bluuebunny/crossref_metadata_2025_split huggingface dataset:
Neurotensin Inhibition of the Hyperpolarization‐Activated Cation Current (Ih) in the Rat Substantia Nigra Pars Compacta Implicates the Protein Kinase C Pathway
Authors: Cathala L. , Paupardin‐Tritsch D. 
Published: September 2004

Whole‐cell patch‐clamp recording was performed from principal neurones of the substantia nigra pars compacta (SNc). In 66% of these neurones, neurotensin (NT) induced, at −60 mV, an inward current associated with an increase in conductance.
Principal neurones displayed, in response to hyperpolarizing voltage steps, the voltage‐dependent inward cationic current, Ih. This current activated at potentials more negative than −65 mV and reached a maximum at −106 ± 4 mV, with a half‐activation potential of −86 ± 3 mV. Its estimated reversal potential was −43 ± 7 mV and its activation curve was fitted with two exponentials.
In 41 % of neurones showing the inward current, NT (0.5 μM) also reversibly reduced the amplitude of Ih. The diminution was 48.5 ± 12% when voltage steps were made from −60 to −95 mV. The decrease in Ih resulted from a reduction in the maximal current with no change in the voltage dependence of activation.
Forskolin (10 μM), an activator of adenylate cyclase, increased Ih by shifting its activation range to more positive potentials, but it did not alter the NT inhibition of Ih.
The effect of NT was blocked by staurosporine (0.5 μM) and by PKC‐(19–31) (0.5 μM), a specific protein kinase C (PKC) inhibitor, but was unaffected by Walsh's peptide (100 μM), a specific inhibitor of protein kinase A. The reduction of Ih was mimicked by 1‐oleoyl‐2‐acetyl‐sn‐glycerol (0.5–10 μM), an analogue of diacylglycerol, an endogenous PKC activator.
These results suggest that the inhibition of Ih by NT involves a phosphorylation mechanism that implies activation of PKC.
Reduced outward K+ conductances generate depolarizing after–potentials in rat supraoptic nucleus neurones
Authors: Li Zhenhuii , Hatton Glenn I. 
Published: September 2004

Whole‐cell patch clamp recordings were obtained from sixty‐five rat supraoptic nucleus (SON) neurones in brain slices to investigate ionic mechanisms underlying depolarizing after‐potentials (DAPs). When cells were voltage clamped around ‐58 mV, slow inward currents mediating DAPs (Idap), evoked by three brief depolarizing pulses, had a peak of 17 ± 1 pA (mean ± s.e.m.) and lasted for 2.8 ± 0.1 s.
No significant differences in the amplitude and duration were observed when one to three preceding depolarizing pulses were applied, although there was a tendency for twin pulses to evoke larger Idap than a single pulse. The Idap was absent when membrane potentials were more negative than ‐70 mV. In the range ‐70 to ‐50 mV, Idap amplitudes and durations increased as the membrane became more depolarized, with an activation threshold of ‐65.7 ± 0.7 mV.
I

dap
with normal amplitude and duration could be evoked during the decay of a preceding Idap. As frequencies of depolarizing pulses rose from 2 to 20 Hz, the times to peak Idap amplitude were reduced but the amplitudes and durations did not change.
A consistent reduction in membrane conductance during the Idap was observed in all SON neurones tested, and averaged 34.6 ± 3.3%. Small hyperpolarizing pulses used to measure membrane conductances appeared not to disturb major ionic mechanisms underlying Idap, since the slope and duration of Idap with and without test pulses were similar.
The Idap had an averaged reversal potential of ‐87.4 ± 1.6 mV, which was close to the K+ equilibrium potential. An elevation in [K+]O reduced or abolished the Idap, and shifted its reversal potential toward more positive levels. Perifusion of slices with 7.5–10 mm TEA, a K+ channel blocker, reversibly suppressed the Idap.
Both Na+ and Ca2+ currents failed to induce an Idap‐like current during perifusion of slices with media containing high [K+]o or TEA. However, the Idap was abolished by replacing external Ca2+ with Co2+, or replacing 82% of external Na+ with choline or Li+. Perifusion of slices with media containing 1–2 μm TTX also reduced Idap by 55.5 ± 9.0 %.
These results suggest that the generation of DAPs in SON neurones mainly involves a reduction in outward K+ current(s), which probably has little or no inactivation and can be inhibited by [Ca2+]i transients, due to Ca2+ influx during action potentials and Ca2+ release from internal stores. Na+ influx might provide a permissive influence for Ca2+‐induced reduction of K+ conductances and/or help to raise [Ca2+]i via reverse‐mode Ca2+‐Na+ exchange. Other conductances, making minor contributions to the Idap, may also be involved.
Peptides Homologous to Extracellular Loop Motifs of Connexin 43 Reversibly Abolish Rhythmic Contractile Activity in Rabbit Arteries
Authors: Chaytor A. T. , Evans W. H. , Griffith T. M. , Thornbury K. D. 
Published: September 2004

Phenylephrine (10 μM) evoked rises in tension in isolated rings of endothelium‐denuded rabbit superior mesenteric artery. These increases consisted of a tonic component with superimposed rhythmic activity, the frequency of which generally remained constant over time but whose amplitude exhibited cycle‐to‐cycle variability.
The amplitude, but not the frequency, of the rhythmic activity was affected by a series of short peptides possessing sequence homology with extracellular loops 1 and 2 of connexin 43 (Cx43). Oscillatory behaviour was abolished at concentrations of 100–300 μM (IC50 of 20–30 μM), without change in average tone. No synergy was evident between peptides corresuponding to the extracellular loops, and cytoplasmic loop peptides were biologically inactive.
The putative gap junction inhibitor heptanol mimicked the action of the extracellular loop peptides and abolished rhythmic activity at concentrations of 100–300 μM without effects on frequency. However, in marked contrast to the peptides, heptanol completely inhibited the contraction evoked by phenylephrine (IC50, 283 ± 28 μM).
The presence of mRNA encoding Cx32, Cx40 and Cx43 was detected in the rabbit superior mesenteric artery by reverse transcriptase‐polymerase chain reaction. Western blot analysis showed that Cx43 was the major connexin in the endothelium‐denuded vessel wall.
We conclude that intercellular communication between vascular smooth muscle cells via gap junctions is essential for synchronized rhythmic activity in isolated arterial tissue, whereas tonic force development appears to be independent of cell‐cell coupling. The molecular specificity of the peptide probes employed in the study suggests that the smooth muscle relaxant effects of heptanol may be non‐supecific and unrelated to inhibition of gap junctional communication.
Immunoglobulins from motoneurone disease patients enhance glutamate release from rat hippocampal neurones in culture
Authors: Andjus Pavle R. , Stevic‐Marinkovic Zorica , Cherubim Enrico 
Published: September 2004

The whole‐cell configuration of the patch‐clamp technique was used to study the effects of immunoglobulins (IgGs) from patients affected by amyotrophic lateral sclerosis (ALS) on spontaneous glutamatergic currents in rat hippocampal cells in culture.
Focal application of ALS IgGs (100 μg ml−1) to hippocampal cells induced a rise in frequency but not in amplitude of spontaneous excitatory postsynaptic currents (SEPSC) which outlasted the period of IgG application. The mean frequency ratio (ALS over control) was 3.2 ± 0.6 (n. 19). No changes in frequency or amplitude of SEPSCs were observed after treatment with IgGs obtained from healthy donors (n=5) or from patients with Alzheimer's disease (n=4).
ALS IgGs also increased the frequency (by a factor of 2.0 ± 0.3) but not the amplitude of miniature excitatory postsynaptic currents (mEPSC) recorded in the presence of TTX (n=19). A rise in frequency of mEPSC was also seen in cells superfused with a calcium‐free solution (n=4).
In the presence of TTX, ALS IgGs did not modify the amplitude or the shape of currents evoked by AMPA (100 μm), recorded at a holding potential of −50 mV.
It is concluded that ALS IgGs enhance both SEPSCs and mEPSCs through a presynaptic type of action. The excessive release of glutamate from nerve endings may be the cause of motoneurone death in ALS patients.
Hypoxia‐induced inhibition of calcium channels in guinea‐pig taenia caeci smooth muscle cells
Authors: Rekalov Vladimir , Juránek Ivo , Máleková L'ubica , Bauer Viktor 
Published: September 2004

The effects of hypoxia on whole‐cell current in single smooth muscle cells and on a high K+‐induced contraction of strips of the guinea‐pig taenia caeci were studied.
In physiological salt solution (PSS) and K+‐based pipette solution, hypoxia (PO2= 20 mmHg) reversibly inhibited both the inward Ca2+ current (ICa) and outward Ca2+‐activated K+ current (IK(Ca)) components of the whole‐cell current.
In PSS and Cs+‐based pipette solution, hypoxia reversibly suppressed ICa by 30 ± 5% at 0mV.
When Ba2+ was used as a charge carrier, the IBa was suppressed by hypoxia in a potential‐dependent manner, with the maximum of 40 ± 7% at +10mV. Alterations of concentrations of egta, GDBβS or ATP in the pipette solution did not change the inhibitory effects of hypoxia on ICa and IBa.
In PSS with 2 mm CaCl2 replaced by CoCl2, hypoxia did not affect the Ca2+ influx‐independent potassium current.
In cells voltage clamped at ‐20 mV hypoxia reversibly inhibited the spontaneous transient outward currents.
The response of high K+‐contracted taenia caeci to hypoxia was composed of an initial rapid relaxation followed by a small transient contraction and slow relaxation. The transient contraction was blocked by atropine (1–10 μm), while relaxations were unaffected by atropine and guanethidine (10 μm).
The results show that hypoxia reversibly inhibits ICa and secondarily suppresses IK(Ca) due to decreased Ca2+ influx through Ca2+ channels.
It is suggested that inhibition of ICa was responsible for the rapid relaxation, whereas transient contraction may have been due to release of acetylcholine from nerve terminals upon hypoxia.
Aminergic Modulation of Glycine Release in a Spinal Network Controlling Swimming in Xenopus Laevis
Authors: McDearmid Jonathan R. , Scrymgeour‐Wedderburn John F. , Sillar Keith T. 
Published: September 2004

Neuromodulators can effect changes in neural network function by strengthening or weakening synapses between neurons via presynaptic control of transmitter release. We have examined the effects of two biogenic amines on inhibitory connections of a spinal rhythm generator in Xenopus tadpoles.
Glycinergic inhibitory potentials occurring mid‐cycle in motoneurons during swimming activity are reduced by 5‐hydroxytryptamine (5‐HT; serotonin) and enhanced by noradrenaline (NA). These opposing effects on inhibitory synaptic strength are mediated presynaptically where 5‐HT decreases and NA increases the probability of glycine release from inhibitory terminals.
The amines also have contrasting effects on swimming: 5‐HT increased motor burst durations while NA reduced swimming frequency. Aminergic modulation of glycinergic transmission may thus control fundamental parameters of swimming and force the spinal network to generate opposite extremes of its spectrum of possible outputs.
The effects of calcium buffering and cyclic AMP on mechano‐electrical transduction in turtle auditory hair cells
Authors: Ricci A. J. , Fettiplace R. 
Published: September 2004

The effects of intracellular Ca2+ buffering on hair cell mechanotransduction were studied in an intact cochlear epithelium where the endolymphatic and perilymphatic surfaces could be separately perfused with different Ca2+ solutions.
The speed and extent of transducer adaptation increased as the concentration in the patch electrode of the Ca2+ buffer BAPTA was lowered. In 0.1 mm BAPTA or less, the transducer adapted almost completely, with a mean time constant of 0.8 ms.
For a fixed internal BAPTA concentration, the transducer conductance varied with hair cell location, increasing towards the high‐frequency end of the cochlea, and the time constant of adaptation decreased proportionally. At a given cochlear location, hair cells with larger transducer conductances displayed faster adaptation. We suggest that transducer adaptation accounts for a variable high‐pass filter observed in the acoustic tuning curve.
The effects of perfusion of 50 μm Ca2+ endolymph depended on the BAPTA concentration of the electrode: with 3 mm BAPTA, adaptation was abolished, but in most recordings with 0.01 or 0.1 mm BAPTA, rapid adaptation was retained. The current–displacement curve was also shifted less the lower the intracellular BAPTA concentration. Cells in the high‐frequency half of the papilla retained adaptation at a higher BAPTA concentration.
Treatment with the cAMP agonist, 8‐bromo‐cAMP, or with the phosphodiesterase inhibitor 3‐isobutyl‐1‐methylxanthine, caused a rightward shift in the current–displacement curve which was independent of the internal BAPTA concentration.
We conclude that the free Ca2+ and cyclic nucleotide concentrations of the hair bundle modulate the position of the activation curve of the transducer. The factors which may be important for the correct functioning of adaptation in vivo are discussed.
Inhibition of spontaneous EPSCs and IPSCs by presynaptic GABAB receptors on rat supraoptic magnocellular neurons
Authors: Kabashima Narutoshi , Shibuya Izumi , Ibrahim Nurhadi , Ueta Yoichi , Yamashita Hiroshi 
Published: September 2004

The function of presynaptic GABA receptors in the regulation of transmitter release in supraoptic nucleus (SON) magnocellular neurons was investigated by recording spontaneous postsynaptic currents from rat magnocellular SON neurons in a slice preparation (150μM thick, 1.8 mm in diameter) using the whole‐cell patch‐clamp technique.
Both the spontaneous EPSCs and IPSCs were TTX resistant. The EPSCs were abolished by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX), whereas the IPSCs were abolished by picrotoxin, suggesting that the EPSCs and IPSCs are synaptic inputs from glutamatergic and GABAergic neurons, respectively.
The selective GABAB agonist, baclofen, reduced the frequency of both the EPSCs and IPSCs without affecting the amplitude. The time constant of the decay phase of both the EPSCs and IPSCs remained unchanged after baclofen application.
The reduction of the frequency of the synaptic currents by baclofen was dose dependent (10 nM to 100 μm) and the EC50 values were 5.8 and 8.5 μm for the EPSCs and IPSCs, respectively.
The effect of baclofen (10μM) was antagonized by the selective GABAB antagonist, 2‐hydroxy‐saclofen (2OH‐saclofen), at 300 μm.
When given alone, 2OH‐saclofen (100 μm) increased the frequency of both the EPSCs and IPSCs without affecting their amplitude, suggesting that endogenously released GABA in the slice acts on presynaptic GABAB receptors.
The GABAA agonist, muscimol, reduced the frequency of EPSCs, and picrotoxin increased the frequency of the EPSCs, suggesting that GABAA receptors also participate in the presynaptic inhibition of glutamate release.
Taken together, these data suggest that GABAB receptors are present on the presynaptic terminals of both GABA and glutamate neurons in the SON, and that these presynaptic GABAB receptors play an important role in the regulation of the neuronal activity in SON magnocellular neurons.
Stimulation of α1‐adrenoceptors and Protein Kinase C‐mediated Activation of Ecto‐5′‐Nucleotidase in Rat Hearts in vivo
Authors: Sato Toshiaki , Obata Toshio , Yamanaka Yasumitsu , Arita Makoto 
Published: September 2004

To determine whether protein kinase C (PKC)‐mediated activation of ecto‐5′‐nucleotidase would increase interstitial adenosine concentrations in the rat heart in vivo, we made use of the microdialysis technique and a flexibly mounted probe, which was implanted in the left ventricular myocardium and perfused with Tyrode solution.
The baseline level of dialysate adenosine was 0.51 ± 0.09 μM (n= 16). Perfusion of adenosine 5′‐monophosphate (AMP, 100 μM) through the probe increased the dialysate adenosine concentration markedly to 9.25 ± 0.46μM (n= 15). αβ‐Methyleneadenosine 5′‐diphosphate (AOPCP, 100 μM), an inhibitor of ecto‐5′‐nucleotidase, abolished the AMP‐induced increase in dialysate adenosine, but did not affect the baseline level of adenosine. These observations suggest that the dialysate adenosine obtained during the perfusion with AMP, but not the baseline levels of adenosine, originated from the dephosphorylation of AMP by ecto‐5′‐nucleotidase. Thus, the level of adenosine measured during AMP perfusion gives an index of the activity of ecto‐5′‐nucleotidase in the tissue.
Noradrenaline (10 μm) increased the adenosine concentration measured in the presence of 100 μm AMP (i.e. the activity of ecto‐5′‐nucleotidase) by 38.7 ± 9.6 % (n= 5, P < 0.05), an increase which was inhibited by an antagonist of the α1adrenoceptor (prazosin, 50 μM) or of PKC (chelerythrine, 10 μm). Further application of either the α1‐adrenoceptor agonist methoxamine (100 μM) or the diacylglycerol analogue 1,2‐dioctanoyl‐sw‐glycerol (DOG, 100 μm) also increased the adenosine concentration by 35.1 ± 10.0% (n= 6, P < 0.05) or 40.6 ± 8.3% (n= 5, P < 0.05), respectively.
The presence of okadaic acid (50 μm), an inhibitor of protein phosphatase, enhanced the noradrenaline‐induced increase in adenosine concentration by 112.4 ± 35.9% (n= 4, P < 0.05), to a level significantly (P < 0.05) greater than the increase caused by noradrenaline alone (38.7 ± 9.6%).
These data provide the first evidence that α1‐adrenoceptor stimulation and the subsequent activation of PKC can increase adenosine concentrations in interstitial spaces of ventricular muscle in vivo, through activation of endogenous ecto‐5′‐nucleotidase.
Pressor effect mediated by bradykinin in the paratrigeminal nucleus of the rat
Authors: Lindsey C. J. , Buck H. S. , Fior‐Chadi D. R. , Lapa R. C. R. S. 
Published: September 2004

The participation of the paratrigeminal nucleus (Pa5) in the pressor response produced by bradykinin in the dorsolateral medulla of rats was investigated. The microinjection of 6 pmol of bradykinin directly over the paratrigeminal nucleus of unanaesthetized rats produced a significant increase in arterial pressure and a moderate increase in heart rate.
Bradykinin microinjections in different sites surrounding the Pa5 compromising the external cuneate nucleus, the trigeminal nucleus, the lateral and ventral spinal trigeminal tract and the dorsal trigeminal tract rostral and caudal to the Pa5 did not elicit significant pressor responses. In contrast, microinjections in the paratrigeminal nucleus produced pressor effects. Injections in the dorsolateral medulla directly over the paratrigeminal nucleus produced larger responses than when injections were made in the nucleus. Saline injections in the different nuclei did not produce pressor effects.
Neurochemical lesioning of the Pa5, with microinjections of ibotenic acid in the Pa5, abolished the pressor response to bradykinin injected over the lesioned nucleus. The effect was present, however, when bradykinin was injected on the contralateral side to the lesion, over the intact nucleus of the same animal. Pretreatment with capsaicin (injected in the lateral cerebral ventricle), which causes selective degeneration of afferent sensory fibres, did not alter the pressor effect of bradykinin injected over the paratrigeminal nucleus.
Dose‐related responses were produced by different concentrations of bradykinin (0.6–1.8 pmol) microinjected over the nucleus. The bradykinin receptor antagonist HOE 140, injected over the paratrigeminal nucleus 30 min earlier, abolished the pressor response caused by bradykinin.
Low doses of bradykinin injected in or directly over the paratrigeminal nucleus increased arterial pressure and caused a small increase in heart rate by stimulating kinin receptors of the paratrigeminal nucleus in the dorsolateral medulla of awake and unrestrained rats. The pattern of the response was consistent with that of sympathetic stimulation. The paratrigeminal nucleus, which receives primary afferents and projects to the nucleus tractus solitarii and the rostral ventral lateral medulla, may be positioned as relay nucleus possibly connecting sensory input to structures that regulate blood pressure.
Ca2+ current and Ca2+ ‐activated chloride current in isolated smooth muscle cells of the sheep urethra
Authors: Cotton K. D. , Hollywood M. A. , McHale N. G. , Thornbury K. D. 
Published: September 2004

Isolated sheep urethral cells were studied using the perforated patch clamp technique (T= 37 °C). Depolarizing steps ranging from ‐40 to ‐10 mV evoked an inward current that peaked within 10 ms and a slower inward current. Stepping back to the holding potential of ‐80 mV evoked large inward tail currents. All three currents were abolished by nifedipine (1 μm). Substitution of external Ca2+ with Ba2+ resulted in potentiation of the fast inward current and blockade of the slow current and tails.
Changing the chloride equilibrium potential (ECl) from 0 to + 27 mV shifted the reversal potential of the tail currents from 1 ± 1 to 27 ± 1 mV (number of cells, n= 5). Chloride channel blockers, niflumic acid (10 μm) and anthracene‐9‐carboxylic acid (9AC, 1 mm), reduced the slow current and tails suggesting that these were Ca2+‐activated CF currents, ICl(Ca).
Caffeine (10 mm) induced currents that reversed at ECl and were blocked by niflumic acid (10 μm).
In current clamp mode, some cells developed spontaneous transient depolarizations (STDs) and action potentials. Short exposure to nifedipine blocked the action potentials and unmasked STDs. In contrast, 9AC and niflumic acid reduced the amplitude of the STDs and blocked the action potentials.
In conclusion, these cells have both L‐type ICa and ICl(Ca). The former appears to be responsible for the upstroke of the action potential, while the latter may act as a pacemaker current.
Regulation of Quantal Secretion by Neurotrophic Factors at Developing Motoneurons in Xenopus Cell Cultures
Authors: Liou Jau‐Cheng , Yang Rong‐Sen , Fu Wen‐Mei 
Published: September 2004

The ability of different neurotrophic factors to maintain and regulate synaptic function at the developing motoneuron was studied in Xenopus nerve–muscle co‐cultures. Spontaneous synaptic currents (SSCs) were measured by using whole‐cell voltage‐clamped myocytes.
Compared with natural synapses, motoneurons without contact on a myocyte (naive neurons) released ACh in smaller quantal packets, the amplitude being inversely proportional to the days in culture. The mean SSC amplitudes of naive neurons, which were measured by manipulating a myoball into contact with the myocyte‐free nerve terminals to form a manipulated synapse, were 99.5 ± 6.7 and 48.2 ± 1.9 pA for day‐1 and day‐3 cultures, respectively.
Chronic treatment of day‐1 cultures with brain‐derived neurotrophic factor (BDNF), neurotrophin‐3 (NT‐3), neurotrophin‐4 (NT‐4), ciliary neurotrophic factor (CNTF) or glial cell line‐derived neurotrophic factor (GDNF) for 2 days, increased the ACh quantal size of naive motoneurons in a concentration‐dependent manner, whereas insulin‐like growth factor‐1 (IGF‐1) and basic fibroblast growth factor (bFGF) had no effect, even at high concentrations.
The interaction of various neurotrophic factors was examined, using concentrations that gave maximal effects. Combination of CNTF plus BDNF or CNTF plus NT‐3 had synergistic effects in potentiating SSC amplitude of the manipulated synapse of naive neurons, whereas NT‐3 plus BDNF, NT‐3 plus GDNF, BDNF plus GDNF or CNTF plus GDNF had no synergistic action.
Chronic treatment with d‐tubocurarine for 2 days resulted in a reduction of the quantal size of natural synapses. Concomitant treatment with BDNF, NT‐3, GDNF, CNTF but not bFGF or IGF‐1, reconstituted the SSC amplitude.
Taken together, these findings suggest that BDNF, NT‐3, NT‐4, CNTF and GDNF may regulate and maintain the synaptic function of developing motoneurons, and different neurotrophic factors utilizing distinct signalling mechanisms may have synergistic actions.