirty or fewer, stimuli at 1 Hz applied at a holding potential of −40 mV.
A conditioning LFS of just five stimuli at 1 Hz was found to induce LTD if preceded 1–5 min, but not 15 min, by a priming LFS of five stimuli at 1 Hz, −40 mV, which did not by itself induce LTD.
A low concentration of the protein kinase C (PKC) activator (−)‐indolactam V, which did not itself induce LTD, reduced the threshold for the number of stimuli inducing LTD following the priming stimulus, while a high concentration of (−)‐indolactam V directly induced a depression of the test excitatory postsynaptic current (EPSC), which occluded LFS‐induced LTD. This suggests that the priming of LTD and also the direct induction of LTD involves the activation of PKC.
The pseudosubstrate peptide inhibitor PKC19–36 inhibited the induction of LTD by the priming protocol and by the control induction conditioning protocol.
These experiments demonstrate that a covert synaptic change involving generation of PKC is very effective in producing conditions whereby LTD is induced by very brief synaptic stimulation.