bluuebunny/crossref_metadata_2025 huggingface dataset:
Pairing of pre‐ and postsynaptic activities in cerebellar Purkinje cells induces long‐term changes in synaptic efficacy in vitro.
Authors: Crepel F , Jaillard D
Published: December 2014

1. An in vitro slice preparation of rat cerebellar cortex was used to analyse long‐lasting modifications of synaptic transmission at parallel fibre (PF)‐Purkinje cell (PC) synapses. These use‐dependent changes were induced by pairing PF‐mediated EPSPs evoked at low frequency (1 Hz) with different levels of membrane polarization (or bioelectrical activities) of PCs for 15 min. 2. Experiments were performed on forty‐eight PCs recorded intracellularly in a conventional perfused chamber, and in fifty other cells maintained in a static chamber either in the presence (n = 21) or in the absence (n = 29) of 400 nM‐phorbol 12,13‐dibutyrate (PDBu). 3. In these three experimental conditions, PF‐mediated EPSPs were always measured on PCs maintained at a holding potential of ‐75 mV, and further hyperpolarized by constant hyperpolarizing pulses. This allowed us both to test the input resistance of PCs and to avoid their firing during PF‐mediated EPSPs. 4. In all cells retained for the present study, latencies of PF‐mediated EPSPs evoked at 0.2 Hz were stable during the pre‐pairing period, and the same was true for their amplitude and time course. 5. In the perfused chamber, pairing of PF‐mediated EPSPs with the same hyperpolarization of PCs as that used for measurements of synaptic responses had no effect on these EPSPs in 30% of PCs. It induced long‐term depression (LTD) and long‐term potentiation (LTP) in 23 and 47% of the tested cells respectively (n = 17). 6. In the perfused chamber, pairing of PF‐mediated EPSPs with moderate depolarization of PCs (n = 19) giving rise to a sustained firing of sodium spikes significantly favoured the appearance of LTP as compared to the previous pairing protocol. However, there were still 27 and 15% of cells which showed no modification and LTD respectively. 7. In contrast, pairing of PF‐mediated EPSPs with calcium (Ca2+) spikes evoked by strong depolarization of PCs (n = 12) led to LTD of synaptic transmission in nearly half of the tested cells, whereas LTP was now observed in less than 20% of them. 8. In the static chamber and in the absence of PDBu, LTD of PF‐mediated EPSPs was observed in most cells, whatever the pairing protocol with sodium or Ca2+ spikes. 9. This shift towards LTD was significantly reversed by PDBu in the pairing protocol using firing of sodium spikes, but not in the case of pairings with Ca2+ spikes.(ABSTRACT TRUNCATED AT 400 WORDS)
Currents through single glutamate receptor channels in outside‐out patches from rat cerebellar granule cells.
Authors: Howe J R , Cull‐Candy S G , Colquhoun D
Published: December 2014

1. Single‐channel currents evoked in outside‐out membrane patches from rat cerebellar granule cells by glutamate, aspartate, N‐methyl‐D‐aspartate (NMDA), kainate and quisqualate were studied. Each agonist produced openings to five discrete amplitude levels. At a membrane potential of ‐70 mV, these levels correspond to single‐channel conductances of about 8, 17, 30, 40 and 50 pS. NMDA, aspartate and glutamate evoked mainly 50 pS openings and also substantial numbers of 40 pS events. Kainate evoked primarily 8 and 17 pS openings. 2. The relative proportion of openings to each conductance level showed no dependence on membrane potential. At membrane potentials negative to ‐100 mV, current‐voltage plots for 30, 40 and 50 pS openings showed substantial inward rectification. 3. With NMDA, aspartate and glutamate, the most common type of direct transition was between the 50 pS open level and the shut level. Transitions between the 30, 40 and 50 pS levels were also relatively common. With few exceptions, 8 and 17 pS openings appeared to arise directly from, and return directly to, the shut level. The differences between granule cells and certain other central neurones, in the types of transitions associated with NMDA receptor channels, provide evidence for the existence of more than one type of NMDA receptor. 4. Four exponential components were identified consistently in the shut‐time distributions that were obtained with NMDA, aspartate and glutamate. Mean time constants for the briefest two components were 30 to 65 microseconds and 0.65 to 1.00 ms. The mean duration of these ‘gaps within bursts’ differed for different agonists, but did not vary with membrane potential. 5. Two exponential components were distinguished in most open‐time distributions for the 50 pS level (time constants, 0.9‐1.2 and 3.2‐3.9 ms at ‐100 mV), whereas open‐time distributions for 30 and 40 pS events were described adequately by single exponentials with time constants below 1.0 ms. The duration of 50 pS openings decreased with hyperpolarization. 6. Mean open times for 8 and 17 pS events produced by NMDA, aspartate and glutamate were 0.3 to 0.7 ms. The longest such openings were observed with quisqualate. 7. Three exponential components were present in distributions of burst length, and of total open time per burst, that were obtained with NMDA, aspartate and glutamate. The slowest two burst‐length components had mean time constants of 1.7‐2.4 and 10.6‐13.0 ms and originated from the kinetic behaviour of the 50 pS state.(ABSTRACT TRUNCATED AT 400 WORDS)
Activation of glutamate receptors and glutamate uptake in identified macroglial cells in rat cerebellar cultures.
Authors: Wyllie D J , Mathie A , Symonds C J , Cull‐Candy S G
Published: December 2014

1. Patch‐clamp methods have been used to examine the action of excitatory amino acids on three types of glial cell in cultures of rat cerebellum, namely type‐1‐like astrocytes, type‐2 astrocytes and oligodendrocytes. In addition we have examined glutamate sensitivity of the precursor cell (the O‐2A progenitor) that gives rise to type‐2 astrocytes and oligodendrocytes. 2. Glutamate (30 microM), quisqualate (3‐100 microM), (S)‐alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole‐propionic acid (AMPA, 10‐30 microM) and kainate (10‐500 microM) were applied to cerebellar type‐2 astrocytes examined under whole‐cell voltage clamp. Each of these agonists induced inward currents in cells held at negative membrane potentials. The currents reversed direction near 0 mV holding potential. N‐Methyl‐D‐aspartate (NMDA, 30‐100 microM) or aspartate (30 microM) in the presence of glycine (1 microM) did not evoke any whole‐cell current changes in type‐2 astrocytes. 3. The distribution of glutamate receptors in type‐2 astrocytes was mapped with single‐ or double‐barrelled ionophoretic pipettes containing quisqualate or kainate. Application of these agonists (current pulses 100 ms, 50‐100 nA) to cells held at ‐60 mV evoked inward currents of 20‐120 pA in the cell soma and 10‐80 pA in the processes. Responses could also be obtained at the extremities of processes (approximately 60 microns from the soma). 4. Quisqualate or kainate (at 30 microM) applied to O‐2A progenitor cells from rat cerebellum or optic nerve induced whole‐cell currents (quisqualate 20‐30 pA; kainate 20‐50 pA, holding potential, Vh = ‐60 mV) that reversed near 0 mV. In common with type‐2 astrocytes, the progenitor cells did not respond to NMDA (30 microM). 5. Type‐1‐like astrocytes produced large inward currents to glutamate (30 microM). These currents remained inward‐going at holding potentials as positive as +80 mV and were not accompanied by any apparent noise increase. This result can be explained by the presence of an electrogenic glutamate uptake carrier. In cells kept up to 4 days in vitro, quisqualate, kainate and NMDA each failed to produce any whole‐cell current changes, indicating the absence of receptors in type‐1‐like astrocytes at this stage in culture. Furthermore the glutamate uptake currents in type‐1‐like astrocytes were inhibited when external Na+ was replaced by Li+, although Li+ was found to pass through the glutamate channel in type‐2 astrocytes.(ABSTRACT TRUNCATED AT 400 WORDS)
Suppression of steady membrane currents by acetylcholine in single smooth muscle cells of the guinea‐pig gastric fundus.
Authors: Lammel E , Deitmer P , Noack T
Published: December 2014

1. Single smooth muscle cells from the fundus region of the guinea‐pig stomach, which showed contractile responses to acetylcholine (ACh) at concentrations greater than or equal to 10(‐7) mol/l, were obtained by enzymatic digestion using highly purified collagenase and papain. They were studied by recording membrane currents under voltage clamp with the patch pipette technique in the whole‐cell configuration at 25‐28 degrees C. 2. By applying voltage jumps from negative holding levels (‐70 to ‐60 mV) to more positive levels, we identified two major activating currents: an initial inward Ca2+ current (ICa) was followed, and partly overlapped, by an outward K+ current (IK). 3. Cholinergic effects on membrane currents were investigated in the range of negative membrane potentials by determining current‐voltage relations in the absence of ACh and during its continuous presence in the bathing fluid. 4. ACh induced a decrease in the steady‐state conductance which was reversibly blocked by atropine. At physiological external K+ concentration [( K+]o = 6 mmol/l), the reversal potential (Erev) of the current suppressed by ACh (3 x 10(‐6) mol/l) was about 20 mV more positive than the calculated K+ equilibrium potential (EK). 5. When [K+]o was increased, Erev was shifted positively; but at each [K+]o, Erev was more positive than EK. 6. Like ACh (10(‐6) mol/l), tetraethylammonium (TEA, 1 mmol/l) also suppressed a current with a reversal potential that was, at physiological [K+]o, 20 mV more positive than EK. ACh (10(‐5) mol/l) applied in the presence of 1 mmol/l TEA suppressed a pure K+ current (Erev = EK), which was also suppressed by 10 mmol/l TEA. 7. When K+ in the pipette and in the bathing solution was completely replaced by Na+, both ACh (10(‐5) mol/l) and TEA (1 mmol/l) caused a reduction of the membrane conductance that appeared to be identical. TEA added to the bathing solution in the presence of ACh did not produce a significant additional conductance decrease. These results did not depend on whether Cl‐ was present as a charge carrier or not. 8. It is concluded that in fundus muscle of the guinea‐pig stomach a major mechanism underlying muscarinic activation is a decrease of a K+ conductance. In addition the results indicate a suppression of a small Na+ conductance which is made up by a population of channels that are also blocked by TEA.
Role of Ca2+ channel in cardiac excitation‐contraction coupling in the rat: evidence from Ca2+ transients and contraction.
Authors: Cleemann L , Morad M
Published: December 2014

1. Optical methods were used to measure simultaneously unloaded cell shortening and intracellular Ca2+ transients in whole‐cell voltage clamped rat ventricular myocytes. Red light (greater than 670 nm) was used to measure cell shortening with a linear photodiode array. The dyes Fura‐2 (Kd = 140 nM) and Mag‐Fura‐2 (Kd = 44 microM) were used as Ca2+ indicators with fluorescence excitation at 340 and 410 nm and emission at 510 nm. 2. Repeated measurements at 6 s intervals as 0.4 mM‐Fura‐2 diffused into the cell from the tip of the voltage clamp pipette showed no decrease in the rate of rise and peak value of the intracellular Ca2+ transient and only a small suppression of cell shortening, suggesting that the molecular mechanisms regulating the Ca2+ release were not significantly altered by the buffering capacity of the Fura‐2. 3. Experiments in which the sarcoplasmic reticulum (SR) was depleted of Ca2+ either by exposure to caffeine or by repeated brief (20 ms) voltage clamp depolarizations confirm that the SR is the major source of activator Ca2+. 4. Mag‐Fura‐2 (1 or 5 mM) was used to register the initial rapid development of the [Ca2+]i transient but the later time course of the Ca2+ transients measured with this dye was obscured by motion artifacts resulting from cell shortening. 5. Both Fura‐2 and Mag‐Fura‐2 showed that depolarization to 0 mV from a holding potential of ‐80 mV resulted in a [Ca2+]i transient which developed with a delay of 3‐9 ms and approached its peak value in an additional 8‐19 ms. Both Ca2+ indicators also showed that the Ca2+ transient approached its peak value more slowly as the clamped membrane potential was made increasingly more positive. 6. The voltage dependencies of the Ca2+ signal (Fura‐2) and cell shortening were both bell‐shaped and were qualitatively similar to the voltage dependence of Ca2+ current simultaneously measured. This was observed with holding potentials of both ‐40 and ‐80 mV. 7. Comparison of the temporal relation of the Ca2+ current, ICa, and intracellular Ca2+ transient (Fura‐2) and cell shortening at different membrane potentials showed that Ca2+ transient measured 25 ms into the depolarization correlated closely to the integral of the Ca2+ current measured prior to this time. Cell shortening, on the other hand, peaked about 100 ms later and correlated with measurements of the Ca2+ activity at the later time.(ABSTRACT TRUNCATED AT 400 WORDS)
Central nervous pathways underlying synchronization of human motor unit firing studied during voluntary contractions.
Authors: Datta A K , Farmer S F , Stephens J A
Published: December 2014

1. Motor unit firing has been studied during weak voluntary isometric contractions with pairs of needle electrodes in normal human subjects. 2. Pre‐ and post‐stimulus time histograms of the firing time of firing of one event unit before and after the time of firing of another reference (stimulus) unit showed a clear central peak, indicative of synchronization. 3. Synchronization was seen in all the muscles studied. The mean strength of synchronization, expressed as the number of concomitant discharges of the two units as a proportion of the number of stimulus unit discharges, was 0.095 extra event unit spikes/reference unit spike (range 0.042‐0.28) for first dorsal interosseous muscle, 0.016 extra event unit spikes per reference unit spike (range 0‐0.043) for medial gastrocnemius and 0.056 extra event unit spikes per reference unit spike range 0.016‐0.079) for tibialis anterior. 4. The mean duration of synchronization was 11.3 ms (range 5.0‐21.0 ms) for first dorsal interosseous, 10.3 ms (range 3.5‐21.7 ms) for medial gastrocnemious and 13.5 ms (range 3.0‐25.0) for tibialis anterior. 5. Seven patients with radiographically and clinically identified central strokes were studied while they made weak voluntary isometric contractions. The duration of synchronization was significantly prolonged compared to that found in normal subjects. In these stroke patients the mean duration of synchronization on the affected side was longer than that seen in the normal subjects, and in first dorsal interosseous muscle was 35.4 ms (range 12.0‐65.0 ms), in medial gastrocnemius was 21.3 ms (range 4.0‐43.0 ms) and in tibialis anterior was 28.8 ms (range 14.0‐49.0 ms). 6. The mean strength of synchronization of motor unit discharge was found to be greater in the stroke patients than that seen in the normal subjects for first dorsal interosseous muscle (0.161 extra event unit spikes per reference unit spike, range 0.017‐0.391) and for medial gastrocnemius (0.030 extra event unit spikes per reference unit spike) but only significantly so when pooled data was compared. There was no difference in the strength of motor unit synchronization in tibialis anterior between stroke patients and normal subjects. 7. Broad duration synchronization among first dorsal interosseous motor units was also found in a patient with a rostral cervical spine lesion (total duration range 43‐46 ms; n = 2), but not in a patient with a caudal (thoracic) spinal lesion.(ABSTRACT TRUNCATED AT 400 WORDS)
A physiological study of the prenatal development of cutaneous sensory inputs to dorsal horn cells in the rat.
Authors: Fitzgerald M
Published: December 2014

1. The response of fetal dorsal horn cells to natural and electrical stimulation of the skin of the hindpaw was recorded in vivo from the lumbar spinal cord of anaesthetized rat fetuses still in contact with their mother via the maternal circulation. 2. Responses to electrical stimulation were obtained from embryonic day 17 (E17) but spikes were not evoked by natural skin stimulation until embryonic day 19 (E19). 3. At E19 responses were evoked by pressure or pinching the skin, but responses to low intensity brush and touch were not clear until E20. 4. Receptive fields were small and response amplitudes and frequencies initially very low. However, by E20 bursts of up to fifty spikes were recorded to a single pinch and some cells displayed responses that outlasted the stimulus by 10‐15 s. 5. The development of dorsal horn cutaneous evoked spike activity and consequently the ability to transmit cutaneous sensory information to the brain therefore occurs some 2 days after the development of peripheral afferent receptive fields. It is concluded that this represents the maturation time for central synaptic connections.
Actions of ketamine, phencyclidine and MK‐801 on NMDA receptor currents in cultured mouse hippocampal neurones.
Authors: MacDonald J F , Bartlett M C , Mody I , Pahapill P , Reynolds J N , Salter M W , Schneiderman J H , Pennefather P S
Published: December 2014

1. Stable N‐methyl‐D‐aspartic acid (NMDA) receptor‐mediated currents in cultured mouse hippocampal neurons were evoked by 20 ms pressure pulse applications of L‐aspartate, repeatedly applied at 30 or 40 s intervals, to the cell body region of the neurone. We have characterized the voltage‐ and use‐dependent blockade of the currents by three dissociative anaesthetics: ketamine, phencyclidine (PCP) and MK‐801 in mouse hippocampal neurones grown in dissociated tissue culture. 2. We have used a simple model of the blockade, based on the ‘guarded receptor hypothesis’ to interpret our data. The model assumes that receptors are maximally activated at the peak of the response with an open probability (Po) approaching 1, that there is no desensitization and that the blocking drug only associates with, or dissociates from, receptor channels which have been activated by agonist (e.g. open channels). 3. The model allows us to estimate forward and reverse rate constants for binding of the blockers to open channels from measurements of the steady‐state level of blockade and the rate of change of the current amplitude per pulse during onset and offset of blockade. As predicted by the model, the estimated reverse rate was independent of blocker concentration while the forward rate increased with concentration. Changing the level of positively charged ketamine (pKa 7.5) tenfold by changing pH from 6.5 to 8.5 caused a corresponding change in the forward rate while having no effect on the reverse rate. Most of the voltage dependence of the blockade could be accounted for by reduction of the reverse rate by depolarization. 4. Estimated forward rate constants for ketamine, PCP and MK‐801 were similar to one another when measured under similar conditions and were 3 x 10(4) ‐ 3 x 10(5) M‐1 S‐1. Most of the differences in potency of the three blockers could be accounted for by differences in the reverse rate constants which were approximately 0.2, 0.03 and 0.003 s‐1 for ketamine, PCP and MK‐801, respectively. The estimated rate constants actually are the product of the rate constants and 1/Po. Suggestions that maximum Po is much less than 1 for NMDA channels imply that both forward and reverse rate constants of blockade may in fact be larger than we have calculated. However, their magnitudes, relative to one another, are unaffected by this consideration. 5. The reverse rate constant of blockade increased at positive potentials. This increase was prevented when the neurone was loaded with N‐methyl‐D‐glucamine, an impermeant cation which prevented outward currents.(ABSTRACT TRUNCATED AT 400 WORDS)
The influence of short‐term adaptation of human rods and cones on cone‐mediated grating visibility.
Authors: Naarendorp F , Frumkes T
Published: December 2014

1. The influences of short‐term visual adaptation of either rods or cones upon cone‐mediated grating visibility were compared with their influences upon detection threshold in both the fovea and parafoveal retina. Short‐term visual adaptation was induced by 20 deg diameter adapting fields (AFs) generally of 500 ms duration. The AF was either ‐0.5 log td in illuminance and too dim to influence cones, or 2.5 log td and bright enough to stimulate cones as well as rods. 2. In control experiments, we replicated previous results of Crawford (1947), Baker (1963), and other investigators and determined the influence of these AFs upon the detection threshold of a homogeneous test flash (TF) of 54 min of arc diameter and 10 ms duration. If the AF was 2.5 log td in illuminance and stimuli were presented foveally, TF threshold began to rise several hundred milliseconds before AF onset, was maximal when AF and TF were simultaneous in onset but was less elevated during the remaining presentation of the AF. TF threshold decreased to control value within several seconds after AF offset. These data represent a cone adaptation function since action spectra for both the test and adapting flashes adhere to the spectral sensitivity of the CIE standard luminous efficiency function V lambda. 3. If the AF was ‐0.5 log td in illuminance and if stimuli were presented parafoveally, the time course of TF detection threshold changes were similar to those described in paragraph 2 above. But these data represent a rod adaptation function since action spectra for both the test and adapting flashes adhered to the spectral sensitivity of the CIE standard luminous efficiency function V' lambda. In the fovea, the ‐0.5 log td AF had no influence upon the detection threshold of the TF suggesting complete rod‐cone independence. 4. The influence of short‐term adaptation upon spatial visibility was studied using a vertically oriented, 18 cycle/deg grating which was also 54 min of arc in diameter and 10 ms in duration. We determined the illuminance just necessary to see the bars of the grating (i.e. threshold grating illuminance or TGI) at various time intervals in respect to the onset of an AF. 5. Rod‐stimulating (‐0.5 log td) AFs, whether 0.5 or 2 s in duration, only influenced TGI after AF onset. TGI gradually decreased (i.e. an increase in sensitivity) during the first 250 ms of AF presentation and then remained stable until AF offset.(ABSTRACT TRUNCATED AT 400 WORDS)
Responses of cat muscle spindles which lack a dynamic fusimotor supply.
Authors: Gioux M , Petit J , Proske U
Published: December 2014

1. The experiments reported here support the view that some spindles in the peroneus tertius muscle of the anaesthetized cat lack a nuclear bag1 intrafusal fibre. 2. The bag1 fibre is characterized by the fact that it is innervated exclusively by dynamic fusimotor axons. A method was devised to test each spindle in peroneus tertius for a dynamic fusimotor innervation. The ventral roots containing the muscle's motor supply were subdivided into five portions, approximately equal in terms of the tension they generated, and each piece was stimulated in turn, repetitively, at fusimotor strength, during ramp stretch of the muscle, to look for a large increase in dynamic response. 3. The method allowed confirmation that the majority of spindles in peroneus tertius had a dynamic fusimotor innervation. However, where the dynamic effect was weak and accompanied by a strong static fusimotor action and extrafusal unloading, it risked being overlooked. 4. The confirmatory test for the presence of a bag1 fibre was whether or not the spindle showed a large increase in dynamic response in the presence of the drug succinyl choline (SCh) injected arterially close to the muscle in which the spindle is located. SCh is known to induce a contracture in the bag1 fibre and therefore mimics tonic dynamic fusimotor stimulation. 5. In five experiments, of a total of forty‐two spindles with afferents conducting within the group I range, five examples were encountered where there was no increase in dynamic response, either with ventral root stimulation or perfusion with SCh. It was concluded that these were spindles which lacked a bag1 fibre. 6. Passive stretch of such spindles revealed no feature in the response which allowed them to be distinguished from spindles in which the bag1 fibre was present. This conclusion posed the question, what contribution, if any, does the bag1 fibre make to the stretch response? 7. It was possible to show that under some conditions the bag1 fibre did contribute to the response to stretch. If the spindle was conditioned by repetitive nerve stimulation, at fusimotor strength, at a length longer than that at which a test stretch was applied, the response to the stretch was delayed, and it began at a lower rate than after conditioning stimulation at the test length. The delayed response was attributed to the presence of slack in intrafusal fibres.(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of somatic nerve stimulation on the kidney in intact, vagotomized and carotid sinus‐denervated rats.
Authors: Davis G , Johns E J
Published: December 2014

1. The influence of cardiopulmonary and arterial baroreceptors on the renal nerve‐dependent functional responses of the kidney to electrical stimulation of somatic afferent nerves was studied in pentobarbitone‐anaesthetized rats. 2. Electrical stimulation of the left brachial nerve plexus at 3 Hz, 0.2 ms and 15 V in the intact animals increased blood pressure by 22%, and while renal perfusion pressure was maintained at pre‐stimulus levels, renal blood flow and glomerular filtration rate decreased by 14 and 22% respectively. At the same time urine flow rate and absolute and fractional sodium excretion decreased by 36, 42 and 27% respectively. In animals subjected to acute renal nerve section these renal functional responses could not be elicited. 3. Following bilateral vagotomy the systemic and renal haemodynamic responses to brachial nerve stimulation were similar to the intact group. However, urine flow rate and absolute and fractional sodium excretions decreased by 50, 59 and 47% respectively, responses which were significantly greater than in the intact group. 4. In a group of rats in which the carotid sinus nerves had been sectioned, stimulation of the brachial plexus caused reductions of renal blood flow and glomerular filtration rate of the same magnitude as in the intact group; however, urine flow rate and absolute and fractional sodium excretion fell by 51, 60 and 48%, respectively, which were significantly larger than in the intact group. 5. These results demonstrate that the afferent nerve information arising from muscle joints and skin and carried via the brachial plexus caused reflex renal nerve‐dependent reductions in renal haemodynamics and an antidiuresis and antinatriuresis. The cardiopulmonary and carotid sinus baroreceptors exert a tonic inhibitory action on these reflex renal responses insofar as they appeared to attenuate the antidiuretic and antinatriuretic responses to somatic afferent nerve stimulation.
Cross‐bridge kinetics in the presence of MgADP investigated by photolysis of caged ATP in rabbit psoas muscle fibres.
Authors: Dantzig J A , Hibberd M G , Trentham D R , Goldman Y E
Published: December 2014

1. The interaction between MgADP and rigor cross‐bridges in glycerol‐extracted single fibres from rabbit psoas muscle has been investigated using laser pulse photolysis of caged ATP (P3‐1(2‐nitrophenyl)ethyladenosine 5'‐triphosphate) in the presence of MgADP and following small length changes applied to the rigor fibre. 2. Addition of 465 microM‐MgADP to a rigor fibre caused rigor tension to decrease by 15.3 +/‐ 0.7% (S.E.M., n = 24 trials in thirteen fibres). The half‐saturation value for this tension reduction was 18 +/‐ 4 microM (n = 23, thirteen fibres). 3. Relaxation from rigor by photolysis of caged ATP in the absence of Ca2+ was markedly slowed by inclusion of 20 microM‐2 mM‐MgADP in the photolysis medium. 4. Four phases of tension relaxation occurred with MgADP in the medium: at, a quick partial relaxation (in pre‐stretch fibres); bt, a slowing of relaxation or a rise in tension for 50‐100 ms; ct, a sudden acceleration of relaxation; and dt, a final, nearly exponential relaxation. 5. Experiments at varied MgATP and MgADP concentrations suggested that phase at is due to MgATP binding to nucleotide‐free cross‐bridges. 6. Phase bt was abbreviated by including 1‐20 mM‐orthophosphate (Pi) in the photolysis medium, or by applying quick stretches before photolysis or during phase bt. These results suggest that phases bt and ct are complex processes involving ADP dissociation, cross‐bridge reattachment and co‐operative detachment involving filament sliding and the Ca(2+)‐regulatory system. 7. Stretching relaxed muscle fibres to 3.2‐3.4 microns striation spacing followed by ATP removal and release of the rigor fibre until tension fell below the relaxed level allowed investigation of the strain dependence of relaxation in the regions of negative cross‐bridge strain. In the presence of 50 microM‐2 mM‐MgADP and either 10 mM‐Pi or 20 mM‐2,3‐butanedione monoxime, relaxation following photolysis of caged ATP was 6‐ to 8‐fold faster for negatively strained cross‐bridges than for positively strained ones. This marked strain dependence of cross‐bridge detachment is predicted from the model of A. F. Huxley (1957). 8. In the presence of Ca2+, activation of contraction following photolysis of caged ATP was slowed by inclusion of 20‐500 microM‐MgADP in the medium. An initial decrease in tension related to cross‐bridge detachment by MgATP was markedly suppressed in the presence of MgADP. 9. Ten millimolar Pi partly suppressed active tension generation in the presence of MgADP.(ABSTRACT TRUNCATED AT 400 WORDS)
Two types of Ca2+ currents are found in bovine chromaffin cells: facilitation is due to the recruitment of one type.
Authors: Artalejo C R , Dahmer M K , Perlman R L , Fox A P
Published: December 2014

1. Whole‐cell Ca2+ currents in cultured bovine chromaffin cells were studied using patch‐clamp electrophysiology. With Ba2+ or Ca2+ as the current carriers, two separate components of whole‐cell current could be distinguished by biophysical and pharmacological criteria. These components of Ca2+ current were different from T‐ or N‐type Ca2+ channels previously described, as they were not inactivated at a holding potential of ‐60 mV. 2. Depolarization of the cells past ‐20 mV in 10 mM‐Ba2+ activated a single component of Ca2+ current, called the 'standard’ current. This current showed no detectable voltage‐dependent inactivation, but did show marked current‐dependent inactivation as steady‐state inactivation (H‐infinity) plots obtained in the presence of Ba2+ were quite different from those obtained from Ca2+. 3. In most chromaffin cells large pre‐depolarizations or repetitive depolarizations in the physiological range activated a second component of Ca2+ current called ‘facilitation’. Facilitation was observed with either Ca2+ or Ba2+ as the charge carrier. Recruiting facilitation increased whole‐cell currents by an average of 60%. 4. Pre‐pulses to +120 mV lasting 200 ms completely activated facilitation. Pre‐pulses longer than 800 ms started to inactivate facilitation, while pre‐pulses longer than 2500 ms completely inactivated this component of Ca2+ current. Because only outward currents were recorded at +120 mV, it is likely that facilitation inactivated in a voltage‐dependent manner. 5. When the extracellular Ba2+ concentration was increased in the range from 2 to 90 mM activation of both facilitation and standard Ca2+ currents shifted in the depolarizing direction. In 2 mM‐Ba2+ facilitation activated at potentials 10 mV more negative than the standard component, while in 90 mM‐Ba2+, facilitation activated at a potential about 10 mV more depolarized than the standard component. Thus, the voltage sensor for the facilitation Ca2+ current appeared to sense more surface charge than did the standard Ca2+ current. 6. Tail currents measured at ‐20 and ‐30 mV in the absence of facilitation (without pre‐pulses) showed one time constant for current deactivation. Tail currents measured with both facilitation and standard currents activated showed a significantly slower deactivation rate than that seen with the standard current alone. 7. The dihydropyridine antagonist nisoldipine (1 microM) completely suppressed the facilitation Ca2+ current even when cells were held at negative holding potentials (‐80 mV). In contrast, the standard current was unaffected by 1 microM‐nisoldipine, even at depolarized holding potentials (‐20 mV).(ABSTRACT TRUNCATED AT 400 WORDS)
Protons activate a cation conductance in a sub‐population of rat dorsal root ganglion neurones.
Authors: Bevan S , Yeats J
Published: December 2014

1. The responses of adult and neonatal rat dorsal root ganglion (DRG) neurones to buffered acidic solutions were studied with both voltage clamp and radioactive ion flux techniques. Electrophysiological experiments were made on acutely isolated neurones and ion flux experiments were made on cells that had been in culture for 3‐6 days. 2. Acid solutions of pH < 6.2 evoked a sustained, slowly inactivating inward current in neurones voltage clamped at negative holding potentials. The size of the current increased with increasing proton concentrations. This response was restricted to a sub‐population (approximately 45%) of adult and neonatal rat DRG neurones and was distinct from a rapidly activating and inactivating proton‐induced inward sodium current that was also found in DRG neurones. 3. The proton‐activated sustained current was due to an increase in cation conductance that allowed K+, Cs+ and Na+ to pass with PK/PNa = 1.32 and PCs/PNa = 1.12. 4. Radioactive ion efflux experiments made on neonatal rat cultured DRG neurones showed that protons also increased the permeability to both [14C]guanidinium and 86Rb+ ions. The half‐maximal increase in efflux rate for 86Rb+ occurred at pH 5.8. Acid solution also stimulated the efflux of 86Rb+ in cultures of adult rat neurones. 5. Cells that showed a late, sustained proton‐activated current also responded to capsaicin. In addition, no proton‐activated fluxes of either [14C]guanidinium or 86Rb+ ions were observed in cultures of DRG neurones that had been treated with high concentrations of capsaicin (10 microM) to kill the capsaicin‐sensitive neurones. Thus this proton‐activated current is restricted largely, if not exclusively, to capsaicin‐sensitive peripheral sensory neurones.
On the active form of 4‐aminopyridine: block of K+ currents in rabbit Schwann cells.
Authors: Howe J R , Ritchie J M
Published: December 2014

1. The blocking action of 4‐aminopyridine (4‐AP) on the outward potassium currents evoked by depolarization of rabbit Schwann cells in short‐term primary culture was studied with the whole‐cell configuration of the patch‐clamp method. 2. We have determined the apparent equilibrium dissociation constant, K, for the action of 4‐AP to block potassium currents at a series of different extracellular and intracellular pH values. 4‐Aminopyridine is an organic base and exists in both charged and uncharged forms in aqueous solution. Changes in the pH of the extracellular and intracellular solutions therefore also change the extracellular and intracellular proportions of these two forms, and the values of K that were obtained were found to depend in a consistent way on both the extracellular and the intracellular pH. 3. At alkaline extracellular pH, K was decreased. At acidic extracellular pH, K was increased. In contrast, increasing the intracellular pH from 7.2 to 8.1 reduced the apparent potency of extracellularly applied 4‐AP (i.e. increased K), and decreasing the intracellular pH (to 6.4) increased this apparent potency (i.e. decreased K). 4. The 4‐AP analogues, 2‐aminopyridine, 3‐aminopyridine and 3,4‐diaminopyridine, were also tested. At half‐block of the potassium current, the intracellular concentration of the cationic form of the various aminopyridines (applied extracellularly at pH 7.2) varied by a factor of less than five, whereas that of the uncharged form varied by a factor of over 700. 5. The results are inconsistent with the hypothesis that the cationic form of the aminopyridines, acting from the extracellular solution, contributes in any substantial way to potassium channel block. It also seems unlikely that the uncharged form, acting either extracellularly or intracellularly, is solely responsible for the block. However, the results as a whole are consistent with the idea that it is the cation acting from the intracellular side that blocks the 4‐AP‐sensitive potassium channel and that the affinity with which 4‐AP blocks the channel depends on the intracellular pH. The results would be explained if the cation competes with protons for a binding site that has an apparent pKa of about 7.0. 6. The results, nevertheless, are not inconsistent with the possibility that both the uncharged form and the intracellular charged form of 4‐AP are active in blocking the 4‐AP‐sensitive potassium channel.(ABSTRACT TRUNCATED AT 400 WORDS)
Caffeine inhibits inositol trisphosphate‐mediated liberation of intracellular calcium in Xenopus oocytes.
Authors: Parker I , Ivorra I
Published: December 2014

1. Voltage‐clamp recording of Ca(2+)‐activated chloride currents in Xenopus oocytes was used to study the effects of caffeine on the liberation of intracellular Ca2+ induced by photo‐release of inositol 1,4,5‐trisphosphate (InsP3) from caged InsP3. Bath application of caffeine, at concentrations between 0.1 and 10 mM, reduced or abolished the current evoked by photo‐release of InsP3 and by microinjection of InsP3. 2. Caffeine did not appreciably reduce currents evoked by injection of Ca2+ into oocytes, whereas measurements using the Ca2+ indicator Rhod‐2 showed that it instead inhibited the liberation of Ca2+ by InsP3. 3. Caffeine increased the threshold amount of InsP3 required to evoke a current response and proportionally reduced the currents evoked by suprathreshold levels of InsP3. 4. Theophylline and 3‐isobutyl‐1‐methylxanthine (IBMX) were much less potent than caffeine, and few changes were seen in the InsP3 responses following application of forskolin or intracellular injection of cyclic AMP. Thus, inhibition of InsP3 responses by caffeine does not arise through inhibition of phosphodiesterase enzymes. 5. Even at high (10 mM) concentrations, caffeine did not itself elicit any clear Ca(2+)‐activated current. It is therefore unlikely that inhibition of the InsP3 responses arise because caffeine itself liberates Ca2+ from intracellular stores. 6. The site of action of caffeine is intracellular, because injections of caffeine into the oocyte strongly inhibited responses to InsP3, whereas local extracellular applications of similar amounts were almost without effect.
Two types of potassium currents seen in isolated Necturus enterocytes with the single‐electrode voltage‐clamp technique.
Authors: Valverde M A , Sheppard D N , Giraldez F , Sepúlveda F V
Published: December 2014

1. The ionic permeability of Necturus maculosus small intestine epithelial cells was investigated using intracellular microelectrodes to measure membrane potential in intact tissue or by the single‐electrode voltage‐clamp technique in isolated cells. 2. The basolateral membrane of enterocytes appears to be K+ selective as demonstrated by the dependence of membrane potential and fractional serosal resistance measured in the intact epithelium on serosal K+ concentration. 3. Isolated cells had membrane potentials similar to those measured in the intact tissue. Voltage‐clamp experiments in a physiological Ringer solution showed the presence of both large outward and inward currents. 4. Removal of Cl‐ from the bathing medium, linear subtraction or the use of a Cl‐ channel blocker revealed outwardly rectifying currents. The quasi‐linear component was also revealed following K+ channel inhibition; it reversed near ECl, suggesting that the charge carrier was Cl‐. 5. Outwardly rectifying currents could be kinetically resolved into two components. A fast component (tau for activation < 4 ms) accounted for 60‐80% of the total current at positive potentials. A slowly activating component appeared at voltages positive to 50 mV with tau for activation of > 25 ms. 6. The slow outward current showed strong voltage dependence of both activation and relaxation, which were faster at more depolarized potentials. 7. Both fast and slow outward currents seem to be carried by K+ as they were blocked by Ba2+ and tetraethylammonium (TEA). Tail current analysis of the slow component indicated a reversal potential very similar to EK. 8. Fast outward currents were half‐activated at about ‐40 mV whereas slow outward currents were only apparent at more positive potentials. It is proposed that the fast outward K+ current plays a role, together with Cl‐ currents, in determining the resting membrane potential of Necturus enterocytes.
Investigation of the Flow Around Two Interacting Ship-Like Sections
Authors: Arslan Tufan , Pettersen Bjørnar , Andersson Helge I.
Published: December 2014

This paper reports calculations of three-dimensional (3D) unsteady cross flow over two ship sections in close proximity and compares the results with measurements. The ship sections have different breadth and draft conditions which represent typical situations in a ship-to-ship marine operation in a cross current. The behavior of the vortex-shedding around the two different ship hull sections is investigated numerically by computational fluid dynamics (CFD) methods. For the two sections, simulations are done for Reynolds number Re = 68,000, Froude number Fr = 0.25, and Re = 6800, Fr = 0.025 by using the dynamic Smagorinsky large eddy simulation (LES) turbulence model. The simulations are performed by using the software ansysfluent and the numerical results are compared with particle image velocimetry (PIV) results taken from the literature. The hydrodynamic forces acting on the two ship sections are predicted by numerical simulations and interaction effects between the two ships are evaluated.
Experimental Observations on Wake Characteristics of a Rising Bubble in a Vertical Narrow Rectangular Channel
Authors: Song Mingliang , Huang Yanping , Zhang Liqin , Wang Junfeng , Zan Yuanfeng
Published: December 2014

Wake characteristics of a rising air and vapor bubble through stagnant and flowing deionized water in a vertical narrow rectangular channel were investigated using particle image velocimetry (PIV). Influence of inlet average fluid velocity on bubble behavior was discussed. The results showed that relative terminal velocities of air bubble under different inlet average fluid velocities were almost equal to the terminal velocity in stagnant fluid, and terminal rising velocities of single air bubble and vapor bubble are very close under adiabatic boundary condition. As flow velocity increased, wake structure simplified. Disturbances in the wake of the vapor bubble were more noticeable.
Power Cycles of Generation III and III+ Nuclear Power Plants
Authors: Dragunov Alexey , Saltanov Eugene , Pioro Igor , Kirillov Pavel , Duffey Romney
Published: December 2014

It is well known that electrical power generation is the key factor for advances in industry, agriculture, and standard of living. In general, electrical energy can be generated by (1) nonrenewable energy sources such as coal, natural gas, oil, and nuclear; and (2) renewable energy sources such as hydro, wind, solar, biomass, geothermal, and marine. However, the main sources for electrical energy generation are (1) thermal—primarily coal and secondary natural gas, (2) “large” hydro, and (3) nuclear. Other energy sources might have a level of impact in some countries. Modern advanced thermal power plants have reached very high thermal efficiencies (55–62%). In spite of that, they are still the largest emitters of carbon dioxide into the atmosphere. Therefore, reliable non–fossil fuel energy generation, such as nuclear power, is becoming more and more attractive. However, current nuclear power plants (NPPs) are way behind in thermal efficiency (30–42%) compared to the efficiency of advanced thermal power plants. Therefore, it is important to consider various ways to enhance the thermal efficiency of NPPs. This paper presents a comparison of thermodynamic cycles and layouts of modern NPPs and discusses ways to improve their thermal efficiencies.
Variable Gain Super-Twisting Control of GMAW Process for Pipeline Welding
Authors: Bera Manas Kr. , Bandyopadhyay Bijnan , Paul A. K.
Published: December 2014

Quality control is the key issue that needs to be addressed in any gas metal arc welding (GMAW) system, especially in robotic pipeline welding system. This paper explores a second-order sliding mode control (SMC) strategy—a variable gain super-twisting control, to maximize the productivity, consistency in welding quality. This is achieved by the robust finite time output tracking of GMAW system. A nonlinear multi-input multi-output (MIMO) model of GMAW system has been considered here for the design of variable gain super-twisting (VGST) controller by which complete rejection of the bounded uncertainties/disturbances is possible and the adaptive characteristic of its gains help to use the control effort effectively. The stability of internal dynamics of the system is studied to establish the feasibility of solving the robust finite time output tracking problem. The stability of the overall system has been analyzed using Lyapunov stability criterion. The performance of the controller is demonstrated using the model of the system emulating the realistic conditions of operation. The simulation results are presented to illustrate the efficacy of the controller.
A Wnt-TGFβ2 axis induces a fibrogenic program in muscle stem cells from dystrophic mice
Authors: Biressi Stefano , Miyabara Elen H. , Gopinath Suchitra D. , M. Carlig Poppy M. , Rando Thomas A.
Published: December 2014

A Wnt-TGFβ2 signaling pathway modulates stem cell dysfunction in muscles of dystrophic mice.
Growing a New Heart from the Old One
Authors: Stecker Eric C.
Published: December 2014

Genetic investigations shed light on how heart muscle may regenerate.
Schistosoma mansoni Soluble Egg Antigens Enhance T Cell Responses to a Newly Identified HIV-1 Gag H-2bEpitope
Authors: Bui Cac T. , Shollenberger Lisa M. , Paterson Yvonne , Harn Donald A.
Published: December 2014

Schistosome infection induces significant T helper type 2 (Th2) and anti-inflammatory immune responses and has been shown to negatively impact vaccine efficacy. Our goal was to determine if the administration of schistosome soluble egg antigens (SEA) would negatively influence the induction of cytotoxic T lymphocyte (CTL) and Th1-type T cell responses to an HIV candidate vaccine in the Th1-biased C57BL/6 mouse strain. Initial experiments failed, as we were unable to detect any response to the defined class I epitope for HIV-1 IIIB Gag. Therefore, we initiated an epitope mapping study to identify C57BL/6 (H-2b) T cell epitopes in HIV-1 IIIB Gag in order to perform the experiments. This analysis defined two previously unreported minimal class I H-2band class II I-Abepitopes for HIV-1 IIIB Gag. The newly defined HIV-1 IIIB Gag epitopes were used to evaluate the influence of SEA on the generation of CTL and Th1-type HIV-1 IIIB Gag responses. Surprisingly, in contrast to our hypothesis, we observed that the coadministration of SEA with aListeria monocytogenesvector expressing HIV-1 IIIB Gag (Lm-Gag) led to a significantly increased frequency of gamma interferon (IFN-γ)-producing CD8+and CD4+T cells in C57BL/6 mice compared to mice immunized with Lm-Gag only. These observations suggest that SEA contains, in addition to Th2-type and immune-suppressive molecules, substances that can act with the Lm-Gag vaccine to increase CTL and Th1-type vaccine-specific immune responses.