bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of altitude hypoxia on glucose homeostasis in men
Authors: Larsen Jens Jørn , Hansen Jesper Melchior , Olsen Niels Vidiendal , Galbo Henrik , Dela Flemming 
Published: September 2004

Exposure to altitude hypoxia elicits changes in glucose homeostasis with increases in glucose and insulin concentrations within the first few days at altitude. Both increased and unchanged hepatic glucose production (HGP) have previously been reported in response to acute altitude hypoxia. Insulin action on glucose uptake has never been investigated during altitude hypoxia.
In eight healthy, sea level resident men (27 ± 1 years (mean ± S.E.M.); weight, 72 ± 2 kg; height, 182 ± 2 cm) hyperinsulinaemic (50 mU min−1 m−2), euglycaemic clamps were carried out at sea level, and subsequently on days 2 and 7 after a rapid passive ascent to an altitude of 4559 m.
Acute mountain sickness scores increased in the first days of altitude exposure, with a peak on day 2. Basal HGP did not change with the transition from sea level (2.2 ± 0.2 mg min− kg−1) to altitude (2.0 ± 0.1 and 2.1 ± 0.2 mg min−1 kg−1, days 2 and 7, respectively). Insulin‐stimulated glucose uptake rate was halved on day two compared with sea level (4.5 ± 0.6 and 9.8 ± 1.1 mg min−1 kg−1, respectively; P < 0.05), and was partly restored on day 7 (7.4 ± 1.4 mg min−1 kg−1; P < 0.05vs. day two and sea level). Concentrations of glucagon and growth hormone remained unchanged, whereas glucose, C‐peptide and cortisol increased on day 2. Noradrenaline concentrations increased during the stay at altitude, while adrenaline concentrations remained unchanged. In response to insulin infusion, catecholamines increased on day 2 (noradrenaline and adrenaline) and day 7 (adrenaline), but not at sea level.
In conclusion, insulin action decreases markedly in response to two days of altitude hypoxia, but improves with more prolonged exposure. HGP is always unchanged. The changes in insulin action may in part be explained by the changes in counter‐regulatory hormones.
Voltage‐Dependent Interaction Between the Muscarinic ACh Receptor and Proteins of the Exocytic Machinery
Authors: Linial Michal , Ilouz Nili , Parnas Hanna 
Published: September 2004

Release of neurotransmitter into the synaptic cleft is the last step in the chain of molecular events following the arrival of an action potential at the nerve terminal. The neurotransmitter exerts negative feedback on its own release. This inhibition would be most effective if exerted on the first step in this chain of events, i.e. a step that is mediated by membrane depolarization. Indeed, in numerous studies feedback inhibition was found to be voltage dependent.
The purpose of this study is to investigate whether the mechanism underlying feedback inhibition of transmitter release resides in interaction between the presynaptic autoreceptors and the exocytic apparatus, specifically the soluble NSF‐attachment protein receptor (SNARE) complex.
Using rat synaptosomes we show that the muscarinic ACh autoreceptor (mAChR) is an integral component of the exocytic machinery. It interacts with syntaxin, synaptosomal‐associated protein of 25 kDa (SNAP‐25), vesicle‐associated membrane protein (VAMP) and synaptotagmin as shown using both cross‐linking and immunoprecipitation.
The interaction between mAChRs and both syntaxin and SNAP‐25 is modulated by depolarization levels; binding is maximal at resting potential and disassembly occurs at higher depolarization.
This voltage‐dependent interaction of mAChRs with the secretory core complex appears suitable for controlling the rapid, synchronous neurotransmitter release at nerve terminals.
Mental rehearsal of motor tasks recruits α‐motoneurones but fails to recruit human fusimotor neurones selectively
Authors: Gandevia Simon C. , Wilson Linda R. , Inglis J. Timothy , Burke David 
Published: September 2004

As mental rehearsal of movements activates multiple cortical areas associated with movement, we assessed whether this increases fusimotor drive and whether enhanced muscle spindle activity could contribute to the improvement in skill that accompanies mental rehearsal.
Microneurographic recordings were made from six muscle spindle afferents innervating extensor muscles in the forearm or tibialis anterior, which were selected because their discharge increased during very weak contractions. Activity was monitored while subjects imagined performing a range of activities including simple and complex movements involving the relevant muscles.
No activation of muscle spindle afferents occurred during imagined motor tasks without EMG. When the relevant muscles contracted during mental rehearsal, spindle discharge increased, much as in weak contractions.
Mental rehearsal increased background EMG in the involved muscles and also increased H reflex amplitude independently of EMG changes.
Although there was no evidence for selective fusimotor activation during imagined movement, skeletomotor activity and reflex excitability increased. Similar changes occur with preparation for movement following a cue. It is likely that mental rehearsal usually involves unintentional performance of the planned motor task.
Chloride channel blockers inhibit myogenic tone in rat cerebral arteries
Authors: Nelson Mark T. , Conway Mathew A. , Knot Harm J. , Brayden Joseph E. 
Published: September 2004

We have investigated the role of chloride channels in pressure‐induced depolarization and contraction of cerebral artery smooth muscle cells.
Two chloride channel blockers, indanyloxyacetic acid (IAA‐94) and 4,4′‐diisothiocyanato‐stilbene‐2,2′‐disulphonic acid (DIDS), caused hyperpolarizations (10–15 mV) and dilatations (up to 90 %) of pressurized (80 mmHg), rat posterior cerebral arteries. Niflumic acid, a blocker of calcium‐activated chloride channels, did not affect arterial tone.
Dilatations to IAA‐94 and DIDS were unaffected by potassium channel blockers, but were prevented by elevated potassium. IAA‐94 and DIDS had no effect on membrane potential or diameter of arteries at low intravascular pressure, where myogenic tone is absent. Reduction of extracellular chloride (60 mm Cl−) increased the pressure‐induced contractions. Removal of extracellular sodium did not affect the pressure‐induced responses.
Our results suggest that intravascular pressure activates DIDS‐ and IAA‐94‐sensitive chloride channels to depolarize arterial smooth muscle, thereby contributing to the myogenic constriction.
Sodium Channel Distribution Within the Rabbit Atrioventricular Node as Analysed by Confocal Microscopy
Authors: Petrecca Kevin , Amellal Farid , Laird Dale W. , Cohen Sidney A. , Shrier Alvin 
Published: September 2004

Paired 20 μm thick sections of fresh frozen tissue taken from the frontal plane of the rabbit atrioventricular (AV) nodal region were processed for histology and immunohistochemistry. Confocal microscopy was used to image the distribution of sodium channels using IgG (R12) developed against a highly conserved sequence in the interdomain 3–4 region of cloned sodium channels.
In ventricular and atrial cells, sodium channel immunofluorescence was localized to lateral membranes and T‐tubules. In the open AV node, levels of sodium channel immunofluorescence in the transitional cell zone and in the lower nodal cell tract were comparable to that found in the atrial and ventricular myocardium.
In the enclosed AV node a gradation of sodium channel immunofluorescence is present such that peripherally located circumferential transitional cells display high levels of immunofluorescence, comparable to that of atrial and ventricular myocardium, while centrally located midnodal cells display decreased levels of or no immunofluorescence.
In order to correlate the distribution of sodium channels with the distribution of gap junctions, we used IgG directed against the carboxyl terminus of connexin43 (CT‐360). Ventricular cell immunofluorescence was localized primarily to the intercalated disk region, while in the AV node, the pattern of distribution was found to be similar to that of sodium channels.
The reduced levels of and/or absence of immunofluorescence in the midnodal cell region indicates a paucity of sodium channel and connexin43 protein expression in this region of the AV node that would favour slow impulse conduction.
Corticotropin releasing hormone inhibits an inwardly rectifying potassium current in rat corticotropes
Authors: Kuryshev Yuri A. , Haak Lee , Childs Gwen V. , Ritchie Aileen K. 
Published: September 2004

The perforated‐patch‐clamp technique was used to identify an inwardly rectifying K+ current (IK(IR)) in cultured rat anterior pituitary cells highly enriched in corticotropes. IK(IR) was rapidly activating and highly selective for K+. The K+ conductance was approximately proportional to the square root of the extracellular K+ concentration.
I
K(IR) was blocked in a voltage‐dependent manner by external Ba2+ and Cs+, slightly attenuated by 5 mM 4‐aminopyridine (15% inhibition) and insensitive to 10 mM tetra‐ethylammonium, 2 mM Ca2+, 1 mM Cd2+ and 50 μM La3+.
In physiological saline, 100 μM Ba2+, which inhibits 86% of IK(IR) at the cell resting potential, depolarized cells by 6.1 ± 0.7 mV from a mean resting potential of −59.6 ± 0.8 mV.
Corticotropin releasing hormone (CRH), which activates adenylyl cyclase and stimulates adrenocorticotropic hormone (ACTH) secretion from corticotropes, inhibited IK(IR) by 25% and depolarized the cells by 10.2 ± 1.0 mV. Dibutyryl cAMP ((Bu)2cAMP) mimicked these effects.
The membrane depolarization evoked by Ba2+ or CRH increased the cell firing frequency. Comparison of cells exhibiting a membrane potential of approximately −50 mV revealed that spike frequency in the presence of CRH (109 ± 7 spikes (5 min)−1) was greater than in control (60 ± 5 spikes (5 min)−1) or Ba2+‐treated (77 ± 15 spikes (5 min)−1) corticotropes.
The data suggest that IK(IR) contributes to maintenance of the resting membrane potential of rat corticotropes. Inhibition of IK(IR) plays a role in, but does not account for all of, the membrane depolarization and enhancement of firing frequency evoked by CRH.
The Prostacyclin Analogue Carbacyclin Inhibits Ca2+‐Activated K+ Current in Aortic Baroreceptor Neurones of Rats
Authors: Li Zhi , Lee Hon‐Chi , Bielefeldt Klaus , Chapleau Mark W. , Abboud Francois M. 
Published: September 2004

Previous studies indicate that prostacyclin (PGI2) increases the activity of baroreceptor afferent fibres. The purpose of this study was to test the hypothesis that PGI2 inhibits Ca2+‐activated K+ current (IK(Ca)) in isolated baroreceptor neurones in culture.
Rat aortic baroreceptor neurones in the nodose ganglia were labelled in vivo by applying a fluorescent dye (DiI) to the aortic arch 1–2 weeks before dissociation of the neurones. Outward K+ currents in baroreceptor neurones evoked by depolarizing voltage steps from a holding potential of −40 mV were recorded using the whole‐cell patch‐clamp technique.
Exposure of baroreceptor neurones to the stable PGI2 analogue carbacyclin significantly inhibited the steady‐state K+ current in a dose‐dependent and reversible manner. The inhibition of K+ current was not caused indirectly by changes in cytosolic Ca2+ concentration. The Ca2+‐activated K+ channel blocker charybdotoxin (ChTX, 10−7m) also inhibited the K+ current. In the presence of ChTX or in the absence of Ca2+, carbacyclin failed to inhibit the residual K+ current. Furthermore, in the presence of high concentrations of carbacyclin, ChTX did not cause further reduction of K+ current.
Carbacyclin‐induced inhibition of IK(Ca) was mimicked by 8‐bromo‐cAMP and by activation of G‐protein with GTPγS. The inhibitory effect of carbacyclin on IK(Ca) was abolished by GDPβS, which blocks G‐protein activation, and by a selective inhibitor of cAMP‐dependent protein kinase, PKI5–24.
The results demonstrate that carbacyclin inhibits ChTX‐sensitive IK(Ca) in isolated aortic baroreceptor neurones by a G‐protein‐coupled activation of cAMP‐dependent protein kinase. This mechanism may contribute to the PGI2‐induced increase in baroreceptor activity demonstrated previously.
‘Quantal’ calcium release operated by membrane voltage in frog skeletal muscle
Authors: Pizarro Gonzalo , Shirokova Natalia , Tsugorka Alexander , Ríos Eduardo 
Published: September 2004

Ca2+ transients and Ca2+ release flux were determined optically in cut skeletal muscle fibres under voltage clamp. ‘Decay’ of release during a depolarizing pulse was defined as the difference between the peak value of release and the much lower steady level reached after about 100 ms of depolarization. Using a double‐pulse protocol, the inactivating effect of release was measured by ‘suppression’, the difference between the peak values of release in the test pulse, in the absence and presence of a conditioning pulse that closely preceded the test pulse.
The relationship between decay and suppression was found to follow two simple arithmetic rules. Whenever the conditioning depolarization was less than or equal to the test depolarization, decay in the conditioning release was approximately equal to suppression of the test release. Whenever the conditioning depolarization was greater than that of the test, suppression was complete, i.e. test release was reduced to a function that increased monotonically to a steady level. The steady level was the same with or without conditioning.
These arithmetic rules suggest that inactivation of Ca2+ release channels is strictly and fatally linked to their activation. More than a strict linkage, however, is required to explain the arithmetic properties.
The arithmetic rules of inactivation result in three other properties that are inexplicable with classical models of channel gating: constant suppression, incremental inactivation and increment detection. These properties were first demonstrated for inositol trisphosphate (IP3)‐sensitive channels and used to define IP3‐induced release as quantal. In this sense, it can now be stated that skeletal muscle Ca2+ release is activated by membrane voltage in a quantal manner.
For both classes of intracellular Ca2+ channels, one explanation of the observations is the existence of subsets of channels with different sensitivities (to voltage or agonist dose). In an alternative explanation, channels are identical, but have a complex repertoire of voltage‐ or dose‐dependent responses.
Selective inhibition of a slow‐inactivating voltage‐dependent K+ channel in rat PC 12 cells by hypoxia
Authors: Conforti Laura , Millhorn David E. 
Published: September 2004

Electrophysiological (single‐channel patch clamp) and molecular biological experiments (reverse transcriptase‐polymerase chain reaction) were performed to attempt to identify the O2‐sensitive K+ channel in rat phaeochromocytoma (PC12) cells.
Four types of K+ channels were recorded in PC12 cells: a small‐conductance K+ channel (14 pS), a calcium‐activated K+ channel (KCa; 102 pS) and two K+ channels with similar conductance (20 pS). These last two channels differed in their time‐dependent inactivation: one was a slow‐inactivating channel, while the other belonged to the family of fast transient K+ channels.
The slow‐inactivating 20 pS K+ channel was inhibited by hypoxia. Exposure to hypoxia produced a 50% reduction in channel activity (number of active channels in the patch × open probability). Hypoxia had no effect on the 20 pS transient K+ channels, whereas reduced O2 stimulated the KCa channels.
The genes encoding the α‐subunits of slow‐inactivating K+ channels for two members of the Shaker subfamily of K+ channels (Kvl.2 and Kvl.3) together with the Kv2.1, Kv3.1 and Kv3.2 channel genes were identified in PC12 cells.
The expression of the Shaker Kv1.2, but none of the other K+ channel genes, increased in cells exposed to prolonged hypoxia (18 h). The same cells were more resuponsive to a subsequent exposure to hypoxia (35% inhibition of K+ current measured in whole‐cell voltage clamp) compared with the cells maintained in normoxia (19% inhibition).
These results indicate that the O2‐sensitive K+ channel in PC12 cells is a 20 pS slow‐inactivating K+ channel that is upregulated by hypoxia. This channel appears to belong to the Shaker subfamily of voltage‐gated K+ channels.
The ion channel properties of a rat recombinant neuronal nicotinic receptor are dependent on the host cell type
Authors: Lewis Trevor M. , Harkness Patricia C. , Sivilotti Lucia G. , Colquhoun David , Millar Neil S. 
Published: September 2004

A stable mammalian cell line (L‐α3β4) has been established which expresses the cloned rat neuronal nicotinic acetylcholine receptor (nAChR) subunits α3 and β4, which are the most abundant in autonomic ganglia. Ion channel properties of nAChRs expressed in L‐α3β4 cells were investigated by single‐channel and whole‐cell recording techniques, and compared with both rat α3β4 nAChRs expressed in Xenopus oocytes, and endogenous nicotinic receptors in rat superior cervical ganglion (SCO) neurones, using identical solutions for all cell types.
Acetylcholine (ACh) caused activation of single ion channel currents with a range of amplitudes. Some channels had high conductances (30–40 pS), and relatively brief lifetimes; these resembled the predominant native channel from SCG. Other channels had low conductances (20–26 pS) and long bursts of openings which were quite unlike native channels, but which were similar to channels formed by α3β4 in oocytes. Both types often occurred in the same patch.
Cytisine was about 3 times more potent than ACh (low‐concentration potency ratio) in L‐α3β4 cells, which is not dissimilar to the 5‐fold potency ratio found in both SCG and oocytes, whereas 1,1‐dimethyl‐4‐phenylpiperazinium (DMPP) was less potent than ACh in some cells (as in the oocyte), but more potent in others (as in SCG).
While the channels expressed in L‐α3β4 cells do not mimic exactly those expressed in rat SCG, they differ considerably from the same subunit combination expressed in oocytes. Larger conductance, SCG‐like channels were detected frequently in L‐α3β4, but were rarely, if ever, seen in oocytes injected with α3 and β4 mRNA. Our results indicate that ion channel properties such as single‐channel conductance can be influenced by the choice of heterologous expression system.
The Role of Na+−Ca2+ Exchange Current in Electrical Restitution in Ferret Ventricular Cells
Authors: Janvier N. C. , McMorn S. O. , Harrison S. M. , Taggart P. , Boyett M. R. 
Published: September 2004

The mechanisms underlying electrical restitution (recovery of action potential duration after a preceding beat) were investigated in ferret ventricular cells. The time to 80% recovery (t80) of action potential duration was ∼204 ms.
At a holding potential of −80 mV, the Ca2+ current (ICa) reactivated and the delayed rectifier K+ current (IK) deactivated very rapidly (t80: ∼32 and ∼93 ms, respectively). The kinetics of both currents are too fast to account for electrical restitution alone.
The putative inward Na+−Ca2+ exchange current (INa‐Ca) produced by the Na+−Ca2+ exchanger in response to the intracellular Ca2+ transient reprimed (t80: 189 ms) with the same time course as mechanical restitution (recovery of contraction) and with a similar time course to electrical restitution.
Substantial reduction of inward INa‐Ca, by buffering intracellular Ca2+ with the acetyl methyl ester form of BAPTA, shortened the action potential and greatly altered the electrical restitution curve. Subsequent addition of nifedipine (to block ICa) or 4–aminopyridine (4–AP) (to block the transient outward current, ITO) further altered the electrical restitution curve.
Any time‐dependent current that contributes to the action potential is likely to affect the time course of electrical restitution. Although ICa:, IK and ITO were previously thought to be the only currents involved in electrical restitution, we conclude that inward INa‐Ca also plays an important role.
Extracellular Nucleotides Activate non‐Selective Cation and Ca2+‐Dependent K+ Channels in Rat Osteoclasts
Authors: Weidema A. Frederik , Barbera Joseph , Dixon S. Jeffrey , Sims Stephen M. 
Published: September 2004

Extracellular ATP elevates cytosolic free Ca2+ concentration ([Ca2+]i) in osteoclasts, but its effects on ion channels have not been reported previously. Membrane currents and [Ca2+]i were recorded in isolated rat osteoclasts using patch clamp and fluorescence techniques.
At negative membrane potentials, ATP (1–100 μm) activated an inward current that peaked rapidly and then declined. A later current was outward at potentials positive to the equilibrium potential for K+ (EK) and showed oscillations.
The initial inward current, studied in isolation using Cs+ in the electrode solution, showed rapid activation, inward rectification and reversal at +3 ± 4 mV. Reduction of [Na+]o to 10 mM shifted the reversal potential to –21 ± 3 mV, indicating that ATP activates a non‐selective cation current, consistent with involvement of P2X receptors.
The later current activated by ATP, studied with K+ in the electrode solution, exhibited a linear I–V relationship, and reversed at –71 ± 4 mV. The reversal potential shifted 51 mV per 10‐fold change of [K+]o, indicating that ATP activates a K+ current (IK).
In fura‐2‐loaded cells, ATP caused elevation of [Ca2+]i that persisted in Ca2+‐free solution, indicating that ATP induced release of Ca2+ from intracellular stores, consistent with involvement of P2Y receptors. Simultaneous patch clamp and fluorescence recordings revealed that IK was associated with the elevation of [Ca2+]i. Using a Ca2+ ionophore (4Br‐A23l87) to elevate [Ca2+]iIK activated when [Ca2+]i exceeded ∼400 nm, with half‐maximal activation at 580 ± 50 nM.
In cell‐attached patches, ATP activated a channel with a conductance of 48 ± 6 pS, that reversed direction near EK Channel open probability increased with elevation of [Ca2+]i, indicating the Ca2+ dependence of this channel.
These results demonstrate that rat osteoclasts express two types of purinoceptors. P2X receptors give rise to non‐selective cation current. P2Y receptors mediate Ca2+ release from stores, causing activation of a Ca2+‐dependent K+ channel.
Functional and Morphological Features of Skeletal Muscle from Mutant Mice Lacking Both Type 1 and Type 3 Ryanodine Receptors
Authors: Ikemoto Takaaki , Komazaki Shinji , Takeshima Hiroshi , Nishi Miyuki , Noda Tetsuo , Iino Masamitsu , Endo Makoto 
Published: September 2004

We generated mice with targeted disruptions in the genes for both ryanodine receptor type 1 (RyR‐1) and type 3 (RyR‐3) to study the functional roles of RyR subtypes in skeletal muscle.
In permeabilized myocytes lacking both the RyRs, the Ca2+‐induced Ca2+ release (CICR) mechanism was completely lost, and caffeine failed to induce Ca2+ release.
Replacement of potassium methanesulphonate in an experimental intracellular solution with choline chloride resulted in Ca2+ release in the wild‐type muscle but not in the mutant muscle lacking RyR‐1.
The double‐mutant mice exhibited more severe muscular degeneration than RyR‐1‐deficient mice with formation of large vacuoles and swollen mitochondria while structural coupling between T‐tubules and the sarcoplasmic reticulum was retained.
These results demonstrate that CICR is mediated solely by RyR‐1 and RyR‐3 in skeletal muscle cells, and suggest that RyR‐1 is involved in Cl−‐induced Ca2+ release. The results also suggest the presence of molecular components other than RyRs responsible for the triad formation. RyR‐3 may have a role in the normal morphogenesis of skeletal muscle cells, although functionally it can be replaced by RyR‐1.