bluuebunny/crossref_metadata_2025_split huggingface dataset:
A swelling‐activated chloride current in rat sympathetic neurones
Authors: Leaney J. L. , Marsh S. J. , Brown D. A. 
Published: September 2004

We have tested whether neurones show a swelling‐induced Cl− current following hypotonic shock, by recording membrane current responses and cell volume changes in voltage clamped isolated rat sympathetic neurones during application of hypotonic solutions.
Using both whole‐cell and perforated patch recording methods, hypotonic solution caused cell swelling and the activation of an inward Cl− current at –60 mV. This current showed weak outward rectification with no obvious time dependence. It was inhibited by SITS (0.3–1 mm), NPPB (30–300 μm and niflumic acid (50–200 μm) but not by tamoxifen (10 μm)
Hypotonic solution did not cause a rise in intracellular Ca2+ concentration as measured by simultaneous indo‐1 fluorescence. Also, neither the volume change nor Cl− current were affected by the removal of external Ca2+ or internal Ca2+ buffering to ≤ 1 nm with EGTA.
The Cl− current was unaffected by an inhibitor of protein kinase C (PKC; GF109203X, 3 μm or by omission of ATP from the pipette solution.
Cells exhibited a regulatory volume decrease during sustained exposure to hypotonic solution. This was completely inhibited by 0'5 mm niflumic acid.
It is concluded that osmotic swelling induces an outwardly rectifying, Ca2+‐ and PKC‐independent Cl− current in these nerve cells. It is suggested that this current may be involved in volume regulatory mechanisms.
A rapidly activating sustained K+ current modulates repolarization and excitation–contraction coupling in adult mouse ventricle
Authors: Fiset C. , Clark R. B. , Larsen T. S. , Giles W. R. 
Published: September 2004

The K+ currents which control repolarization in adult mouse ventricle, and the effects of changes in action potential duration on excitation–contraction coupling in this tissue, have been studied with electrophysiological methods using single cell preparations and by recording mechanical parameters from an in vitro working heart preparation.
Under conditions where Ca2+‐dependent currents were eliminated by buffering intracellular Ca2+ with EGTA, depolarizing voltage steps elicited two rapidly activating outward K+ currents: (i) a transient outward current, and (ii) a slowly inactivating or ‘sustained’ delayed rectifier.
These two currents were separated pharmacologically by the K+ channel blocker 4‐amino‐pyridine (4–AP). 4–AP at concentrations between 3 and 200 μm resulted in (i) a marked increase in action potential duration and a large decrease in the sustained K+ current at plateau potentials, as well as (ii) a significant increase in left ventricular systolic pressure in the working heart preparation.
The current‐voltage (I–V) relation, kinetics, and block by low concentrations of 4–AP strongly suggest that the rapid delayed rectifier in adult mouse ventricle is the same K+ current (Kv1.5) that has been characterized in detail in human and canine atria.
These results show that the 4–AP–sensitive rapid delayed rectifier is a very important repolarizing current in mouse ventricle. The enhanced contractility produced by 4–AP (50 μm) in the working heart preparation demonstrates that modulation of the action potential duration, by blocking a K+ current, is a very significant inotropic variable.
Different G proteins mediate somatostatin‐induced inward rectifier K+ currents in murine brain and endocrine cells
Authors: Takano Koji , Yasufuku‐Takano Junko , Kozasa Tohru , Nakajima Shigehiro , Nakajima Yasuko 
Published: September 2004

Types of G proteins (G protein α‐subunit subtypes) which mediate the activation of inward rectifier K+ currents by somatostatin (somatotrophin release‐inhibiting factor, SRIF) were determined in cultured locus coeruleus neurones from newborn rats and in AtT‐20 cells (a mouse pituitary cell line).
The whole‐cell patch clamp technique was used together with injection of antibodies against pertussis toxin (PTX)‐sensitive G protein α‐subunits or with injection of antisense (or sense) oligonucleotides against these G proteins.
In locus coeruleus neurones, the SRIF‐induced activation of inward rectifier K+ currents was inhibited by anti‐Gαi1/Gαi2 antibody injection, but not by anti‐Gαi3 or by anti‐Gαo/Gαi3 antibody injection, suggesting that the SRIF response is mediated through Gαi1 and/or Gαi2.
The SRIF‐induced activation of the inward rectifier was suppressed in locus coeruleus neurones after injection of antisense oligonucleotides against Gαi2, but not by injection of sense oligonucleotides against Gαi2. Injection of antisense (or sense) oligonucleotides against Gαi1, Gαi3 and Gαo(common) had no effect. These results suggest that Gαi2 is involved in this SRIF response.
In AtT‐20 cells, the SRIF‐induced activation of inward rectifier K+ currents was suppressed by injection of anti‐Gαi3 antibody, but not by injection of anti‐Gαi1/Gαi2 antibody.
The above results indicate that Gi mediates the SRIF effects on inward rectifier K+ currents. However, different subtypes of Gi are involved in the brain neurones and in the endocrine cells: Gi2 in locus coeruleus neurones and Gi3 in AtT‐20 cells.
Charge Movement in Cut Twitch Fibres of Rana Temporaries Containing 0.1 mm EGTA
Authors: Hui Chin Shuen , Chen Wei 
Published: September 2004

Charge movement was studied in the cut twitch fibres of Rana temporaria with a double Vaseline‐gap voltage‐clamp technique.
In fibres containing 0.1 mm EGTA, the Iγ hump component of charge movement was either unresolvable or had a brief duration at all potentials. In the steady‐state charge‐voltage (Q–V) plots that were separable into the less voltage dependent (Qβ) and more voltage dependent (Qγ) components, the amount of Qγ was 0.9 ± 0.1 nC μF−1 (mean ±s.e.m., n= 18).
Fibres containing 20 mm EGTA showed broad Iγ humps at about −45 mV. The addition of 1.8 mm total Ca2+ to the end‐pools accelerated the rising phase and abbreviated the duration of the hump.
I
γ humps in fibres containing 0.1 mm EGTA resembled those in intact fibres when recorded at similar low temperatures.
These results explain the controversy concerning the variable appearance of Iγ humps in cut fibres.
Calcium‐induced release of strontium ions from the sarcoplasmic reticulum of rat cardiac ventricular myocytes
Authors: Spencer C. Ian , Berlin Joshua R. 
Published: September 2004

The effects of strontium ions, Sr2+, on Ca2+‐dependent feedback mechanisms during excitation‐contraction coupling were examined in voltage‐clamped rat ventricular myocytes in which intracellular [Ca2+] and [Sr2+] were monitored with the fluorescent indicator, indo‐1.
Voltage clamp depolarizations and caffeine applications during superfusion in Ca2+‐free, Sr2+‐containing solutions were employed to exchange intracellular Ca2+ with Sr2+. Myocytes were loaded with Sr2+ by applying voltage clamp depolarizations during superfusion in Na+‐free, Sr2+‐containing solutions.
Caffeine applications produced large fluorescence transients in Sr2+‐loaded cells. Thus, Sr2+ could be sequestered and released from the sarcoplasmic reticulum.
Ca2+ influx, but not Sr2+ influx, via sarcolemmal Ca2+ channels evoked ryanodine‐sensitive fluorescence transients in Sr2+‐loaded cells. These results demonstrated that Ca2+ influx‐induced Sr2+ release (CISR) from the sarcoplasmic reticulum occurred in these experiments, even though Sr2+ influx‐induced Sr2+ release was not observed.
The amplitude of the Ca2+ influx‐induced fluorescence transient was 17 ± 1% of the caffeine‐induced transient (n= 5 cells), an indication that fractional utilization of Sr2+ sequestered in the sarcoplasmic reticulum during CISR was low.
With increased Sr2+ loading, the amplitude of Ca2+ influx‐ and caffeine‐induced fluorescence transients increased, but fractional utilization of sarcoplasmic reticulum divalent cation stores was independent of the degree of Sr2+ loading. These data suggest that Ca2+ influx directly activated the release of divalent cations from the sarcoplasmic reticulum, but mechanisms promoting positive feedback of Sr2+ release were minimal during CISR.
By comparison, in Ca2+‐loaded myocytes, Ca2+ influx‐induced Ca2+ release (CICR) utilized a greater fraction of caffeine‐releasable stores than CISR. Fractional utilization of Ca2+ stores during CICR increased with the degree of Ca2+ loading.
Taken together, these results suggest that Ca2+‐dependent feedback mechanisms play a major role in determining the extent of sarcoplasmic reticulum Ca2+ release during cardiac excitation‐contraction coupling under a wide range of conditions.
Calcium dependence and distribution of calcium‐activated chloride channels in Xenopus oocytes
Authors: Gomez‐Hernandez Juan‐Manuel , Stühmer Walter , Parekh Anant B. 
Published: September 2004

The Ca2+‐dependent Cl− current (ICl,Ca), expressed in the plasma membrane of Xenopus oocytes, was examined in excised inside‐out macropatches using a rapid perfusion system.
Application of Ca2+‐containing Ringer solution resulted in the activation of a current whose reversal potential shifted to the right by 51 + 5.2 mV when Cl− in the pipette solution was lowered from 119.3 to 10 mm. No currents were generated when Ca2+ was omitted from the solution. The current is therefore a Ca2+‐activated Cl− one.
Following exposure to Ca2+, the half‐time for activation of ICl,Ca was not voltage dependent, whereas deactivation was strongly so.
I
Cl,Ca was stable in the continuous presence of Ca2+ and showed no sign of inactivation or adaptation.
Comparison of the size of the currents (normalized to pipette resistance) from the animal and vegetal poles revealed that ICl,Ca had a highly polarized distribution. The current density was almost 10 times higher in the animal pole.
The results suggest that Cl− channels provide a continuous and reliable indication of submembranous Ca2+, at least in an excised patch, and the clustering of the Cl− channels renders it necessary to exert caution in interpreting results involving the kinetics of Ca2+ signalling, when ICl,Ca is used as the sole monitor of calcium.
Regulation of Na+–K+ pump activity in contracting rat muscle
Authors: Nielsen O. B. , Clausen T. 
Published: September 2004

In rat soleus muscle, high frequency electrical stimulation produced a rapid increase in intra‐cellular Na+ (Na+i) content. This was considerably larger in muscles contracting without developing tension than in muscles contracting isometrically. During subsequent rest a net extrusion of Na+ took place at rates which, depending on the frequency and duration of stimulation, approached the maximum transport capacity of the Na+–K+ pumps present in the muscle.
In isometrically contracting muscles, the net extrusion of Na+ continued for up to 10 min after stimulation, reducing Na+i to values 30% below the resting level (P < 0.001). This undershoot in Na+i, seen in both soleus and extensor digitorum longus muscles, could be maintained for up to 30 min and was blocked by ouabain or cooling to 0 °C.
The undershoot in Na+i could be elicited by direct stimulation as well as by tubocurarine‐suppressible stimulation via the motor endplate. It could not be attributed to a decrease in Na+ influx, to effects of noradrenaline or calcitonin gene‐related peptide released from nerve endings, to an increase in extracellular K+ or the formation of nitric oxide.
The results indicate that excitation rapidly activates the Na+–K+ pump, partly via a change in its transport characteristics and partly via an increase in intracellular Na+ concentration. This activation allows an approximately 20‐fold increase in the rate of Na+ efflux to take place within 10 s.
The excitation‐induced activation of the Na+–K+ pump may represent a feed‐forward mechanism that protects the Na+–K+ gradients and the membrane potential in working muscle. Contrary to previous assumptions, the Na+–K+ pump seems to play a dynamic role in maintenance of excitability during contractile activity.
Decay of calcium transients after electrical stimulation in rat fast‐ and slow‐twitch skeletal muscle fibres
Authors: Carroll Stefanie L. , Klein Michael G. , Schneider Martin F. 
Published: September 2004

Calcium transients were calculated from fura‐2 fluorescence signals (corrected for kinetic delays in the Ca2+–fura‐2 reaction) from single rat skeletal muscle fibres, either fully dissociated from the fast‐twitch flexor digitorum brevis (FDB) muscle or in small bundles from the slow‐twitch soleus muscle. Fibres or bundles were embedded in agarose gel to inhibit movement and stimulated by single or trains of 1–2 ms electrical pulses (100 Hz, 2–400 ms train duration).
The rate constant of decay of [Ca2+] determined from single‐exponential fits to the final decay phase of [Ca2+] after a single action potential was considerably faster in FDB fibres than in soleus fibres. As the stimulation duration increased, the rate constant of [Ca2+] decay decreased for both the FDB and soleus fibres, but the effect was greater in FDB than in soleus fibres.
Using the magnitude of the decline in the rate constant of [Ca2+] decay with increasing stimulation duration as an index of relative contribution of the saturable Ca2+ binding sites on parvalbumin, subpopulations termed ‘high’, ‘medium’ and ‘low’, referring to estimated parvalbumin content, were determined within each group of FDB and soleus fibres. In fibres assigned to the ‘high’ and ‘medium’ groups, parvalbumin was the major contributor (50.73%) to the [Ca2+] decay rate constant after a single action potential. In fibres in the ‘low’ group, parvalbumin contributed only 0–28% to the rate constant of [Ca2+] decay.
Fluorescence recordings using mag‐fura‐2, a lower‐affinity Ca2+ indicator expected to be in equilibrium with myoplasmic Ca2+, gave similar values for both the [Ca2+] decay rate constant after a single action potential and the decrease in this rate constant with increased stimulation duration, as found for the fura‐2 [Ca2+] transients from FDB and soleus fibres. Thus, the observed differences in decay rate of Ca2+ were not introduced by kinetic correction of the fura‐2 recordings, but are attributed to differences in the Ca2+ binding and transport properties of fast‐ and slow‐twitch mammalian fibres.
Permeation and block of rat glur6 glutamate receptor channels by internal and external polyamines
Authors: Bähring Robert , Bowie Derek , Benveniste Morris , Mayer Mark L. 
Published: September 2004

Polyamine block of rat GluR6(Q) glutamate receptor channels was studied in outside‐out patches from transiently transfected HEK 293 cells. With symmetrical 150 mm Na+ and 30 μm internal spermine there was biphasic voltage dependence with 95% block at +40 mV but only 20% block at +140mV. Dose–inhibition analysis for external spermine also revealed biphasic block; the Ka at +40 mV (54 μm) was lower than at +80 (167μm) and –80 mV (78 μm).
For internal polyamines relief from block was most pronounced for spermine, weaker for N‐(4‐hydroxyphenylpropanoyl)‐spermine (PPS), and virtually absent for philanthotoxin 343 (PhTX 343), suggesting that permeation of polyamines varies with cross‐sectional width (spermine, 0.44 nm; PPS, 0.70 nm; PhTX 343, 0.75 nm).
With putrescine, spermidine, or spermine as sole external cations, inward currents at –120 mV confirmed permeation of polyamines. For bi‐ionic conditions with 90 mm polyamine and 150 mm Na+i reversal potentials were –12.4 mV for putrescine (permeability ratio relative to Na+, PPut/PNa= 0.42) and –32.7 mV for spermidine (PSpd/PNa= 0.07). Currents carried by spermine were too small to analyse accurately in the majority of patches.
Increasing [Na+]i from 44 to 330 mm had no effect on the potential for 50% block (V½) by 30 μm internal spermine; however, relief from block at positive membrane potentials increased with [Na+]i. In contrast, raising [Na+]o from 44 to 330 mm resulted in a depolarizing shift in V½, indicating a strong interaction between internal polyamines and external per meant ions.
The Woodhull infinite barrier model of ion channel block adequately described the action of spermine at membrane potentials insufficient to produce relief from block. For 30 μm internal spermine such analysis gave Kd(0)= 2.5 μm, z θ= 1.97; block by 30 μm external spermine was weaker and less voltage dependent (Kd(0)= 37.8 μm and zδ= 0.55); δ and θ are electrical distances measured from the outside and inside, respectively.
Fits of the Woodhull equation for a permeable blocker adequately described both onset and relief from block by spermine over a wide range of membrane potentials. However, the rate constants and zδ values estimated for block by internal spermine predicted much stronger external block than was measured experimentally, and vice versa.
An Eyring rate theory model with two energy wells and three barriers explained qualitatively many characteristic features of the action of polyamines on GluPvs, including biphasic I–V relationships, weaker block by external than internal spermine and low permeability.
Calcium homeostatic mechanisms operating in cultured postnatal rat hippocampal neurones following flash photolysis of nitrophenyl‐EGTA
Authors: Sidky Adam O. , Baimbridge Kenneth G. 
Published: September 2004

We examined Ca2+ homeostatic mechanisms in cultured postnatal rat hippocampal neurones by monitoring the recovery of background‐subtracted fluo‐3 fluorescence levels at 20–22°C immediately following a rapid increase in Ca2+ levels induced by flash photolysis of the caged Ca2+ compound nitrophenyl‐EGTA (NP‐EGTA).
A variety of methods or drugs were used in an attempt to block specifically efflux of Ca2+ by the plasmalemmal Na+–Ca2+ exchanger or uptake of Ca2+ into mitochondria.
Many of the experimental manipulations produced a decrease in intracellular pH (pHi) measured in sister cultures using the pH‐sensitive dye 2′,7′‐bis‐(2‐carboxyethyl)‐5‐(and‐6)‐carboxyfluorescein (BCECF). Accordingly, in each case, we determined the appropriate amount of the weak base trimethylamine (TMA) required to restore baseline pHi prior to flash photolysis.
Blockade of the plasmalemmal Na+‐Ca2+ exchanger by replacement of external Na+ with either Li+ or N‐methyl‐d‐glucamine (NMDG) markedly reduced pHi, but did not affect the rate of recovery of fluo‐3 fluorescence intensities once pHi was restored.
Inhibition of mitochondrial Ca2+ uptake, using the protonophore carbonyl cyanide m‐chlorophenylhydrazone (CCCP), resulted in a reduction in pHi, which could be restored by the addition of 2 mm TMA. Under these conditions the rate of recovery of Ca2+ levels was significantly slower than in the controls. Similar results were found using the respiratory chain inhibitor rotenone.
We conclude that, when the potential effects of changes in pHi are taken into account, mitochondria appear to sequester significant amounts of Ca2+ in the neuronal preparations used.
H+ transporters in the main excretory duct of the mouse mandibular salivary gland
Authors: Chaturapanich G. , Ishibashi H. , Dinudom A. , Young J. A. , Cook D. I. 
Published: September 2004

We used microspectrofluorimetry with the pH‐sensitive fluoroprobe 2′,7′‐bis(2‐carboxy‐ethyl)‐5(and‐6)‐carboxyfluorescein (BCECF) to study the regulation of cytosolic pH (pHi) in the isolated, perfused main excretory duct of the mouse mandibular gland.
In nominally HCO3−free solutions, removal of Na+ from the lumen alone caused pHi to decline whereas removing it from the bath alone did not.
Readmission of Na+ to the lumen of ducts studied under zero‐Na+ conditions caused pHi to recover fully. This recovery was blocked by 5‐(N‐ethyl‐N‐isopropyl)‐amiloride (EIPA) with a half‐maximum concentration of 0.5 μmol l−1, indicating the presence of an apical Na+–H+ exchanger.
Readmission of Na+ to the bath of ducts studied under zero‐Na+ conditions also caused pHi to recover. This recovery was blocked by 100 μmol l−1 EIPA, indicating the presence of a basolateral Na+‐H+ exchanger.
Measurements of H+ fluxes indicated that the apical Na+–H+ exchanger was approximately four times more active than the basolateral Na+‐H+ exchanger.
In three sets of experiments (in the absence of Na+, in the presence of Na+, and in the presence of Na+ plus 100 μmol l−1 EIPA), the effects of changing luminal K+ concentration on pHi were examined. We found no evidence for the presence of K+–H+ exchange or Na+‐coupled K+–H+ exchange in the apical membranes of duct cells.
pHi recovery under nominally HCO3−‐free conditions following acidification with an NH4Cl pulse was abolished by removal of Na+ from the bath and luminal solutions, indicating that no Na+‐independent systems such as H+‐ATPases were present.
A repeat of the above experiments in the presence of 25 mmol l−1 HCO3− plus 5% CO2 did not reveal any additional H+ transport systems. The removal of luminal Cl−, however, caused a small rise in pHi. This latter effect was blocked by 500 μmoll−1 4,4′‐diisothio‐cyanatodihydrostilbene‐2,2′‐disulphonic acid (H2‐DIDS), suggesting that a Cl−–HCO3− exchanger in the apical membrane might contribute in a minor way to pHi regulation.
We conclude that the predominant H+ transport systems in the mouse mandibular main excretory duct are Na+‐H+ exchangers in the apical and the basolateral membranes. The model we postulate to account for electrolyte transport across the main duct in the mouse mandibular gland is quite different from that previously developed for the rat duct but is similar to that developed for the rabbit duct. The difference is in concordance with the known ability of the mandibular gland of the rat, but not the rabbit or the mouse, to secrete a HCO3−‐rich final saliva.
Localized detection of action potential‐induced presynaptic calcium transients at a Xenopus neuromuscular junction
Authors: DiGregorio David A. , Vergara Julio L. 
Published: September 2004

Action potential (AP)‐induced fluorescence transients were measured, using Ca2+ indicators and a spot‐detection method, at single nerve terminals of a cultured Xenopus neuromuscular junction preparation with simultaneous measurement of neurotransmitter release.
Transients obtained using the low affinity Ca2+ indicator Oregon Green™ 488 BAPTA‐5N (OGB‐5N) exhibited rapid rising (t1/2(time at which one‐half of the peak fluorescence was attained) = 0.54 ms) and decaying (Tfast= 1.9 ms) phases. The higher affinity indicator Oregon Green™ 488 BAPTA‐2 (OGB‐2) produced transients with significantly slower kinetics (t1/2= 2 ms; Tslow= 73 ms).
Tetanic stimulation elicited distinct increases in fluorescence in response to each AP. Each OGB‐5N fluorescence increase was more rapid than those observed using OGB‐2. Furthermore, a smaller proportion of residual fluorescence at the end of the train was observed using OGB‐5N.
When OGB‐5N was used, a significant [Ca2+] increase was observed prior to the release of neurotransmitter. This was not observed when OGB‐2 was used.
We conclude that the use of localized optical detection coupled with low affinity Ca2+ indicators can help elucidate rapid changes in presynaptic [Ca2+] dynamics underlying evoked neurotransmitter release.