bluuebunny/crossref_metadata_2025 huggingface dataset:
A novel mechanosensitive cationic channel from the endothelium of rat aorta.
Authors: Marchenko S M , Sage S O
Published: December 2014

1. Single channel currents were recorded from the lumenal surface of endothelium of excised intact rat aorta using the patch clamp technique. 2. The majority of cell‐attached and inside‐out patches contained cationic channels with an equal permeability to Na+ and K+. Positive pressure applied through the pipette reversibly increased their open probability, whereas negative pressure reversibly decreased it. The dependence of the channel activity on pressure was sigmoidal in all tested patches. 3. The slope conductance of the channel for inward current was 33.9 +/‐ 2.1 pS in a nominally Ca(2+)‐free extracellular solution. With 1 mM CaCl2 in the extracellular solution, the channel conductance for inward current was reduced to 21.2 +/‐ 2.3 pS. In isotonic CaCl2 solution, the slope conductance of the channel was 5.9 +/‐ 1.3 pS. The ionic permeability ratio was PCa: PNa: PK = 3.5:1:1. 4. Gadolinium and lanthanum at a concentration of 10 microM did not affect the channels, but at higher concentrations (> or = 100 microM) reduced inward currents through the channels. 5. The mechanosensitive channel reported here is different in its gating mechanism and pharmacology from stretch‐activated channels described previously. This channel may be involved in mechanotransduction of haemodynamic stimuli in endothelium.
An ATP‐gated cation channel with some P2Z‐like characteristics in gastric smooth muscle cells of toad.
Authors: Ugur M , Drummond R M , Zou H , Sheng P , Singer J J , Walsh J V
Published: December 2014

1. Whole‐cell and single‐channel currents elicited by extracellular ATP were studied in freshly dissociated smooth muscle cells from the stomach of the toad Bufo marinus using standard patch clamp and microfluorimetric techniques. 2. This ATP‐gated cation channel shares a number of pharmacological and functional properties with native rat myometrium receptors, certain native P2Z purinoceptors and the recently cloned P2X7 purinoceptor. But, unlike the last two, the ATP‐gated channel does not mediate the formation of large non‐specific pores. Thus, it may represent a novel member of the P2X or P2Z class. 3. Extracellular application of ATP (> or = 150 microM) elicited an inward whole‐cell current at negative holding potentials that was inwardly rectifying and showed no sign of desensitization. Na+, Cs+ and, to a lesser degree, the organic cation choline served as charge carriers, but Cl‐ did not. Ratiometric fura‐2 measurements indicated that the current is carried in part by Ca2+. The EC50 for ATP was 700 microM in solutions with a low divalent cation concentration. 4. ATP (> or = 100 microM) at the extracellular surface of cell‐attached or excised patches elicited inwardly rectifying single‐channel currents with a 22 pS conductance. Cl‐ did not serve as a charge carrier but both Na+ and Cs+ did, as did choline to a lesser extent. The mean open time of the channel was quite long, with a range in hundreds of milliseconds at a holding potential of ‐70 mV. 5. Mg2+ and Ca2+ decreased the magnitude of the ATP‐induced whole‐cell currents. Mg2+ decreased both the amplitude and the activity of ATP‐activated single‐channel currents. 6. ADP, UTP, P1, P5‐di‐adenosine pentaphosphate (AP5A), adenosine and alpha, beta‐methylene ATP (alpha, beta‐Me‐ATP) did not induce significant whole‐cell current. ATP‐gamma‐S and 2‐methylthio ATP (2‐Me‐S‐ATP) were significantly less effective than ATP in inducing whole‐cell currents, whereas benzoylbenzoyl ATP (BzATP) was more effective. BzATP, alpha, beta‐Me‐ATP, ATP‐gamma‐S and 2‐Me‐S‐ATP induced single‐channel currents, but a higher concentration of alpha, beta‐Me‐ATP was required. 7. BzATP did not induce the formation of large non‐specific pores, as assayed using mag‐fura‐2 as a high molecular mass probe.
Long‐term influence of neonatal hypoxia on catecholamine activity in carotid bodies and brainstem cell groups of the rat.
Authors: Soulier V , Dalmaz Y , Cottet-Emard J M , Lagercrantz H , Pequignot J M
Published: December 2014

1. In order to determine the long‐term influence of neonatal hypoxia on catecholaminergic activity in peripheral arterial chemoreceptors and brainstem noradrenergic cell groups (A1, A2, A5 and A6), 1‐day‐old male rat pups were subjected to hypoxia (10% oxygen) for 6 days and then supplied with normal air. Control animals were kept at normoxia from birth. Rats were killed at either 3 or 8 weeks of age. 2. The content of dopamine and noradrenaline in carotid bodies of neonatally hypoxic rats was increased at both 3 and 8 weeks of age. 3. Noradrenaline turnover was selectively decreased in the caudal portion of A2 (located in the area of chemosensory afferent projection) at 8 weeks of age (‐76 +/‐ 2%), while this turnover was unaffected in rostral A2 cells. Noradrenergic activity in A1, A5 and A6 was altered by neonatal hypoxia in an age‐dependent fashion. 4. The data suggest that neonatal hypoxia induces long‐term changes in the basal activity of the carotid body and brainstem noradrenergic cell groups. Such changes might contribute to neuronal regulation of the delayed respiratory, arousal and neural sequelae associated with neonatal hypoxia. These changes could also be involved in the early programming of respiratory and blood pressure control.
Analysis of a protein region involved in permeation and gating of the voltage‐gated Torpedo chloride channel ClC‐0.
Authors: Ludewig U , Jentsch T J , Pusch M
Published: December 2014

1. The chloride channel from the Torpedo electric organ, ClC‐0, is controlled by two distinct (‘fast’ and ‘slow’) voltage‐dependent gates. Here we investigate the effects of mutations in a region after putative transmembrane domain D12. A mutation in this region has previously been shown to change fast gating and permeation. 2. We used a combination of site‐directed mutagenesis with two‐electrode voltage‐clamp and patch‐clamp measurements. 3. Most conservative substitutions have minor effects, while more drastic mutations change kinetics and voltage dependence of fast gating, as well as ion selectivity and rectification. 4. While ClC‐0 wild‐type (WT) channels deactivate fully in two‐electrode voltage clamp at negative voltages, channels do not close completely in patch‐clamp experiments. Open probability is increased by intracellular chloride in a concentration‐ but not voltage‐dependent manner. 5. In several mutants, including K519R, the minimal macroscopic open probability of fast gating is larger than in WT. Mutant channels fluctuate at negative potentials between open and closed conformations. Open probability is much more effectively increased by intracellular chloride than in WT. The observations support the idea that permeating ions inside the pore stabilize the open state. 6. Besides effects on permeation and gating of single protopores, some mutations affect ‘slow’ gating. In summary, the region after D12 participates in fast as well as in slow gating; mutations additionally influence permeation properties.
Shaker B K+ conductance in Na+ solutions lacking K+ ions: a remarkably stable non‐conducting state produced by membrane depolarizations.
Authors: Gómez-Lagunas F
Published: December 2014

1. Shaker B K+ channels, expressed in the insect cell line Sf9, were studied in zero K+, Na+ or N‐methyl‐D‐glucamine (NMG)‐containing solutions. In the absence of K+ ions on both sides of the membrane, the K+ conductance collapsed with the delivery of short depolarizing pulses that activated the channels. The collapse of the conductance was fully prevented when the channels were kept closed at a holding potential of ‐80 mV. 2. The fall in K+ conductance had the notable characteristic of being strikingly stable. At ‐80 mV or more negative holding potentials, the conductance never recovered (cells observed for up to 1 h). 3. The extent of collapse of the K+ conductance depended on the number of depolarizing activating pulses applied in zero K+ solutions. For moderate to low frequencies of pulsing (1 to 0.002 Hz), the extent of the collapse did not depend on the frequency. 4. K+, Rb+, Cs+ and NH4+ added to the external Na+ solution impeded the fall in K+ conductance. 5. TEA added to the external, zero K+, Na(+)‐containing solution also precluded the fall of the conductance. The protection by TEA paralleled its block of the outward K+ currents recorded with standard recording solutions. 6. The fall in K+ conductance was prevented by depolarized holding potentials. 7. The K+ conductance that was thought to be irreversibly lost at ‐80 mV or more negative holding potentials was fully recovered, however, after a prolonged (tens of seconds to minutes) change in the holding potential to depolarized values (above ‐50 mV). Full recovery could be obtained at any time after the former halt of the conductance.
Membrane properties and synaptic inputs of suprachiasmatic nucleus neurons in rat brain slices.
Authors: Jiang Z G , Yang Y , Liu Z P , Allen C N
Published: December 2014

1. Whole‐cell recordings were made from 390 neurons of the suprachiasmatic nucleus (SCN) in horizontal brain slices during different portions of the circadian day. The locomotor activity of the rats was measured prior to the preparation of brain slices to insure that each rat was entrained to a 12 h‐12 h light‐dark cycle. 2. The mean input conductance was 42% higher (1.58 nS) in neurons recorded near the subjective dawn than those (1.11 nS) recorded near the subjective dusk. The current required to hold the neurons at ‐60 mV also showed a circadian variation with a peak in the middle of the subjective day and a nadir in the middle of the subjective night. Analysis of the variations in the input conductance and the holding current at ‐60 mV suggested that at least two ion conductances are involved in the pacemaking of the circadian rhythms. 3. Voltage‐clamped SCN neurons often had both outward and inward spontaneous postsynaptic currents. The outward currents were blocked by bicuculline but not by strychnine, and were identified as IPSCs mediated by GABAA receptors. The inward currents were blocked by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) and were identified as EPSCs mediated by glutamate. Most spontaneous synaptic currents were miniature currents but action potential‐dependent large events were seen more often in IPSCs than in EPSCs. 4. Stimulation of the optic nerve or chiasm usually evoked a monosynaptic EPSC which was mediated by both NMDA and non‐NMDA receptors. In 13% of cells, optic nerve stimulation evoked an outward current or an inward current followed by an outward current; all the evoked currents were blocked by 4‐aminophosphonovaleric acid (APV) and CNQX whereas the outward current only was blocked by bicuculline, suggesting involvement of an inhibitory interneuron. 5. SCN neurons sum the excitatory inputs from both optic nerves; on average each SCN cell receives innervation from at least 4.8 retinohypothalamic tract (RHT) axons. 6. Focal stimulation in the vicinity of the recorded neuron revealed that nearly all SCN neurons receive local or extranuclear GABAergic inputs operating via GABAA receptors. The EPSCs activated by such stimulation were not significantly different in amplitude and pharmacological properties from those induced by RHT stimulation. 7. One hundred and one neurons were labelled with neurobiotin during whole‐cell recording. Based on the dendritic structures, four types of SCN neurons (monopolar, radial, simple bipolar and curly bipolar) were identified. The curly bipolar cells had a higher membrane conductance, holding current and hyperpolarization‐activated current (Ih) amplitude than the other neuronal types. Radial neurons did not respond to optic nerve stimulation, which activated EPSCs in the other cell types.
Albumin transfer across the choroid plexus of South American opossum (Monodelphis domestica).
Authors: Knott G W , Dziegielewska K M , Habgood M D , Li Z S , Saunders N R
Published: December 2014

1. Blood‐cerebrospinal fluid (CSF) transfer of various exogenous albumins has been investigated in developing Monodelphis domestica (South American grey short‐tailed opossum) and compared with the steady‐state CSF: plasma ratios for endogenous (Monodelphis) albumin. Ratios for Monodelphis albumin and human albumin were similar and were the highest at postnatal day 5 (P5) (48.2 +/‐ 4.4 and 40.6 +/‐ 4.5%, respectively). The ratio for bovine albumin was similar to the steady‐state ratio for Monodelphis albumin at P7‐8 but became consistently lower than the Monodelphis albumin ratio at all other ages until P32‐36 when all albumins tested attained a similar low ratio. The CSF:plasma ratio of chemically modified (succinylated) bovine albumin was always significantly lower than that of other albumins, except at the oldest age examined (P32‐36). 2. Immunocytochemistry showed that within the brain, albumin was confined to the lumen and endothelial cells of blood vessels. In the choroid plexus only a small proportion (0.2‐1.7% of the total cell number) of epithelial cells was positive for albumin, both endogenous and exogenous, at all ages studied (except the 3rd ventricle where cells were only positive from P8). The CSF was strongly positive for all albumins. The peak proportion of positive cells and of albumin concentrations in CSF occurred at P8. These findings suggest that the primary route for penetration of albumin into CSF is directly across the choroid plexus rather than via the brain. 3. Double‐labelling immunocytochemistry revealed that the same epithelial cells contained both endogenous (Monodelphis) and exogenous (human) albumin. In contrast, for succinylated albumin, at P7 only about 35% (lateral ventricle) and 50% (4th ventricle) of Monodelphis albumin‐positive cells were also positive for succinylated albumin, but by P30 this proportion increased to 90% at both sites. 4. Thus the developing choroid plexus distinguishes between different albumins. Chemical modification of albumin (succinylation) disrupts this mechanism. It is proposed that in older animals (P32‐36) all of the albumin in the CSF is derived from plasma by diffusion (as in adult animals). At earlier stages of development, a proportion of the albumin in CSF also appears to be transferred from the plasma by diffusion with an additional component transferred by a mechanism that can distinguish between different species of albumin. The main route of entry of albumin to CSF seems likely to be via the choroid plexus epithelial cells.
The effects of tetrodotoxin‐induced muscle paralysis on the physiological properties of muscle units and their innervating motoneurons in rat.
Authors: Gardiner P F , Seburn K L
Published: December 2014

1. Although the inactivity of a slow muscle (cat soleus) induced via nerve impulse blockade has been demonstrated to have some axotomy‐like effects (decreased after‐hyperpolarization (AHP) duration) on its innervating motoneurons, the reported effects of inactivity on motoneurons which innervate fast muscles containing mixtures of motor unit types are equivocal. This study was designed to determine the effect of a period (2 weeks) of complete hindlimb muscle paralysis, via tetrodotoxin (TTX) blockade of sciatic nerve impulses, on the contractile (muscle units) and electrophysiological (motoneurons) properties of motor units in the rat gastrocnemius. Motoneuron properties were also compared with those of rats subjected to sciatic nerve axotomy 2 weeks earlier. 2. At the time of the terminal experiment (24 h after the removal of the TTX delivery system) in anaesthetized animals, properties of tibial motoneurons (i.e. rheobase current, input resistance, time course of after‐potentials) were determined using conventional microelectrode techniques. For those tibial motoneurons innervating the gastrocnemius, muscle unit responses (i.e. twitch force and time course, maximum tetanic tension, fatigability) were also recorded in response to current injection. 3. Consistent with previously reported whole‐muscle responses to TTX‐induced disuse, the TTX‐treated gastrocnemius muscle units showed weaker tetanic forces, prolonged twitches and elevated twitch/tetanic ratios. These effects were similar for motor units classified as small, medium and large according to their tetanic tension‐generating capacities. Muscle unit fatigue resistances appeared to be unchanged. 4. The mean values, distributions and ranges of tibial motoneuron properties were similar between control and TTX‐treated groups for rheobase, input resistance and AHP half‐decay time. In the case of the latter, the proportion of motoneurons possessing ‘slow’ AHP half‐decay times (> 20 ms) was not significantly different in control (17%) and TTX‐treated groups (11%). 5. Motoneurons axotomized 2 weeks earlier had a significantly higher (42‐69%) mean input resistance and a longer (34‐42%) mean AHP half‐decay time when compared with the control and TTX‐treated groups. 6. It appears that, for fast muscles containing several different motor unit types, TTX‐induced axon blockade does not produce similar effects on motoneuron intrinsic properties to those evoked by axotomy. This lack of effect on the distribution and range of these properties of tibial motoneurons indicates that none of the motoneurons which innervate muscles of mixed fibre type are particularly susceptible to the decreased activity and the atrophy‐associated muscle changes produced by this condition. Thus, the apparent ‘retrograde signalling’ of muscle on motoneuron properties reported previously for the cat soleus may be specific to this particular muscle or species.
Cross‐correlation analysis of motor unit activity recorded from two separate thumb muscles during development in man.
Authors: Gibbs J , Harrison L M , Stephens J A
Published: December 2014

1. Multi‐unit surface EMG signals were recorded from the short and long thumb abductor muscles of seventy‐five children aged from 4 to 15 years and from nine adults during simultaneous abduction and extension of the left and right thumb. Ability to perform independent finger movements was investigated by timing a series of sequential finger‐to‐thumb oppositions. 2. Cross‐correlograms were constructed from the discharges of motor units recorded from the long and short abductor muscles acting on the same thumb. In the majority of subjects, short duration central peaks were present indicating the presence of a common drive to the motoneurone pools innervating these two muscles. Except for those subjects aged 4 and 5 years, the size of these central correlogram peaks did not differ significantly between the dominant and non‐dominant hands. 3. The prevalence of central cross‐correlogram peaks in different subjects increased from the age of 4 years to 15 years. The size of the central cross‐correlogram peak increased with age up to 10 years but did not alter significantly after this age. The duration of the central peak steadily decreased over the age range of 4 to 15 years. 4. Multilinear regression analysis of data recorded from children revealed that there was a positive, but weak, correlation between the size of the cross‐correlogram peak and the rate of performance of sequential finger movements after having controlled for age.
Inwardly rectifying potassium channels expressed by gene transfection into the green Monkey kidney cell line COS‐1.
Authors: Omori K , Oishi K , Matsuda H
Published: December 2014

1. cDNA encoding a functional inwardly rectifying K+ (IRK1) channel was transfected into COS‐1 cells (a Green Monkey kidney cell line) using the liposome method, and voltage clamp experiments were done after 48‐72 h. 2. Transfected cells showed inward rectification under whole‐cell recording. The unitary current‐voltage relationships in the inside‐out configuration were almost linear in the absence of internal Mg2+ and polyamines, and the channel conductance averaged 34.1 +/‐ 2.0 pS (n = 15) at 23‐26 degrees C. 3. Internal Mg2+ (2‐10 microM) induced sublevels in the outward current with one‐third and two‐thirds of the unitary amplitude as in native channels. 4. To determine the subunit stoichiometry, we constructed tandem multimeric cDNAs consisting of the coding sequences of the IRK1 gene linked in a head‐to‐tail fashion. Cells transfected with tandem homomultimers up to octamers showed similar inwardly rectifying K+ channels. 5. A mutation (E138Q) eliminated the ionic conductance of the channel. Channels expressed by dimeric constructs containing a single mutant have a conductance ranging between 5 and 35 pS. 6. The E138Q mutant cotransfected with a wild‐type dimeric, trimeric or tetrameric construct did not alter the channel conductance. The results do not support the notion that IRK1 channel proteins consist of four subunits.
Modulation of plateau properties in dorsal horn neurones in a slice preparation of the turtle spinal cord.
Authors: Russo R E , Nagy F , Hounsgaard J
Published: December 2014

1. Modulation of plateau properties in dorsal horn neurones was studied in a transverse slice preparation of the spinal cord of the turtle. In plateau‐generating neurones high frequency stimulation of the ipsilateral dorsal root (10‐20 Hz, 0.5‐2 min) produced a slow depolarization (2.9 +/‐ 0.6 mV, mean +/‐ S.E.M.; n = 6) and enhanced the properties mediated by dihydropyridine‐sensitive Ca2+ channels. The tetanic stimulus facilitated wind‐up and after‐discharges even when fast synaptic transmission was blocked by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX, 10‐20 microM), (+/‐)‐2‐amino‐5‐phosphonopentanoic acid (AP5, 100 microM), bicuculline (10‐20 microM) and strychnine (5‐20 microM). 2. Application of cis‐(+/‐)‐1‐aminocyclopentane‐1,3‐dicarboxylic acid (ACPD, 10‐50 microM) produced a slow depolarization (5.9 +/‐ 0.5 mV, n = 21) accompanied by an increase in input resistance (28.8 +/‐ 5.1%, n = 12). 3. ACPD increased the excitability by facilitating the plateau properties. In the presence of tetrodotoxin (TTX, 1 microM) a lower threshold and a slower decay of the plateau potential were observed. These effects resulted in facilitation of wind‐up and prolonged after‐discharges. 4. All ACPD‐induced effects were blocked by alpha‐methyl‐4‐carboxyphenylglycine (MCPG, 0.5‐1 mM), a selective antagonist of metabotropic glutamate receptors. The selective agonist for the type I metabotropic glutamate receptor ((RS)‐3,5‐dihydrophenylglycine (DHPG, 50 microM)) reproduced all the effects of ACPD. 5. Application of a supposed neuromodulator, substance P (1‐2 microM) produced a transient depolarization (4 +/‐ 0.6 mV) lasting 4‐6 min during continued application of substance P. Variable effects on the input resistance were observed, a slight increase (12 +/‐ 2%) being the most frequent. In 61% of the cells, substance P induced a clear increase in excitability with no detectable change in input resistance or membrane potential. 6. The effects of substance P on plateau properties were indistinguishable from those produced by ACPD. Unlike the transient depolarization, the facilitation of the plateau properties persisted in the presence of the agonist. 7. The substance P‐induced facilitation of the plateau potential was blocked by GR 82334 (5‐10 microM), a selective NK‐1 tachykinin‐receptor antagonist, and was not affected by MEN 10376 (2 microM), a selective NK‐2 antagonist. 8. The facilitation of plateau properties produced by dorsal root stimulation was also reduced by antagonists of metabotropic glutamate receptors and NK‐1 tachykinin receptors. 9. We propose that modulation of postsynaptic plateau properties in dorsal horn neurones by activation of type I metabotropic glutamate receptors and NK‐1 tachykinin receptors is involved in processing nociceptive information.
Sulphonylurea receptor 2B and Kir6.1 form a sulphonylurea‐sensitive but ATP‐insensitive K+ channel.
Authors: Yamada M , Isomoto S , Matsumoto S , Kondo C , Shindo T , Horio Y , Kurachi Y
Published: December 2014

1. We analysed the K+ channel composed of the sulphonylurea receptor 2B (SUR2B) and an inwardly rectifying K+ channel subunit Kir6.1 coexpressed in a mammalian cell line, HEK293T, with the patch clamp technique. 2. In the cell‐attached configuration, K+ channel openers (pinacidil and nicorandil) activated approximately 33 pS K+ channels (approximately 145 mM external K+), which were inhibited by the sulphonylurea glibenclamide. 3. Although SUR2B forms an ATP‐sensitive K+ channel with Kir6.2, whose amino acid sequence is approximately 70% homologous with that of Kir6.1, the K+ channel composed of SUR2B and Kir6.1 surprisingly did not spontaneously open on patch excision in the absence of intracellular ATP. 4. In inside‐out patches, uridine diphosphate and guanosine diphosphate induced channel activity, which was inhibited by glibenclamide but not ATP. Intracellular ATP on its own activated the channels. K+ channel openers and intracellular nucleotides synergistically activated the channel. 5. Therefore, the K+ channel composed of SUR2B and Kir6.1 is not a classical ATP‐sensitive K+ channel but closely resembles the nucleotide diphosphate‐dependent K+ channel in vascular smooth muscle cells.
Nitric oxide regulates NMDA‐driven GABAergic inputs to type I neurones of the rat paraventricular nucleus.
Authors: Bains J S , Ferguson A V
Published: December 2014

1. Whole‐cell recordings were obtained from type I paraventricular nucleus (PVN) neurones in coronal slices of rat hypothalamus to study the involvement of nitric oxide (NO) in the modulation of inhibitory transmission resulting from the activation of N‐methyl‐D‐aspartate (NMDA) receptors by the high affinity receptor agonist D,L‐tetrazol‐5‐ylglycine. 2. A brief pulse of NMDA agonist (0.1‐10 microM) faithfully elicited increases in action potential firing frequency in all type I cells tested (n = 55). In cells with membrane potentials positive to ‐75 mV, this excitation was accompanied by an underlying depolarization (> 2 mV) in the majority of cases (n = 45). At membrane potentials negative to ‐75 mV, NMDA agonist application elicited an initial monotonie depolarization, which was auxiliary to profound, rhythmic oscillations of the membrane potential, resulting in the emergence of burst‐like activity in these cells (n = 8). 3. In addition to depolarizing the neurones, the NMDA agonist also elicited inhibitory postsynaptic potentials (IPSPs) in 40% (n = 22) of the cells tested. The IPSPs were inhibited by the GABAA receptor antagonist bicuculline methiodide (BMI). 4. Microdialysis of NO into the PVN has been shown to increase local levels of inhibitory neurotransmitters, including GABA. The possibility that NO‐induced increases in GABA lead to an increase in inhibitory synaptic activity in PVN was investigated by administering NO by three different methods. Bath application of the donor compound, S‐nitroso‐N‐acetyl‐penicillamine (SNAP; n = 7), bubbled NO solution (n = 5), or the NO precursor L‐arginine (n = 6) all elicited increases in IPSP frequency. 5. Production of NO in other brain centres has been linked to the activation of the NMDA receptor. In order to determine whether the increase in IPSPs following NMDA was the result of activation of NO, the production of NO was blocked with the NO synthase inhibitor N omega‐nitro‐L‐arginine methylester (L‐NAME). Subsequent NMDA receptor activation elicited more pronounced depolarizations, but there was no accompanying increase in IPSP frequency (n = 5). 6. This study demonstrates that GABAergic inhibition resulting from NMDA receptor activation can be regulated profoundly by NO. By increasing inhibitory transmission within a nucleus, NO may serve as an important intermediary in the regulation of neuronal excitability in the central nervous system.
Is resting state HCO3‐ secretion in frog gastric fundus mucosa mediated by apical Cl(‐)‐HCO3‐ exchange?
Authors: Caroppo R , Debellis L , Valenti G , Alper S , Frömter E , Curci S
Published: December 2014

1. We have tested the widely accepted hypothesis that resting‐state bicarbonate secretion of gastric fundus mucosa is mediated by Cl(‐)‐HCO3‐ exchange in the apical membrane of surface epithelial cells (SECs). To this end, SECs of isolated fundus mucosa of Rana esculenta were punctured with double‐barrelled microelectrodes to measure intracellular pH (pHi). 2. No significant pHi changes were observed in response to changing luminal HCO3‐ and/or Cl‐ concentrations. The change in pHi (delta pHi) in response to luminal chloride substitution averaged 0.00 +/‐ 0.01 pH units (mean +/‐ S.E.M.; n = 48), and did not change after blocking putative basolateral acid/base transporters which could have masked the pHi response. 3. On the other hand, pHi responded readily and reversibly to luminal perfusion with either low‐pH (pH 2.5) solution (delta pHi = ‐0.36 +/‐ 0.05; n = 4; P < 0.01) or CO2‐free HCO3‐ Ringer solution (delta pHi = +0.10 +/‐ 0.01; n = 29; P < 0.001). These observations demonstrate that the solution change was effective and complete within 1 min and show that the apical membrane of SECs is permeable to CO2. 4. The apical membrane of frog SECs could not be stained with an antibody against the C‐terminal end of the mouse Cl(‐)‐HCO3‐ exchanger isoform AE2, although this antibody readily stained the basolateral membrane of the oxyntopeptic cells (OCs). 5. In conclusion, the presence of a Cl(‐)‐HCO3‐ exchanger in the apical membrane of SECs of frog gastric fundus mucosa in the resting state could not be confirmed, but other models of HCO3‐ secretion cannot be fully excluded. Observations from electrical measurements, favouring a model of conductive HCO3‐ secretion, point to the OCs rather than the SECs as a site of origin of HCO3‐ secretion.
Serotonin‐induced intercellular calcium waves in salivary glands of the blowfly Calliphora erythrocephala.
Authors: Zimmermann B , Walz B
Published: December 2014

1. Blowfly salivary glands have been used extensively as a model system for the analysis of inositol phosphate‐dependent signal transduction. To detect and characterize changes in intracellular free calcium ([Ca2+]i) that might be expected to be triggered by stimulation with serotonin (5‐HT), we have carried out digital calcium‐imaging experiments on intact glands using the Ca2+‐sensitive dye fura‐2. 2. 5‐HT (1‐10 nM) induced repetitive transient increases in [Ca2+]i, i.e. Ca2+ spikes whose frequency was a function of agonist concentration (EC50 = 2.8 nM). 3. Pre‐incubation in EGTA decreased the frequency but did not inhibit spiking. Thapsigargin abolished periodic spike activity indicating that the [Ca2+]i rise results from Ca2+ release. Neither caffeine (10 mM) nor ryanodine (10 and 50 microM) induced increases in [Ca2+]i. 4. Oscillatory activity in individual cells was synchronized by regenerative intercellular Ca2+ waves that propagated over distances greater than 400 microm. Colliding waves annihilated each other. 5. Desynchronization of the oscillation pattern by 100 microM 1‐octanol suggests the involvement of gap junctions and an intracellular messenger in wave propagation. 6. Local stimulation of glands elicited [Ca2+]i elevations in the stimulated area, but not in adjacent cells, indicating that local increases in [Ca2+]i are not sufficient to trigger Ca2+ waves. However, local stimulation was capable of evoking propagating Ca2+ waves when combined with low‐dose 5‐HT stimulation of the whole gland. 7. The data are consistent with the hypothesis that: (1) Ca2+ acts as the intercellular messenger and modulates its own release via positive and negative feedback on the inosital 1,4,5‐trisphosphate (InsP3) receptor, and (2) sensitization of the InsP3 receptor to Ca2+ by InsP3 is required for the propagation of intercellular Ca2+ waves, as proposed for intracellular Ca2+ waves in Xenopus oocytes.
Desensitization of human adipose tissue to adrenaline stimulation studied by microdialysis.
Authors: Stallknecht B , Bülow J , Frandsen E , Galbo H
Published: December 2014

1. Desensitization of fat cell lipolysis to catecholamine exposure has been studied extensively in vitro but only to a small extent in human adipose tissue in vivo. 2. We measured interstitial glycerol concentrations by microdialysis in subcutaneous, abdominal adipose tissue in healthy humans during intravenous adrenaline infusion for three 35 min periods with 30 min breaks in between. Local blood flow, interstitial adrenaline and arterial glycerol concentrations were also measured. Adrenaline was infused to result in either a high, a low and a high arterial concentration (5.8, 3.1 and 5.6 nM, respectively) or a low, a high and a low concentration (2.5, 4.6 and 2.6 nM, respectively) in order to examine both desensitization and the dose dependency of adipose tissue lipolysis to adrenaline. 3. Adipose tissue lipolysis was calculated and was found to vary directly with arterial adrenaline concentration. However, lipolytic responses to adrenaline decreased markedly during repeated stimulation at a given concentration. Further, arterial glycerol and free fatty acid concentrations varied directly with arterial adrenaline concentrations and showed reduced responses upon repeated exposure. 4. The increase in adipose tissue blood flow in response to adrenaline was also reduced by prior adrenaline exposure, but no consistent desensitization could be demonstrated for whole‐body energy expenditure, blood pressure and heart rate. 5. In the basal state, arterial plasma and interstitial adrenaline concentrations did not differ. During perturbations of arterial adrenaline concentrations, changes in interstitial concentrations were highly reproducible but smaller than changes in arterial concentrations. 6. In conclusion, in vivo adrenaline‐mediated adipose tissue lipolysis and blood flow increments are desensitized by prior adrenaline exposure.
Endothelial‐derived superoxide anions in pig coronary arteries: evidence from lucigenin chemiluminescence and histochemical techniques.
Authors: Brandes R P , Barton M , Philippens K M , Schweitzer G , Mügge A
Published: December 2014

1. The generation of superoxide anions (O2‐) by intact pig coronary artery rings was measured using a lucigenin‐enhanced chemiluminescence technique and a histochemical technique with Nitroblue Tetrazolium (NBT) staining. 2. Isolated arteries with intact endothelium generated O2‐ at a rate of 9.0 +/‐ 0.8 pmol min‐1 (mg dry weight)‐1; this rate was diminished by about 24% when the endothelium was removed. The NBT staining of arterial ring preparations showed formazan precipitation mainly in the intima. Arterial rings were pretreated with diethylthiocarbamate in order to inhibit Cu‐Zn superoxide dismutase (SOD) activity which increased the O2‐ generation by 184 +/‐ 55% (n = 10; P < 0.01). Stimulation of protein kinase C with phorbol 12‐myristate 13‐acetate (5 microM) enhanced endothelium‐dependent O2‐ generation by 136 +/‐ 20% (n = 19; P < 0.01). Neither stimulation with bradykinin or substance P, nor inhibition with NG‐nitro‐L‐arginine methyl ester of endothelial nitric oxide synthase had a significant effect on O2‐ generation. In contrast, the inhibition of flavoproteins with diphenyliodonium decreased concentration‐dependent O2‐ generation (IC50, 1.85 +/‐ 5.33 microM). Inhibition of tetrahydrobiopterin synthesis with 2,4‐diamino‐6‐hydroxy‐pyrimidine resulted in a reduced generation of O2‐ by about 55%. 3. The addition of 100 microM NADH and 100 microM NADPH resulted in an excessive generation of O2‐ at a rate of 0.68 +/‐ 0.03 and 0.26 +/‐ 0.01 nmol O2‐ min‐1 (mg protein)‐1, respectively, in the membrane fraction, but not in the cytosolic fraction, of homogenates obtained from arteries. 4. The results suggest that intact coronary arteries do generate O2‐ under basal conditions and that the endothelial layer significantly contributes to this phenomenon. This generation of O2‐ is greatly influenced by intrinsic SOD activity. It is suggested that basal vascular O2‐ generation is mainly due to membrane‐bound NAD(P)H oxidase activity and/or tetrahydrobiopterin‐dependent processes.
Mechanisms involved in increased iron uptake across rat duodenal brush‐border membrane during hypoxia.
Authors: O'Riordan D K , Debnam E S , Sharp P A , Simpson R J , Taylor E M , Srai S K
Published: December 2014

1. Chronic hypoxia enhances intestinal iron transport but the cellular processes involved are poorly understood. In order to assess the effects of 3 days of hypoxia on iron uptake across the duodenal brush‐border membrane, we have measured the membrane potential difference (Vm) of villus‐attached enterocytes by direct microelectrode impalement and have used semi‐quantitative autoradiography to study changes in expression of iron uptake during enterocyte maturation. 2. Hypoxia increased duodenal Vm (‐57.7 vs. ‐49.3 mV, P < 0.001). Ion substitution experiments revealed that hyperpolarization was due, at least in part, to a reduction in brush‐border Na+ permeability. 3. Autoradiography revealed that hypoxia increased by 6‐fold the rate of iron accumulation during enterocyte transit along the lower villus and enhanced by 3‐fold the maximal accumulation of iron. Depolarization of the brush border, using a high‐K(+)‐containing buffer, caused a proportionally greater reduction in iron uptake in control compared with hypoxic tissue suggesting that the raised iron uptake is only partly driven by brush‐border hyperpolarization. 4. We conclude that hypoxia increases the expression of iron transport in duodenal brush‐border membrane and an enhanced electrical driving force may be involved in this response.
Laminar Heat Transfer for Gas-Liquid Segmented Flows in Circular and Non-Circular Ducts With Constant Wall Temperature
Authors: Muzychka Y. S.
Published: December 2014

A new model is developed for gas-liquid segmented flows in ducts and channels. This model is an improvement of an earlier analysis presented and published by the author. In the present work, it is shown that for constant wall temperature, the dimensionless mean wall flux has two characteristic behaviours: thermal boundary layer flow and fully developed flow. These can also be viewed as short and long residence times as the plug train moves through the tube or channel. The boundary layer limit is dominant for short residence times while fully developed flow occurs for longer residence times. An additional parameter, the plug length to duct length ratio, (Ls/L), is shown to have significant impact on the rate of heat transfer. This parameter has the limits 0 < Ls/L < 1. The new model is compared with data from several published studies in which the variables were well controlled. It is also shown that careful experiments must be undertaken to demonstrate the characteristics of this type of flow under constant wall temperature conditions.
Capillary Imbibition Dynamics in Porous Media
Authors: Bhaduri Swayamdipta , Sahu Pankaj , Das Siddhartha , Kumar Aloke , Mitra Sushanta K.
Published: December 2014

The phenomenon of capillary imbibition through porous media is important both due to its applications in several disciplines as well as the involved fundamental flow physics in micro-nanoscales. In the present study, where a simple paper strip plays the role of a porous medium, we observe an extremely interesting and non-intuitive wicking or imbibition dynamics, through which we can separate water and dye particles by allowing the paper strip to come in contact with a dye solution. This result is extremely significant in the context of understanding paper-based microfluidics, and the manner in which the fundamental understanding of the capillary imbibition phenomenon in a porous medium can be used to devise a paper-based microfluidic separator.
Boiling at Macro- and Microscale: Totally Neglected Universal Context
Authors: Shekriladze I. G.
Published: December 2014

A paper discusses consequences of the neglect of universal features of macro- and microscale boiling uncovered by the basic model “theater of a director”, such as control of developed boiling heat transfer by nucleation at microscale, regardless of the inputs and composition of individual cooling mechanisms, pumping effect of growing bubble, micro-membrane pumping, and multi-factoring phenomenon. Average effective radius of nucleation sites, representing universal characteristic length of the process, irrespective to its scale, also remained outside the attention of boiling researchers. It is shown that neglect of above fundamentals and, especially, full misunderstanding with the characteristic length, turned the sphere of boiling at mini- and microscale into a purely experimental research. Even the attempts to classify boiling channels with respect to the transverse size are deprived of physical grounds. The ways to overcome the existing deadlock situation are also addressed.
Conjugate Heat Transfer Performances for Gaseous Flows in Short Micro Channels
Authors: Croce Giulio , Coppola Michele A. , Rovenskaya Olga
Published: December 2014

A fully conjugate heat transfer analysis of gaseous flow, within slip flow regime, in short microchannels is presented. A Navier Stokes code, coupled with Maxwell slip and Smoluchowski temperature jump models, is adopted.

The main focus is on the interaction between compressibility and heat transfer; in particular, due to the link between temperature and velocity field in highly compressible flow, it is important to recast the channel performance parameters in order to take into account the flow cooling due to the conversion between internal and kinetic energy. Results are presented for Nusselt number and a corrected heat sink thermal resistance, as well as resulting wall temperature.
Single-Phase Cryogenic Flows Through Microchannel Heat Sinks
Authors: Rasouli Erfan , Narayanan Vinod
Published: December 2014

Cryogenic fluids are used widely in several thermal management applications such as in regenerative cooling of rocket engine combustor liners, missile warning receivers, satellite tracking systems and cryo-adsorbent hydrogen storage systems. Single phase laminar flow and heat transfer rate of liquid nitrogen in microchannels is studied experimentally in this paper.

The performance of two distinct geometries of microchannel heat sinks are evaluated and compared for simultaneous developing laminar flow in the Reynolds number range from 180 to 610. The first geometry pertains to parallel microchannels while the second corresponds to a staggered microscale pin fin array. Two parallel microchannel geometries having identical widths of 140μm and identical laminar thermal resistances but with different aspect ratios of 4.7 and 7.6 are compared. The pin fin heat sink consisted of square pins of 395μm side and oriented at 45 degrees to the flow. All three heat sinks have identical heat source surface area.

Results are presented in a non-dimensional form in terms of the friction factor, Nusselt, Reynolds numbers and compared with the predictions of existing correlations in the literature for parallel microchannels and micro pin fin heat sinks.
A New Diffuser/Nozzle Structure With Extended Sidewalls for Maximising the Valveless Micropump Performance
Authors: Wang Jiaqi , Miki Hirofumi , Aw Kean C. , Sharma Rajnish N.
Published: December 2014

A micropump is a crucial component in a microfluidic device, as it could generate accurate tiny amounts of fluid and hence reduces the reagents cost and shortens the analysis time. A conventional pump requires valves, which are difficult to be assembled when reduced to micro scale. Hence valveless pump would be the obvious solution.

To achieve the flow directing capability, gradually expanding/contracting diffuser/nozzle elements are used as the “fixed valves” in valveless micropumps. The fluid flowing along the nozzle direction receives a larger pressure loss than that along the diffuser direction. Therefore, with periodic oscillation of the flow, there would be a net flux along the diffuser direction. Based on previous researches, the performance of a valveless micropump primarily relies on the flow-directing capability of the diffuser/nozzle element, which is also known as diffuser efficiency, η. A higher η means a higher flow-directing ability and thus, a larger flux of a valveless micropump.

There are many researchers attempting to maximise η. In this work, a new diffuser/nozzle structure with extended sidewalls at the large end, named as “lips”, is proposed, investigated and simulated. Introducing more frictional pressure loss in the nozzle direction, the “lips” could increase the η by a maximum of 31%, which correlates to an improvement of 23% for the net flux of the entire micropump. Later, more simulations with different lip lengths, thicknesses and extended angles of the “lips” were also investigated and compared. The results show that η increases with the “lips” length at the beginning and reaches a peak at some length. Further, the thickness of the “lips” has nearly no influence on the performance improvement. Finally it was found that the highest η occurs when the “lips” are almost perpendicular to the outlet plane.
Quantifying Elastic Vortex Growth of DNA Solutions in Planar Micro-Bends
Authors: Gulati Shelly , Muller Susan , Liepmann Dorian
Published: December 2014

Quantitative measurements are obtained for DNA flows in planar abrupt 90° micro-bends. Micro-particle image velocimetry (μPIV) is utilized to characterize flow fields including the secondary flow region in the inner, upstream corner of the bend where vortex growth is observed. The presence and strength of the elastic vortex is quantified at high resolution for increasing Reynolds and Weissenberg number (9.9 × 10−7 < Re < 4.2 × 10−3, 0.42 < Wi < 42). Velocity fields of a Newtonian fluid (water) in the micro-bend do not contain a secondary flow. Understanding the viscoelastic flow behavior of complex biological fluids anticipated for use in biomedical microdevices is critical for the advancement of optimized designs comprised of numerous spatially varying canonical microfluidic components.
Numerical Simulation on the Formation of a Toroidal Microvortex by the Optoelectrokinetic Effect
Authors: Kim Kyung Chun , Kim Dong
Published: December 2014

Optoelectrokinetic effects were effectively used for rapid concentration of particles in microfluidics. In this study, we clarified detail mechanism of particle aggregation by numerical simulation using COMSOL v4.2a multiphysics software. A 3D simulation was conducted with axisymmetric boundary conditions. AC voltage was applied to the two parallel electrodes in a microchannel to generate temperature gradient in the fluids. In addition to the AC electrothermal (ACET) effect, local heating by a laser illumination was also considered. Numerical simulations were carried out for dielectric fluids. A toroidal microvortex induced by the optoelectrokinetic effect shows that fluid motions in the middle of bottom boundary are cancelled out by flows in opposite directions and consequently producing stagnation. It is expected that micro/nano particles can be deposited in the bottom electrode. Local heating by the laser illumination enhanced the intensity of microvortex substantially. It is confirmed that the dominant driving force for the microvortex is natural convection by the laser illumination, however AC voltage is necessary for particle aggregation in the spot area.