bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differential inhibition of N and P/Q Ca2+ currents by 5‐HT1A and 5‐HT1D receptors in spinal neurons of Xenopus larvae
Authors: Sun Qian‐Quan , Dale Nicholas 
Published: September 2004

In whole‐cell patch clamp recordings made from non‐sensory neurons acutely isolated from the spinal cord of Xenopus (stage 40–42) larvae, two forms of inhibition of the high voltage‐activated (HVA) Ca2+ currents were produced by 5‐HT. One was voltage dependent and associated with both slowing of the activation kinetics and shifting of the voltage dependence of the HVA currents. This inhibition was relieved by strong depolarizing prepulses. A second form of inhibition was neither associated with slowing of the activation kinetics nor relieved by depolarizing prepulses and was thus voltage independent.
In all neurons examined, 5‐HT (1 μM) reversibly reduced 34 ± 1.6 % (n= 102) of the HVA Ca2+ currents. In about 40 % of neurons, the inhibition was totally voltage independent. In another 5 %, the inhibition was totally voltage dependent. In the remaining neurons, inhibition was only partially (by around 40 %) relieved by a large depolarizing prepulse, suggesting that in these, the inhibition consisted of both voltage‐dependent and ‐independent components.
By using selective channel blockers, we found that 5‐HT acted on both N‐ and P/Q‐type channels. However, whereas the inhibition of P/Q‐type currents was only voltage independent, the inhibition of N‐type currents had both voltage‐dependent and ‐independent components.
The effects of 5‐HT on HVA Ca2+ currents were mediated by 5‐HT1A and 5‐HT1D receptors. The 5‐HT1A receptors not only preferentially caused voltage‐independent inhibition, but did so by acting mainly on the ω‐agatoxin‐IVA‐sensitive Ca2+ channels. In contrast, the 5‐HT1D receptor produced both voltage‐dependent and ‐independent inhibition and was preferentially coupled to ω‐conotoxin‐GVIA sensitive channels. This complexity of modulation may allow fine tuning of transmitter release and calcium signalling in the spinal circuitry of Xenopus larvae.
Anemone toxin (ATX II)‐induced increase in persistent sodium current: effects on the firing properties of rat neocortical pyramidal neurones
Authors: Mantegazza Massimo , Franceschetti Silvana , Avanzini Giuliano 
Published: September 2004

The experiments were performed on sensorimotor cortex using current‐clamp intracellular recordings in layer V pyramidal neurones and whole‐cell voltage‐clamp recordings in dissociated pyramidal neurones. The intracellularly recorded neurones were classified on the basis of their firing characteristics as intrinsically bursting (IB) and regular spiking (RS). The RS neurones were further subdivided into adapting (RSAD) or non‐adapting (RSNA), depending on the presence or absence of spike frequency adaptation. Since burst firing in neocortical pyramidal neurones has previously been suggested to depend on the persistent fraction of Na+ current (INa,p), pharmacological manipulations with drugs affecting INa inactivation have been employed.
ATX II, a toxin derived from Anemonia sulcata, selectively inhibited INa fast inactivation in dissociated neurones. In current‐clamp experiments on neocortical slices, ATX II enhanced the naturally occurring burst firing in IB neurones and revealed the ability of RSNA neurones to discharge in bursts, whereas in RSAD neurones it increased firing frequency, without inducing burst discharges. During the ATX II effect, in all the three neuronal subclasses, episodes of a metastable condition occurred, characterized by long‐lasting depolarizing shifts, triggered by action potentials, which were attributed to a peak in the toxin‐induced inhibition of INa inactivation. The ATX II effect on IB and RSNA neurones was compared with that induced by veratridine and iodoacetamide. Veratridine induced a small increase in the INa and a large shift to the left in the voltage dependence of INa activation. Accordingly, its major effect on firing characteristics was the induction of prolonged tonic discharges, associated with burst facilitation less pronounced than that induced by ATX II. The alkylating agent iodoacetamide was able to induce a selective small increase in the INa,p, with a similar but less pronounced effect than ATX II on firing behaviour.
The present results show that pharmacological manipulations capable of slowing down INa inactivation significantly enhance burst behaviour in IB neurones and promote burst firing in otherwise non‐bursting RSNA neurones. We suggest that IB and, to a lesser extent, RSNA neurones are endowed with a relatively large fraction of INa,p which, in physiological conditions, is sufficient to sustain bursting in IB but not in RSNA neurones.
ATP‐sensitive K+ channel activation by calcitonin gene‐related peptide and protein kinase A in pig coronary arterial smooth muscle
Authors: Wellman G. C. , Quayle J. M. , Standen N. B. 
Published: September 2004

We used patch clamp to study whole‐cell K+ currents activated by calcitonin gene‐related peptide (CGRP) in smooth muscle cells freshly dissociated from pig coronary arteries.
CGRP (50 nm) activated an inward current at −60 mV in symmetrical 140 mm K+ that was blocked by glibenclamide (10 μm), an inhibitor of ATP‐sensitive potassium (KATP) channels. CGRP‐induced currents were larger in cells dialysed with 0.1 mm ATP than with 3.0 mm ATP.
Forskolin (10 μm) activated a glibenclamide‐sensitive current, as did intracellular dialysis with cAMP (100 μm). The catalytic subunit of cAMP‐dependent protein kinase (protein kinase A, PKA), added to the pipette solution, activated equivalent currents in five out of twelve cells.
CGRP‐induced currents were reduced by the PKA inhibitors adenosine 3′,5′‐cyclic monophosphorothioate, RP‐isomer, triethylammonium salt (Rp‐cAMPS; 100 μm) and N‐[2‐((p‐bromocinnamyl)amino)ethyl]‐5‐isoquinolinesulphonamide dihydrochloride (H‐89; 1 μm), and abolished by inclusion of a PKA inhibitor peptide in the pipette solution.
The β‐adrenergic agonist isoprenaline (10 μm) also activated a glibenclamide‐sensitive K+ current.
CGRP‐induced currents were unaffected by the inhibitor of cGMP‐dependent protein kinase (PKG) KT5823 (1 μm). Sodium nitroprusside (10 μm) did not activate a glibenclamide‐sensitive current in cells held at −60 mV, but did activate an outward current at +60 mV that was abolished by KT5823, or by 100 nm iberiotoxin (an inhibitor of BKCa channels).
Our findings suggest that CGRP activates coronary KATP channels through a pathway that involves adenylyl cyclase and PKA, but not PKG.
Role of Na+ conductance, Na+‐H+ exchange, and Na+‐K+‐2Cl− symport in the regulatory volume increase of rat hepatocytes
Authors: Wehner Frank , Tinel Hanna 
Published: September 2004

In rat hepatocytes under hypertonic stress, the entry of Na+ (which is thereafter exchanged for K+ via Na+‐K+‐ATPase) plays the key role in regulatory volume increase (RVI).
In the present study, the contributions of Na+ conductance, Na+‐H+ exchange and Na+‐K+‐2Cl− symport to this process were quantified in confluent primary cultures by means of intracellular microelectrodes and cable analysis, microfluorometric determinations of cell pH and buffer capacity, and measurements of frusemide (furosemide)/bumetanide‐sensitive 86Rb+ uptake, respectively. Osmolarity was increased from 300 to 400 mosmol l−1 by addition of sucrose.
The experiments indicate a relative contribution of approximately 4:1:1 to hypertonicity‐induced Na+ entry for the above‐mentioned transporters and the overall Na+ yield equalled 51 mmol l−1 (10 min)−1.
This Na+ gain is in good agreement with the stimulation of Na+ extrusion via Na+‐K+‐ATPase plus the actual increase in cell Na+, namely 55 mmol l−1 (10 min)−1, as was determined on the basis of ouabain‐sensitive 86Rb+ uptake and by means of Na+‐sensitive microelectrodes, respectively.
The overall increase in Na+ and K+ activity plus the expected concomitant increase in cell Cl− equalled 68 mmol l−1, which fits well with the increase in osmotic activity expected to occur from an initial cell shrinkage to 87.5 % and a RVI to 92.6 % of control, namely 53 mosmol l−1.
The prominent role of Na+ conductance in the RVI of rat hepatocytes could be confirmed on the basis of the pharmacological profile of this process, which was characterized by means of confocal laser‐scanning microscopy.
The development of conduction block in single human axons following a focal nerve injury
Authors: Inglis J. Timothy , Leeper James B. , Wilson Linda R. , Gandevia Simon C. , Burke David 
Published: September 2004

Using microneurography with a conventional monopolar electrode, the action potentials of ten myelinated axons in the peripheral nerves of human subjects were followed while they developed conduction block.
The action potentials had initially (n= 6) or developed (n= 4) a positive double‐peaked morphology. The time interval between the two positive peaks represents the conduction time across the impaled internode.
When the interpeak interval was < 500 μs, conduction across the site of impalement was secure, even if the conduction time was markedly prolonged. When the interval was > 600 μs, intermittent conduction failure occurred. For all units the longest interpeak interval recorded just prior to complete conduction failure was, on average, 1.12 ms (range, 0.8–1.4 ms).
For five axons, there was evidence that natural activity triggered the conduction failure.
Impalement of the nerve fibre by the microelectrode impairs the ability of the axon to conduct impulses across the site of injury, but impulse transmission can be secure even when the conduction time across individual internodes is prolonged to 500 μs. These findings are therefore relevant to the conduction deficits that occur in focal injuries of human axons.
A mutation in the pore region of HERG K+ channels expressed in Xenopus oocytes reduces rectification by shifting the voltage dependence of inactivation
Authors: Zou Anruo , Xu Qing P. , Sanguinetti Michael C. 
Published: September 2004

The effects of a mutation in the human ether‐a‐go‐go‐related gene (HERG) (Ser631 to Ala, S631A) on the voltage‐ and extracellular [K+] dependence of inactivation were studied in Xenopus oocytes using two microelectrode and single channel voltage‐clamp techniques.
The voltage required for half‐inactivation of S631A HERG was 102 mV more positive than for wild‐type (WT)‐HERG, resulting in reduced rectification of the steady‐state current‐voltage relationship. In contrast, the voltage dependence of channel activation was not altered by the S631A mutation. These findings indicate that inactivation of HERG channels is not linked to activation.
Rectification of whole‐cell S631A HERG current was caused by a voltage‐dependent reduction in open probability, and inward rectification of the current‐voltage relationship of single channels.
Elevation of extracellular [K+] from 2 to 20 mm shifted the half‐point for inactivation by +20 mV for WT‐HERG, and +25 mV for S631A HERG. Thus, elevated [K+]o and the S631A mutation affect HERG inactivation by different mechanisms.
The S631A mutation altered the ion translocation rate of HERG channels. The single channel conductance (γ) of S631A HERG was 20 pS between ‐40 and‐100 mV, and 6.0 pS between +40 and +100 mV (120 mm extracellular K+). This compares to a γ of 12.1 and 5.1 pS for WT‐HERG channels under the same conditions.
Contribution of sarcoplasmic reticular calcium to smooth muscle contractile activation: gestational dependence in isolated rat uterus
Authors: Taggart Michael J. , Wray Susan 
Published: September 2004

The contribution of Ca2+ released from the sarcoplasmic reticulum (SR) to smooth muscle contractile activation remains poorly understood. By simultaneously monitoring cytosolic [Ca2+] ([Ca2+]i) and force in isolated rat uterine smooth muscle, we report the influence of SR Ca2+ release on contractility during conditions (a) of altered SR Ca2+ homeostasis and (b) where the only source of activating Ca2+ was derived from the SR.
In myometria of non‐pregnant rats, ryanodine (1‐50 μM), a modulator of calcium‐induced calcium release (CICR), had no effect on the spontaneous [Ca2+]i or force transients. However, depletion of SR Ca2+ by inhibiting the SR Ca2+‐ATPase (with cyclopiazonic acid (CPA), 20 μM) resulted in an enhancement of spontaneous [Ca2+]i and force transients.
In myometria of pregnant rats, although ryanodine had no effect in 40 % of tissues studied it produced a small but significant enhancement of the integrated spontaneous [Ca2+]i and force transient in 60 % of cases. The potentiating effects of CPA were enhanced in myometria of pregnant rats compared with non‐pregnant rats, often resulting in maintained [Ca2+]i increases and contraction.
In zero external Ca2+, agonist‐induced SR Ca2+ release resulted in transient increases in [Ca2+]i and force. The magnitude of these agonist‐induced [Ca2+]i and force changes were significantly enhanced in myometria of pregnant rats. No evidence for agonist‐induced Ca2+‐independent force production was observed.
These results indicate that CICR plays little role in SR Ca2+ release from the myometrium, and that there are gestational‐dependent alterations in the ability of SR Ca2+ mobilization to contribute to contractile activation. The implications of these findings for the co‐ordination of myometrial [Ca2+]i signalling and contractility are discussed.
Transmitter release modulation in nerve terminals of rat neocortical pyramidal cells by intracellular calcium buffers
Authors: Ohana Ora , Sakmann Bert 
Published: September 2004

Dual whole‐cell voltage recordings were made from synaptically connected layer 5 (L5) pyramidal neurones in slices of the young (P14‐P16) rat neocortex. The Ca2+ buffers BAPTA or EGTA were loaded into the presynaptic neurone via the pipette recording from the presynaptic neurone to examine their effect on the mean and the coefficient of variation (c.v.) of single fibre EPSP amplitudes, referred to as unitary EPSPs.
The fast Ca2+ buffer BAPTA reduced unitary EPSP amplitudes in a concentration dependent way. With 0.1 mm BAPTA in the pipette, the mean EPSP amplitude was reduced by 14 ± 2.8 % (mean ±s.e.m., n= 7) compared with control pipette solution, whereas with 1.5 mm BAPTA, the mean EPSP amplitude was reduced by 72 ± 1.5 % (n= 5). The concentration of BAPTA that reduced mean EPSP amplitudes to one‐half of control was close to 0.7 mm.
Saturation of BAPTA during evoked release was tested by comparing the effect of loading the presynaptic neurone with 0.1 mm BAPTA at 2 and 1 mm[Ca2+]o. Reducing [Ca2+]o from 2 to 1 mm, thereby reducing Ca2+ influx into the terminals, decreased the mean EPSP amplitude by 60 ± 2.2 % with control pipette solution and by 62 ± 1.9 % after loading with 0.1 mm BAPTA (n= 7).
The slow Ca2+ buffer EGTA at 1 mm reduced mean EPSP amplitudes by 15 ± 2.5 % (n= 5). With 10 mm EGTA mean EPSP amplitudes were reduced by 56 ± 2.3 % (n= 4).
With both Ca2+ buffers, the reduction in mean EPSP amplitudes was associated with an increase in the c.v. of peak EPSP amplitudes, consistent with a reduction of the transmitter release probability as the major mechanism underlying the reduction of the EPSP amplitude.
The results suggest that in nerve terminals of thick tufted L5 pyramidal cells the endogenous mobile Ca2+ buffer is equivalent to less than 0.1 mm BAPTA and that at many release sites of pyramidal cell terminals the Ca2+ channel domains overlap, a situation comparable with that at large calyx‐type terminals in the brainstem.
Electrophysiological characterization of Na+ currents in acutely isolated human hippocampal dentate granule cells
Authors: Reckziegel G. , Beck H. , Schramm J. , Elger C. E. , Urban B. W. 
Published: September 2004

Properties of voltage‐dependent Na+ currents were investigated in forty‐two dentate granule cells (DGCs) acutely isolated from the resected hippocampus of twenty patients with therapy‐refractory temporal lobe epilepsy (TLE) using the whole‐cell patch‐clamp technique.
Depolarizing voltage commands elicited large, rapidly activating and inactivating Na+ currents (140 pS μm−2; 163 mm extracellular Na+) that were reduced in amplitude by lowering the Na+ gradient (43 mm extracellular Na+). At low temperatures (8‐12 °C), the time course of Na+ currents slowed and could be well described by the model of Hodgkin & Huxley.
Na+ currents were reversibly blocked by tetrodotoxin (TTX) and saxitoxin (STX) with a half‐maximal block of 4.7 and 2.6 nm, respectively. In order to reduce series resistance errors, the Na+ current was partially blocked by low toxin concentrations (10‐15 nm) in the experiments described below. Under these conditions, Na+ currents showed a threshold of activation of about ‐50 mV, and the voltages of half‐maximal activation and inactivation were ‐29 and ‐55 mV, respectively.
The time course of recovery from inactivation could be described with a double‐exponential function (time constants, 3‐20 and 60‐200 ms). The rapid and slow time constants showed a distinct voltage dependence with maximal values around ‐55 and ‐80 mV, respectively. These properties contributed to a reduction of the Na+ currents during repetitive stimulation that was more pronounced with higher stimulation frequencies and also showed a dependence on the holding potential.
In summary, the most striking features of DGC Na+ currents were the large current density and the presence of a current component showing a slow recovery from inactivation. Our data provide a basis for comparison with properties of Na+ currents in animal models of epilepsy, and for the study of drug actions in therapy‐refractory epilepsy.
Adrenergic regulation of calcium‐activated potassium current in cultured rabbit pigmented ciliary epithelial cells
Authors: Ryan Jennifer S. , Tao Qian‐Ping , Kelly Melanie E. M. 
Published: September 2004

The effects of adrenergic agonists on K+ currents were studied in cultured rabbit pigmented ciliary epithelial (PCE) cells.
Outward K+ current (IK) was reduced by tetraethylammonium chloride, the Ca2+‐activated K+ (K(Ca)) channel blocker iberiotoxin (IbTX), or Ca2+‐free external Ringer solution. The calcium ionophore ionomycin increased an IbTX‐sensitive IK in PCE cells.
The adrenergic agonists adrenaline and phenylephrine increased IK in PCE cells. The induced current was blocked by IbTX and the α1‐antagonist prazosin, suggesting that adrenergic agonists activate IK(Ca) via α1‐adrenoreceptors.
Internal dialysis of D‐myo‐inositol 1,4,5‐trisphosphate (IP3) increased IK, whilst pre‐incubation of PCE cells with thapsigargin or the phospholipase C (PLC) inhibitor U‐73122 reduced phenylephrine‐induced increases in IK(Ca). Adrenergic increases in IK(Ca) were mediated by a pertussis toxin‐insensitive G protein.
These results demonstrate that IK(Ca) channels in rabbit PCE cells are coupled to α1‐adrenergic receptors and a PLC/IP3 signalling pathway. Activation of these channels may modulate fluid secretion by the ciliary epithelium.
The role of Ca2+ in volume regulation induced by Na+‐coupled alanine uptake in single proximal tubule cells isolated from frog kidney
Authors: Mounfield P. R. , Robson L. 
Published: September 2004

It has been suggested that epithelial cells maintain cell volume and function, in the face of changes in the rate of transepithelial transport, by activation of volume‐regulatory pathways.
The aim of the following study was to examine directly the effect of an alteration in Na+‐coupled alanine transport on cell length in single proximal tubule cells isolated from frog kidney.
An optical technique was used to examine the change in cell length induced by 5 mM L‐alanine.
On addition of L‐alanine to the bath there was an initial increase in cell length to a peak value. This was followed by two types of response. In eighteen out of thirty‐one cells a typical volume‐regulatory response was observed. The remaining cells showed no volume regulation.
Volume regulation was not affected by the removal of extracellular Ca2+. The mean degrees of recovery were 159 ± 21 % (n= 18) and 144 ± 18 % (n= 8) in the presence and absence of Ca2+, respectively.
Volume regulation was inhibited by depletion of intracellular Ca2+ stores, or in the presence of either Gd3+ or DIDS. The mean degrees of regulation were 55.4 ± 9.2 % (n= 7), 68.2 ± 18.8 % (n= 7) and 69.1 ± 14.3 % (n= 7), respectively.
The alanine‐induced increases in cell length were both stereospecific and Na+ dependent.
The evidence suggests that volume regulation induced by Na+‐coupled alanine uptake may be dependent on the release of Ca2+ from intracellular stores. This is in contrast to volume regulation induced by hypotonic shock, which appears to require extracellular Ca2+. Results obtained using a hypotonic shock should, therefore, be viewed with caution.
Facilitation of presynaptic calcium currents in the rat brainstem
Authors: Borst J. G. G. , Sakmann B. 
Published: September 2004

To study use‐dependent changes in the presynaptic Ca2+ influx and their contribution to transmitter release, we made simultaneous voltage clamp recordings from presynaptic terminals (the calyces of Held) and postsynaptic cells (the principal cells of the medial nucleus of the trapezoid body) in slices of the rat auditory brainstem.
Following a short (2 ms) prepulse to 0 mV, calcium channels opened faster during steps to negative test potentials. During trains of action potential waveforms the Ca2+ influx per action potential increased. At the same time, however, the amplitude of the EPSCs decreased.
The facilitation of the calcium currents appeared to depend on a build‐up of intracellular Ca2+, since its magnitude was proportional to the Ca2+ influx and it was reduced in the presence of 10 mm BAPTA.
Facilitation of the presynaptic calcium currents may contribute to short‐term facilitation of transmitter release, observed when quantal output is low. Alternatively, it may counteract processes that contribute to synaptic depression.
Two types of parasympathetic preganglionic neurones in the superior salivatory nucleus characterized electrophysiologically in slice preparations of neonatal rats
Authors: Matsuo Ryuji , Kang Youngnam 
Published: September 2004

The electrophysiological properties of parasympathetic preganglionic neurones in the superior salivatory nucleus were studied in thin‐ and thick‐slice preparations of rats aged 1 and 2 weeks using the whole‐cell patch‐clamp technique.
The superior salivatory neurones were identified by a retrograde tracing method with dextran‐tetramethylrhodamine‐lysine. The injection of the tracer into the chorda‐lingual nerve labelled the neurones innervating the submandibular ganglia and those innervating the intra‐lingual ganglia, while the injection into the tip of the tongue labelled the latter group of neurones.
Firing characteristics were investigated mainly in the neurones of 6–8 days postnatal rats. In response to an injection of long depolarizing current pulses at hyperpolarized membrane potentials (< −80 mV) under a current clamp, the neurones labelled from the nerve displayed a train of action potentials with either a long silent period preceding the first spike (late spiking pattern) or a long silent period interposed between the first and second spikes (interrupted spiking pattern). The neurones labelled from the tongue invariably displayed the interrupted spiking pattern.
Under a voltage clamp, among the neurones from 6–8 days postnatal rats, those labelled from the nerve expressed either a fast or a slow transient outward current (A‐current), while those labelled from the tongue invariably showed a slow transient outward current. Both the fast and slow A‐currents were largely depressed by 1 mm 4‐aminopyridine.
Similar fast and slow A‐currents were observed in the neurones of rats aged 14–15 days. Both the time to peak and decay time constant of these A‐currents were accelerated, suggesting a developmental trend of maturation in the activation and inactivation kinetics between 6 and 15 days postnatal.
Based on the differences in the firing pattern and outward current, the superior salivatory neurones can be separated into two distinct types. We discuss the functional aspects of these two types of neurones with reference to their target organs.