bluuebunny/crossref_metadata_2025_split huggingface dataset:
Excitation‐induced force recovery in potassium‐inhibited rat soleus muscle
Authors: Nielsen Ole Bækgaard , Hilsted Linda , Clausen Torben 
Published: September 2004

Excitation markedly stimulates the Na+‐K+ pump in skeletal muscle. The effect of this stimulation on contractility was examined in rat soleus muscles exposed to high extracellular K+ concentration ([K+]o).
At a [K+]o of 10 mm, tetanic force declined to 58 % of the force in standard buffer with 5.9 mm K+. Subsequent direct stimulation of the muscle at 1 min intervals with 30 Hz pulse trains of 2 s duration induced a 97 % recovery of force within 14 min. Force recovery could also be elicited by stimulation via the nerve. In muscles exposed to 12.5 mm K+, 30 Hz pulse trains of 2 s duration at 1 min intervals induced a recovery of force from 16 ± 2 to 62 ± 4 % of the initial control force at a [K+]o of 5.9 mm.
The recovery of force was associated with a decrease in intracellular Na+ and was blocked by ouabain. This indicates that the force recovery was secondary to activation of the Na+‐K+ pump.
Excitation stimulates the release of calcitonin gene‐related peptide (CGRP) from nerves in the muscle. Since CGRP stimulates the Na+‐K+ pump, this may contribute to the excitation‐induced force recovery. Indeed, reducing CGRP content by capsaicin pre‐treatment or prior denervation prevented both the excitation‐induced force recovery and the drop in intracellular Na+.
The data suggest that activation of the Na+‐K+ pump in contracting muscles counterbalances the depressing effect of reductions in the chemical gradients for Na+ and K+ on excitability.
The characterization of butyrate transport across pig and human colonic luminal membrane
Authors: Ritzhaupt Armin , Ellis Antony , Hosie Ken B. , Shirazi‐Beechey Soraya P. 
Published: September 2004

Luminal membrane vesicles (LMV) were isolated from human and pig colonic tissues. They were characterized in terms of purity and ability to transport [14C]butyrate.
The activity of cysteine‐sensitive alkaline phosphatase, and the abundance of villin, NHE2 and NHE3 proteins, markers of the colonic luminal membrane, were significantly enriched in the LMV compared with the original cellular homogenate. The LMV were free from contamination by other cellular organelles and basolateral membranes, as revealed by the negligible presence of either specific marker enzyme activity or characteristic immunogenic protein.
The transport of butyrate into the luminal membrane vesicles was enhanced 5‐fold at pH 5.5 compared with pH 8.0. Butyrate transport was temperature dependent, and was stimulated in the presence of an outward‐directed anion gradient in the order of butyrate > bicarbonate > propionate > chloride. Kinetic analysis of increasing substrate concentration showed saturation kinetics with an apparent Km value of 14.8 ± 3.6 mM and a Vmax of 54 ± 14 nmol min−1 (mg protein)−1.
Butyrate transport was significantly reduced in the presence of short chain fatty acids (SCFA), acetate, propionate and other monocarboxylates (pyruvate and L‐lactate). Butyrate uptake was inhibited by several cysteine group modifying reagents such as p‐chloromercuribenzosulphonic acid (pCMBS), p‐chloromercuribenzoate (pCMB), mersalyl acid and HgCl2, but not by the stilbene anion exchange inhibitors, 4,4′‐diisothiocyanostilbene‐2,2′‐disulphonate (DIDS) and 4,4′‐dinitrostilbene‐2,2′‐disulphonate (SITS).
The described properties of butyrate transport across the luminal pole of the colon suggest the involvement of a carrier protein, in the form of a pH‐activated anion exchange process. The transporter is distinct from the erythrocyte band‐3 type anion exchanger and may belong to the monocarboxylate‐type transport proteins (MCT1).
Modulation of transient outward current by extracellular protons and Cd2+ in rat and human ventricular myocytes
Authors: Stengl Milan , Carmeliet Edward , Mubagwa Kanigula , Flameng Willem 
Published: September 2004

The effects of extracellular acidosis and Cd2+ on the transient outward current (Ito) have been investigated in rat and human ventricular myocytes, using the whole‐cell patch‐clamp technique.
In rat myocytes, exposure to acidic extracellular solution (pH 6.0) shifted both steady‐state activation and inactivation curves to more positive potentials, by 20.5 ± 2.7 mV (mean ± s.e.m.; n= 4) and 19.8 ± 1.2 mV, respectively. Cd2+ also shifted the activation and inactivation curves in a positive direction in a concentration‐dependent manner.
In human myocytes, the steady‐state activation and inactivation curves were located at more positive potentials. The effect of Cd2+ was similar, but acidosis had less effect than in rat myocytes (e.g. pH 6.0 shifted activation by only 7.2 ± 2.2 mV and inactivation by 13.7 ± 0.5 mV; n= 4).
In both species, the effect of acidosis decreased with increasing concentrations of Cd2+ and vice versa, suggesting competition between H+ and Cd2+ for a common binding site.
The data indicate that acidosis and divalent cations influence Ito via a similar mechanism and act competitively in both rat and human myocytes, but that human cells are less sensitive to the effects of acidosis.
Intracellular recording from myenteric neurons of the guinea‐pig ileum that respond to stretch
Authors: Kunze W. A. A. , Furness J. B. , Bertrand P. P. , Bornstein J. C. 
Published: September 2004

Isolated longitudinal muscle‐myenteric plexus preparations from guinea‐pig ileum were used to investigate the activity of myenteric neurons when the tissue was stretched in the circumferential direction. Membrane potentials were recorded via flexibly mounted intracellular recording electrodes containing Neurobiotin in 1 M KCl. The preparations were stretched to constant widths (+20 % and +40 % beyond slack width).
Multipolar neurons (Dogiel type II morphology) discharged spontaneous action potentials and proximal process potentials during maintained stretching, three of twenty‐one at +20 % stretch and seven of nine at +40 % stretch. At the maximum extent of stretch tried, +40 % beyond slack tissue width, action potentials in Dogiel type II neurons occurred at 10‐33 Hz. Neurons with other morphologies were all uniaxonal. Some displayed spontaneous fast EPSPs or action potentials, three of forty‐one at +20 % stretch and seven of nineteen at +40 % stretch.
In seven of eight Dogiel type II neurons, action potentials or proximal process potentials persisted when membrane hyperpolarization was imposed via the recording electrode. Action potential discharge was abolished by hyperpolarization in seven of nine uniaxonal neurons; the exceptions were two orally projecting neurons.
Dogiel type II and uniaxonal neurons were classified as rapidly accommodating if they discharged action potentials only at the beginning of a 500 ms intracellular depolarizing pulse and slowly accommodating if they discharged for more than 250 ms. For Dogiel type II neurons, three of thirteen were slowly accommodating at +20 % stretch and two of four at 40 % stretch. For uniaxonal neurons the corresponding data were twelve of twenty‐six and fifteen of nineteen neurons. The slowly accommodating state was associated with increased cell input resistance in uniaxonal neurons.
The spontaneous action potential discharge in Dogiel type II and uniaxonal neurons ceased when the muscle was relaxed pharmacologically by nicardipine (3 μM) or isoprenaline (1 μM), although the applied stretch was maintained. At the same time, evoked spike discharge became rapidly accommodating
We conclude that many Dogiel type II neurons, and possibly some orally projecting uniaxonal neurons, are intrinsic, stretch‐sensitive, primary afferent neurons that respond to muscle tension with sustained action potential discharge.
Characterization of sensory and corticothalamic excitatory inputs to rat thalamocortical neurones in vitro
Authors: Turner J. P. , Salt T. E. 
Published: September 2004

Using an in vitro slice preparation of the rat dorsal lateral geniculate nucleus (dLGN), the properties of retinogeniculate and corticothalamic inputs to thalamocortical (TC) neurones were examined in the absence of GABAergic inhibition.
The retinogeniculate EPSP evoked at low frequency (<= 0.1 Hz) consisted of one or two fast‐rising (0.8 ± 0.1 ms), large‐amplitude (10.3 ± 1.6 mV) unitary events, while the corticothalamic EPSP had a graded relationship with stimulus intensity, owing to its slower‐rising (2.9 ± 0.4 ms), smaller‐amplitude (1.3 ± 0.3 mV) estimated unitary components.
The retinogeniculate EPSP exhibited a paired‐pulse depression of 60.3 ± 5.6 % at 10 Hz, while the corticothalamic EPSP exhibited a paired‐pulse facilitation of > 150 %. This frequency‐dependent depression of the retinogeniculate EPSP was maximal after the second stimulus, while the frequency‐dependent facilitation of the corticothalamic EPSP was maximal after the fourth or fifth stimulus, at interstimulus frequencies of 1‐10 Hz.
There was a short‐term enhancement of the <= 0.1 Hz corticothalamic EPSP (64.6 ± 9.2 %), but not the retinogeniculate EPSP, following trains of stimuli at 50 Hz.
The <= 0.1 Hz corticothalamic EPSP was markedly depressed by the non‐NMDA antagonist 1‐(4‐amino‐phenyl)‐4‐methyl‐7,8‐methylene‐dioxy‐5H‐2,3‐benzodiazepine (GYKI 52466), but only modestly by the NMDA antagonist 3‐((RS)‐2‐carboxypiperazin‐4‐yl)‐propyl‐1‐phosphonic acid ((RS)‐CPP), and completely blocked by the co‐application of GYKI 52466, 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX), (RS)‐CPP and (5R,10S)‐(+)‐5‐methyl‐10,11‐dihydro‐5H‐dibenzo[a,d]cyclohepten‐5,10‐imine (MK‐801). Likewise, the corticothalamic responses to trains of stimuli (1‐500 Hz) were greatly reduced by this combination of ionotropic glutamate receptor antagonists.
In the presence of GYKI 52466, CNQX, (RS)‐CPP and MK‐801, residual corticothalamic responses and slow EPSPs, with a time to peak of 2‐10 s, could be generated following trains of five to fifty stimuli. Neither of these responses were occluded by 1S,3R‐1‐aminocyclopentane‐1,3‐dicarboxylic acid (1S,3R‐ACPD), suggesting they are not mediated via group I and II metabotropic glutamate receptors.
The contribution of pH‐dependent mechanisms to fatigue at different intensities in mammalian single muscle fibres
Authors: Chin E. R. , Allen D. G. 
Published: September 2004

The contribution of intracellular pH (pHi) to the failure of Ca2+ release and inhibition of contractile proteins observed during fatigue was assessed in single intact mouse muscle fibres at 22 °C. Fatigue was induced by repeated tetani at intensities designed to induce different levels of intracellular acidosis. Force and either intracellular free Ca2+ concentration ([Ca2+]i; measured using indo‐1) or pHi (measured using SNARF‐1) were recorded in fibres fatigued at two different intensities.
Intensity was varied by the repetition rate of tetani and quantified by the duty cycle (the fraction of time when the muscle was tetanized). Stimulation at the low intensity (duty cycle ∼0.1) reduced force to 30 % of initial values in 206 ± 21 s (60 ± 7 tetani); at the high intensity (duty cycle ∼0.3) force was reduced to 30 % in 42 ± 7 s (43 ± 7 tetani) (P < 0.05; n= 14).
When force was reduced to 30 % of initial values, tetanic [Ca2+]i had fallen from 648 ± 87 to 336 ± 64 nm (48 % decrease) at the low intensity but had only fallen from 722 ± 84 to 468 ± 60 nm (35 % decrease) at the higher intensity (P < 0.05 low vs. high intensity; n= 7).
Fatigue resulted in reductions in Ca2+ sensitivity of the contractile proteins which were greater at the high intensity (pre‐fatigue [Ca2+]i required for 50 % of maximum force (Ca50) = 354 ± 23 nm; post‐fatigue Ca50= 421 ± 48 nm and 524 ± 43 nm for low and high intensities, respectively). Reductions in maximum Ca2+‐activated force (Fmax) were similar at the two intensities (pre‐fatigue Fmax= 328 ± 22 μN; post‐fatigue Fmax= 271 ± 20 and 265 ± 19 μN for low and high intensities, respectively).
Resting pHi was 7.15 ± 0.05. During fatigue at the low intensity, pHi was reduced by 0.12 ± 0.02 pH units and at the high intensity pHi was reduced by 0.34 ± 0.07 pH units (P < 0.05; n= 5).
Our results indicate that the more rapid fall in force at a high intensity is due to a reduction in Ca2+ sensitivity of the contractile proteins, probably related to the greater acidosis. Our data also indicate that the failure of Ca2+ release and reduced maximum Ca2+‐activated force observed during fatigue are not due to reductions in intracellular pH.
Apamin‐ and nitric oxide‐sensitive biphasic non‐adrenergic non‐cholinergic inhibitory junction potentials in the rat anococcygeus muscle
Authors: Selemidis S. , Ziogas J. , Cocks T. M. 
Published: September 2004

Changes in membrane potential following electrical field stimulation (EFS; 1, 2 and 5 pulses at 5 Hz, 0.5 ms duration, 60–80 V) of non‐adrenergic non‐cholinergic (NANC) inhibitory nerves in the rat isolated anococcygeus muscle were measured using standard intracellular recording techniques. Resting membrane potential ranged between −60 and −70 mV.
In the presence of guanethidine (30 μm), atropine (1 μm), propranolol (1 μm) and phentolamine (0.05 μm) to establish NANC conditions, the membrane potential depolarized to between −40 and −50 mV. Under these conditions, EFS caused pulse‐dependent, tetrodotoxin (1 μm)‐sensitive biphasic inhibitory junction potentials (IJPs) comprising a fast onset and time‐to‐peak phase followed by a second, slower phase that delayed repolarization. The duration of NANC IJPs ranged between 10 and 20 s.
Inhibition of small‐conductance Ca2+‐activated K+ channels with apamin (0.1 μm) selectively blocked the first fast phase of the NANC IJP, whereas inhibitors of large‐conductance Ca2+‐activated K+ channels (charybdotoxin and iberiotoxin) and ATP‐sensitive K+ channels (glibenclamide) all had no effect on NANC IJPs.
Both the nitric oxide synthase inhibitor NG‐nitro‐L‐arginine (l‐NOARG; 100 μm) and the inhibitor of soluble guanylate cyclase 1‐H‐oxodiazol‐[1,2,4]‐[4,3‐a] quinoxaline‐1‐one (ODQ; 10 μm) had no effect on the first fast phase of the NANC IJP. Each treatment, however, markedly inhibited the slow phase with the duration of the IJP reduced to between 1 and 3 s. The l‐NOARG‐resistant fast phase of the NANC IJP was almost abolished by the subsequent addition of apamin (0.1 μm).
In conclusion, the present study demonstrates unequivocal NANC nerve‐mediated biphasic IJPs in the rat isolated anococcygeus. We propose that nitric oxide (NO), via activation of cGMP‐dependent K+ channels, and a non‐NO inhibitory factor which activates apamin‐sensitive K+ channels contribute to NANC nerve‐evoked IJPs in the rat anococcygeus.
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.