bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sr2+ supports depolarization‐induced suppression of inhibition and provides new evidence for a presynaptic expression mechanism in rat hippocampal slices
Authors: Morishita W. , Alger B. E. 
Published: September 2004

We studied the transient suppression of evoked GABAAergic inhibitory postsynaptic currents (eIPSCs) that follows brief membrane depolarization in rat CA1 hippocampal pyramidal cells, a Prs called depolarization‐induced suppression of inhibition (DSI). We used whole‐cell patch electrodes filled with a CsCl‐based solution to voltage clamp the currents. All experiments were done in the Presence of 50 μm 2‐amino‐5‐phosphonovaleric acid (APV) and 20 μm 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) to block ionotropic glutamate‐induced currents and polysynaptic transmission in the slice Preparation.
Substituting strontium (Sr2+) for extracellular calcium (Ca2+) led to the appearance of numerous ‘asynchronous’ small IPSCs following an eIPSC. These asynchronous IPSCs were indistinguishable from TTX‐insensitive quantal IPSCs.
Although somewhat less effective than Ca2+, Sr2+ was capable of supporting DSI, and both asynchronous and synchronous IPSCs were blocked by the DSI Process.
During DSI, quantal content of eIPSCs, but not quantal size, was significantly reduced.
Sr2+ converted paired‐pulse depression (PPD) of eIPSCs to a paired‐pulse facilitation (PPF), Presumably by altering the Probability of release at inhibitory nerve terminals. DSI had no effect on either PPD or PPF.
The results show that Sr2+ induces asynchronous release of GABA as it does of other neurotransmitters and changes the Probability of release at GABAAergic terminals as well. Most importantly, the results support the hypothesis that, despite being induced postsynaptically, DSI is expressed Presynaptically as a decrease in GABA release, possibly by acting at a site other than the Ca2+‐dependent release step.
Actions of Serum and Plasma Albumin on Intracellular Ca2+ in Human Endothelial Cells
Authors: Fuentes Esther , Nadal Angel , Jacob Ron , McNaughton Peter 
Published: September 2004

The effects of serum and plasma albumin on [Ca2+]i in human endothelial cells were examined using single‐cell Ca2+ imaging. Two types of endothelial cell were used: human umbilical vein endothelial cells (HUVEC) in primary culture, and the endothelial‐derived cell line ECV304.
Serum albumin caused a large and transient rise in [Ca2+]i, due to Ca2+ release from an IP3‐sensitive internal store, followed by a maintained elevation in [Ca2+]i attributable to Ca2+ influx from the external medium. A half‐maximal rise in [Ca2+]i was produced by a concentration of serum albumin of about 1 μg ml−1.
The Ca2+‐releasing action of serum albumin is abolished by methanol extraction and is therefore attributable to an attached polar lipid. A possible candidate is lysophosphatidic acid, known to be released from platelets during blood coagulation, which produced similar effects to those of serum albumin.
In HUVEC, plasma albumin caused a sustained decrease in [Ca2+]i from the mean resting level of 114 nm to 58 nm. No effect of plasma albumin was observed in ECV304 cells.
The decrease in [Ca2+]i caused by plasma albumin is due to an uptake into intracellular stores. The store loading substantially potentiates the action of Ca2+‐releasing agonists such as histamine.
The results show that normal plasma albumin, which carries few lipids, lowers [Ca2+]i and potentiates the actions of Ca2+‐releasing agonists by promoting Ca2+ uptake into intracellular stores. When converted to the serum form, by binding lysophosphatidic acid released during blood coagulation, albumin has a potent effect in elevating [Ca2+]i. Blood coagulation may therefore play a role in regulating vascular tone and capillary permeability.
K+ Channels Which Contribute to the Acetylcholine‐Induced Hyperpolarization in Smooth Muscle of the Guinea‐Pig Submucosal Arteriole
Authors: Hashitani H. , Suzuki H. 
Published: September 2004

Membrane potentials were recorded from submucosal arterioles (diameter, 30–80 μm) of the guinea‐pig small intestine, using conventional microelectrode techniques. In control solution the resting membrane potential was about −73 mV, and the addition of 0.5 mm Ba2+ depolarized the membrane to about −43 mV.
ACh (10 nm to 10 μM), or substance P (0.1 μM), caused a membrane hyperpolarization in preparations which had been depolarized by Ba2+ but not in control preparations. ACh produced a sustained hyperpolarization, whereas substance P produced a transient hyperpolarization, without being affected by either nitroarginine (0.1 mm) or indomethacin (10 μM).
In the presence of 50 μM BAPTA (acetoxymethyl ester form), the membrane potentials were not altered in the control solution or in the presence of Ba2+, but Ba2+ caused a smooth depolarization of the membrane. Following this procedure, both ACh and substance P caused membrane depolarization instead of hyperpolarization, suggesting that the ACh‐ and substance P‐induced hyperpolarization in arteriolar smooth muscle are intracellular [Ca2+] dependent.
In short segments (200–500 μM) of arteriole, the time constant of electrotonic potentials produced by passing current pulses through the recording electrode was about 75 ms. The addition of Ba2+ increased both the input resistance and the time constant.
The hyperpolarizations produced by ACh or substance P were associated with a reduction in the amplitude and the time constant of electrotonic potential.
The reversal potential for the ACh‐induced hyperpolarization, estimated from the current‐voltage relationship, was about −86 mV, a value close to the equilibrium potential for K+.
In the presence of 50 nM charybdotoxin the hyperpolarization produced by ACh became transient and was reduced in amplitude: the residual response was further reduced by apamin (0.1 μM). The response produced by substance P was also reduced by 50 nM charybdotoxin: again the residual response was sensitive to 0.1 μM apamin. The hyper‐polarizations produced by either ACh or substance P were insensitive to glibenclamide (10 μM) and 4‐aminopyridine (1 mm).
It is suggested that in submucosal arterioles of the guinea‐pig ileum, ACh‐ or substance P‐induced hyperpolarizations of smooth muscle result from activation of both charybdotoxin‐sensitive and apamin‐sensitive K+ channels, with the former being predominant. The results are discussed in relation to the possible involvement of one or more endothelium‐dependent hyperpolarizing factors in ACh‐ and substance P‐induced hyperpolarization.
Evidence Against the Involvement of Cytochrome P450 Metabolites in Endothelium‐Dependent Hyperpolarization of the Rat Main Mesenteric Artery
Authors: Vanheel Bert , Van de Voorde Johan 
Published: September 2004

The influence of different inhibitors of cytochrome P450 mono‐oxygenase on the endothelium‐dependent and ‐independent hyperpolarization in the isolated rat main mesenteric artery was investigated.
Application of acetylcholine (ACh; 1 μm) for 10 min evoked an endothelium‐dependent peak hyperpolarization of about 18 mV followed by a partial recovery to a level 7 mV more negative than the resting value (‐50.2 ± 0.5 mV).
Proadifen (30 μm) completely and reversibly inhibited the ACh‐induced hyperpolarization. Conversely, the imidazole antimycotics clotrimazole (30 μm) and miconazole (100 μm) had less effect on the peak endothelium‐dependent hyperpolarization. The suicide substrate inhibitors 17‐octadecynoic acid (17‐ODYA; 5 μm) and 1‐aminobenzotriazole (1‐ABT; 2 mm) did not significantly influence endothelium‐dependent hyperpolarization.
The endothelium‐independent hyperpolarization (16 mV) evoked by levcromakalim (300 nm) was completely inhibited by proadifen as well as by clotrimazole and miconazole but was not affected by 17‐ODYA or 1‐ABT.
These results do not support the view that the ACh‐induced endothelium‐dependent hyperpolarization in the rat mesenteric artery is mediated by cytochrome P450 mono‐oxygenase metabolites. Proadifen and imidazole antimycotics impair the activation of ATP‐regulated K+ channels in mesenteric artery cells, rendering non‐specific inhibition of smooth muscle K+ channel activation an alternative explanation for the inhibitory influence of some (but not all) P450 inhibitors on endothelium‐dependent hyperpolarization in this preparation.
Stretch‐Activated Whole‐Cell Currents in Smooth Muscle Cells from Mesenteric Resistance Artery of Guinea‐Pig
Authors: Setoguchi Motoko , Ohya Yusuke , Abe Isao , Fujishima Masatoshi 
Published: September 2004

Stretch‐activated (SA) channels were studied in smooth muscle cells isolated from mesenteric resistance arteries using the whole‐cell patch‐clamp method. Membrane stretch was achieved by cell inflation after application of positive pressure through a patch electrode.
In the voltage‐clamp configuration, cell inflation increased and cell deflation decreased the membrane conductance. Conductance of the evoked current depended on the increase in cross‐sectional area of the cell. The current‐voltage relationship was linear between ‐80 and 0 mV, while further hyperpolarization showed a slight inward rectification.
The reversal potential of the SA current depended on the extracellular Na+ concentration, suggesting that the inward SA current was carried predominantly by Na+. The SA current was also carried by other cations, suggesting that the channel responsible for this current is a non‐selective cation channel. The permeability sequence of cations as assessed by reversal potential was as follows: K+≥ Cs+≥ Na+ > Li+. The channel was also permeable to Ca2+.
Extracellular Ca2+ and Gd3+ inhibited the SA current carried by monovalent cations in a concentration‐dependent manner with IC50 (concentration giving 50% of maximal inhibition) values of 0.9 mm and 14 μm, respectively.
In the current‐clamp configuration, membrane stretch depolarized the cell, and 100 μm Gd3+ inhibited the stretch‐induced depolarization.
The results suggest that SA cation channels exist in arterial smooth muscle cells. Activation of the channels may modify membrane potential and intracellular ionic environment, and promote stretch‐mediated cell responses.
Role of Q‐type Ca2+ Channels in Vasopressin Secretion From Neurohypophysial Terminals of the Rat
Authors: Wang Gang , Dayanithi Govindan , Kim Sinnei , Hom Dennis , Nadasdi Laszlo , Kristipati Ramasharma , Ramachandran J. , Stuenkel Edward L. , Nordmann Jean J. , Newcomb Robert , Lemos José R. 
Published: September 2004

The nerve endings of rat neurohypophyses were acutely dissociated and a combination of pharmacological, biophysical and biochemical techniques was used to determine which classes of Ca2+ channels on these central nervous system (CNS) terminals contribute functionally to arginine vasopressin (AVP) and oxytocin (OT) secretion.
Purified neurohypophysial plasma membranes not only had a single high‐affinity binding site for the N‐channel‐specific ω‐conopeptide MVIIA, but also a distinct high‐affinity site for another ω‐conopeptide (MVIIC), which affects both N‐ and P/Q‐channels.
Neurohypophysial terminals exhibited, besides L‐ and N‐type currents, another component of the Ca2+ current that was only blocked by low concentrations of MVIIC or by high concentrations of ω‐AgaIVA, a P/Q‐channel‐selective spider toxin.
This Ca2+ current component had pharmacological and biophysical properties similar to those described for the fast‐inactivating form of the P/Q‐channel class, suggesting that in the neurohypophysial terminals this current is mediated by a ‘Q’‐type channel.
Pharmacological additivity studies showed that this Q‐component contributed to rises in intraterminal Ca2+ concentration ([Ca2+]i) in only half of the terminals tested.
Furthermore, the non‐L‐ and non‐N‐component of Ca2+‐dependent AVP release, but not OT release, was effectively abolished by the same blockers of Q‐type current.
Thus Q‐channels are present on a subset of the neurohypophysial terminals where, in combination with N‐ and L‐channels, they control AVP but not OT peptide neurosecretion.
Tetrodotoxin‐blockable calcium currents in rat ventricular myocytes; a third type of cardiac cell sodium current
Authors: Aggarwal R. , Shorofsky S. R. , Goldman L. , Balke C. W. 
Published: September 2004

Whole‐cell patch clamp currents from freshly isolated adult rat ventricular cells, recorded in external Ca2+ (Ca2+o) but no external Na+ (Ma4o), displayed two inward current components: a smaller component that activated over more negative potentials and a larger component (L‐type Ca2+ current) that activated at more positive potentials. The smaller component was not generated by Ca2+ channels. It was insensitive to 50 μm M2+ and 10 μm La3+, but suppressed by 10 μm tetrodotoxin (TTX). We refer to this component as ICa(TTx).
The conductance–voltage, g(V), relation in Ca2+o only was well described by a single Boltzmann function (half‐maximum potential, V½, of –44.5; slope factor, k, of –4.49 mV, means of 3 cells). g(V) in Ca2+o plus Na4o was better described as the sum of two Boltzmann functions, one nearly identical to that in Ca2+o only (mean V½ of –45.1 and k of – 3.90 mV), and one clearly distinct (mean V½ of –35.6 and k of –2.31 mV). Mean maximum conductance for ICa(TTX) channels increased 23.7 % on adding 1 mm Na+o to 3 mm Ca2+o. ICa(TTx) channels are permeable to Na+ ions, insensitive to Ni2+ and La3+ and blocked by TTX. They are Na+ channels.
I
Ca(TTx) channels are distinct from classical cardiac Na+ channels. They activate and inactivate over a more negative range of potentials and have a slower time constant of inactivation than the classical Na+ channels. They are also distinct from yet another rat ventricular Na+ current component characterized by a much higher TTX sensitivity and by a persistent, non‐fast‐inactivating fraction. That ICa(TTx) channels activate over a more negative range of potentials than classical cardiac Na+ channels suggests that they may be critical for triggering the ventricular action potential and so of importance for cardiac arrhythmias.
pH‐Dependent Interactions of Cd2+ and a Carboxylate Blocker with the Rat ClC‐1 Chloride Channel and Its R304E Mutant in the Sf‐9 Insect Cell Line
Authors: Rychkov G. Y. , St J. Astill D. , Bennetts B. , Hughes B. P. , Bretag A. H. , Roberts M. L. 
Published: September 2004

Gating of the skeletal muscle chloride channel (ClC‐1) is sensitive to extracellular pH. In this study, whole‐cell recording of currents from wild‐type (WT) ClC‐1 and a mutant, R304E, expressed in the Sf‐9 insect cell line was used to investigate further the nature of the pH‐sensitive residues.
Extracellular Cd2+ produced a concentration‐dependent block of WT ClC‐1 with an IC50 of 1.0 ± 0.1 mm and a Hill coefficient of 2.0 ± 0.3. This block was sensitive to external pH, reducing at low pH, with an apparent pKa of 6.8 ± 0.1 and a Hill coefficient for proton binding of 3.0 ± 0.3. Anthracene‐9‐carboxylate (A‐9‐C) block of WT ClC‐1 was also pH sensitive, increasing at low pH, with an apparent pKa of 6.4 ± 0.1 and a Hill coefficient for proton binding of 1.0 ± 0.2.
Compared with WT ClC‐1, R304E had a lower affinity for Cd2+ (IC50, 3.0 ± 0.3 mm) but it had a similar Hill coefficient for transition metal ion binding. The Hill coefficient for proton binding to the Cd2+ binding site was reduced to 1.4 ± 0.3. In contrast, the A‐9‐C binding site in R304E showed the same pH sensitivity and affinity for the blocker as that seen in WT ClC‐1.
ClC‐1 has at least two binding sites for Cd2+, each of which has at least three residues which can be protonated. Binding of A‐9‐C is influenced by protonation of a single residue. Arg 304 is not sufficiently close to the A‐9‐C binding site to affect its characteristics, but it does alter Cd2+ binding, indicating that transition metal ions and aromatic carboxylates interact with distinct sites.
The block of ClC‐1 by transition metal ions and the apparent pKa of this block, together with the apparent pKa for A‐9‐C block and gating are all compatible with the involvement of His residues in the pore and gate of ClC‐1.
Activation of NMDA receptors is necessary for the induction of associative long‐term potentiation in area CA1 of the rat hippocampal slice
Authors: Murphy K. P. S. J. , Reid G. P. , Trentham D. R. , Bliss T. V. P. 
Published: September 2004

It is commonly assumed that the role of the strongly activated heterosynaptic input during the induction of associative long‐term potentiation (LTP) is to relieve the magnesium blockade of NMDA receptors located at the weakly stimulated synapses and thereby allow the weak input to undergo potentiation. We tested this assumption by using a caged form of the NMDA receptor antagonist, d‐(–)‐2‐amino‐5‐phosphonopentanoic acid (d‐AP5) to block the activation of NMDA receptors at the weak input in a conditioning protocol for the induction of associative LTP in area CA1 of the rat hippocampal slice.
The effect of releasing d‐AP5 by flash photolysis of 100 μm caged d‐AP5 (N‐[l‐(2‐nitro‐phenyl)ethoxycarbonyl]‐d‐AP5) on pharmacologically isolated NMDA receptor‐mediated field EPSPs was examined in area CA1. The slope of the EPSP was reduced by 71% within 50 ms of the initiation of the photolytic reaction when the concentration of released d‐AP5 had reached 2.0‐2.5 μm and was reduced by 95% within 1 min (10 μmd‐AP5 released).
Associative LTP was induced by pairing a strong tetanus to one input with a weak tetanus (subthreshold for homosynaptic LTP) to a second input. The strong tetanus preceded the weak by 50 ms. Rapid application of d‐AP5, by flash photolysis of caged d‐AP5, coincident with the last shock of the strong tetanus, resulted in the blockade of NMDA receptor activation during the period of the weak tetanus. Associative LTP was blocked by photolysis of caged d‐AP5 but was normally expressed in experiments using caged l‐AP5.
We conclude that activation of NMDA receptors at the weakly activated input is an essential requirement for synaptically induced associative LTP.
Sarcoplasmic reticulum Ca2+ content, L‐type Ca2+ current and the Ca2+ transient in rat myocytes during β‐adrenergic Stimulation
Authors: Hussain M. , Orchard C. H. 
Published: September 2004

The effect of β‐adrenergic stimulation on the relationship between the intracellular Ca2+ transient and the amplitude of the L‐type Ca2+ current (ICa) has been investigated in ventricular myocytes isolated from rat hearts. Intracellular [Ca2+] was monitored using fura‐2 during field stimulation and while membrane potential was controlled using voltage clamp techniques.
The increase in the amplitude, and the rate of decline, of the Ca2+ transient produced by isoprenaline (1.0 μmol l−1) was not significantly different in myocytes generating action potentials and in those voltage clamped with pulses of constant duration and amplitude.
Under control conditions, the current‐voltage (I‐ V) relationship for ICa was bell shaped. The amplitude of the Ca2+ transient also showed a bell‐shaped voltage dependence. In the presence of isoprenaline, the amplitude of both ICa and the Ca2+ transient was greater at all test potentials and the I–V relationship maintained its bell‐shaped voltage dependence. However, the size of the Ca2+ transient was no longer graded with changes in the amplitude of ICa: a small ICa could now elicit a maximal Ca2+ transient.
Rapid application of caffeine (10 mmol l−1) was used to elicit Ca2+ release from the sarcoplasmic reticulum (SR). Isoprenaline increased the integral of the subsequent rise in cytoplasmic [Ca2+] to 175 ± 13% of control.
Abbreviation of conditioning pulse duration in the presence of isoprenaline was used to reduce the amplitude of the Ca2+ transient to control levels. Under these conditions, the amplitude of the Ca2+ transient was again graded with the amplitude of ICa in the same way as under control conditions.
Nifedipine (2 μmol l−1) was also used to decrease Ca2+ transient amplitude in the presence of isoprenaline. In the presence of isoprenaline and nifedipine, the amplitude of the Ca2+ transient again showed a bell‐shaped voltage dependence.
The SR Ca2+ ‐ATPase inhibitor thapsigargin (2.5 μmol 1−1) reduced the effect of isoprenaline on the amplitude of the Ca2+ transient. In the presence of thapsigargin, the size of the Ca2+ transient increased as ICa increased in response to isoprenaline.
These data suggest that the increase in the amplitude of the Ca2+ transient produced by β‐adrenergic stimulation in cardiac muscle is due to an increase in the gain of the SR Ca2+ release process, due principally to an increase in the Ca2+ content of the SR.
Multiple Modulatory Effects of the Neuroactive Steroid Pregnanolone on GABAA Receptor in Frog Pituitary Melanotrophs
Authors: Le Foll Frank , Castel Hélène , Louiset Estelle , Vaudry Hubert , Cazin Lionel 
Published: September 2004

The effects of the neuroactive steroid pregnanolone (5β‐pregnan‐3α‐ol‐20‐one) on the electrical response to GABA were investigated in cultured frog pituitary melanotrophs using the patch‐clamp technique.
Low concentrations of pregnanolone (0.01–1 μm) in the extracellular solution enhanced the current evoked by submaximal concentrations of GABAA receptor agonists and prolonged the GABA‐induced inhibition of the spontaneous action potentials in a dose‐dependent manner.
Pregnanolone augmented the opening probability of the single GABA‐activated channels but did not modify the conductance levels.
Pregnanolone (1 μm) shifted the GABA dose–response curve towards the low GABA concentrations, reducing the EC50 from 4.2 to 1.8 μm.
Internal cell dialysis with pregnanolone (1 or 10 μm) did not alter the GABA‐evoked current.
Pregnanolone accelerated the desensitization of both the current and conductance increases caused by GABA.
High concentrations of pregnanolone (30 μm) markedly and reversibly diminished the current evoked by 10 μm GABA.
At high concentrations (10–30 μm), pregnanolone induced an outward current which reversed at the chloride equilibrium potential.
It is concluded that, in frog pituitary melanotrophs, pregnanolone exerts a dual inverse modulation and a direct activation of the GABAA receptor–channel depending on the concentrations of both GABA and steroid. Pregnanolone acts on an extracellular site on the GABAA receptor inducing conformational changes of the receptor–channel complex, resulting in a desensitized less‐conducting state.
Differential Na+–K+‐ATPase activity in rat lemniscal and non ‐ lemniscal auditory Thalami
Authors: Senatorov V. V. , Hu Bin 
Published: September 2004

Using whole‐cell recording and confocal immunofluorescent microscopy, we have investigated the differential electrogenic activity, subunit expression and subcellular distribution of the Na+–K+‐ATPase in the lemniscal (ventral) and non‐lemniscal (dorsal) pathways of the rat medial geniculate body (MGB)in vitro.Bath application of Na+–K+‐ATPase inhibitors strophanthidin or dihydroouabain produced a transient, dose‐dependent inward current or membrane depolarization which were significantly larger in dorsal MGB neurones than in ventral cells (45.9 ± 6.45vs. 24.3 ± 4.l pA;P < 0.05). Electrophysiological and morphometric measurements showed that the dorsal MGB neurones had a significantly lower input conductance and a smaller somata than their ventral counterparts. The level of the resting membrane potential also differed by about 6 mV between the two cell populations, with the dorsal cells being more hyperpolarized (−74.2 ± 0.6vs. −67.7 ± 1.3 mV;P< 0.001).Incubation of enzymatically dissociated MGB neurones with fluorescent monoclonal antibodies against α1‐α3 isoforms of Na+–K+‐ATPase showed that both dorsal and ventral cells expressed primarily α3 subunits. Confocal laser scanning revealed, however, that the mean pixel density of α3 fluorescent antibodies in the plasma membrane domain, but not in the cytoplasmic compartment, was about 40 % higher in dorsal neurones than in the ventral cells (29.7 ± 4.7vs. 16.9 ± 2.3 grey shadow per pixel;P< 0.05).The above results suggest that the electrogenic activity of the Na+–K+‐ATPase is differentially regulated between lemniscal and non‐lemniscal auditory thalami through a mechanism that probably involves differential pump densities in the cell membrane.