bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in motor cortical excitability during human muscle fatigue.
Authors: Taylor J L , Butler J E , Allen G M , Gandevia S C
Published: December 2014

1. The excitability of the motor cortex was investigated during fatiguing con of the elbow flexors in human subjects. During sustained contractions at 30 and 1 voluntary force (MVC), the short‐latency electromyographic responses (EMG) evoke brachii and brachioradialis by transcranial magnetic stimulation increased in si EMG in the elbow flexors following the evoked muscle potential (silent period), duration during a sustained MVC but not during 30% MVCs nor during a sustained M muscle (adductor pollicis). 2. When the blood supply to brachioradialis was blocked with sphygmomanometer cuff sustained MVC, the changes in EMG responses to transcranial stimulation rapidly control values, This suggests that changes in these responses during fatigue wer small‐diameter muscle afferents. 3. Tendon vibration during sustained MVCs indicated that the changes in the resp cortial stimulation were not mediated by reduced muscle spindle inputs. 4. Muscle action potentials evoked in brachioradialis by electrical stimulation cervicomedullary junction did not increase in size during sustained MVCs. Thus, cortically evoked responses during sustained MVCs reflects a change in cortical Although the silent period following cervicomedullary stimulation lengthened, it substantially shorter than the cortically evoked silent period. 5. The altered EMG responses to transcranial stimulation during fatigue suggest exitation and increased inhibition in the motor cortex. As these changes were un manipulation of afferent input they presumably result from intrinsic cortical pr altered voluntary drive to the motor cortex.
The characteristics and frequency of augmented breaths during CO2‐induced hyperpnoea of newborn infants.
Authors: Cohen G , Henderson-Smart D J
Published: December 2014

1.Hypercapnic ventilatory responses of thirty‐five full term infants aged 1‐7 days were evaluated, and the characteristics and incidence of augmented breaths were determined. 2. According to the inspiratory airflow profile and tidal volume (VT), augmented breaths were categorized as ‘type A’ (biphasic, VT > or = 2 x control VT), or ‘type M’ (multiphasic, VT < 2 x control VT). 3. Steady‐state inhalation of 2‐4% CO2 resulted in a 3‐fold increase in the frequency of augmented breaths after 8 min; 80 s rebreathing a mixture containing 5‐6% CO2 resulted in a 20‐fold increase in the frequency of these breaths. 4. During eupnoea, 85% of spontaneously occurring augmented breaths were type A. With increasing respiratory drive, there was a disproportionate increase in type M compared with type A breaths: after 80 s rebreathing, 86% of augmented breaths were type M and only 14% were type A. 5. These findings indicate that the hypercapnic hyperpnoea facilitates an inspiration‐augmenting reflex in newborn infants. The significance of type M breaths is unclear; they appear to be characteristic of the newborn, and may represent the response of an immature respiratory system to load.
Spontaneous and uniquantal‐evoked endplate currents in normal frogs are indistinguishable.
Authors: Van der Kloot W
Published: December 2014

1. A recent paper concludes that the shapes of spontaneous and uniquantal‐evoked signals are different. The signals were recorded with extracellular electrodes, often in the presence of neostigmine. Differences were reported between the voltage‐time integrals, and between the decay times of spontaneous and evoked signals. 2. These results disagree with earlier studies using the two‐electrode voltage clamp technique. 3. We recorded miniature‐endplate currents (MEPCs) and uniquantal‐endplate currents (u‐EPCs) in a low‐Mg(2+)‐Ca2+ solution, sometimes with neostigmine present. Evoked quantal outputs were estimated by the method of failures, so we could reject the appropriate number of the largest evoked releases. The twenty‐nine experiments showed that there were no consistent differences between the current‐time integrals or half‐decay times (t1/2), regardless of whether or not neostigmine was present. 4. When recording simultaneously with intracellular and extracellular electrodes, on average about 25% of the miniatures were seen in both recordings. On average, 63% of the endplate potentials were also seen in both recordings. Extracellular recording may not give the precise localization generally assumed. 5. We again conclude that quanta released by nerve stimulation and spontaneously are indistinguishable at normal frog neuromuscular junctions.
A novel synaptic interaction underlying induction of long‐term depression in the area CA1 of adult rat hippocampus.
Authors: Otani S , Connor J A
Published: December 2014

1. We describe a novel synaptic property that regulates induction of homosynaptic long‐term depression (LTD), and slowly developing heterosynaptic LTD, of Schaffer collateral‐pyramidal cell synapses in adult rat hippocampus. 2. Two independent pathways converging on the same neuron were alternately tested with 0.017 Hz single pulses, and LTD was induced by 900 conditioning stimuli delivered at 2 Hz. All experiments were performed in the presence of the GABA(A) antagonists picrotoxin or bicuculline. 3. After delivery of the 2 Hz stimulation to the homosynaptic pathway, the 0.017 Hz test pulses to the heterosynaptic pathway were interrupted for 25 min. When the test stimulations were resumed, heterosynaptic LTD could not be observed. Homosynaptic LTD also failed to be induced in this protocol. Interruption of test pulses did not itself cause a general increase of synaptic responses. 4. Doubling the frequency of homosynaptic test pulses (to 0.033 Hz) during a 25 min interruption of heterosynaptic stimulus did not preserve homosynaptic LTD. This suggests that the failure of homosynaptic LTD induction seen when the test pulses were interrupted was not caused by a decrease in the number of synaptic inputs at the postsynaptic neuron following conditioning. 5. When only the homosynaptic pathway was involved, with no heterosynaptic stimulation, as in conventional experiments, 2 Hz conditioning successfully induced homosynaptic LTD. 6. We propose that when a heterosynaptic pathway has been recently used, continuous input to that pathway following conditioning is necessary for induction of homosynaptic LTD on the same neuron.
Stimulation of secretion from bovine adrenal chromaffin cells by microsecond bursts of therapeutic levels of ultrasound.
Authors: Robinson I M , Kinnick R R , Greenleaf J F , Fernandez J M
Published: December 2014

1. In this study the secretory response of individual bovine adrenal chromaffin cells was monitored using amperometric carbon‐fibre microelectrodes. Cells were stimulated to secrete by exposure to 20‐100 microseconds long tonebursts of ultrasound (2‐4 x 10(5) Pa; peak pressure at 1 MHz). 2. Three types of secretory responses were observed: an almost instantaneous response, a delayed release of catecholamines, or a series of ‘burst‐like’ secretory bouts. 3. Fura‐2 measurements of intracellular Ca2+ concentrations showed that the release of catecholamines was accompanied by an increase in the intracellular Ca2+ concentration. In the absence of extracellular Ca2+, secretory responses were not evoked showing that Ca2+ entry was necessary to elicit catecholamine release.
The effects of beta‐stimulation on the Na(+)‐K+ pump current‐voltage relationship in guinea‐pig ventricular myocytes.
Authors: Gao J , Mathias R T , Cohen I S , Shi J , Baldo G J
Published: December 2014

1. The whole cell patch clamp technique was used to study effects of the beta agonist isoprenaline (Iso) on the current‐voltage (I‐V) relationship of the Na(+)‐K+ pump current (Ip) in acutely isolated guinea‐pig ventricular myocytes. 2. The effect of Iso on Ip at high [Ca2+]i (1.4 microM) was voltage dependent. The I‐V relationship of Ip in Iso shifted by approximately 30 mV in the negative direction on the voltage axis, increasing Ip at negative voltages but leaving Ip unchanged at positive voltages. 3. Intracellular application of the calmodulin antagonist, calmodulin‐dependent protein kinase II fragment 290‐309, did not eliminate or reduce the Iso‐induced voltage shift, suggesting calmodulin‐dependent protein kinase II was not involved. 4. The Iso inhibition of Ip at low [Ca2+]i (15 nM) was not voltage dependent. Ip was reduced by 20 to 30% in the presence of Iso at each holding potential. 5. When the voltage dependence of Ip was largely reduced by substitution of N‐methyl‐D‐glucamine+ for external Na+, the magnitude of the low [Ca2+]i, Iso‐induced inhibition of Ip was progressively eliminated by increasing the [Ca2+]i. At a [Ca2+]i of 1.4 microM, this inhibition disappeared. 6. At intermediate values of [Ca2+]i, the I‐V curves in Na(+)‐containing solution in the presence and the absence of Iso crossed over. The higher the [Ca2+]i, the more positive the voltage at which the two I‐V curves intersected. 7. During beta‐adrenergic activation our results suggest intracellular Ca2+ has two effects: (a) It prevents protein kinase A (PKA) phosphorylation‐induced inhibition of Ip. (b) It causes a PKA phosphorylation‐induced shift of the pump I‐V relationship in the negative direction on the voltage axis. These effects may have important physiological significance in the regulation of heart rate and cardiac contractility.
The sulphonylurea receptor confers diazoxide sensitivity on the inwardly rectifying K+ channel Kir6.1 expressed in human embryonic kidney cells.
Authors: Ammälä C , Moorhouse A , Ashcroft F M
Published: December 2014

1. We have examined the effects of diazoxide and intracellular ATP (ATPi) on whole‐cell currents in HEK293 cells transfected transiently with the inwardly rectifying K+ channel Kir6.1 (uKATP1) or cotransfected with Kir6.1 and the sulphonylurea receptor (SUR1). 2. Kir6.1 currents were unaffected by the K+ channel opener diazoxide or by dialysis with 0.3 mM ATPi. 3. Kir6.1‐SUR1 currents increased in amplitude when cells were dialysed with 0.3 mM ATP, but not with 5 mM ATP. This activation may be explained by the loss of endogenous ATP from the cell when the intracellular solution contains 0.3 mM ATP. Kir6.1‐SUR1 currents were also activated by diazoxide; this activation was greater with 0.3 mM ATP1 than with 5 mM ATP1. 4. We conclude that SUR1 is required to confer both diazoxide and ATP sensitivity on Kir6.1.
Pancreatic secretion evoked by cholecystokinin and non‐cholecystokinin‐dependent duodenal stimuli via vagal afferent fibres in the rat.
Authors: Li Y , Owyang C
Published: December 2014

1. We have recently demonstrated that cholecystokinin (CCK) at physiological levels stimulates pancreatic enzyme secretion via gastroduodenal mucosal vagal afferent fibres in the rat. The present study was designed to investigate if non‐CCK‐mediated pancreatic stimuli which activate duodenal receptors also utilize similar vagal afferent pathways. 2. Intraduodenal administration of maltose (300 mM), hypertonic saline (500 mosmol l‐1) and mucosal light stroking in anaesthetized rats evoked 70, 57 and 200% increases, respectively, in pancreatic protein secretion with no changes in plasma CCK concentration. Administration of the CCK receptor antagonist L364,718 did not affect pancreatic secretion evoked by these luminal stimuli. 3. Administration of atropine, acute vagotomy and duodenal mucosal application of capsaicin each completely abolished the pancreatic response to these stimuli. 4. Infusion of a subthreshold dose of the octapeptide of CCK (15 pmol (kg body wt)‐1 h‐1) potentiated the pancreatic response to duodenal infusion of maltose (300 mM) and hypertonic saline (500 mosmol l‐1). 5. In conscious rats, perivagal application of capsaicin abolished the pancreatic response evoked by physiological doses of CCK and intraduodenal administration of maltose or hypertonic saline, confirming the physiological relevance of the observations in anaesthetized rats. 6. These results suggest that like CCK, non‐CCK‐mediated luminal stimuli evoke pancreatic enzyme secretion via stimulation of a vagal afferent pathway originating from the duodenal mucosa.
Amino acid substitutions in the rat Na+, K(+)‐ATPase alpha 2‐subunit alter the cation regulation of pump current expressed in HeLa cells.
Authors: Yamamoto S , Kuntzweiler T A , Wallick E T , Sperelakis N , Yatani A
Published: December 2014

1. To study the functional role of negatively charged amino acids (E327 and D925) located in the transmembrane region of the rat alpha 2‐isoform of the Na+, K(+)‐ATPase (rat alpha 2*) in ion transport, the effects of mutations on external K+ dependence and internal Na+ dependence of pump currents were assessed by the patch‐clamp technique in combination with a system for rapid solution changes. 2. Amino acid residues were replaced by glutamine (E327Q) or leucine (D925L) and were introduced into rat alpha 2* cDNA which encodes a ouabain‐resistant isoform. These mutant enzymes were stably expressed in HeLa cells. The endogenous ouabain‐sensitive HeLa cell Na+, K(+)‐ATPase activity was selectively inhibited by 1 microM ouabain present in both the growing media and the assay solution. 3. External K(+)‐ and internal Na(+)‐dependent pump activation was observed in all cells expressing rat alpha 2*, E327Q or D925L; however, the apparent affinities were significantly reduced by the mutations. 4. In E327Q, the activation of pump current was slightly slower than for rat alpha 2*, whereas the deactivation rate was faster. In contrast, D925L produced pump current having dramatically slower activation and deactivation kinetics. 5. These results indicate that these negatively charged amino acids (E327 and D925) are important in cation‐induced conformational changes of the protein, which are intermediate steps in the pump mechanism.
Studies on the blocking action of human Kv3.4 inactivation peptide variants in the mouse cloned Kv1.1 K+ channel.
Authors: Stephens G J , Owen D G , Opalko A , Pisano M R , MacGregor W H , Robertson B
Published: December 2014

1. Whole‐cell patch clamp recordings were made from Chinese hamster ovary (CHO) cells stably expressing homomeric mouse Kv1.1 (delayed rectifier K+; mKv1.1) channels. The effects of internal application of a number of different peptides, based on part of the amino terminal sequence of the human Kv3.4 channel subunit (hKv3.4), were examined in order to determine their influence on N‐type inactivation. 2. For the native hKv3.4 peptide, the association rate constant (kon) increased with membrane depolarization, whilst the dissociation rate constant (koff) had little dependence on voltage. This resulted in the apparent dissociation constant (KD) of the hKv3.4 peptide tending to increase with depolarization. 3. In general, kon increased and apparent KD decreased with positive charge of the hKv3.4 peptide variants; in peptides lacking a hydrophobic amino terminal this correlation was not maintained. In contrast, the rate of dissociation of the variant peptides (koff) was independent of net charge. 4. The blocking activity of the hKv3.4 peptide was not dependent on a disulphide bridge between cysteine residues C6 and C24 and the presence of cysteine residues in the hKv3.4 peptide was not a prerequisite for rapid inactivation. All cysteine‐substituted variants, especially at C6, showed a more rapid recovery from inactivation than the hKv3.4 peptide. Substitutions at C24, and not C6, reduced kon. 5. The present results concerning the action of the mammalian hKv3.4 channel inactivation particle on mKv1.1 channels complement earlier models for the invertebrate Shaker K+ channel. It is proposed that the hydrophobic amino terminal region of the hKv3.4 inactivation peptide blocks the channel pore, whilst the adjacent positively charged region interacts with negative charges on the channel protein.
Calcium permeability increase of endplate channels in rat muscle during postnatal development.
Authors: Villarroel A , Sakmann B
Published: December 2014

1. Patches of endplate membrane were isolated from rat flexor digitorum brevis muscle at different postnatal stages to measure the time course of development changes in conductance, deactivation time constant and relative Ca2+ permeability of endplate channels. 2. The predominant channel conductance was 40 +/‐ 1 pS (n = 9) at postnatal day 9 (P9) or younger whereas it was 59 +/‐ 3 pS (n = 5) at P21 or in older muscle. The deactivation time constant of ensemble patch currents evoked by brief ACh application, decreased from 8 +/‐ 3 ms (n = 45) at P5‐9 to 2.3 +/‐ 0.3 ms (n = 5) in P21‐28 muscle. 3. The relative Ca2+ permeability, measured by the shift of biionic (Ca2+/Cs+) reversal potential of ensemble patch currents upon the replacement of high [Cs+] by high [Ca2+] extracellular solution and with Cs+ as internal reference ion, increased during postnatal development. THe biionic reversal potential shift changed from ‐21 +/‐ 1 mV (n = 8) at P5 to ‐8 +/‐ 1 mV (n = 10) in P15 or older muscle. 4. Recombinant gamma‐AChR channels expressed in Xenopus laevis oocytes had a biionic (Ca2+/Cs+) reversal potential shift of ‐24.9 +/‐ 2 mV (n = 14) comparable to that of neonatal endplate channels whereas the reversal potential shift for recombinant epsilon‐AChR channels was ‐7.6 +/‐ 0.9 mV (n = 13), comparable to that of endplate channels in adult muscle. 5. It is concluded that an approximately 3‐fold increase in Ca2+ current through endplate channels during postnatal development is caused by replacement of the fetal gamma‐subunit by the epsilon‐subunit in juvenile and adult muscle.
Ca2+ diffusion and sarcoplasmic reticulum transport both contribute to [Ca2+]i decline during Ca2+ sparks in rat ventricular myocytes.
Authors: Gómez A M , Cheng H , Lederer W J , Bers D M
Published: December 2014

1. We sought to evaluate the contribution of the sarcoplasmic reticulum (SR) Ca2+ pump (vs. diffusion) to the kinetics of [Ca24]i decline during Ca2+ sparks, which are due to spontaneous local SR Ca2+ release, in isolated rat ventricular myocytes measured using fluo‐3 and laser scanning confocal microscopy. 2. Resting Ca2+ sparks were compared before (control) and after the SR Ca2(+)‐ATPase was either completely blocked by 5 microM thapsigargin (TG) or stimulated by isoprenaline. Na(+)‐Ca2+ exchange was blocked using Na(+)‐free, Ca(2+)‐free solution (0 Na+, O Ca2+) and conditions were arranged so that the SR Ca2+ content was the same under all conditions when Ca2+ sparks were measured. 3. The control Ca2+ spark amplitude (281 +/‐ 13 nM) was not changed by TG (270 +/‐ 21 nM) or isoprenaline (302 +/‐ 10 nM). However, the time constant of [Ca2+]i decline was significantly slower in the presence of TG (29.3 +/‐ 4.3 ms) compared with control (21.6 +/‐ 1.5 ms) and faster with isoprenaline (14.5 +/‐ 0.9 ms), but in all cases was much faster than the global [Ca2+]i decline during a control twitch (177 +/‐ 10 ms). 4. The spatial spread of Ca2+ during the Ca2+ spark was also influenced by the SR Ca2+ pump. The apparent ‘space constant’ of the Ca2+ sparks was longest when the SR Ca2+ pump was blocked, intermediate in control and shortest with isoprenaline. 5. We conclude that while Ca2+ diffusion from the source of Ca2+ release is the dominant process in local [Ca2+]i decline during the Ca2+ spark, Ca2+ transport by the SR contributes significantly to both the kinetics and spatial distribution of [Ca2+]i during the Ca2+ spark.
Disulphonic stilbene block of cystic fibrosis transmembrane conductance regulator Cl‐ channels expressed in a mammalian cell line and its regulation by a critical pore residue.
Authors: Linsdell P , Hanrahan J W
Published: December 2014

1. The disulphonic stilbenes 4,4'‐dinitrostilbene‐2,2'‐disulphonic acid (DNDS) and 4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid (DIDS) were shown to cause a voltage‐dependent inhibition of macroscopic cystic fibrosis transmembrane conductance regulator (CFTR) Cl‐ currents expressed in baby hamster kidney cells when applied to the cytoplasmic face of the membrane. These compounds are known to be relatively ineffective at blocking CFTR from the extracellular side of the membrane. 2. Mutation of a positively charged arginine, previously suggested to be located in the channel pore (R347), to a negatively charged aspartate significantly reduced the affinity of block by both DNDS and DIDS, suggesting that this residue contributes to the binding site for disulphonic stilbenes. 3. It is suggested that the CFTR Cl‐ channel may contain a relatively large inner vestibule in which a number of large anions bind and block Cl‐ permeation. Arginine 347 may be involved in anion binding within this region.
Postsynaptic mechanism of depression of GABAergic synapses by oxytocin in the supraoptic nucleus of immature rat.
Authors: Brussaard A B , Kits K S , de Vlieger T A
Published: December 2014

1. Oxytocin is known to act on autoreceptors of oxytocin neurones in the supraoptic nucleus (SON). We investigated whether oxytocin modulates putative oxytocin neurones by suppressing the GABAA receptor‐mediated synaptic inputs on these cells. 2. GABAergic inhibitory postsynaptic currents (IPSCs) were recorded from SON neurones in hypothalamic slices from young rats. Oxytocin specifically reduced the amplitude of both spontaneous and evoked IPSCs, without altering their current kinetics. 3. The effect of oxytocin was observed in 70% of the magnocellular neurones recorded from the dorsomedial part of the SON. d(CH2)5OVT, a specific antagonist of oxytocin receptors, blocked the effect of oxytocin on the IPSCs. Vasopressin had no effect on oxytocin‐sensitive SON neurones. 4. The intervals between spontaneous IPSCs were not affected by oxytocin. This suggested that oxytocin had a postsynaptic effect on SON neurones. 5. This postsynaptic origin was further substantiated by application of TTX, which blocked all evoked release but did not prevent the suppressive effect of oxytocin on the amplitude of the spontaneous IPSCs still present in the recording. The selective effect of oxytocin on IPSC amplitude was also maintained in nominally zero extracellular calcium. 6. Intracellular perfusion of SON neurones with GTP gamma S mimicked the effect of oxytocin on IPSCs, while GDP beta S, similarly applied, abolished the effect of oxytocin. 7. Application of calcium mobilizers such as thapsigargin and caffeine also reduced the amplitude of spontaneous IPSCs without significantly altering the frequency at which IPSCs occurred. 8. Thus, oxytocin depresses GABAergic synapses in the SON via modulation of the postsynaptic GABAA receptors. This would lead to disinhibition of SON neurones sensitive to oxytocin and could, therefore, be a powerful means of controlling the firing of oxytocin neurones.
Dissociation of hypoxia‐induced chemosensory responses and catecholamine efflux in cat carotid body superfused in vitro.
Authors: Iturriaga R , Alcayaga J , Zapata P
Published: December 2014

1. To examine the correlation between chemosensory response and dopamine release induced by hypoxic stimulation, we studied carotid bodies excised from anaesthetized cats. 2. The carotid bodies with their carotid (sinus) nerves were superfused in vitro with modified Tyrode solution (pH 7.40, at 37.5 degrees C) equilibrated with 20 or 100% O2. The PO2 of the superfusing channel was monitored polarographically. The frequency of chemosensory discharges (fx) was recorded from the whole carotid nerve. Catecholamine (CA) efflux‐mostly consisting of dopamine‐was measured by high‐speed chronoamperometry, through Nafion‐coated carbon electrodes placed on the carotid body tissue. Chemosensory stimulation was induced by intrastream injections of NaCN, by superfusion with 100% N2‐equilibrated saline (lowering PO2 to 25‐40 Torr) or by flow interruption. 3. Low doses of NaCN increased fx, but had no measurable effect on CA efflux, while larger doses produced fast increases in fx, preceding delayed and prolonged increases in CA efflux. Repeated injections of NaCN, still increasing fx, gave reduced CA effluxes. 4. Switching to hypoxic superfusion for 6‐8 min produced large and fast fx increases, but delayed and prolonged augmentations of CA efflux. 5. Administration of three to four boluses of dopamine (7‐15 micrograms; augmenting CA concentration by up to 35 microM) initially decreased fx, after which hypoxic stimulation resulted in enhanced and faster CA effluxes, without changing the speed and intensity of chemosensory responses. 6. Flow interruptions induced fast increases in fx and delayed increases in CA efflux. Repeated flow interruptions produced similar increases in fx but progressively attenuated CA effluxes. 7. Our results suggest that CA efflux is not essential for hypoxia‐induced chemosensory excitation in the cat carotid body. They also suggest the presence of two pools of releasable CAs in the carotid body, one of slow turnover and release, and another of recently incorporated dopamine and fast release, both pools being rapidly depleted by repeated stimulation of the carotid body.
Vesicle‐associated proteins and calcium in nerve terminals of chick ciliary ganglia during development of facilitation.
Authors: Lin Y Q , Brain K L , Nichol K A , Morgan J J , Bennett M R
Published: December 2014

1. The developmental appearance of synaptic vesicle‐associated proteins and nerve terminal calcium ([Ca2+]i) sequestering processes were determined for the chick ciliary ganglia in relation to the maturation of the different phase of increased efficacy of transmitter release following nerve impulses. The maturation phases studied were from stages 34‐35, at the time of synapse formation, to stage 46 at hatching. 2. Western blots and immunohistochemical localization indicated that synaptotagmin 1 and synapsin IIa were detectable at stages 34‐35 and were clearly localized at the nerve terminals by stage 37. Syntaxin was clearly localized at the nerve terminals at stage 34. 3. The relative size of the postganglionic compound action potential, used to measure the transmission efficacy through the ganglion, showed that the slope of the relationship between log efficacy and log extracellular calcium concentration ([Ca2+]o) in low [Ca2+]o was about 4 by stage 46. 4. A mature facilitatory mechanism for transmission was not present at stage 34 and did not emerge until stage 38. A mature augmentation was not present at stages 34 or 38 and was not established until stages 41‐42. Post‐tetanic potentiation (PTP) was not present at stage 34; it was evident at stages 37‐38 and only reached maturity by stages 41‐42. 5. The time course of calcium changes in the nerve terminals following trains of impulses that give rise to facilitation, augmentation and PTP was determined for different stages of development using the indicator Calcium Green‐1 in the nerve terminal. The mature time course of the phases of calcium decline in the nerve terminal associated with facilitation and augmentation was observed as early as stage 38, whereas that of the PTP phase did not mature until after stage 42. 6. These results are discussed in terms of the maturation of the vesicle‐associated proteins and calcium influx into the terminal following trains of impulses that give rise to the different components of increased synaptic efficacy.
Functional analysis of a chimeric mammalian peptide transporter derived from the intestinal and renal isoforms.
Authors: Döring F , Dorn D , Bachfischer U , Amasheh S , Herget M , Daniel H
Published: December 2014

l. Recently two genes have been identified by expression cloning that encode mammalian epithelial peptide transporters capable of translocating di‐ and tripeptides and selected peptidomimetics by stereoselective and rheogenic substrate‐H+ cotransport. PepT1 from rabbit or human small intestine induces a transport activity with high transport capacity but rather low substrate affinity when expressed in Xenopus oocytes. In contrast, the renal carrier PepT2 is a high affinity‐type transporter with a lower maximal transport capacity. In addition, both transporters show differences in pH dependence and substrate specificity. 2. As a first approach to identify structural components of the transport proteins that determine their phenotypical characteristics, we constructed a recombinant chimeric peptide transporter (CH1Pep) in which the aminoterminal region (residues 1‐401) is derived from PepT2 whereas the carboxyterminal region (residues 402‐707) starting at the end of transmembrane domain 9 is derived from PepT1. Expression of PepT1, PepT2 and CH1Pep in Xenopus oocytes allowed the characteristics of the transporters to be determined by flux studies employing a radiolabelled dipeptide and by the two‐electrode voltage clamp technique. 3. Our studies indicate that CH1Pep conserves the characteristics of PepT2 including the high affinity for dipeptides and peptidomimetics, the substrate specificity, the pH dependence of transport activation and the electrophysiological parameters. We conclude that the phenotypical characteristics of the renal peptide transporter are determined by its amino‐terminal region.
Electrogenic arginine transport mediates stimulus‐secretion coupling in mouse pancreatic beta‐cells.
Authors: Smith P A , Sakura H , Coles B , Gummerson N , Proks P , Ashcroft F M
Published: December 2014

1. We have investigated the mechanism by which L‐arginine stimulates membrane depolarization, an increase of intracellular calcium ([Ca2+]i) and insulin secretion in pancreatic beta‐cells. 2. L‐Arginine failed to affect beta‐cell metabolism, as monitored by NAD(P)H autofluorescence. 3. L‐Arginine produced a dose‐dependent increase in [Ca2+]i, which was dependent on membrane depolarization and extracellular calcium. 4. The cationic amino acids L‐ornithine, L‐lysine, L‐homoarginine (which is not metabolized) and NG‐monomethyl‐L‐arginine (L‐NMMA, a nitric oxide synthase inhibitor) produced [Ca2+]i responses similar to that produced by L‐arginine. The neutral nitric oxide synthase inhibitors NG‐nitro‐L‐arginine (L‐NNA) and N omega‐monomethyl‐L‐arginine (L‐NAME) also increased [Ca2+]i. D‐Arginine was ineffective. 5. L‐Arginine did not affect whole‐cell Ca2+ currents or ATP‐sensitive K+ currents, but produced an inward current that was carried by the amino acid. 6. The reverse transcriptase‐polymerase chain reaction demonstrated the presence of messenger RNA for the murine cationic amino acid transporters mCAT2A and mCAT2B within the beta‐cell. 7. L‐Arginine did not affect beta‐cell exocytosis as assayed by changes in cell capacitance. 8. Our data suggest that L‐arginine elevates [Ca2+]i and stimulates insulin secretion as a consequence of its electrogenic transport into the beta‐cell. This uptake is mediated by the mCAT2A transporter.
Basal release of nitric oxide induces an oscillatory motor pattern in canine colon.
Authors: Keef K D , Murray D C , Sanders K M , Smith T K
Published: December 2014

1. The consequences of intrinsic, basal nitric oxide release on electrical and contractile activity of canine proximal colon were examined. Membrane potential and contraction were simultaneously recorded from the circular muscle in the presence of drugs to block adrenergic and cholinergic responses. 2. Electrical slow waves were recorded from muscle cells near the submucosal surface of the circular layer. Spontaneous contractions were initiated by each slow wave. Contractile amplitude increased 1.9‐fold when nerves were blocked with tetrodotoxin (TTX, 1 microM). 3. Muscle cells near the myenteric surface displayed myenteric potential oscillations (MPOs) averaging 16 cycles per minute (c.p.m.) in frequency and 10 mV in amplitude. Twenty‐five per cent of muscles displayed an additional slow, neurogenic oscillation (mean frequency, 1 c.p.m.; amplitude, 14 mV) superimposed upon the MPO rhythm. 4. The nitric oxide (NO) synthase inhibitor N omega ‐nitro‐L‐arginine (L‐NA, 100 microM; n = 16) abolished neurogenic oscillations, depolarized cells, and increased MPO upstroke velocity, amplitude and frequency. The actions of L‐NA were mimicked by N omega‐nitro‐L‐arginine methylester (L‐NAME, 100 microM) and oxyhaemoglobin (3%). 5. Spontaneous contractions were increased 2.3‐fold by L‐NA, and TTX had no effect on contractions after addition of L‐NA. 6. The NO‐donor sodium nitroprusside (SNP, 1 microM) reversed the electrical and mechanical effects of L‐NA and initiated slow oscillations similar to the neurogenic oscillations. Slow oscillations were also evoked with S‐nitroso‐N‐acetylpenicillamine (SNAP, 1 microM). The effects of NO donors were blocked by oxyhaemoglobin. 7. Slow electrical oscillations could not be elicited by SNP after removal of a thin strip of circular muscle along the myenteric edge. 8. These data suggest that the spontaneous electrical and contractile activity of the proximal colon is tonically suppressed by basal release of NO. Basal NO causes an oscillatory pattern of electrical and mechanical activity. This activity does not require patterned firing of nerves; rather a continuous, low level release of NO would be capable of producing the neurogenic oscillatory behaviour. The slow oscillatory activity depends upon the presence of the myenteric region of the circular muscle layer, which contains cell bodies of enteric neurons and interstitial cells of Cajal.
Restoration of the transient outward potassium current by noradrenaline in chagasic canine epicardium.
Authors: Han W , Barr S C , Pacioretty L M , Gilmour R F
Published: December 2014

1. The transient outward potassium current (Ito) is reduced in canine epicardial myocytes during the acute stage of infection with Trypanosoma cruzi (Chagas' disease). Sympathetic nerve terminals are also destroyed during the acute stage of this disease. To test whether the reduction of Ito is related to the absence of sympathetic innervation, acutely infected isolated epicardial myocytes were exposed in vitro to the sympathetic neurotransmitter noradrenaline (NA) and the effects of NA exposure on Ito were determined. 2. Continuous exposure to NA (1.0 microM) for 0‐6 h had no effect on Ito density, whereas exposure to NA for 24 h significantly increased Ito density. Ito was also restored 24 h after a 1 h exposure to NA. Cell capacitance was not significantly affected by NA. 3. The alpha1‐adrenergic receptor antagonist prazosin (0.1 microM) blocked the effects of NA on Ito, but the beta‐adrenergic receptor antagonist propranolol (20 microM) did not. The beta‐adrenergic receptor agonist isoprenaline (1 microM) had no effect on Ito. 4. Restoration of Ito by NA was prevented by pretreatment with neomycin (100 microM), a phospholipase C inhibitor, but not by pretreatment with 100‐400 ng ml(‐1) pertussis toxin (PTX). 5. The protein kinase C (PKC) activator phorbol 12‐myristate 13‐acetate (0.1 microM) mimicked the effect of NA on Ito, whereas the inactive analogue 4alpha‐phorbol (20 microM) had no effect on Ito. Pretreatment with bisindolylmaleimide (0.1 microM), a specific PKC inhibitor, completely blocked the effect of NA on Ito. 6. Thus, NA restores Ito in chagasic canine epicardial myocytes. The induction of Ito by NA appears to result from alpha1‐adrenergic stimulation of PKC via a PTX‐insensitive signalling cascade. These results suggest that the reduction of Ito in chagasic myocytes during the acute stage of Chagas' disease may reflect the lack of the trophic effects of sympathetic innervation.
A Multibody Dynamics Framework for Simulation of Rovers on Soft Terrain
Authors: Azimi Ali , Holz Daniel , Kövecses Jozsef , Angeles Jorge , Teichmann Marek
Published: December 2014

A new framework is developed for efficient implementation of semi-empirical terramechanics models in multibody dynamics environments. In this approach, for every wheel in contact with soft soil, unilateral contact constraints are added for both the normal direction and the tangent plane. The forces associated with the latter, like traction and rolling resistance, are formulated in this approach as set-valued force laws, their properties being determined by deregularization of the terramechanics relations. As shown in the paper, this leads to the dynamics representation in the form of a linear complementarity problem (LCP). With this formulation, stable simulation of rovers is achieved even at relatively large time steps. In addition, a high-resolution height-field (HF) is employed to model terrain-surface deformation and changes in hardening of soil under the wheel. As a result, the multipass effect is captured in the presented approach. In addition, an extensive set of experiments was conducted using a version of the Juno rover (Juno II). The experimental results are analyzed and compared with the model developed in the paper.
Investigation on Air-Water Two-Phase Flow in Downward Minichannel
Authors: Mehta Hemant B. , Banerjee Jyotirmay
Published: December 2014

Experimental investigations are reported for gas-liquid two-phase flow through 2.15 mm circular minichannel. Influence of premixing of air-water two-phase flow through T-junction (TJ) and Y-junction (YJ) geometries is established. Vertical downward orientation (VDW) is selected for the experiments. Different flow patterns are observed and flow pattern maps are developed. The developed flow pattern maps are then compared with available literature. It is observed that inlet premixing play an important role for establishing the flow patterns and to develop flow pattern maps in VDW orientation.
Losses due to the Flow Through Conduit Components in Mini- and Micro- Systems Accounted for by Head Loss/Change Coefficients
Authors: Schmandt Bastian , Herwig Heinz
Published: December 2014

The definition of head loss/change coefficients should be based on the dissipation in the flow field or, in a more general sense, on the entropy generation due to a conduit component. When, in the simplest case, unbranched flow is considered, an entropy based approach is straight forward since the flow rate can be used as the general reference quantity. If, however, one mass flow rate is split or two partial flow rates are united like in junctions, a new aspect appears: There is an energy transfer between the single branches that has to be accounted for appropriately. It turns out that this energy transfer changes the total head in each flow branch in addition to the loss of total head due to entropy generation. Therefore, appropriate coefficients for junctions should be named head change coefficients. As an example, head change coefficients for dividing and combining flows due to T-shape micro-junctions are investigated and discussed with respect to their physical meaning. For combining flows, the special case of engulfment, leading to enhanced mixing in micro mixers, is considered in detail.
A Liquid Metal Based Capacitive Microsensor
Authors: Gao Meng , Gui Lin
Published: December 2014

Capacitive microsensor is a widely used detection technique for the analysis and assays in biochemistry, biomedicine, environmental monitoring and force measurement in MEMS. In this study, a liquid-metal based capacitive microsensor is proposed. A pair of high aspect ratio polydimethylsiloxane (PDMS) microchannels were fabricated symmetrically and vertically to both sides of detection channel. These two microchannels were filled with room temperature liquid-metal to form two electrodes. These two liquid-metal microchannels worked as two polar plates of a micro parallel-plate capacitor with the detection channel going between them. When the fluid changes in the detection channel, the capacitance of the micro parallel-plate capacitor will also change. Thus, by measuring the change in the capacitance of the micro capacitor, the fluid in the detection channel can be therefore detected. The capacitive microsensor can provide a wide range of applications in microfluidic technologies, such as detection of droplets, cells, particles or biological macromolecules. For better understanding of the capacitive microsensor, theoretical model was developed to reveal the working principle. To evaluate the capacitive microsensor, experiments were also performed to measure the microparticle concentration in deionized water by measuring its dielectric constant.
A Comparative Study of Subcooled Flow Boiling in Uniform, Diverging Cross-Section and Segmented Finned Microchannels
Authors: Prajapati Yogesh K. , Pathak Manabendra , Khan Mohd. Kaleem
Published: December 2014

In this work an experimental investigation has been performed to assess the heat transfer characteristics during subcooled flow boiling in diverging and segmented finned microchannels relevant to applications in electronics cooling systems. Experiments have been also performed in uniform cross-section microchannels to compare their performances with other two types of channels configurations. Arrays of microchannel consisting of 12 numbers of channels with rectangular cross-section have been fabricated on individual copper block for these three different geometrical configurations. Deionized water has been used as the working fluid in the experiment. Experiments have been performed mostly in subcooled boiling regions relevant to cooling of electronic components where bulk fluid was below the saturation temperature and the surface temperature was around the saturation temperature of the coolant. The heat transfer characteristics of all three configurations have been compared in terms of heat transfer coefficient and thermal instability during highly subcooled and developed subcooled flow boiling. Although diverging channel performs significantly better in saturated and superheated regions of boiling with high heat flux as observed in literature, in present work its performance has been found slightly better in subcooled boiling regions compared to uniform cross-section channel. Segmented finned channels have shown the best performance both in sensible heating and subcooled region and thus demonstrate high potential for electronics cooling applications.
Experimental Investigation of Single-Phase Liquid Flow and Heat Transfer in Multiport Minichannels
Authors: Altinoz Mesru , Yazicioglu Almila Guvenc , Baker Derek
Published: December 2014

Small channels have been an area of interest since the 1970s owing to their enhanced heat transfer characteristics. However a wide number of studies in literature show inconsistent results. In this work, an experimental set-up has been designed and constructed to investigate pressure drop and heat transfer characteristics of single-phase water flow in rectangular multiport minichannels. Laminar flow inside three minichannels with different hydraulic diameters and different port numbers were examined under a constant heat flux boundary condition. The results are presented in terms of Poiseuille number (Po) and average Nusselt number (Nu). Generally, average Nusselt number results and Poiseuille number results showed good agreement with constant Po theory and constant Nu theory, excluding developing effects and experimental errors. On the other hand, developing effects are found to be increasing as hydraulic diameter decreases. Similarly, constant Nu value showed a decrease with increasing hydraulic diameter. The experimental results are compared with conventional correlations. While the agreement with conventional correlations is satisfactory, the predictions of the correlations overestimated most of the results. No early transition was observed for Reynolds number (Re) smaller than 1800.
A Microchannel With Repeated Sharp Corners for Single Stream Particle Focusing
Authors: Fan Liangliang , He Xukun , Zhao Liang , Han Yu , Zhe Jiang
Published: December 2014

A new microfluidic device for fast and high throughput microparticle focusing is reported. The particle focusing is based on the combination of inertial lift force effect and centrifugal force effect generated in a microchannel with a series of repeated sharp corners on one side of the channel wall. The inertial lift force effect induces two focused particles streams in the microchannel, and the centrifugal force generated at the sharp corner structures tends to drive the particles laterally away from the corner. With the use of a series of the repeated, sharp corner structures, a single and highly focused particle stream was achieved near the straight channel wall at a wide range of flow rates. In comparison to other hydrodynamic particle focusing methods, this method is less sensitive to the flow rate and can work at a higher flow rate (high throughput). With its simple structure and operation, and high throughput, this method can be potentially used in microparticle focusing processes in a variety of lab-on-a chip applications.
Bubble Removal in Microfluidic Devices Using Nanofibrous Membranes
Authors: Vundavilli Ravindra , Darabi Jeff
Published: December 2014

This paper presents an experimental study to determine bubble removal characteristics of nanofibrous membranes in microfluidic devices. It is well known that the presence of gas bubbles in fluidic channels can cause significant flow disturbances and adversely affect the overall performance and operation of microfluidic devices. In this study, a microfluidic device is designed and fabricated to generate and extract bubbles from a microfluidic channel. A T-junction is used to produce controllable bubbles at the entrance of fluidic channel. The generated bubbles are then transported to a bubble removal region and vented through a highly porous hydrophobic membrane. Four different hydrophobic PTFE membranes with different pore sizes ranging from 0.45 to 3 μm were used to permeate air bubbles. The fluidic channel width was 500 μm and channel height ranged from 100 to 300 μm. The effects of pore size, channel height, and liquid flow rate on the bubble removal rate are investigated. The results reveal that the rate of bubble removal increases with increasing the pore size and channel height but decreases with increasing the liquid flow rate.
Effect of Electrode Geometry on Droplet Splitting in Digital Microfluidic Platforms
Authors: Samiei Ehsan , Rezaei Nejad Hojatollah , Hoorfar Mina
Published: December 2014

This paper studies the effect of the electrode aspect ratio on droplet splitting in a digital microfluidics (DMF) chip including an array of 3 electrodes in which the middle electrode is kept square while the two side electrodes have different aspect ratios. The aspect ratio is changed from 0.9 to 1.3 while the surface area of the electrodes is kept constant for all cases. Results show that changing the aspect ratio can severely change the required voltage for splitting with a nonlinear behavior. It is also shown that for a constant gap between the top and bottom plates and a constant volume of the droplet, the relation between the threshold voltage and the aspect ratio is parabolic, for which there is an aspect ratio with a minimum threshold voltage. Changing the volume of the droplet changes the threshold voltage and hence the aspect ratio corresponding to the minimum threshold voltage required for splitting.