bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical properties of resting and acetylcholine‐stimulated endothelium in intact rat aorta.
Authors: Marchenko S M , Sage S O
Published: December 2014

1. The passive electrical properties and the effects of acetylcholine on the membrane potential of the endothelium of intact rat aorta were investigated using the whole cell mode of the patch clamp technique. 2. Unstimulated endothelium had a membrane potential of ‐58 +/‐ 8 mV (S.E.M., n = 193; range ‐47 to ‐76 mV). The input resistance was 43 +/‐ 13 M omega (S.E.M., n = 8; range 26‐64 M omega). KCl and BaCl2, but not tetraethylammonium (2 mM), 4‐aminopyridine (5 mM) or 4,4'‐diisothiocyanatostilbene‐2,2'‐disulphonic acid (DIDS; 100 microM) depolarized the endothelium. 3. Acetylcholine (0.2‐4 microM) evoked in most preparations a biphasic response with a transient hyperpolarization to a value close to the K+ reversal potential, followed by depolarization beyond the resting potential. In 46% of recordings, the depolarization was followed by oscillations in membrane potential. The duration of the hyperpolarization and magnitude of the depolarization was similar in all recordings from a given aorta, but varied greatly between different preparations. 4. Hyperpolarization of the endothelium below the K+ reversal potential reversed the direction of the first phase of the acetylcholine‐evoked response, which was unaffected by tetraethylammonium, 4‐aminopyridine, or DIDS. 5. The removal of extracellular Ca2+ evoked a depolarization of the endothelium from ‐61 +/‐ 3 to ‐34 +/‐ 3 mV (S.E.M., n = 9) over 2‐15 min. Restoration of external Ca2+ evoked a transient hyperpolarization. 6. ACh applied in nominally Ca(2+)‐free medium shortly after Ca2+ removal evoked only a transient hyperpolarization. After the establishment of a stable membrane potential in Ca(2+)‐free medium, acetylcholine was without effect. 7. NiCl2 (2 mM) evoked a small depolarization of the endothelium (6 +/‐ 2 mV; S.E.M., n = 7). The subsequent removal of Ni2+ evoked a transient hyperpolarization. 8. In the presence of Ni2+, acetylcholine evoked a short‐lived hyperpolarization. Both the application of Ni2+ and the removal of extracellular Ca2+ immediately blocked oscillations in membrane potential evoked by acetylcholine. 9. The blockers of voltage‐operated Ca2+ channels, nifedipine (1‐10 microM) and verapamil (20 microM) were without effect on the biphasic acetylcholine‐evoked responses. 10. In preparations in which acetylcholine evoked large (20‐45 mV) oscillations in membrane potential, depolarization of the endothelium alone, by current injection or application of KCl, did not evoke oscillations. 11. The activator of protein kinase C, phorbol 12, 13‐dibutyrate (200 nM) depolarized and greatly increased the input resistance of the endothelium, presumably due to an effect on gap junctions.(ABSTRACT TRUNCATED AT 400 WORDS)
Endothelial control of the pulmonary circulation in normal and chronically hypoxic rats.
Authors: Barer G , Emery C , Stewart A , Bee D , Howard P
Published: December 2014

1. The effect of blockade of nitric oxide synthesis in pulmonary endothelium by two L‐arginine analogues was tested in isolated blood‐perfused lungs of normal rats and rats exposed chronically to 10% O2. 2. In both groups of rats the analogues (N‐monomethyl‐L‐arginine (L‐NMMA) and N‐nitro‐L‐arginine methyl ester (L‐NAME)) enhanced hypoxic vasoconstriction. In normal rats, with rare exceptions, these analogues had little or no effect on pulmonary artery pressure (Ppa) at constant blood flow during normoxia. However, chronically hypoxic rats have pulmonary hypertension and in these rats the analogues always raised Ppa; the rise in Ppa after L‐NMMA but not L‐NAME could be partially reversed by L‐arginine. L‐NAME was more potent than L‐NMMA. 3. To see whether the difference between rat groups was due to the high Ppa in chronically hypoxic rats, in control rats we raised Ppa passively by lung inflation to values higher than found in chronically hypoxic rats. L‐NAME did not alter the effects of lung inflation on Ppa. 4. Ppa was also raised passively by plotting pressure‐flow lines up to high flow rates; the lines were changed minimally by both analogues in control rats but in chronically hypoxic rats the lines were raised to higher pressures and steepened substantially. 5. In control rats, during vasoconstriction caused by hypoxia, endothelin 1 and almitrine, L‐NAME caused further rises in pressure. We conclude that a stimulus for nitric oxide release in control rats is the narrowing of vessels caused by vasoconstriction rather than passive increases in intravascular pressure. 6. In chronically hypoxic rats arterioles are narrowed by growth of new muscle and there is some muscle tone even in normoxia. Thus narrowing of the vascular lumen is the stimulus common to both groups of rats which leads to nitric oxide synthesis and attenuation of Ppa by a negative feedback process. Narrowing is associated with a large increase in shear stress due to two factors; the pressure drop along a vessel segment is increased and the surface area of the lining of the affected segment is decreased. 7. Atrial natriuretic peptide caused dose‐dependent pulmonary vasodilation in both rat groups but had a greater effect in chronically hypoxic rats. The action persisted and was enhanced after blockade of NO synthesis.
Permeability of the fetal villous microvasculature in the isolated perfused term human placenta.
Authors: Eaton B M , Leach L , Firth J A
Published: December 2014

1. Capillary permeability‐surface area (PS) products for the low molecular weight radioactive tracers, 22Na, 51Cr‐EDTA (relative molecular mass 357) and 57Co‐cyanocobalamin (relative molecular mass 1353) were measured in the fetal circulation of isolated dually perfused lobules of normal term human placentae using the single circulation, multiple‐tracer dilution technique. 2. In lobules perfused with M199 medium, containing dextran and 5 g l‐1 bovine albumin, the extractions of all three tracers decreased as the flow was increased over the range of 2‐8 ml min‐1, and PS products for 51Cr‐EDTA and 57Co‐cyanocobalamin, but not for 22Na, reached constant values at flows above 0.1 ml min‐1 g‐1. 3. Flow‐independent PS products in the presence of albumin were 0.025 +/‐ 0.002 ml min‐1 g‐1 (mean +/‐ S.E.M., n = 25) for 57Co‐cyanocobalamin and 0.057 +/‐ 0.003 ml min‐1 g‐1 (n = 25) for 51Cr‐EDTA. The ratio of PS values (51Cr‐EDTA/57Co‐cyanocobalamin) was 2.28, while the ratio of the corresponding free diffusion coefficients was 1.79, indicating substantial restriction to the diffusion of the 57Co‐cyanocobalamin. 4. In another series of lobules perfused in the absence of albumin, extraction values for all three test tracers were constant over the same flow range. Values at high flow rates were therefore about twice those measured in the presence of albumin, and PS products for all three tracers failed to reach diffusion‐limited values. 6. Lobules perfused with and without albumin were fixed using a glutaraldehyde fixative containing 1% Alcian Blue dye. An ultrastructural examination of the endothelium showed no significant changes in cell or cleft morphology, or in the glycocalyx, in the absence of albumin which might account for the observed permeability change. 7. These data are the first physiological measurements specifically characterizing fetal microvascular permeability in the human placenta. The results suggest that permeability resembles that found in skeletal muscle and, as such, the endothelium presents a significant barrier to the diffusion of large solutes. The observed ‘protein effect’ indicates that albumin can interact with elements of the solute pathway to increase its restrictiveness.
ATP‐regulated K+ channels are modulated by intracellular H+ in guinea‐pig ventricular cells.
Authors: Koyano T , Kakei M , Nakashima H , Yoshinaga M , Matsuoka T , Tanaka H
Published: December 2014

1. The ATP‐regulated potassium channel (K+ATP) was investigated with respect to modulation by intracellular pH (pHi) by using the inside‐out membrane patch clamp technique in ventricular cells isolated from the heart of the guinea‐pig. Channels which had been closed by internal ATP (0.3‐3 mM) were dose‐dependently activated by decreasing the pHi over the range of pH 7.6‐6.0. However, the channel was conversely inhibited when the pHi was further decreased below 6.0. Inwardly rectifying K+ channels were also decreased in activity when pHi fell from 7.2 to 6.0. 2. The channel activation was also observed with constant concentration of free Ca2+ (1 nM) and Mg2+ (1 mM) in the bathing solution, suggesting that a change in divalent cation concentration is not involved in channel modulation by pHi. 3. When the dose‐response relations of the channel activity for ATP concentrations at different pHi were examined, the channel activity obtained at 1 microM ATP was increased by decreasing pH from 7.2 to 6.4. The half‐maximal inhibition for ATP concentration at pH 7.2 and 6.4 was 20 and 40 microM, respectively, and the Hill coefficient was 2.5 in both curves. 4. In the absence of ATP, internal H+ was able to reactivate run‐down channels but it had less effect on the channel as long as the activity was maintained at a higher level. The increase in the channel activity by H+ was facilitated with a proceeding of the run‐down. However, after the channel was completely inactivated by a long exposure of the membrane patch to ATP‐free solution, a reduction of pH could not activate the channel. 5. The decrease of pH from 7.2 to 6.4 reduced single channel conductance from 89.0 to 77.7 pS in the absence of Mg2+, whereas it reduced the conductance only at the negative membrane potentials in the presence of 2 mM Mg2+. 6. Mean open and closed times within the burst‐like openings of the channel remained unaffected during the change in pHi. 7. We conclude that the cardiac K+ATP channel is modulated by a change in the intracellular pH. The channel modulation consisted of the increase in the channel activity and a decrease in the permeability. The former effect was due to the decrease in the sensitivity of the channel to ATP and the reactivation of the channel which is during the process of run‐down in activity.
Regulation of the intracellular free calcium concentration in acutely dissociated neurones from rat nucleus basalis.
Authors: Tatsumi H , Katayama Y
Published: December 2014

1. Neurones were acutely dissociated from the rat nucleus basalis. Whole‐cell patch clamp recordings of calcium currents (ICa) and fura‐2 microfluorimetric recordings of intracellular free Ca2+ concentration ([Ca2+]i) were made simultaneously. 2. Depolarization from ‐60 to 0 mV elicited ICa and a gradual increase in [Ca2+]i. After repolarization, ICa terminated in 0.7 ms, and [Ca2+]i recovered to control exponentially (1‐5 s). 3. Both ICa and the transient [Ca2+]i increase in response to step depolarizations, were abolished in Ca2+ free extracellular solution and in Cd(2+)‐containing solution. 4. Depolarizations from ‐90 mV to membrane potentials less negative than ‐40 mV induced ICa and an increase in [Ca2+]i. Depolarization to 0 mV elicited the maximum ICa, and produced the largest increase in [Ca2+]i. There was a parallel relationship between the [Ca2+]i increase and the magnitude of the ICa. 5. The [Ca2+]i increase was associated with an increase in total Ca2+ influx when the duration of the step depolarization was varied. The relationship between the total Ca2+ influx and the peak of [Ca2+]i transient reached an asymptote as total Ca2+ influx exceeded 200 pC. A similar finding was made when more than thirty action potentials were used in increasing [Ca2+]i. 6. The process of the [Ca2+]i recovery was slowed down by lowering the temperature, by an intracellular dialysis with vanadate, by extracellular application of a mitochondrial inhibitor, carbonyl cyanide m‐chlorophenyl‐hydrazone (CCCP), and by Na(+)‐free external solution. It was unaffected by membrane potential (‐50 to ‐130 mV). 7. When pipette solution contained a high concentration of fura‐2 (200 microM), the [Ca2+]i increase per 1 pC of Ca2+ influx decreased, and the [Ca2+]i recovery was slowed. 8. The results indicate that the ICa through voltage‐dependent Ca2+ channels elevates [Ca2+]i. The neurones possess a large capacity for Ca2+ buffering, and the recovery of [Ca2+]i requires both the Ca2+ pump and membrane Na(+)‐Ca2+ exchange.
Mechanical factors in the initiation of eccentric contraction‐induced injury in rat soleus muscle.
Authors: Warren G L , Hayes D A , Lowe D A , Armstrong R B
Published: December 2014

1. Mechanical factor(s) associated with the initiation of eccentric contraction‐induced muscle injury were investigated in isolated rat soleus muscles (n = 180; 42 protocols with 4‐6 muscles per protocol). Five eccentric contractions were performed with 4 min between contractions. Three levels of peak eccentric contraction force (100, 125 and 150% of pre‐injury maximal isometric tetanic tension, P0), length change (0.1, 0.2 and 0.3 muscle length, L0) and lengthening velocity (0.5, 1.0 and 1.5 L0/s) were utilized. Force was varied with stimulation frequency (10‐150 Hz). The eccentric contractions were initiated at muscle lengths of 0.85 or 0.90 L0. Following the fifth eccentric contraction, the muscle was incubated in Krebs‐Ringer buffer for 60 min. Peak isometric twitch tension (PT), P0, maximal rate of tension development (+ dP/dt), maximal rate of relaxation (‐dP/dt), and creatine kinase (CK) release were measured prior to the five eccentric contractions and at 15 min intervals during the incubation period. Total muscle [Ca2+] was measured after 60 min incubation. 2. The mean (+/‐ S.E.M.) initial decline in P0 for the muscles performing the most injurious protocol was 13.6 +/‐ 4.8% (n = 6); P0 in control muscles immediately following performance of five isometric contractions was elevated 1.2 +/‐ 1.0% (n = 8). These means were different at probability, p = 0.005. Mean [ATP] in muscles immediately following the isometric control and most injurious protocols, respectively, were 16.30 +/‐ 1.49 and 19.84 +/‐ 1.38 mumol/g dry wt (p = 0.229). 3. Decrements in P0, PT, +dP/dt, and ‐dP/dt immediately after the injury protocol were related most closely to the peak forces produced during the eccentric contractions; greater initial declines in P0, +dP/dt and ‐dP/dt were also observed at higher lengthening velocities independent of peak force. Slow declines in P0 and ‐dP/dt during the 60 min incubation following the injury protocol were greatest for muscles performing contractions at the longer initial length. CK release was independent of all mechanical factors with the exception of lengthening velocity. CK activity at 45 and 60 min into the incubation period was greater for muscles lengthened at the highest velocity used (1.5 L0/s). Mean total muscle [Ca2+] for muscles performing the eccentric contractions was elevated by 38% over isometric control muscles but the elevation was unrelated to any of the four mechanical factors. 4. These data support the hypothesis that eccentric contraction‐induced injury is initiated by mechanical factors, with muscle tension playing the dominant role.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of repeated tetanic stimulation on excitation‐contraction coupling in cut muscle fibres of the frog.
Authors: Györke S
Published: December 2014

1. The effects of prolonged intermittent fatiguing stimulation were studied on various steps of excitation‐contraction (E‐C) coupling in cut single frog muscle fibres using the triple Vaseline voltage clamp and the fluorescent Ca2+ indicator rhod‐2. 2. There were two phases of changes in amplitude of Ca2+ transients during fatiguing stimulation: first a 5‐10% increase, then a larger decrease. The decrease in amplitude of Ca2+ transients was accompanied by a slowing down of the rate of decay of the transients and by an increase in resting [Ca2+]. 3. A complete recovery of both amplitude and time course of Ca2+ transients as well as of the resting [Ca2+] occurred within 1‐3 min after cessation of fatiguing stimulation. 4. The changes in Ca2+ release signals during fatiguing stimulation were accompanied by decreases in the amplitude and the rate of decay of the action potentials as well as by a decrease in resting potential. However, these alterations are not likely to contribute to fatigue significantly, since fibres stimulated under voltage‐clamp conditions, when the T‐tubule voltage sensor is activated directly by applied voltage steps, showed similar fatiguability to fibres stimulated by action potentials under current‐clamp conditions. 5. Simultaneous measurements of intramembrane charge movement and [Ca2+] revealed that the decrease in sarcoplasmic reticulum (SR) Ca2+ release during fatiguing stimulation is not accompanied by any significant change in charge movement. 6. These results suggest that fatigue caused by repeated tetanic stimulation develops primarily at the level of SR Ca2+ release with only small possible additional effects at the level of membrane excitability and action potential propagation along the surface/T‐tubule membrane. The T‐tubule voltage sensor with this type of stimulation is virtually fatigue resistant.
Intracellular sodium activity and its regulation in guinea‐pig atrial myocardium.
Authors: Wang G X , Schmied R , Ebner F , Korth M
Published: December 2014

1. Intracellular Na+ activity (aNai) and membrane resting potential were studied in quiescent guinea‐pig atrial and papillary muscles by means of Na(+)‐sensitive and conventional microelectrodes. The effects of the cardioactive steroid dihydroouabain (DHO) on aiNa, force of contraction and sarcolemmal Na+, K(+)‐ATPase activity were also investigated. 2. In thirty atria and twenty‐two papillary muscles, aNai amounted to 8.0 +/‐ 0.2 and 4.7 +/‐ 0.3 mM, respectively (mean +/‐ S.E.M.). When both tissues were from the same animal, with the same ion‐sensitive microelectrode mean aNai values of 7.9 +/‐ 0.2 and 5.1 +/‐ 0.5 mM (P < 0.01) were obtained from eight atrial and eight papillary muscles, respectively. 3. Membrane resting potentials (Em) were significantly (P < 0.001) more negative in the papillary muscles (‐83.5 +/‐ 0.7 mV; n = 8) than in the atrium (‐78.1 +/‐ 0.5 mV; n = 8). Deviation of Em from EK (determined by K(+)‐sensitive microelectrodes) was 3.0 +/‐ 0.2 mV in ventricular (P < 0.05) and 6.1 +/‐ 0.3 mV in atrial preparations (P < 0.05). 4. Inhibition of the Na+ pump by DHO increased aNai of the atrium within 10 min by 0.6 +/‐ 0.1 (n = 7), 1.3 +/‐ 0.1 (n = 5) and 3.2 +/‐ 0.2 mM (n = 5) at 5, 10 and 30 microM, respectively. In the papillary muscle, 10 microM DHO was without effect while aNai rose by 1.0 +/‐ 0.1 (n = 5) and 2.9 +/‐ 0.2 mM (n = 6) at 30 and 120 microM DHO. 5. Consistent with the aNai measurements, the potency of DHO to increase force of the isometric contraction was three times higher in atrium than in papillary muscle (stimulation frequency 0.2 Hz). 6. Hydrolytic activity of sarcolemmal Na+,K(+)‐ATPase isolated from atria amounted to only one third of that detected in ventricles (0.07 +/‐ 0.01, n = 6, versus 0.2 +/‐ 0.01 mumol phosphate released min‐1 (g tissue)‐1, n = 5). The inhibitory potencies of DHO on sarcolemmal Na+,K(+)‐ATPase preparations were found to be identical in the enzymes from either tissue. 7. It is concluded that a lower Na+ pump density is responsible for the higher aNai and for the lower resting membrane potential in atrial as compared to ventricular cells. The regulation of cellular Na+ homeostasis in atrial muscle appears to be closer to the limits of its capacity than in ventricle, explaining the higher sensitivity of the atrium to interventions which impede Na+ pump activity.
Innervation of the cat lip by two groups of parasympathetic vasodilator fibres.
Authors: Izumi H , Karita K
Published: December 2014

1. Electrical stimulation of the peripheral cut ends of the chorda tympani nerve proper (CTNP) and the chorda‐lingual nerve (CLN) elicited a blood flow increase in the ipsilateral lower lip, tongue and submandibular gland in a stimulus intensity‐dependent manner in anaesthetized cats. 2. Pretreatment with hexamethonium (1.0 mg kg‐1, i.v.), an autonomic ganglionic blocker, significantly reduced the CTNP‐induced blood flow increases in all of the above three sites as well as the CLN‐induced blood flow in the lower lip, but it had no effects on the CLN‐induced blood flow increases in the tongue and submandibular gland. 3. The CTNP stimulation‐induced lower lip blood flow was not influenced by sectioning the lingual nerve proper, but it was abolished by section of either the CLN or the inferior alveolar nerve (IAN) in the mandibular canal. 4. The lip blood flow increases elicited reflexly by electrical stimulation of the upper gingiva, the central cut ends of the mylohyoid nerve and CLN were not affected by cutting of the CTNP, but were markedly reduced by pretreatment with hexamethonium and abolished by the section of the inferior alveolar nerve just distal to the mylohyoid nerve. These observations imply that the parasympathetic vasodilator fibres involved in trigeminally induced reflex vasodilatation responses do not travel with the CTNP. 5. These results suggest that there is a dual innervation of the cat lower lip by two groups of parasympathetic vasodilator fibres; in one case fibres originating from the facial nerve root are distributed to the lower lip via the CTNP, CLN and IAN and in the other fibres emanating from the glossopharyngeal nerve root project to the lower lip via the mandibular nerve and the IAN.
Role of periodontal mechanoreceptors in evoking reflexes in the jaw‐closing muscles of the cat.
Authors: Bonte B , Linden R W , Scott B J , van Steenberghe D
Published: December 2014

1. In anaesthetized cats the left maxillary and mandibular canine and incisor teeth were extracted. Nine weeks later the animals were anaesthetized again and titanium implants were placed into the edentulous ridge of the maxilla and mandible. 2. Terminal experiments were performed between 9 weeks and 10 months after inserting the implants. Recordings were made from the trigeminal ganglia and peripheral nerves of anaesthetized cats. Neurones were identified which responded to forces applied to the maxillary teeth but none was found which responded to forces applied to the implant. 3. The responses of motor units in the temporalis muscle were studied in response to ramp‐plateau forces applied to the maxillary canine tooth and maxillary implant using peristimulus time histograms and cumulative sum (cusum) analysis. A small amount of inhibition of the motor units was observed in response to the applied forces to the implant. However, the inhibition was much more profound when similar forces were applied to the tooth. 4. The results confirm that when forces are applied to a tooth, periodontal mechanoreceptors are stimulated which evoke reflex inhibitions to motor units in the jaw‐closing muscles. However, there is evidence that mechanoreceptors situated distant to the periodontium can also evoke such reflexes. 5. The results are discussed in relation to the overall functional role of periodontal mechanoreceptors in the reflexes of mastication.
Calcium spikes and calcium plateaux evoked by differential polarization in dendrites of turtle motoneurones in vitro.
Authors: Hounsgaard J , Kiehn O
Published: December 2014

1. The ability of dendrites in turtle motoneurones to support calcium spikes and calcium plateaux was investigated using differential polarization by applied electric fields. 2. Electric fields were generated by passing current through transverse slices of the turtle spinal cord between two plate electrodes. The linear extracellular voltage gradient generated by the field implied that the tissue was ohmic and homogeneous. 3. The transmembrane potential at the cell body of motoneurones was measured as the voltage difference between an intracellular and an extracellular microelectrode. 4. In normal medium an applied field induced synaptic activity as well as intrinsic polarization of motoneurones. Synaptic activity was suppressed by tetrodotoxin (TTX, 1 microM). 5. In the presence of TTX and tetraethylammonium (TEA, 1‐5 mM), applied fields evoked multicomponent Ca2+ spikes in both the soma‐hyperpolarizing and soma‐depolarizing direction of the field. The different components of Ca2+ spikes were discrete and additive. High amplitude components had higher threshold and faster time course and were followed by larger after‐hyperpolarizations, than low amplitude components. The frequency of field‐evoked regenerative responses was relatively insensitive to somatic bias current. 6. TTX‐resistant Ca(2+)‐mediated plateau potentials promoted by apamin were evoked by differential polarization in both the soma‐depolarizing and soma‐hyperpolarizing direction. 7. It is concluded that Ca2+ channels responsible for Ca2+ spikes and Ca2+ plateaux are present in dendrites of spinal motoneurones of the turtle.
Excitation failure in eccentric contraction‐induced injury of mouse soleus muscle.
Authors: Warren G L , Lowe D A , Hayes D A , Karwoski C J , Prior B M , Armstrong R B
Published: December 2014

1. Histological evidence suggests that the force deficit associated with eccentric contraction‐induced muscle injury is due to structural damage to contractile elements within the muscle fibre. Alternatively, the force deficit could be explained by an inability to activate the contractile proteins. It was the objective of this study to investigate the latter possibility. 2. Mouse soleus muscles were isolated, placed in an oxygenated Krebs‐Ringer buffer at 37 degrees C, and baseline measurements were made. The muscle then performed one of three contraction protocols: (1) twenty eccentric (n = 10 muscles); (2) ten eccentric (n = 12); or (3) twenty isometric (n = 10) contractions. At the end of the injury protocol, measurements were made during performance of a passive stretch, twitch and tetanus. Next, force was recorded during exposure of the muscle to buffer containing 50 mM caffeine. 3. Decrements in maximal isometric tetanic force (P0) observed for muscles in the twenty eccentric, ten eccentric, and twenty isometric contraction protocols were 42.6 +/‐ 4.2, 20.0 +/‐ 2.3 and 3.9 +/‐ 2.4%, respectively. However, the caffeine‐elicited forces in muscles from the three protocols were not different when corrected for initial differences in P0 (64.9 +/‐ 1.3, 64.2 +/‐ 2.1 and 68.9 +/‐ 2.5% of pre‐injury P0). The peak caffeine‐elicited force was 118.4 +/‐ 8.6% of post‐injury P0 for the muscles in the twenty eccentric contraction protocol, which was significantly different from that observed for the other protocols (71.8‐80.2% post‐injury P0). These findings indicate that the force deficit in this muscle injury model results from a failure of the excitation process at some step prior to calcium (Ca2+) release by the sarcoplasmic reticulum. 4. In an attempt to locate the site of failure, intracellular measurements were made in injured muscles to test whether injury to the sarcolemma might have resulted in a shift of the resting membrane potential of the muscle fibre. However, microelectrode measurements of resting membrane potential for muscles in the twenty eccentric contraction protocol (‐74.4 +/‐ 0.6 mV) were not different from muscles in the twenty isometric contraction protocol (‐73.4 +/‐ 1.0 mV). These data suggest that membrane resting conductances were normal and are compatible with the idea that the ability of the injured fibres to conduct action potentials was probably not impaired.
Ventilatory responses to exercise in humans lacking ventilatory chemosensitivity.
Authors: Shea S A , Andres L P , Shannon D C , Banzett R B
Published: December 2014

1. In healthy humans during aerobic exercise ventilation increases and mean arterial PCO2 usually remains constant over a wide range of CO2 production. 2. Congenital central hypoventilation syndrome (CCHS) is associated with ineffective chemoreceptor regulation of breathing and severe hypoventilation during sleep (requiring mechanical ventilation) reflecting abnormalities in the brainstem respiratory complex or its chemoreceptor input. Such patients can have adequate spontaneous ventilation during resting wakefulness and participate in normal activities. 3. If children with CCHS have normal ventilatory responses to exercise then chemoreceptors are not necessary for this ventilatory response or the resultant control of Pa,CO2 during exercise. We studied five children with CCHS (aged 8‐17 years) with abnormally low ventilatory responses to steady‐state increased end‐tidal PCO2 (< 9 ml min‐1 kg‐1 mmHg‐1) and five age‐matched controls. 4. Depth and rate of breathing, end‐tidal PCO2, end‐tidal PO2, CO2 production, O2 utilization and heart rate were monitored during the following conditions: whilst subjects stood at rest; following the onset of treadmill exercise (4 m.p.h.); during steady‐state exercise (4 m.p.h.); during an incremental maximal exercise test; and during recovery from exercise. 5. There were no significant differences in the ventilatory responses between CCHS subjects and controls during the onset of treadmill exercise, in the dynamic response in achieving the steady‐state exercise, during steady‐state exercise, in the recovery from steady‐state exercise, or during incremental exercise (up to the point of presumed blood lactate accumulation, as indicated by gas exchange criteria). There was a very small mean increase in PCO2 in both groups during steady‐state exercise (controls 1.4 mmHg; CCHS 2.2 mmHg). 6. The only differences which emerged between groups were (i) slightly more variability in PCO2 in the CCHS group during steady‐state exercise, and (ii) the CCHS subjects did not hyperventilate, as the controls did, at exercise levels above the point of presumed blood lactate accumulation. 7. Breath‐by‐breath coefficient of variation of ventilation was significantly reduced in both groups during steady‐state exercise compared to rest. There were no differences between groups in either state. 8. We conclude that chemoreceptors are not necessary for an appropriate ventilatory response to aerobic exercise. Hence, other stimuli, such as afferent information from the exercising limbs or signals related to activation of the motor cortex, can increase alveolar ventilation in close proportion to CO2 production. 9. The lack of hyperventilatory response to blood lactate accumulation during heavy exercise provides good evidence that these CCHS patients have ineffective peripheral chemoreception.
Mechanisms of oscillatory activity in guinea‐pig nucleus reticularis thalami in vitro: a mammalian pacemaker.
Authors: Bal T , McCormick D A
Published: December 2014

1. The ionic mechanisms of rhythmic burst firing and single spike, tonic discharge were investigated with extracellular and intracellular recordings of single neurones in the guinea‐pig nucleus reticularis thalami (NRT) maintained as a slice in vitro. 2. Activation of cortical/thalamic afferents to NRT neurones resulted in a short latency burst of action potentials which could be followed by a rhythmic sequence of oscillatory burst firing. Intracellularly, this oscillatory activity was associated with an alternating sequence of low threshold Ca2+ spikes separated by after‐hyperpolarizing potentials. Intracellular injection of short duration hyperpolarizing current pulses resulted in a similar sequence of oscillatory burst firing, suggesting that this activity is an intrinsic property of NRT cells. The frequency of rhythmic burst firing was highly voltage and temperature dependent and was between 7‐12 Hz at ‐65 to ‐60 mV at 38 degrees C. In addition, at depolarized membrane potentials, oscillatory burst firing was typically followed by a prolonged tail of single spike activity. 3. Application of the Na+ channel poison tetrodotoxin blocked the generation of fast action potentials, but left intact the rhythmic sequence of low threshold Ca2+ spikes separated by after‐hyperpolarizing potentials (AHPs). The reversal potential of the AHPs was ‐94 mV, suggesting that it was mediated by an increase in K+ conductance. Extracellular application of tetraethylammonium or apamin, or intracellular injection of Cs+ or the Ca2+ chelating agent EGTA, blocked the Ca2+ spike AHP, indicating that it is mediated by a Ca(2+)‐activated K+ current. 4. Block of the AHP resulted in the marked enhancement of a slow after‐depolarizing potential (ADP). The slow ADP occurred only following the generation of low threshold Ca2+ spikes. Replacement of extracellular Ca2+ with Mg2+ or Sr2+ resulted in an abolition of the slow ADP. In addition, the increase in [Mg2+]o resulted in an abolition of the low threshold Ca2+ spike. In contrast, replacement of extracellular Ca2+ with Ba2+ did not abolish the slow ADP. These results indicate that the ADP can be activated by either Ca2+ or Ba2+, but not by Mg2+ or Sr2+. 5. Replacement of extracellular Na+ with choline+ did not abolish the slow ADP, while replacement with N‐methyl‐D‐glucamine+ did, indicating that the slow ADP can be supported by choline+, but not by N‐methyl‐D‐glucamine+. Neither chemical affected the low threshold Ca2+ spike. These results are consistent with the slow ADP being mediated by a Ca(2+)‐activated non‐selective cation (CAN) current.(ABSTRACT TRUNCATED AT 400 WORDS)
Skeletal muscle substrate utilization during submaximal exercise in man: effect of endurance training.
Authors: Kiens B , Essen‐Gustavsson B , Christensen N J , Saltin B
Published: December 2014

1. The influence of training‐induced adaptations in skeletal muscle tissue on the choice between carbohydrates (CHO) and lipids as well as the extra‐ vs. intracellular substrate utilization was investigated in seven healthy male subjects performing one‐legged knee‐extension exercise. In each subject one of the knee extensors was endurance trained for eight weeks, whereafter the trained (T) and non‐trained (NT) thighs were investigated a week apart. 2. The activity of beta‐hydroxy‐acyl‐coenzyme A dehydrogenase (HAD) and capillary density in the knee extensors were significantly larger in T than in NT. 3. During dynamic knee‐extension exercise, performed at the same absolute intensity for 2 h, femoral venous blood flow was lower in T than in NT (P < 0.05), but oxygen uptake was similar. 4. Respiratory quotient (RQ) values over the exercising thigh, averaging 0.81 (T) vs. 0.91 (NT; P < 0.05) indicated that a shift towards a larger fat combustion occurred with endurance training. 5. Both free fatty acids (FFA) and serum triacylglycerol contributed to the utilization of fat in NT and T muscles with no significant contribution from muscle fibre triacylglycerol. 6. At high plasma FFA concentrations net uptake of FFA plateaued in NT but not in T muscles. 7. The findings suggest that FFA uptake in exercising muscle is a saturable process and that the transport capacity is enhanced by training. The lower CHO utilization in the T leg was mainly a function of the glycogenolysis of the muscle being reduced. Hormones such as insulin, noradrenaline and adrenaline are unlikely to play a role in this shift as differences in plasma levels during T and NT leg exercise were small and insignificant, implying that local structural and functional adaptations of the training muscle are crucial for the observed shifts in the metabolic response to exercise.
Effect of vision and stance width on human body motion when standing: implications for afferent control of lateral sway.
Authors: Day B L , Steiger M J , Thompson P D , Marsden C D
Published: December 2014

1. Measurements of human upright body movements in three dimensions have been made on thirty‐five male subjects attempting to stand still with various stance widths and with eyes closed or open. Body motion was inferred from movements of eight markers fixed to specific sites on the body from the shoulders to the ankles. Motion of these markers was recorded together with motion of the point of application of the resultant of the ground reaction forces (centre of pressure). 2. The speed of the body (average from eight sites) was increased by closing the eyes or narrowing the stance width and there was an interaction between these two factors such that vision reduced body speed more effectively when the feet were closer together. Similar relationships were found for components of velocity both in the frontal and sagittal planes although stance width exerted a much greater influence on the lateral velocity component. 3. Fluctuations in position of the body were also increased by eye closure or narrowing of stance width. Again, the effect of stance width was more potent for lateral than for anteroposterior movements. In contrast to the velocity measurements, there was no interaction between vision and stance width. 4. There was a progressive increase in the amplitude of position and velocity fluctuations from markers placed higher on the body. The fluctuations in the position of the centre of pressure were similar in magnitude to those of the markers placed near the hip. The fluctuations in velocity of centre of pressure, however, were greater than of any site on the body. 5. Analysis of the amplitude of angular motion between adjacent straight line segments joining the markers suggests that the inverted pendulum model of body sway is incomplete. Motion about the ankle joint was dominant only for lateral movement in the frontal plane with narrow stance widths (< 8 cm). For all other conditions most angular motion occurred between the trunk and leg. 6. The large reduction in lateral body motion with increasing stance width was mainly due to a disproportionate reduction in the angular motion about the ankles and feet. A mathematical model of the skeletal structure has been constructed which offers some explanation for this specific reduction in joint motion.(ABSTRACT TRUNCATED AT 400 WORDS)
Control of resting membrane potential by delayed rectifier potassium currents in ferret airway smooth muscle cells.
Authors: Fleischmann B K , Washabau R J , Kotlikoff M I
Published: December 2014

1. In order to determine the physiological role of specific potassium currents in airway smooth muscle, potassium currents were measured in freshly dissociated ferret trachealis cells using the nystatin‐permeabilized, whole‐cell method, at 35 degrees C. 2. The magnitude of the outward currents was markedly increased as bath temperature was increased from 22 to 35 degrees C. This increase was primarily due to the increase in maximum potassium conductance (gK,max), although there was also a small leftward shift in the relationship between gK and voltage at higher temperatures. The maximum conductance and the kinetics of current activation and inactivation were also temperature dependent. At 35 degrees C, gating of the current was steeply voltage dependent between ‐40 and 0 mV. Current activation was well fitted by fourth‐order kinetics; the mean time constants of activation (30 mV clamp step) were 1.09 +/‐ 0.17 and 1.96 +/‐ 0.27 ms at 35 and 22 degrees C, respectively. 3. Outward currents using the nystatin method were qualitatively similar to delayed rectifier currents recorded in dialysed cells with high calcium buffering capacity solutions. 4‐Aminopyridine (4‐AP; 2 mM), a specific blocker of delayed rectifier potassium channels in this tissue, inhibited over 80% of the outward current evoked by voltage‐clamp steps to between ‐10 and +20 mV (n = 6). Less than 5% of the outward current was blocked over the same voltage range by charybdotoxin (100 nM; n = 15), a specific antagonist of large‐conductance, calcium‐activated potassium channels in this tissue. 4. The degree to which delayed rectifier and calcium‐activated potassium conductances control resting membrane potential was examined in current‐clamp experiments. The resting membrane potential of current clamped cells was ‐33.6 +/‐ 1.0 mV (n = 62). Application of 4‐AP (2 mM) resulted in a 14.4 +/‐ 1.0 mV depolarization (n = 8) and an increase in input resistance. Charybdotoxin (100 nM) had no effect on resting membrane potential (n = 6). 5. Force measurements were made in isolated strips of trachealis muscle to determine the effect of pharmacological blockade of individual potassium conductances on resting tone. In the presence of tetrodotoxin (1 microM) and atropine (1 microM), 4‐AP increased baseline tension in a dose‐dependent manner, with an EC50 of 1.8 mM (n = 13); application of 5 mM 4‐AP increased tone to 86.8 +/‐ 8.1% of that produced by 1 microM methacholine, and this tone was almost completely inhibited by nifedipine (1 microM).(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium currents and calcium‐dependent potassium currents in mammalian medullary respiratory neurones.
Authors: Richter D W , Champagnat J , Jacquin T , Benacka R
Published: December 2014

1. Respiratory neurons of mammals are rhythmically active because their membrane potential fluctuates periodically over a voltage range of ‐70 to ‐55 mV. These respiratory drive potentials lead to periodic discharges of bursts of action potentials lasting for 1‐2 s. The neuronal processes stabilizing this rhythmic activity involve excitatory and inhibitory synaptic processes that interact with specific membrane properties of the postsynaptic neurones. In the present experiments, performed on dorsal and ventral groups of respiratory neurones under in vivo and in vitro conditions, we verified the modulating feature of such intrinsic neuronal properties. 2. Intrinsic neuronal properties involve Ca2+ mechanisms that lead to intracellular Ca2+ accumulation, and consequently to activation of Ca(2+)‐dependent K+ currents. 3. Blockade of intracellular Ca2+ accumulation significantly changed the amplitude and pattern of respiratory drive potentials, and blocked initial hyperpolarizing shifts of the membrane potential following each period of synaptic activation. 4. The data demonstrate that postsynaptic activities and action potential discharges activate low and high voltage‐activated Ca2+ currents leading to intracellular Ca2+ accumulation and to activation of Ca(2+)‐dependent K+ currents that significantly modulate the voltage response of medullary respiratory neurones to on‐going synaptic activation. These intrinsic membrane properties also seem to be involved in the processes controlling termination of rhythmic burst discharges.
The frequency content of common synaptic inputs to motoneurones studied during voluntary isometric contraction in man.
Authors: Farmer S F , Bremner F D , Halliday D M , Rosenberg J R , Stephens J A
Published: December 2014

1. The discharges of pairs of individual motor units were recorded from intrinsic hand muscles in man. Single motor unit recordings were obtained either when both members of the motor unit pair were within first dorsal interosseous muscle (1DI:1DI recordings) or where one motor unit was within 1DI and the other in second dorsal interosseous muscle (1DI:2DI recordings). The pairs of motor unit spike trains were cross‐correlated in the time domain and the results compared to those of coherence analysis performed on the same spike train data. Central peaks were present in the cross‐intensity functions, indicating the presence of common synaptic input to the motoneurone pair. Coherence analysis of these data indicated significant association between motor unit firing in the frequency ranges 1‐12 and 16‐32 Hz. 2. Analysis of sequential non‐overlapping segments of data recorded from individual motor unit pairs, demonstrated that both the central cross‐intensity peak and coherence in the frequency bands 1‐12 and 16‐32 Hz were consistent features throughout a long recording. In these sequential recordings, the size of the central cross‐intensity peak and the maximal value of coherence in the frequency band 16‐32 Hz covaried from segment to segment. Analysis of the entire population of motor unit pairs confirmed a positive relationship between the magnitude of peak coherence and the size of the central cross‐intensity peak. 3. Voluntary sinusoidal co‐modulation of the firing rates of pairs of individual motor units recorded from within 1DI was found to produce significant values of coherence corresponding to the frequency of the common modulation. However, firing rate co‐modulation was not found to affect either the size of the central cross‐intensity peak or the maximum value of coherence in the frequency band 16‐32 Hz. 4. Pairs of single motor units were recorded from within 1DI and biceps brachii muscles of healthy subjects. The number and size of the central cross‐intensity peaks and coherence peaks detected were compared for the two muscles. The incidence and size of central cross‐intensity peaks and the incidence and magnitude of 16‐32 Hz coherence peaks were both found to be greater for 1DI recordings when compared to biceps brachii recordings. 5. Single motor unit recordings were made from the intrinsic hand muscles of a patient with severe peripheral deafferentation. Time‐ and frequency‐domain analysis of these recordings revealed cross‐intensity peaks and frequency bands of coherence similar to those seen in healthy subjects.(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium‐mediated modulation of N‐methyl‐D‐aspartate (NMDA) responses in cultured rat hippocampal neurones.
Authors: Vyklický L
Published: December 2014

1. Agonist‐independent (inactivation) and agonist‐induced (desensitization) refractory states of N‐methyl‐D‐aspartate (NMDA) receptors were studied on cultured rat hippocampal neurones using whole‐cell and inside‐out patch‐clamp techniques and a fast perfusion system. 2. Shortly after whole‐cell formation, application of 100 microM NMDA in the presence of 10 microM glycine and 0.2 mM [Ca2+]o induced membrane currents that desensitized by 23%. Repeated application of NMDA at 30 s intervals resulted in a progressive increase in the degree and rate of onset of NMDA receptor desensitization. 3. Test responses to NMDA recorded in the presence of 0.2 mM [Ca2+]o were reversibly inactivated by 60% following a train of ten 1 s applications of NMDA delivered at 0.5 Hz in the presence of 2 mM [Ca2+]o; similar results were obtained with 2 mM [Sr2+]o and 2 mM [Ba2+]o. In the presence of Ca2+ or Sr2+, desensitization during the train of responses to NMDA increased by 14 and 19% respectively, while with Ba2+ there was no increase in desensitization. 4. In the presence of 0.2 mM [Ca2+]o at a holding potential of ‐60 mV, or in the presence of 2 mM [Ca2+]o at a holding potential of +50 mV, a train of ten applications of NMDA failed to induce either inactivation or an increase in desensitization of test responses to NMDA. These results suggest an important role for [Ca2+]o in the induction of both inactivation and desensitization of NMDA receptors. 5. Increasing the intracellular calcium concentration, [Ca2+]i, via repeated activation of voltage‐gated Ca2+ channels, resulted in a reversible inactivation of test responses to NMDA by 35% but failed to increase desensitization. In neurones dialysed with intracellular solution containing 2.5 mM Ca2+ NMDA receptor desensitization was similar to that in neurones dialysed with 10 nM Ca2+. 6. Block of NMDA receptor‐channels by 2 mM [Mg2+]o during the train application of NMDA prevented the induction of both inactivation and desensitization. In contrast 3 mM [Mg2+]i was ineffective. 7. The magnitude of both inactivation and desensitization of NMDA receptors was not affected by intracellular dialysis of ATP, the non‐hydrolysable ATP analogue 5'‐adenylylimido‐diphosphate (AMP‐PNP), different Ca2+ chelators (EGTA or BAPTA), the Ca(2+)‐activated protease inhibitor (leupeptin), dithiothreitol, or the phosphatase inhibitors (okadaic acid and a calcineurin inhibitor). 8. Application of 2.5 mM Ca2+ to the cytoplasmic side of inside‐out patches induced inactivation of NMDA responses similar in magnitude to the inactivation seen in whole‐cell recording.(ABSTRACT TRUNCATED AT 400 WORDS)