bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport mechanisms for iron and other transition metals in rat and rabbit erythroid cells
Authors: Savigni Donna L. , Morgan Evan H.
Published: September 2004

Earlier studies have shown that Fe2+ transport into erythroid cells is inhibited by several transition metals (Mn2+, Zn2+, Co2+, Ni2+) and that Fe2+ transport can occur by two saturable mechanisms, one of high affinity and the other of low affinity. Also, the transport of Zn2+ and Cd2+ into erythroid cells is stimulated by NaHCO3 and NaSCN. The aim of the present investigation was to determine whether all of these transition metals can be transported by the processes described for Fe2+, Zn2+ and Cd2+ and to determine the properties of the transport processes.

Rabbit reticulocytes and mature erythrocytes and reticulocytes from homozygous and heterozygous Belgrade rats were incubated with radiolabelled samples of the metals under conditions known to be optimal for high‐ and low‐affinity Fe2+ transport and for the processes mediated by NaHCO3 and NaSCN.

All of the metals were transported by the high‐ and low‐affinity Fe2+ transport processes and could compete with each other for transport. The Km and Vmax values and the effects of incubation temperature and metabolic inhibitors were similar for all the metals. NaHCO3 and NaSCN increased the uptake of Zn2+ and Cd2+ but not the other metals.

The uptake of all of the metals by the high‐affinity process was much lower in reticulocytes from homozygous Belgrade rats than in those from heterozygous animals, but there was no difference with respect to low‐affinity transport.

It is concluded that the high‐ and low‐affinity ‘iron’ transport mechanisms can also transport several other transition metals and should therefore be considered as general transition metal carriers.
Membrane capacitance changes induced by thrombin and calcium in single endothelial cells cultured from human umbilical vein
Authors: Carter T. D. , Zupancic G. , Smith S. M. , Wheeler‐Jones C. , Ogden D.
Published: September 2004

Vesicular secretion from single human umbilical vein endothelial cells (HUVECs) was monitored by changes in membrane capacitance (Cm). Secretion was evoked by dialysis with strongly buffered intracellular free Ca2+ concentrations ([Ca2+]i), flash photolysis of Ca2+‐loaded DM‐nitrophen or caged InsP3, or by thrombin. [Ca2+]i was monitored spectrofluorimetrically with furaptra. The results show that a large, slowly rising component of vesicular secretion requires prolonged exposure to high [Ca2+]i.

C

m
increased during intracellular perfusion with [Ca2+] buffered in the range 1.0–20 μM. Changes in Cm comprised an initial slowly rising small component of 0.1–0.5 pF followed by a faster rising larger component of up to ∼7 pF, seen when [Ca2+]i > 2 μM and which was maximal at 10–20 μM Ca2+.

Thrombin evoked rapid initial elevations of [Ca2+]i to a peak of 7.1 ± 1.5 μM (mean ± s.e.m., n= 5) that declined within ∼20–30 s with thrombin present either to resting levels or to a maintained elevated level of 2.0 ± 0.7 μM (mean ± s.e.m., range 1.0–3.6 μM, n= 3). Transient [Ca2+]i rises were associated with small, slowly rising increases in Cm of 0.1–0.2 pF, that recovered to pre‐application levels over 2–3 min. Maintained elevations of [Ca2+]i caused larger, faster‐rising sustained increases in Cm to 1.14 ± 0.12 pF (mean ± s.e.m., n= 3). Separate specific enzyme‐linked immunosorbent assay (ELISA) showed that 1.0 U ml−1 thrombin produced secretion of von Willebrand factor in HUVEC cultures.

Short‐lived [Ca2+]i elevations with a peak of 3–25 μM and a duration of approximately 20 s generated by flash photolysis of caged InsP3 or DM‐nitrophen produced either no net change in Cm, or small slow increases of ∼0.1–0.6 pF at up to 5 fF s−1 that recovered to pre‐flash levels over 2–3 min.

Maintained elevations of [Ca2+]i in the range 1–28 μM produced by flash photolysis of DM‐nitrophen caused large increases in Cm, up to ∼4 pF, corresponding to ∼25–30 % of the initial cell Cm. The maximum rate of change of Cm was up to 50 fF s−1 at steady [Ca2+] up to 20 μM; Cm recovered towards pre‐flash levels only when [Ca2+] had declined.
Astrocytes regulate developmental changes in the chloride ion gradient of embryonic rat ventral spinal cord neurons in culture
Authors: Li Yong‐Xin , Schaffner Anne E. , Walton Marc K. , Barker Jeffery L.
Published: September 2004

Embryonic rat ventral spinal cord neurons were dissociated at day 15 and grown on: (i) poly‐D‐lysine (PDL); (ii) a confluent monolayer of type I astrocytes; or (iii) PDL in astrocyte‐conditioned medium (ACM) to examine the influence of astroglia on the regulation of GABAA receptor/Cl− channel properties.

Potentiometric oxonol dye recordings of intact cells indicated that embryonic neurons were uniformly depolarized by muscimol. The depolarizing effects disappeared in cells dissociated during the early postnatal period and recovered in culture for 24 h. Similar recordings using the calcium‐imaging dye fura‐2 AM revealed that GABA or muscimol triggered a sustained rise in cytosolic Ca2+ (Ca2+c) in embryonic neurons that was dependent on extracellular Ca2+, blocked by bicuculline and nifedipine and sensitive to changes in extracellular chloride. The incidence and amplitude of the Ca2+ response decreased with time in vitro and was accelerated in neurons cultured on astrocytes compared with those on PDL.

Perforated patch‐clamp recordings revealed that GABA depolarized neurons in a Cl−‐dependent and bicuculline‐sensitive manner. Both the resting membrane potential and the GABA equilibrium potential became more hyperpolarized with time in vitro.

Astrocytes and ACM accelerated the transformation of GABAergic potential responses from depolarizing to hyperpolarizing. The change occurred over the first 4 days in co‐culture or in ACM but took more than 2 weeks in neurons cultured on PDL alone.

The intrinsic, elementary properties of GABAA receptor/Cl− channels including open time and unitary conductance changed independently of the presence of astrocytes or ACM. Mean open time of the dominant kinetic component decreased and conductance increased with time in vitro.

In sum, astrocytes accelerate the developmental change in the Cl− ion gradient extrinsic to GABAA receptor/Cl− channels, which is critical for triggering Ca2+ entry, without influencing parallel changes in the intrinsic properties of the channels.
Angiotensin II and cardiovascular chemoreflex responses to acute hypoxia in late gestation fetal sheep
Authors: Green L. R. , McGarrigle H. H. G. , Bennet L. , Hanson M. A.
Published: September 2004

In six intact and nine carotid sinus denervated (CSD) fetal sheep (125–128 days gestation) we measured heart rate (FHR), mean systemic arterial blood pressure (MAP), femoral and carotid blood flows (FBF and CBF), and femoral and carotid vascular resistances (FVR and CVR). Three experiments were conducted on successive days: normoxia followed by acute isocapnic hypoxia (Pa,O2 to ca 12 mmHg) with infusion of vehicle (HV experiment), the same protocol but with infusion of the angiotensin converting enzyme (ACE) inhibitor, captopril (HC experiment), and normoxia alone with captopril infusion (NC experiment). Plasma angiotensin II concentration ([AII]) was measured in these fetuses, and in a separate group of fetuses (n= 5) that were infused with the nitric oxide (NO) synthesis inhibitor NG‐nitro‐L‐arginine methyl ester (L‐NAME) or saline vehicle.

During normoxia, cardiovascular parameters and plasma [AII] were unaltered by captopril infusion, apart from a fall in MAP (NC experiment only, P < 0.05) and FHR (HC experiment only, P < 0.05) in intact and CSD fetuses, respectively. No differences were observed between intact and CSD groups.

At the onset of hypoxia the rapid initial fall in FHR and rise in FVR was attenuated in CSD fetuses. In all fetuses FHR returned towards prehypoxic levels as hypoxia continued. In contrast, during hypoxia with vehicle infusion (HV experiment) plasma [AII] rose to a similar level in intact and CSD fetuses.

In both intact and CSD fetuses, the rise in [AII] during hypoxia was blocked by captopril or L‐NAME infusion. In CSD, but not intact, fetuses infused with captopril the rise in MAP was absent, and the fall in FBF and rise in FVR did not reach significance during hypoxia.

Thus, during normoxia CSD alone, or combined with ACE inhibition, does not consistently alter basal cardiovascular control in the late gestation fetus. The rise in [AII] during hypoxia is not mediated by carotid reflexes but may involve NO‐dependent mechanisms. In intact fetuses, AII does not appear to be pivotal in cardiovascular control during hypoxia. It is only when carotid reflex mechanisms are removed that a role for AII in the regulation of MAP and peripheral blood flow during hypoxia becomes apparent. These findings lend weight to the idea of multiple mechanisms of fetal cardiovascular control during hypoxia.
Developmental changes in EPSC quantal size and quantal content at a central glutamatergic synapse in rat
Authors: Bellingham Mark C. , Lim Rebecca , Walmsley Bruce
Published: September 2004

Developmental changes in amplitude and time course of single‐fibre‐evoked and spontaneous EPSCs mediated by AMPA and NMDA receptors at the endbulb‐bushy cell synapse of rats from 4 to 22 days of age were recorded using whole‐cell patch‐clamp methods inin vitroslices of cochlear nucleus.

The mean conductance of the AMPA component of evoked EPSCs increased by 66 %, while that of the NMDA component decreased by 61 %, for 12‐ to 18‐day‐old rats cf. 4‐ to 11‐day‐old rats.

The mean AMPA spontaneous EPSC conductance increased by 54 %, while mean NMDA spontaneous EPSC conductance decreased by 83 %, for 12‐ to 22‐day‐old rats cf. 4‐ to 11‐day‐old rats. The mean number of quanta contributing to peak evoked AMPA conductance also increased by 78 % in the older age group, after correction for the asynchrony of evoked quantal release.

The decay time constant of spontaneous AMPA EPSCs showed a small decrease in older animals, while the decay time constant of spontaneous NMDA EPSCs was markedly decreased in older animals. The decay time constants of evoked NMDA EPSCs showed a quantitatively similar decrease to that of spontaneous NMDA EPSCs. This suggests that AMPA receptor subunit composition is unlikely to undergo developmental change, while NMDA receptor subunit composition may be substantially altered during synaptic maturation.

These data are consistent with a developmentally increased efficacy of AMPA receptor‐mediated synaptic transmission at the endbulb‐bushy cell synapse, due to an increase in underlying AMPA‐mediated quantal size and content during the same period as a transient co‐localization of NMDA receptors.
Cannabinoids decrease excitatory synaptic transmission and impair long‐term depression in rat cerebellar Purkinje cells
Authors: Lévénès Carole , Daniel Hervé , Soubrié Philippe , Crépel Françis
Published: September 2004

CB‐1 cannabinoid receptors are strongly expressed in the molecular layer of the cerebellar cortex. We have analysed, in patch‐clamped Purkinje cells (PCs) in rat cerebellar slices, the effect of the selective CB‐1 agonists WIN55,212‐2 and CP55,940 and of the selective CB‐1 antagonist SR141716‐A on excitatory synaptic transmission and synaptic plasticity.

Bath application of both agonists markedly depressed parallel fibre (PF) EPSCs. This effect was reversed by SR141716‐A. In contrast, responses of PCs to ionophoretic application of glutamate were not affected by WIN55,212‐2.

The coefficient of variation and the paired‐pulse facilitation of these PF‐mediated EPSCs increased in the presence of WIN55,212‐2.

WIN55,212‐2 decreased the frequency of miniature EPSCs and of asynchronous synaptic events evoked in the presence of strontium in the bath, but did not affect their amplitude.

WIN55,212‐2 did not change the excitability of PFs.

WIN55,212‐2 impaired long‐term depression induced by pairing protocols in PCs. This effect was antagonized by SR141716‐A. The same impairment of LTD was produced by 2‐chloroadenosine, a compound that decreases the probability of release of glutamate at PF‐PC synapses.

The present study demonstrates that cannabinoids inhibit synaptic transmission at PF‐PC synapses by decreasing the probability of release of glutamate, and thereby impair LTD. These two effects might represent a plausible cellular mechanism underlying cerebellar dysfunction caused by cannabinoids.
Altered regulation of natriuretic peptides in the rat heart by prenatal exposure to morphine
Authors: Ernest Sheila , Jankowski Marek , Mukaddam‐Daher Suhayla , Cusson Jean , Gutkowska Jolanta
Published: September 2004

Both endogenous and exogenous opioids modulate blood pressure and cardiac function by stimulating cardiac synthesis of atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP). Since morphine crosses the placental barrier, it could alter the ANF‐BNP system in the fetal heart. The aim of this study was to characterize cardiac natriuretic peptides in normal rat development and in rats prenatally exposed to morphine.

Female rats received either saline or morphine (10 or 20 mg kg−1 day−1) via osmotic minipumps during gestation. The effects of this treatment were investigated in offspring at 1, 4 and 22 days of age.

During maturation, atrial ANF and ANF mRNA increased by 3‐fold from birth to 3 weeks of age, but BNP and BNP mRNA tended to decrease. In the ventricles, both ANF and BNP content decreased at 3 weeks after birth, from 25.11 ± 3.6 to 0.81 ± 0.1 ng (P < 0.001), and from 3.36 ± 0.33 to 0.19 ± 0.01 ng (P < 0.001), respectively. However, whereas ventricular ANF mRNA decreased, BNP mRNA levels did not change during maturation. Prenatal exposure to morphine significantly increased ANF content in the left atria of 22‐day‐old rats, and in the right atria of 1‐, 4‐ and 22‐day‐old rats compared with age‐matched saline controls. In contrast, prenatal exposure to 20 mg kg−1 day−1 morphine significantly inhibited BNP and BNP mRNA in the ventricles at all ages studied.

These observations suggest that alterations in mRNA synthesis or stability and/or post‐translational processing of ANF and BNP occur in the heart during maturation, and that prenatal exposure to morphine alters cardiac production, and possibly release, of both peptides.
Possible involvement of the novel CPI‐17 protein in protein kinase C signal transduction of rabbit arterial smooth muscle
Authors: Li L. , Eto M. , Lee M. R. , Morita F. , Yazawa M. , Kitazawa T.
Published: September 2004

CPI‐17 has recently been identified as a novel protein in vascular smooth muscle. In vitro, its phosphorylation and thiophosphorylation by protein kinase C (PKC) specifically inhibits the type 1 class of protein phosphatases, including myosin light chain (MLC) phosphatase.

Both of the phosphorylated CPI‐17 states dose‐dependently potentiated submaximal contractions at constant [Ca2+] in β‐escin‐permeabilized and Triton X‐100‐demembranated arterial smooth muscle, but produced no effect in intact and less intensely permeabilized (α‐toxin) tissue. Thiophosphorylated CPI‐17 (tp‐CPI) induced large contractions even under Ca2+‐free conditions and decreased Ca2+ EC50 by more than an order of magnitude. Unphosphorylated CPI‐17 produced minimal but significant effects.

tp‐CPI substantially increased the steady‐state MLC phosphorylation to Ca2+ ratios in β‐escin preparations.

tp‐CPI affected the kinetics of contraction and relaxation and of MLC phosphorylation and dephosphorylation in such a manner that indicates its major physiological effect is to inhibit MLC phosphatase.

Results from use of specific inhibitors in concurrence with tp‐CPI repudiate the involvement of general G proteins, rho A or PKC itself in the Ca2+ sensitization by tp‐CPI.

Our results indicate that phosphorylation of CPI‐17 by PKC stimulates binding of CPI‐17 to and subsequent inhibition of MLC phosphatase. This implies that CPI‐17 accounts largely for the heretofore unknown signalling pathway between PKC and inhibited MLC phosphatase.
Magnetic resonance imaging analysis of left ventricular function in normal and spontaneously hypertensive rats
Authors: Wise R. G. , Huang C. L.‐H. , Gresham G. A. , Al‐Shafei A. I. M. , Carpenter T. A. , Hall L. D.
Published: September 2004

We have used magnetic resonance imaging (MRI) to examine acute morphological changes in the left ventricle throughout the cardiac cycle in normal Wistar Kyoto rats (WKY) and also to follow the development of chronic changes in spontaneously hypertensive rats (SHR). This involved the development of MRI and quantitative analysis techniques for characterizing contractile changes during the cardiac cycle.

Images of the cardiac anatomy in two age groups (8 and 12 weeks old) of young anaesthetized adult normal WKY and SHR were acquired in planes both parallel and perpendicular to the principal cardiac axis.

Complete coverage of the heart by imaging planes was achieved with high time resolution (13 ms), with typically 12 time frames in the cardiac cycle, using a short echo time (5 ms) multislice gradient‐echo imaging sequence. Imaging was synchronized to the R wave of the electrocardiogram.

The image slices could be reconstructed into complete geometrically and temporally coherent three‐dimensional data sets. Left ventricular (LV) volumes were thus reconstructed throughout the cardiac cycle by combining transverse cardiac image sections. This volume analysis revealed structural and functional differences between the normal WKY and SHR in both age groups of 8 and 12 weeks. Measurements from the cardiac images were additionally validated against histological measurements.

The SHR showed a raised LV end‐systolic volume and a correspondingly poorer ejection fraction as well as LV hypertrophy when compared with the controls. Left ventricular function in the SHR appeared stable between the two age groups.

We developed a simple geometrical model of the left ventricle based on a single longitudinal image section and successfully used this to describe some functional parameters of the left ventricle in the WKY and SHR. This geometrical model has the potential to greatly reduce the imaging time needed to study the beating heart in future serial investigations of cardiac physiology in rats.

Our experimental and analytical methods together form a powerful set of quantitative techniques which combine both imaging and functional analysis and will be applicable for future studies of chronic physiological changes in animal disease models.
Longitudinal distribution of components of excitatory synaptic input to motoneurones during swimming in young Xenopus tadpoles: experiments with antagonists
Authors: Zhao Fei‐Yue , Wolf Ervin , Roberts Alan
Published: September 2004

Recent studies have revealed that the excitatory synaptic input to spinal motoneurones during fictive swimming in Xenopus tadpoles has three main components: glutamatergic (Glu) from premotor excitatory interneurones, nicotinic cholinergic (nACh) from more rostral motoneurones, and electrotonic coupling from neighbouring motoneurones. During swimming, these components sum to produce two kinds of excitation: phasic excitation (EPSPs) underlying spikes, and tonic depolarization.

We have investigated the longitudinal distribution of these excitatory synaptic inputs to presumed motoneurones at different positions along the spinal cord using intracellular recording techniques. Different antagonists (10 μm dihydro‐β‐erythroidine (DHβE) for nicotinic ACh receptors (nAChRs), 2 mM kynurenate (Kyn) for glutamate receptors (GluRs), and 100 μm Cd2+ for all chemical synapses) were microperfused very locally to unmask the relative contributions of these components to the total excitatory drive, and their distribution along the spinal cord during swimming.

If the potentials remaining when all chemical components were blocked by Cd2+ were subtracted from potentials recorded after blocking nAChRs and GluRs with DHβE plus Kyn, a small unidentified component was observed. This component was blocked by the specific AMPA antagonist 6‐nitro‐7‐sulphamoylbenzo(f)quinoxaline‐2,3‐dione (NBQX, 5 μm), so is glutamate mediated.

We used the potential measurements to calculate the relative synaptic conductances of the different synaptic inputs, and conclude that: (a) there is a rostral‐caudal gradient in input during EPSPs and tonic depolarization; (b) the glutamatergic component accounts for most of the excitation, and decreases caudally; (c) cholinergic and electrotonic components are relatively constant in different positions along the spinal cord; and (d) these two components provide an increasing proportion of the input in more caudal neurones.

We propose that the glutamate components of excitation are fundamental to rhythm generation in the brainstem and rostral cord, while the electrotonic and cholinergic components ensure that the central pattern generator activates motoneurones effectively in all parts of the spinal cord.
Oxygen‐sensing mechanisms are present in the chromaffin cells of the sheep adrenal medulla before birth
Authors: Rychkov G. Y. , Adams M. B. , McMillen I. C. , Roberts M. L.
Published: September 2004

The ability of the fetal adrenal medulla to respond directly to hypoxaemia and secrete catecholamines before the development of a functional innervation of the gland is essential for intrauterine survival. The cellular mechanisms involved in this response to low PO2 are not known, although the presence of oxygen‐sensitive K+ channels in carotid body chemoreceptor cells and other sites suggests that these might underlie the chromaffin cell response.

Whole‐cell patch‐clamp techniques have been used to study K+ currents during normoxia and hypoxia in chromaffin cells isolated from the adrenal glands of fetal sheep.

Two types of chromaffin cells were observed, those with a fast inactivating K+ current and a larger capacitance and those with a delayed K+ current and smaller capacitance. No cell showed both types of current. The fast inactivating current showed voltage‐dependent inactivation and was blocked by 1 mM 4‐aminopyridine, characteristics of an IA‐type current. The delayed current had two components, a TEA‐sensitive, Ca2+‐dependent current and a component with the kinetic behaviour of a delayed rectifier.

Both types of current were oxygen sensitive. The IA‐type current was reduced by 27.4 ± 3.2 % when the PO2 was reduced to about 15 mmHg. With the delayed current, hypoxia reduced the amplitude by 26.9 ± 2.4 %, largely by reduction of the Ca2+‐dependent component.

In the presence of hypoxia, reduction in the amplitude of these oxygen‐sensitive K+ currents would increase the frequency and duration of action potentials, leading to increased activation of the L‐type Ca2+ channels, influx of Ca2+ and the subsequent secretion of catecholamines.
A trauma‐like elevation of plasma cytokines in humans in response to treadmill running
Authors: Ostrowski Kenneth , Hermann Claus , Bangash Aimal , Schjerling Peter , Nielsen Jakob Nis , Pedersen Bente Klarlund
Published: September 2004

Elevated levels of cytokines, especially interleukin (IL)‐6 and IL‐1ra, can be measured in the plasma of athletes after exhaustive long term exercise.

The present study investigates the kinetics of several cytokines and chemokines in ten male athletes before, during and after 2.5 h of treadmill running at 75% of maximal oxygen consumption (VO2,max). Blood was sampled before, every half‐hour during running and every hour in the following 6 h recovery period.

The plasma concentration of IL‐6 increased after 30 min of running, and peaked at the end of running with a 25‐fold increase compared with the pre‐exercise value. IL‐1ra increased only after running, and peaked after 2 h of rest with an 18‐fold increase compared with the pre‐exercise value. No changes were found in the concentrations of IL‐1β, tumour necrosis factor (TNF)α, IL‐15 and macrophage inflammatory protein (MIP)‐1β, and the concentrations of IL‐8 and MIP‐1α were below detection limits.

The results suggest that very early events in exercise trigger the release of IL‐6, and that the cytokine response to exercise has similarities to that observed after trauma.
Nitric oxide modulates cholinergic reflex pathways to the longitudinal and circular muscle in the isolated guinea‐pig distal colon
Authors: Smith Terence K. , McCarron Sarah L.
Published: September 2004

The involvement of nitric oxide (NO) in enteric neural pathways underlying reflex responses of the longitudinal muscle (LM) and circular muscle (CM) layers activated by mucosal stimulation was examined in the isolated guinea‐pig distal colon.

A segment of colon spanned two partitions (10 mm apart), which divided the organ bath into three chambers: a recording chamber where LM and CM tension was measured; a stimulation chamber where mucosal stimulation was applied; and a middle chamber separating them.

Brushing the mucosa anal and oral to the recording site evoked simultaneous oral contraction and anal relaxation of both the LM and CM.

N
ω‐nitro‐L‐argininel‐NA; 100 μm) or Nω‐nitro‐L‐arginine methyl ester (l‐NAME; 100 μm) applied to the middle chamber or stimulation chamber decreased the oral contractile response of the LM and CM (by about 30–40 %), but increased the anal relaxation (> 600 %) and exposed an anal contraction (> 1000 % increase) of both muscles. The addition of l‐NA to the recording chamber reduced the anal relaxation of the LM and CM and the anal contraction of the LM, but slightly increased the anal contraction of the CM.

S‐Nitroso‐N‐acetylpenicillamine (SNAP; 10 μm), an NO donor, reversed the effects of l‐NA in the middle or stimulation chambers.

1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ; 10 μm), a soluble guanylate cyclase inhibitor, mimicked the effects of l‐NAin the middle chamber or stimulation chamber, but these effects were not reversed by SNAP.

The oral contractile responses, and the anal relaxation and contractile responses of the LM and CM produced by l‐NA in the stimulation or middle chambers, were blocked by hexamethonium (300 μm) in any chamber. Atropine (1 μm) in the recording chamber reduced the contractile responses of the LM and CM.

In conclusion, endogenous NO facilitates and depresses release of acetylcholine from interneurons in ascending and descending nervous pathways, respectively. These NO effects are mediated through soluble guanylate cyclase in cholinergic interneurons
Membrane current noise in dark‐adapted and light‐adapted isolated retinal rods of the larval tiger salamander
Authors: Jones Gregor J.
Published: September 2004

Low‐frequency light‐sensitive membrane current noise in isolated rod photoreceptors of the larval tiger salamander was recorded using suction electrodes, in the dark, and during light adaptation by backgrounds or by bleaching visual pigment.

In background light, noise variance increases and then decreases. For rods desensitized to similar levels by bleaching visual pigment, the noise variance either does not change (weak adaptation) or decreases (with stronger adaptation).

The power spectral density of the current noise in dark‐adapted rods shows a component with half‐power cut‐off frequency at about 0.1 Hz, attributed to spontaneous single events and continuous noise from dark phosphodiesterase activity. A second component, with half‐power cut‐off frequency at about 1 Hz, may be due to slow components in the light‐sensitive channel gating.

The power spectral density of the noise in background light is dominated by noise generated by the background. Background light adapts at least the first component of the noise seen in dark‐adapted cells. For cells desensitized by bleaching, light adaptation of both components of the dark‐adapted noise is observed.

The results confirm that the low‐frequency noise in dark‐adapted cells arises from the transduction mechanism of the rod, in that both components can be light adapted, and show that, for rods permanently desensitized by bleaching, the desensitization is not due to the presence of active visual pigment molecules similar to those produced by background light.
Mechanistic analyses of ion dependences in a high‐affinity human serotonin transport system in transfected murine fibroblast cells
Authors: Chang Albert S. , Lam Dominic M.‐K.
Published: September 2004

A clonal cell line, L‐S1, has been identified from transfection of human genomic DNA into cultured mouse L‐M fibroblasts. Because this transfectant cell line stably expresses a high‐affinity serotonin (5‐HT) transport mechanism with kinetic and pharmacological properties comparable to those of other serotonin uptake systems, it was used to investigate the mechanistic involvement of Na+ and Cl− ions in the ligand binding and kinetic uptake processes of this system.

Intact transfectant cells, when incubated at low temperature (4 °C), enabled quantitative assessment of imipramine‐displaceable 5‐[3H]HT binding to the 5‐HT transport system. This binding activity is insensitive to the presence of various ligands specific for 5‐HT receptor subtypes.

Imipramine‐displaceable 5‐[3H]HT binding to intact L‐S1 cells was shown to be a Cl−‐dependent but Na+‐independent process. Chloride ions lack binding co‐operativity in facilitating ligand binding. Changes in external Cl− concentration altered the Kd but not the Bmax of binding.

The overall transport activity was observed to be highly dependent on both external Na+ and Cl− concentrations, characterized by a 5‐HT:Na+:Cl− coupling ratio of 1:1:1 per transport cycle. Alterations in the external concentrations of both Na+ and Cl− ions altered only the Km and not the Vmax of transport.

Both binding and kinetic results are consistent with kinetic modelling predictions of the Cl− ion in facilitating 5‐HT binding to the transport system, and of the Na+ ion in enabling translocation of bound 5‐HT across the plasma membrane. Thus, Na+ and Cl− ions facilitate mechanistically distinct and discernible functions in the transport cycle.
An in vitro study of the properties of vagal afferent fibres innervating the ferret oesophagus and stomach
Authors: Page Amanda J. , Blackshaw L. Ashley
Published: September 2004

A novel preparation of the oesophagus with attached vagus nerve from the ferret maintained in vitro was used to study the properties of single vagal afferent nerve fibres with identified receptive fields.

Recordings were made from three types of gastro‐oesophageal vagal afferent fibres that were classified on the basis of their sensitivity to mechanical stimulation. There were those responding to mucosal stroking (mucosal receptors), to circular tension (tension receptors) and those responding to mucosal stroking and circular tension, which we have termed tension/mucosal (TM) receptors.

The conduction velocities for mucosal, TM and tension receptor fibres were 6.38 ± 1.22 m s−1 (n= 22), 6.20 ± 1.49 m s−1 (n= 13) and 5.33 ± 0.86 m s−1 (n= 22), respectively.

Receptive fields of afferents showed random topographical distribution by fibre type and conduction velocity. They were found mainly distal but also occasionally proximal to the point of vagal dissection.

Twenty‐eight per cent of mucosal, 63 % of TM and 43 % of tension receptors responded to one or more drugs or chemical stimuli applied to the receptive field.

In conclusion, this experimental preparation provides evidence for the existence of three types of oesophageal vagal afferent fibre, namely mucosal, tension and the newly identified tension/mucosal receptors.
Incomplete rematching of nerve and muscle properties in motor units after extensive nerve injuries in cat hindlimb muscle
Authors: Rafuse Victor F. , Gordon Tessa
Published: September 2004

Motor units were characterized in partially denervated or completely denervated and reinnervated cat medial gastrocnemius (MG) muscles where the number of innervating motor axons was severely reduced to determine (1) to what extent the nerve and muscle properties are rematched in enlarged motor units, (2) whether the normal size relationships between axon size, unit tetanic force and contractile speed are re‐established, and (3) whether the type of nerve injury and/or repair affects the re‐establishment of nerve and muscle properties.

Single MG units were sampled in (1) partially denervated muscles and in reinnervated muscles after either (2) crushing or (3) transecting the nerve and suturing its proximal end to either the distal nerve stump (N‐N), or (4) directly to the muscle fascia (N‐M).

The majority (75‐88 %) of motor units in all muscles were classified as S (slow), FR (fast fatigue resistant), FI (fast fatigue intermediate) and FF (fast fatigable). However, there was an increased number of FI and unclassifiable motor units compared to normal. These results suggest that motor unit properties are not entirely regulated by the reinnervating motoneurone.

Despite more overlap in the range of unit force between different motor unit types the tetanic force of each type increased in all muscles when reinnervated by few (< 50 %) motor axons. This increase in unit force was due to an expansion in motor unit innervation ratio.

The normal relationships between axon size, unit tetanic force, and contractile speed were re‐established in all muscles except when reinnervated by < 50 % of their normal complement of motor units after N‐M suture. This lack of correlation was due to the reduced fast glycolytic (FG) fibre size and the proportionately greater increase in force of the S units.

After reinnervation the ranges in fibre cross‐sectional area within single FF units were very similar to those found within the entire FG fibre population.

These results show that when few axons make functional connections in partially denervated or reinnervated muscles the normal relationships between axon size and motor unit contractile properties are re‐established provided the nerves regenerate within the distal nerve sheath. This rematching of motoneurone size and motor unit contractile properties occurs primarily because the size of the motor axon governs the number of muscle fibres it supplies.
The mechanics of running in children
Authors: Schepens B. , Willems P. A. , Cavagna G. A.
Published: September 2004

The effect of age and body size on the bouncing mechanism of running was studied in children aged 2‐16 years.

The natural frequency of the bouncing system (fs) and the external work required to move the centre of mass of the body were measured using a force platform.

At all ages, during running below ≈11 km h−1, the freely chosen step frequency (f) is about equal to fs (symmetric rebound), independent of speed, although it decreases with age from 4 Hz at 2 years to 2.5 Hz above 12 years.

The decrease of step frequency with age is associated with a decrease in the mass‐specific vertical stiffness of the bouncing system (k/m) due to an increase of the body mass (m) with a constant stiffness (k).Above 12 years, k/mand fremain approximately constant due to a parallel increase in both kand mwith age.

Above the critical speed of ≈11 km h−1, independent of age, the rebound becomes asymmetric, i.e. f< fs.

The maximum running speed (Vf,max) increases with age while the step frequency at remains constant (≈4 Hz), independent of age.

At a given speed, the higher step frequency in preteens results in a mass‐specific power against gravity less than that in adults. The external power required to move the centre of mass of the body is correspondingly reduced.
Osmotic hypertonicity of the renal medulla during changes in renal perfusion pressure in the rat
Authors: Dobrowolski Leszek , Badzynska Bozena , Walkowska Agnieszka , Sadowski Janusz
Published: September 2004

The relationship between renal perfusion pressure (RPP) and ion concentration in renal medulla was studied in anaesthetized rats. RPP was changed in steps within the pressure range 130‐80 mmHg, while tissue electrical admittance (Y, index of interstitial ion concentration) and medullary and cortical blood flow (MBF and CBF; laser Doppler flowmetry) were measured, along with glomerular filtration rate (Cin) and renal excretion.

With a RPP reduction from 130 to 120 mmHg, tissue Y remained stable; at 100 and 80 mmHg, Y was 5 and 17 % lower, respectively, than at 120 mmHg.

CBF fell less than RPP (partial autoregulation) in the range 130‐100 mmHg only. MBF was autoregulated within 120‐100 mmHg, but not above or below this range.

Each step of RPP reduction was followed by a decrease in sodium and water excretion (UNaV and V). The osmolality of excised inner medulla fragments was similar at 120 and 105 mmHg (586 ± 45 and 618 ± 35 mosmol (kg H2O)−1, respectively) but lower at 80 mmHg (434 ± 31 mosmol (kg H2O)−1, P < 0.01); the ion concentration changed in parallel.

The data show that medullary hypertonicity was well preserved during RPP fluctuations within 130‐100 mmHg, but not below this range. RPP‐dependent changes of UNaV and V were not clearly associated with changes in solute concentration in medullary tissue.
Developmental regulation of glucogenesis in the sheep fetus during late gestation
Authors: Fowden Abigail L. , Mundy Linda , the late Silver Marian
Published: September 2004

Using tracer methodology, endogenous glucose production was measured in twenty‐six chronically catheterized sheep fetuses during normal fed conditions and in response to a 48 h period of maternal fasting at different gestational ages during the last 10‐15 days of gestation (term, 145 ± 2 days).

In normal fed conditions, the rate of fetal glucose production was negligible until 143‐145 days when it rose significantly to account for 50 % of the glucose used by the fetus. The rise in fetal glucogenesis towards term closely parallelled the normal prepartum rise in fetal plasma cortisol and catecholamines.

Maternal fasting for 48 h induced endogenous glucose production in fetuses at 139‐141 days but not at 133‐135 days of gestation. Maternal fasting also induced increases in the plasma cortisol and noradrenaline levels in all the fetuses studied. Fetal plasma cortisol levels at the end of the fast and the increment in fetal plasma cortisol during maternal fasting were significantly greater in the older groups of fasted animals.

When the data from all the fetuses were combined, partial correlation analysis of fetal glucose production and the log plasma concentrations of cortisol and total catecholamines showed that plasma cortisol was the predominant regulator of fetal glucogenesis during late gestation. However, once plasma cortisol levels exceeded 17.5 ng ml−1, plasma catecholamines were a major influence on fetal glucogenesis.

The results show that glucogenesis occurs in fetal sheep during late gestation in conditions in which the fetal plasma concentrations of cortisol and catecholamines are elevated. They also suggest that cortisol enhances the capacity for glucogenesis in utero, while catecholamines actually activate glucose production in sheep fetuses close to term.
A cross‐bridge mechanism can explain the thixotropic short‐range elastic component of relaxed frog skeletal muscle
Authors: Campbell K. S. , Lakie M.
Published: September 2004

The passive tension and sarcomere length of relaxed frog skeletal muscle fibres were measured in response to imposed length stretches. The tension response to a constant‐velocity stretch exhibited a clear discontinuity. Tension rose more rapidly during the initial ∼ 0.4 %L0 of the stretch than during the latter stages (where L0 is the resting length of the fibre). This initial tension response is attributed to the short‐range elastic component (SREC).

The use of paired triangular stretches revealed that the maximum tension produced during the SREC response of the second stretch was significantly reduced by the first stretch. This history‐dependent behaviour of the SREC reflects thixotropic stiffness changes that have been previously described in relaxed muscle.

The biphasic nature of the SREC tension response to movement was most apparent during the first imposed length change after a period at a fixed length, irrespective of the direction of movement.

If a relaxed muscle was subjected to an imposed triangular length change so that the muscle was initially stretched and subsequently shortened back to its original fibre length, the resting tension at the end of the stretch was reduced relative to its initial pre‐stretch value. Following the end of the stretch, tension slowly increased towards its initial value but the tension recovery was not accompanied by a contemporaneous increase in sarcomere length. This finding suggests that the resting tension of a relaxed muscle fibre is not entirely due to passive elasticity. The results are compatible with the suggestion that a portion of the resting tension ‐ the filamentary resting tension (FRT) ‐ is produced by a low level of active force generation.

If a second identical stretch was imposed on the muscle at a time when the resting tension was reduced by the previous stretch, the maximal tension produced during the second stretch was the same as that produced during the first, despite the second stretch commencing from a lower initial resting tension.

In experiments using paired triangular length changes, an inter‐stretch interval of zero did not produce a substantially greater thixotropic reduction in the second stretch elastic limit force than an inter‐stretch interval in the range 0.5‐1 s.

A theoretical model was developed in which the SREC and FRT arise as manifestations of a small number of slowly cycling cross‐bridges linking the actin and myosin filaments of a relaxed skeletal muscle. The predictions of the model are compatible with many of the experimental observations. If the SREC and FRT are indeed due to cross‐bridge activity, the model suggests that the cross‐bridge attachment rate must increase during interfilamentary movement. A mechanism (based on misregistration between the actin binding sites and the myosin cross‐bridges) by which this might arise is presented.
Evidence that interleukin‐6 is produced in human skeletal muscle during prolonged running
Authors: Ostrowski K. , Rohde T. , Zacho M. , Asp S. , Pedersen B. K.
Published: September 2004

This study was performed to test the hypothesis that inflammatory cytokines are produced in skeletal muscle in response to prolonged intense exercise. Muscle biopsies and blood samples were collected from runners before, immediately after, and 2 h after a marathon race.

The concentration of interleukin (IL)‐6 protein in plasma increased from 1.5 ± 0.7 to 94.4 ± 12.6 pg ml−1 immediately post‐exercise and to 22.1 ± 3.8 pg ml−1 2 h post‐exercise. IL‐1 receptor antagonist (IL‐1ra) protein in plasma increased from 123 ± 23 to 2795 ± 551 pg ml−1, and increased further to 4119 ± 527 pg ml−1 2 h post‐exercise.

The comparative polymerase chain reaction technique was used to evaluate mRNA for IL‐6, IL‐1ra, IL‐1β and tumour necrosis factor (TNF)‐α in skeletal muscle and blood mononuclear cells (BMNC) (n= 8). Before exercise, mRNA for IL‐6 could not be detected either in muscle or in BMNC, and was only detectable in muscle biopsies (5 out of 8) after exercise. Increased amounts of mRNA for IL‐1ra were found in two muscle biopsies and five BMNC samples, and increased amounts of IL‐1β mRNA were found in one muscle and four BMNC samples after exercise. TNF‐α mRNA was not detected in any samples.

This study suggests that exercise‐induced destruction of muscle fibres in skeletal muscles may trigger local production of IL‐6, which stimulates the production of IL‐1ra from circulating BMNC.
The Premonitory Symptoms (Prodrome): A Tertiary Care Study of 893 Migraineurs
Authors: Kelman Leslie
Published: September 2004

Objectives.—This study of premonitory symptoms in migraine was performed to document the frequency, duration, and types of symptoms in a large group of migraine patients.

Background.—Prodrome importance continues to be debated. Intervention early in the migraine attack is assuming more importance and necessitates better knowledge of the prodrome.

Methods.—A total of 893 migraine patients (IHS 1.1‐1.7) were evaluated at first visit. Prodrome frequency, duration, and characteristics were analyzed in the total migraine population IHS 1.1‐1.7 and IHS 1.1‐1.6 migraine.

Results.—A total of 32.9% of IHS migraine 1.1‐1.6 patients reported prodrome symptoms with an average of 9.42 hours. IHS 1.1‐1.7 migraine reported 29.7% and 6.8 hours, respectively. The most commonest symptoms were tiredness, mood change, and gastrointestinal symptoms; all three of these symptoms were present together in 17% of the patients with prodrome. The duration of prodrome was less than 1 hour in 45.1%, 1‐2 hours in 13.6%, 2‐4 hours in 15.0%, 4‐12 hours in 13.1%, and greater than 12 hours in 13.2%. IHS 1.1‐1.7 patients showed similar findings.

IHS 1.1‐1.6 patients with prodrome differed from patients without prodrome in having more triggers as a whole (P < .01), more individual triggers including alcohol (P < .01), hormones (P < .01), light (P < .001), not eating (P < .05), perfume (P < .01), stress (P < .01), and weather changes (P < .05), a longer duration of aura (P < .05), longer time between aura and headache (P < .05), more aura with no headache (P < .05), longer time to peak of headache (P < .05), longer time to respond to triptan (P < .05), longer maximum duration of headache (P < .05), and more headache associated nausea (P < .05), more headache associated running of the nose or tearing of the eyes (P < .05), more postdrome syndrome (P < .05), and longer duration of postdrome syndrome (P < .001).

Conclusions.—This study provides a portrait of prodrome in a large cohort of patients. It highlights differences between patients with prodrome and patients not having prodrome, and it draws attention to the potential of preventing the headache phase of the acute migraine attack.
Quantifying Headache Symptoms and Other Headache Features From Chart Notes
Authors: Hasse Lora A. , Ritchey P. Neal , Smith Robert
Published: September 2004

Objectives.—To describe a method for quantifying headache symptoms/features in family practice charts for patients diagnosed with headache NOS (not otherwise specified, ICD‐9: 784) and to determine the share of NOS headache diagnoses with clinical data strongly suggestive of migraine or probable migraine headache.

Background.—Headache is one of the most common pain symptoms that brings patients to a family physician. However, the majority of headache sufferers do not receive a specific headache diagnosis when they visit physicians.

Methods.—We examined the chart notes of 454 patients exclusively diagnosed with one or more ICD‐9 coded headache NOS diagnoses from July 1, 1995 through December 31, 1999 at a large suburban, university‐affiliated practice. We developed a template containing 20 headache items combining International Headache Society diagnostic criteria and additional headache symptoms/features, and decision rules for coding symptoms/features and collected data from patient charts. We then developed decision rules and reclassified NOS headaches into categories strongly suggestive of migraine, probable migraine headache, or other diagnosis. Our main outcome measure is the consistency in the application of decision rules and diagnostic criteria.

Results.—With this method we estimate 3 in 10 (29%) headache NOS patients may have had migraine (8%) or probable migraine headache (21%). Reclassified migraine visits averaged 6.5 migraine symptoms and reclassified probable migraine headache visits 4.7 migraine symptoms. Logistic regression analysis supports the consistency of diagnostic criteria for classifying headache based on coded symptoms/features—our model correctly predicted 96% of visits. Evidence of physical examination was recorded at 75% of visits suggesting that physician attention is focused on elimination of secondary headache.

Conclusions.—We think the use of our rigorous procedures reveals that a substantial amount of migraine and probable migraine headache may be missed in everyday practice. We hope our findings will provide a basis for the development of diagnostic methods more closely suited to the needs of nonspecialists, and contribute to a better standard of care for headache patients seen in primary care practice. Finally, we are hopeful that other researchers will consider using our template and guideline procedures in their efforts to identify diagnostic patterns and study headache and other health problems.