bluuebunny/crossref_metadata_2025_split huggingface dataset:
Functions of large conductance Ca2+‐activated (BKCa), delayed rectifier (KV) and background K+ channels in the control of membrane potential in rabbit renal arcuate artery
Authors: Prior H. M. , Yates M. S. , Beech D. J. 
Published: September 2004

The types of K+ channel which determine the membrane potential of arcuate artery smooth muscle cells were investigated by patch‐clamp recording from isolated cells and lumenal diameter measurements from intact pressurized renal arcuate arteries.
Single cells had a mean resting potential of ‐38 mV and were depolarized by 130 mM K+ but not by the Cl− channel blocker 4,4′‐diisothiocyanatostilbene‐2,2′‐disulphonic acid (DIDS).
Iberiotoxin did not affect the resting potential but inhibited spontaneous transient hyperpolarizations. Iberiotoxin or 1 mM tetraethylammonium (TEA+) constricted intact arteries. 3,4‐Diaminopyridine (3,4‐DAP)‐sensitive delayed rectifier K+ (KV) channel current was elicited by depolarization but 3,4‐DAP did not affect the resting potential or induce constriction in the intact artery.
A voltage‐independent K+ current was inhibited by ≥ 0·1 mM barium (Ba2+) and unaffected by iberiotoxin, glibenclamide, apamin, 3,4‐DAP and ouabain. In six out of ten cells, 1 mM Ba2+ depolarized the resting potential, while in the other cells the potential was resistant to all of the K+ channel blockers and ouabain. Ba2+ (0·1‐1 mM) constricted the intact artery, but 10 μM Ba2+, 1 μM glibenclamide or 100 nM apamin had no effect.
The data suggest that resting potential is determined by background K+ channels, one type being Ba2+ sensitive and voltage independent, and another type being poorly defined due to its resistance to any inhibitor. Large conductance Ca2+‐activated K+ (BKCa) and KV channels do not determine the resting potential but have separate functions to underlie transient Ca2+‐induced hyperpolarizations and to protect against depolarization past about ‐30 mV.
Calcium permeation of the turtle hair cell mechanotransducer channel and its relation to the composition of endolymph
Authors: Ricci A. J. , Fettiplace R. 
Published: September 2004

Recordings of mechanoelectrical transducer currents were combined with calcium imaging of hair bundles in turtle auditory hair cells located near the high‐frequency end of the cochlea. The external face of the hair bundles was perfused with a range of Ca2+ concentrations to study the quantitative relationship between Ca2+ influx and transducer adaptation.
With Na+ as the monovalent ion, the peak amplitude of the transducer current decreased monotonically as the external [Ca2+] was raised from 25 μM to 20 mM. When Na+ was replaced with the impermeant Tris the transducer current increased with external [Ca2+]. These results indicate that Ca2+ can both permeate and block the transducer channels. The Ca2+ concentration for half‐block of the monovalent current was 1 mM.
To quantify the Ca2+ influx, the fraction of transducer current carried by Ca2+ was measured using the change in bundle fluorescence in cells loaded with 1 mM Calcium Green‐1. The fluorescence change was calibrated by substituting an impermeable monovalent ion to render Ca2+ the sole charge carrier.
In the presence of Na+, the fractional Ca2+ current was ≈10 % in 50 μM Ca2+, a concentration similar to that in endolymph, which bathes the hair bundles in vivo. The amount of Ca2+ entering was dependent on the identity of the monovalent ion, and was larger with K+, suggesting that the transducer channel is a multi‐ion pore.
Over a range of ionic conditions, the rate of transducer adaptation was proportional to Ca2+ influx indicating that adaptation is driven by a rise in intracellular [Ca2+].
Shifts in the current‐displacement function along the displacement axis in different external Ca2+ concentrations were predictable from variation in the resting Ca2+ influx. We suggest that changes in the resting open probability of the transducer channels adjust the entry of Ca2+ to keep its concentration constant at an internal site.
The results demonstrate that endolymph containing high K+, 50 μM Ca2+ and low Mg2+ concentrations, maximizes the transducer current while still allowing sufficient Ca2+ entry to drive adaptation. The hair cell mechanotransducer channel, in its permeation and block by Ca2+, shows behaviour similar to the voltage‐gated Ca2+ channel and the cyclic nucleotide‐gated channel.
Nitric oxide lowers the calcium sensitivity of tension in the rat tail artery
Authors: Tran Nguyen N. P. , Spitzbarth Esther , Robert Alain , Giummelly Philippe , Atkinson Jeffrey , Capdeville‐Atkinson Christine 
Published: September 2004

Controversy exists as to whether a fall in the intracellular Ca2+ concentration ([Ca2+]i) is a requisite element of the vasodilatory response to nitric oxide (NO).
We studied the effect of NO on the coupling between [Ca2+]i and vasoconstriction in arterial segments loaded with the [Ca2+]i‐sensitive, intracellular dye fura‐2. As data interpretation is equivocal when fura‐2 is loaded into both endothelial and smooth muscle cells, we compared results from in vitro experiments on segments of the rat tail artery in which fura‐2 and noradrenaline were applied on the luminal or adventitial side, and endothelium was removed ‘physically’ (rubbing or air) or ‘functionally’ (Nω‐nitro‐l‐arginine methyl ester). The use of air perfusion to remove endothelium is of considerable benefit since it allows paired observations in a single tissue.
Fura‐2 loaded into endothelial cells but endothelial ‘contamination’ of the smooth muscle cell [Ca2+]i signal was minimal.
Endogenous NO decreased vasoconstrictor responses to noradrenaline but had no effect on [Ca2+]i.
Nitroglycerine decreased vasoconstrictor responses in a concentration‐dependent fashion but had no effect on [Ca2+]i.
In conclusion, NO causes vasodilatation via a mechanism which is downstream of [Ca2+]i mobilization.
Evidence for enhancement of gap junctional coupling between rat island of Calleja granule cells in vitro by the activation of dopamine D3 receptors
Authors: Halliwell J. V. , Horne A. L. 
Published: September 2004

Using patch‐clamp techniques, we have studied actions of dopamine and related compounds on granule neurones within the islands of Calleja in vitro, in slices of ≈200 μm thickness or as groups of varying cell number following enzymic digestion.
Prior to agonist application, island of Calleja granule cells displayed spontaneous stepwise shifts in whole‐cell conductance ranging from 104 to 632 pS. The reversal potentials of these conductance changes ranged widely and matched the distribution of the cells' membrane potentials. Reversal potentials and membrane potentials shifted equally when cells were uniformly depolarized in 24 mM external K+.
Bath‐applied dopamine elicited, after a delay of 4‐9 min, an exaggerated form of the spontaneous behaviour that frequently gave way to a sudden large (up to thirtyfold) conductance change. At concentrations of 100‐300 nM, a range of agonists with increasing affinity for the D3 receptor (apomorphine, quinpirole, 7‐OH DPAT and PD 128907) triggered the response. The actions were neither mimicked by SKF‐38393 nor antagonized by SCH‐23390 (a selective D1 agonist and antagonist, respectively). Haloperidol reversibly blocked responses elicited by the D3/D2 agonist quinpirole. The action of effective agonists was maintained when transmitter release was abolished. Given the reported lack of D2 receptors in the islands of Calleja, these findings indicate a direct action of dopamine at the D3 receptor.
The dopaminergic effects were not affected by Gd3+ or substantial replacement of external Na+ with TEA, Tris or choline, eliminating stretch‐activated channels but suggesting that if transmembrane channels were to be involved in this dopaminergic action they posseses a non‐selective permeability to large cations. The reported presence of gap junctions in the islands of Calleja offers the explanation that these effects derive from enhanced activity of such channels or their hemi‐constituents.
In testing the possible involvement of gap junctional coupling the following experimental observations were made: (i) alkalinization of slices mimicked the effect of D3 agonists; (ii) in cell groups, recording from pairs provided evidence of intercellular coupling, and mechanical separation of recorded neurones from neighbouring cells during the agonist‐evoked response caused shutdown of the additional conductance; (iii) when applied to slices, the gap junctional blocker, 18α‐glycyrrhetinic acid, whilst not preventing the full‐blown dopamine response, significantly reduced both the variance of recorded granule cell input conductance and the cells’ apparent capacitance.
Taken together the results indicate a D3 action in granule cells, which is best explained by a dopaminergic promotion of intercellular coupling. The physiological relevance of such a mechanism is discussed.
Single channel currents at six microsecond resolution elicited by acetylcholine in mouse myoballs
Authors: Parzefall Franz , Wilhelm Robert , Heckmann Manfred , Dudel Josef 
Published: September 2004

A patch‐clamp set‐up was optimized for low noise and high time resolution. An Axoclamp 200B amplifier was modified to incorporate a Teflon connector to the electrode. An electrode puller was equipped with a hydrogen‐oxygen burner to produce quartz‐glass pipettes with optimally 0.2 μm openings and 20 MΩ resistance.
The r.m.s. (root mean square) noise of sealed pipettes in the bath ranged from 3.6 fA with 100 Hz filter cut‐off to 1.5 pA with 61 kHz filter cut‐off. At these extremes currents of 17 fA and more than 3 ms, or 9 pA and more than 6 μs could be resolved with a negligible error rate.
The system was tested on mouse myoballs, recording 9–10 pA single channel currents on‐cell at −200 mV polarization which were elicited by 0.1–5000 μm acetylcholine (ACh).
Distributions of open and closed times and of correlations of open times to the preceding closed time defined several open states: single openings with mean durations of 1.2 and 25 μs, from single‐liganded receptors, and bursts of 10 ms mean duration containing on average 800 μs openings and 16 μs closings, from double liganded receptors. Above 0.1 mm ACh these openings are interrupted increasingly by on average 18 μs and 72 μs channel blocks by ACh.
Contribution of the Kv3.1 potassium channel to high‐frequency firing in mouse auditory neurones
Authors: Wang Lu‐Yang , Gan Li , Forsythe Ian D. , Kaczmarek Leonard K. 
Published: September 2004

Using a combination of patch‐clamp, in situ hybridization and computer simulation techniques, we have analysed the contribution of potassium channels to the ability of a subset of mouse auditory neurones to fire at high frequencies.
Voltage‐clamp recordings from the principal neurones of the medial nucleus of the trapezoid body (MNTB) revealed a low‐threshold dendrotoxin (DTX)‐sensitive current (ILT) and a high‐threshold DTX‐insensitive current (IHT).
I
HT displayed rapid activation and deactivation kinetics, and was selectively blocked by a low concentration of tetraethylammonium (TEA; 1 mm).
The physiological and pharmacological properties of IHT very closely matched those of the Shaw family potassium channel Kv3.1 stably expressed in a CHO cell line.
An mRNA probe corresponding to the C‐terminus of the Kv3.1 channel strongly labelled MNTB neurones, suggesting that this channel is expressed in these neurones.
TEA did not alter the ability of MNTB neurones to follow stimulation up to 200 Hz, but specifically reduced their ability to follow higher frequency impulses.
A computer simulation, using a model cell in which an outward current with the kinetics and voltage dependence of the Kv3.1 channel was incorporated, also confirmed that the Kv3.1‐ like current is essential for cells to respond to a sustained train of high‐frequency stimuli.
We conclude that in mouse MNTB neurones the Kv3.1 channel contributes to the ability of these cells to lock their firing to high‐frequency inputs.
Facilitating pyramid to horizontal oriens‐alveus interneurone inputs: dual intracellular recordings in slices of rat hippocampus
Authors: Ali Afia B. , Thomson Alex M. 
Published: September 2004

In adult rat hippocampal slices, simultaneous intracellular recordings from pyramidal cells in CA1 and interneurones near the stratum oriens‐alveus border revealed excitatory connections that displayed facilitation on repetitive activation in twelve of thirty‐six pairs tested.
Postsynaptic interneurones were classified as horizontal oriens‐alveus interneurones by the pronounced ‘sag’ in response to hyperpolarizing current injection, high levels of spontaneous synaptic activity and by the morphology of their somata and dendrites, which were confined to stratum oriens‐alveus and their axons which projected to stratum lacunosum‐moleculare where they ramified extensively, in the region of entorhinal cortex input to CA1.
Excitatory postsynaptic potentials (EPSPs) elicited by single pyramidal cells were 0 to 12 mV in amplitude. Mean EPSP amplitude (single spikes) was 0.93 ± 1.06 mV at −70 ± 2.3 mV (n= 10). The rise time was 1.2 ± 0.5 ms and the width at half‐amplitude was 7.5 ± 4.7 ms.
EPSPs fluctuated greatly in amplitude; the mean coefficient of variation was 0.84 ± 0.37 for the first EPSP and 0.47 ± 0.24 for the second. Apparent failures of transmission frequently occurred after first presynaptic spikes but less frequently after the second or subsequent spikes in brief trains.
EPSPs displayed facilitation at membrane potentials between −80 mV and spike threshold. Second EPSPs within 20 ms of the first were 253 ± 48% (range, 152–324%) of the mean first EPSP amplitude. Third EPSPs within 60 ms were 266 ± 70 % (range, 169–389%) and fourth EPSPs within 60–120 ms were 288 ± 71% (range, 188–393%). Both proportions of apparent failures of transmission and coefficient of variation analysis indicated a presynaptic locus for this facilitation.
Role of cAMP‐dependent protein kinase A in activation of a voltage‐sensitive release mechanism for cardiac contraction in guinea‐pig myocytes
Authors: Ferrier Gregory R. , Zhu Jiequan , Redondo Isabel M. , Howlett Susan E. 
Published: September 2004

Ionic currents and unloaded cell shortening were recorded from guinea‐pig ventricular myocytes with single electrode voltage clamp techniques and video edge detection at 37 °C. Patch pipettes (1–3 MΩ) were used to provide intracellular dialysis with pipette solutions.
Na+ currents were blocked with 200 μm lidocaine. Contractions initiated by the voltage‐sensitive release mechanism (VSRM) and Ca2+‐induced Ca2+ release (CICR) in response to L‐type Ca2+ current (ICa,L) were separated with voltage clamp protocols.
Without 8‐bromo cyclic adenosine 3′,5′‐monophosphate (8‐Br‐cAMP) in the pipette, small VSRM‐induced contractions occurred transiently in only 13 % of myocytes. In contrast, large ICa,L‐induced contractions were demonstrable in 100 % of cells.
Addition of 10 or 50 μm 8‐Br‐cAMP to the pipette increased the percentage of cells exhibiting VSRM contractions to 68 and 93 %, respectively. With 50 μm 8‐Br‐cAMP, contractions initiated by the VSRM and ICa,L were not significantly different in amplitude.
8‐Br‐cAMP‐supported VSRM contractions had characteristics of the VSRM shown previously in undialysed myocytes. Cd2+ (100 μm) blocked ICa,L and ICa,L contractions but not VSRM contractions. 8‐Br‐cAMP‐supported contractions exhibited steady‐state inactivation with parameters characteristic of the VSRM, as well as sigmoidal contraction‐voltage relations.
Without 8‐Br‐cAMP in the pipette, contraction‐voltage relations determined with steps from a post‐conditioning potential (Vpc) of either −40 or −65 mV were bell shaped, with a threshold near −35 mV. With 50 μm 8‐Br‐cAMP in the pipette, contraction‐voltage relations from a Vpc of −65 mV were sigmoidal and the threshold shifted to near −55 mV. Contraction‐voltage relations remained bell shaped in the presence of 8‐Br‐cAMP when the Vpc was −40 mV.
H‐89, which inhibits cAMP‐dependent protein kinase A (PKA), significantly reduced the amplitudes of VSRM contractions by approximately 84 % with 50 μm 8‐Br‐cAMP in the pipette. H‐89 also significantly reduced the amplitudes of peak ICa,L and ICa,L contractions, although to a lesser extent.
We conclude that intracellular dialysis with patch pipettes disrupts the adenylyl cyclase‐PKA phosphorylation cascade, and that the VSRM requires intracellular phosphorylation to be available for activation. Intracellular dialysis with solutions that do not maintain phosphorylation levels inhibits a major mechanism in cardiac excitation‐ contraction coupling.
Does a C3‐C4 propriospinal system transmit corticospinal excitation in the primate? An investigation in the macaque monkey
Authors: Maier M. A. , Illert M. , Kirkwood P. A. , Nielsen J. , Lemon R. N. 
Published: September 2004

Synaptic responses to electrical stimulation of the contralateral pyramidal tract were measured in intracellular recordings from 206 upper limb motoneurones in ten chloralose‐anaesthetized macaque monkeys. The objective was to search for evidence of a disynaptic excitatory pathway via C3‐C4 propriospinal interneurones similar to that in the cat.
In monkeys with intact spinal cords, only a small proportion of motoneurones (19 %) responded with late EPSPs to repetitive stimulation of the pyramid; only 3 % had segmental latencies that were appropriate for a disynaptic pathway.
From previous studies in the cat, it was expected that a lesion to the dorsolateral funiculus (DLF) at C5 would interrupt the corticospinal input to the spinal segments supplying upper limb muscles, whilst leaving intact excitation transmitted via a C3‐C4 propriospinal system, the descending axons of which travel in the ventral part of the funiculus. In five of the monkeys a lesion was made to the DLF at C5 which spared the ventrolateral columns. It severely reduced the monosynaptic EPSPs and disynaptic IPSPs evoked from the pyramidal tract that were present in the intact monkey spinal cord, and which might have masked the presence of disynaptic EPSPs. However, even after the lesion the proportion of motoneurones with such late EPSPs was still low (18 %); 14 % of motoneurones had EPSPs within the disynaptic range.
In addition, some EPSPs with relatively long segmental latencies (> 1·1 ms) were recorded before and after the C5 lesions, but since these effects could be evoked by single stimuli, had stable latencies and did not facilitate with repetitive shocks, it is likely that they represent monosynaptic EPSPs evoked by slowly conducting corticospinal fibres which survived the lesions.
In seven of the monkeys motoneurone responses to stimulation of the ipsilateral lateral reticular nucleus (LRN) were also tested. Most motoneurones showed EPSPs with short latencies (1·2‐2·5 ms) and other properties characteristic of monosynaptic activation. This is consistent with the presence of collaterals of C3‐C4 propriospinal neurones to the LRN, as demonstrated in the cat.
These short‐latency EPSPs evoked from the LRN were just as common before (77 %) as after (75 %) the C5 lesion. They had small amplitudes both before (mean ± s.d. 1·1 ± 0·59 mV) and after (1·2 ± 0·72 mV) the lesion. Unlike the situation in the cat, only a small proportion (16 %) of motoneurones activated from the LRN showed late EPSPs after repetitive stimulation of the pyramid.
The results provide little evidence for significant corticospinal excitation of motoneurones via a system of C3‐C4 propriospinal neurones in the monkey. The general absence of responses mediated by such a system in the macaque, under experimental conditions similar to those in which they are seen in the cat, show that extrapolation of results from the cat to the primate should be made with considerable caution.
CA1 pyramidal to basket and bistratified cell EPSPs: dual intracellular recordings in rat hippocampal slices
Authors: Ali Afia B. , Deuchars Jim , Pawelzik Hannelore , Thomson Alex M. 
Published: September 2004

Dual intracellular recordings in the CA1 region of adult rat hippocampal slices and biocytin filling of synaptically connected cells were used to study the excitatory postsynaptic potentials (EPSPs) elicited in basket (n= 7) and bistratified interneurones (n= 7) by action potentials activated in simultaneously recorded pyramidal cells.
Interneurones could be subdivided according to their electrophysiological properties into classical fast spiking, burst firing, regular spiking and fast spiking cells with a rounded spike after‐hyperpolarization. These physiological classes did not, however, correlate with morphological type. EPSPs were not recorded in regular spiking cells.
Average EPSP amplitudes were larger in bistratified cells (range, 0.5–9 mV) than in basket cells (range, 0.15–3.6 mV) and the probability of obtaining a pyramidal cell‐interneurone EPSP was also higher for the bistratified cells (1:7) than for the basket cells (1:22). EPSP 10–90% rise times in bistratified cells (0.7–2 ms) and their widths at half‐amplitude (3.9–11.2 ms) were slightly longer than in basket cells (rise times, 0.4–1.6 ms; half‐widths, 2.2–9.7 ms).
The majority of these EPSPs (6 of 8 tested) increased in amplitude and duration with postsynaptic depolarization, although in two (of 4) basket cells the voltage relation was conventional.
All EPSPs tested in both basket (n= 7) and bistratified cells (n= 5) decreased in amplitude with repetitive presynaptic firing. The average amplitudes of second EPSPs elicited within 15 ms of the first were between 34 and 94% of the average amplitude of the first EPSP. Third and fourth EPSPs in brief trains were further depressed. This depression was associated with an increase in the incidence of apparent failures of transmission indicating a presynaptic locus.
Axonal conduction velocities of functionally characterized retinal ganglion cells in goldfish
Authors: Northmore D. P. M. , Oh D.‐J. 
Published: September 2004

Visual response properties and conduction velocities of retinal ganglion cells were studied by extracellular recordings in the intact goldfish eye. Visually responsive single units were confirmed as ganglion cells by collision testing, and their receptive fields were mapped.
From compound action potentials, we identified groups I‐V in the optic nerve, with overall conduction velocities of 11.5 ± 1.17, 7.1 ± 0.79, 4.4 ± 0.56, 3.1 ± 0.31 and 2.3 ± 0.18 m s−1 (mean ± s.d.) at 23 °C.
Ganglion cells were classified by their receptive fields as off‐, on‐off‐ or on‐centre. Nearly all confirmed ganglion cells had axonal conduction velocities in groups II, III and IV; none fell in the fastest group, I.
Off‐centre ganglion cells had conduction velocities only in the fast group, II. On‐off‐centre cells fell mainly in group III, with some in group II. On‐centre cells fell in groups II‐V, but mainly in groups III and IV.
Receptive field centre diameters were 5‐30 deg measured with a photopic background. The mean diameters for off‐, on‐off‐ and on‐centres were 24, 15 and 18 deg, respectively. The relatively larger diameter and higher rate of spontaneous firing of the off‐centre cells were maintained under different adaptation conditions.
The off‐centre cells can be identified with an anatomical class of large, α‐like ganglion cells in the goldfish retina.