bluuebunny/crossref_metadata_2025 huggingface dataset:
Mammalian ion‐coupled solute transporters.
Authors: Hediger M A , Kanai Y , You G , Nussberger S
Published: December 2014

Active transport of solutes into and out of cells proceeds via specialized transporters that utilize diverse energy‐coupling mechanisms. Ion‐coupled transporters link uphill solute transport to downhill electrochemical ion gradients. In mammals, these transporters are coupled to the co‐transport of H+, Na+, Cl‐ and/or to the countertransport of K+ or OH‐. By contrast, ATP‐dependent transporters are directly energized by the hydrolysis of ATP. The development of expression cloning approaches to select cDNA clones solely based on their capacity to induce transport function in Xenopus oocytes has led to the cloning of several ion‐coupled transporter cDNAs and revealed new insights into structural designs, energy‐coupling mechanisms and physiological relevance of the transporter proteins. Different types of mammalian ion‐coupled transporters are illustrated by discussing transporters isolated in our own laboratory such as the Na+/glucose co‐transporters SGLT1 and SGLT2, the H(+)‐coupled oligopeptide transporters PepT1 and PepT2, and the Na(+)‐ and K(+)‐dependent neuronal and epithelial high affinity glutamate transporter EAAC1. Most mammalian ion‐coupled organic solute transporters studied so far can be grouped into the following transporter families: (1) the predominantly Na(+)‐coupled transporter family which includes the Na+/glucose co‐transporters SGLT1, SGLT2, SGLT3 (SAAT‐pSGLT2) and the inositol transporter SMIT, (2) the Na(+)‐ and Cl(‐)‐coupled transporter family which includes the neurotransmitter transporters of gamma‐amino‐butyric acid (GABA), serotonin, dopamine, norepinephrine, glycine and proline as well as transporters of beta‐amino acids, (3) the Na(+)‐ and K(+)‐dependent glutamate/neurotransmitter family which includes the high affinity glutamate transporters EAAC1, GLT‐1, GLAST, EAAT4 and the neutral amino acid transporters ASCT1 and SATT1 reminiscent of system ASC and (4) the H(+)‐coupled oligopeptide transporter family which includes the intestinal H(+)‐dependent oligopeptide transporter PepT1.
Contractions in guinea‐pig ventricular myocytes triggered by a calcium‐release mechanism separate from Na+ and L‐currents.
Authors: Ferrier G R , Howlett S E
Published: December 2014

1. Unloaded cell shortening and membrane currents were examined in isolated guinea‐pig ventricular myocytes at 37 degrees C using video edge detection and single‐electrode voltage clamp. 2. Inward Na+ currents were eliminated by lidocaine, tetrodotoxin, replacement of extracellular Na+ with choline chloride or sucrose, or by voltage inactivation of Na+ channels. In the absence of Na+ current, the threshold for contraction was approximately ‐50 or ‐55 mV. 3. Verapamil (5 microM) and nifedipine (2 microM) failed to inhibit contractions at negative membrane potentials when positive conditioning pulses were used to maintain intracellular Ca2+ stores via Na(+)‐Ca2+ exchange. In contrast, 200 microM Ni2+ inhibited these contractions. 4. Contractions were abolished when the extracellular solution was nominally Ca2+ free. However, contractions were restored by as little as 50 microM extracellular Ca2+. 5. Ryanodine (30 nM) completely abolished contractions initiated by depolarizing steps from ‐65 to ‐40 mV, but had minimal effects on contractions initiated by depolarizing steps from ‐40 to +5 mV. Subtraction of contraction‐voltage relations determined in the presence of ryanodine from control relations revealed a ryanodine‐sensitive component of contraction. This component activated at ‐55 mV and reached a plateau near ‐25 mV. 6. The amplitudes of contractions initiated by depolarizing steps from ‐40 mV were directly proportional to the magnitude of Ca2+ current (ICa). In contrast, contractions initiated by steps from either ‐55 or ‐65 mV were not proportional to ICa. These contractions appeared at potentials negative to the threshold for L‐type Ca2+ current, increased to a plateau at more positive potentials and did not decrease at potentials at which ICa decreased. 7. Subtraction of the contraction‐voltage relationship determined from a membrane potential of ‐40 mV from that at ‐55 mV revealed a component of contraction with a negative activation threshold whose amplitude was not proportional to inward current. The shape of this relationship was virtually identical to that of the ryanodine‐sensitive component of contraction. 8. This study identifies a component of contraction associated with Ca2+ release from sarcoplasmic reticulum (SR) which can be separated from other mechanisms of contraction on the basis of membrane potential. Our observations suggest that this voltage‐dependent release mechanism is a true trigger mechanism which activates a portion of cardiac contraction which is attributable to SR Ca2+ release.
Inhibitory effect of muscarinic receptor activation on Ca2+ channel current in smooth muscle cells of guinea‐pig ileum.
Authors: Unno T , Komori S , Ohashi H
Published: December 2014

1. The effect of muscarinic receptor stimulation on voltage‐gated calcium channel currents was examined in whole‐cell voltage‐clamped smooth muscle cells of the guinea‐pig ileum. 2. In cells voltage clamped at ‐60 mV and in which calcium channel currents (ICa) were elicited repeatedly by depolarizing pulses (25 ms duration, 0.25 Hz frequency) to 0 mV, carbachol (CCh, 10 microM) induced an inward current (ICCh) and were suppressed ICa, in a biphasic manner; an initial transient component was followed by a more sustained one. 3. A calcium channel current (IBa), when Ba2+ was used as a charge carrier, was also suppressed by CCh in a biphasic manner, as with ICa. The sustained phase of the IBa suppression was significantly smaller than that of the ICa suppression, suggesting that Ca2+ entry exerts a potentiating effect on the current suppression. 4. CCh had little or no effect on calcium channel currents (ICa and IBa) in cells dialysed with a pipette solution containing EGTA (20 mM). 5. Inclusion of GDP‐beta‐S (1 mM) in the pipette solution abolished ICCh and the suppression of IBa. With GTP‐gamma‐S (10 microM) in the pipette, the sustained phase of the IBa suppression remained almost unchanged even after removal of CCh. 6. Pretreatment with 2 micrograms ml‐1 pertussis toxin (PTX), which abolished ICCh, did not change noticeably the initial transient and sustained phases of IBa suppression. 7. Neomycin (100 microM) or heparin (5 mg ml‐1) in the pipette each abolished the initial transient component of ICCh as well as the initial transient phase of IBa suppression. 8. The biphasic effect of CCh on IBa was observed in the presence of either staurosporine (1 microM) or 1‐(5‐isoquinolinesulphonyl)‐2‐methylpiperazine (100 microM). Phorbol 12‐myristate 13‐acetate and phorbol 12,13‐dibutyrate (up to 10 microM) had no inhibitory effect on ICa and IBa. 9. The results suggest that stimulation of the muscarinic receptor causes a biphasic suppression of the voltage‐gated calcium channel currents through a PTX‐insensitive G protein in guinea‐pig ileal smooth muscle cells. The initial transient phase may be brought about by the release of Ca2+ from internal storage sites, and the sustained phase by a Ca(2+)‐dependent mechanism which is independent of the phosphatidylinositol pathway.
Extracellular and intracellular alkalinization and the constriction of rat cerebral arterioles.
Authors: Apkon M , Boron W F
Published: December 2014

1. Direct observations of perfused cerebral arterioles in vivo and in vitro have demonstrated that alkalinization of blood or cerebrospinal fluid (CSF) causes arteriolar constriction. Inasmuch as such alkalinizations lead to increases in intracellular pH (pHi) as well as interstitial pH (pHo), it is possible that increases in either pHi or pHo (or both) underlie alkalinization‐induced cerebral vasoconstriction. In order to test the hypothesis that changes in pHi alone underline alkalinization‐induced cerebral vasoconstriction, we simultaneously measured vessel diameter and pHi (using the pH‐sensitive dye, SNAFL) in isolated cerebral arterioles from adult rats during imposed alterations in pHo and pHi. 2. Penetrating cerebral arterioles from the distribution of the middle cerebral artery were hand dissected, cannulated on one end and occluded distally. Vessels were inflated hydrostatically to 60 cmH2O under no‐flow conditions. Confocal microscopy verified specific pH‐sensitivity dye staining of the vascular smooth muscle cells within the vessel wall. 3. Extracellular alkalinization from pH 7.3 to 7.8 caused pHi to increase by 0.06 +/‐ 0.01 of a pH unit, and vessel diameter to decrease by 21.8 +/‐ 1.8% (mean +/‐ S.E.M.). 4. Intracellular alkalinization at constant pHo was produced by exposure to weak bases, including NH3 and trimethylamine, or by exposure to, followed by withdrawal of, weak acids, including CO2 and acetic acid. None of these treatments evoked vasoconstriction even though each of them caused increases in pHi greater than those observed in the same vessels during exposure to the pHo 7.8 solution. 5. We conclude that, at least in cerebral arterioles, alkalinization‐induced vasoconstriction is mediated by an increase in pHo, not pHi [corrected].
A small‐conductance Cl‐ channel in the mouse thick ascending limb that is activated by ATP and protein kinase A.
Authors: Guinamard R , Chraïbi A , Teulon J
Published: December 2014

1. Chloride channels were identified in the basolateral membrane of isolated cortical thick ascending limbs (CTALs) of the mouse nephron by the patch‐clamp technique. A channel with a conductance of 45 pS, previously shown to be Cl‐ selective, was detected in 21% of cell‐attached patches when CTAL fragments were pre‐incubated with 10 mumol l‐4 forskolin for at least 15 min. The same channel was found in only 8.5% of cell‐attached patches formed on unstimulated tubules. 2. Another channel with a smaller conductance (7‐9 pS) was found in 42.8% of cell‐attached patches and 57% of inside‐out patches in unstimulated CTAL tubules, but in 82‐87% of patches from forskolin‐treated tubules. 3. The small channels was Cl‐ selective (Cl(‐)‐to‐Na+ permeability ratio, PCl/PNa = 9.8) with the permeability sequence: NO3‐ > Br‐ > Cl‐ > F‐ > gluconate. Channel activity decreased (Br‐) or disappeared (NO3‐) at negative voltages. At 140 mmol l‐1, I‐ completely inhibited channel activity at all voltages, but a PI/PCl ratio of 1.6 was estimated using a low I‐ concentration (10 mmol l‐1). 4. Internal adenosine triphosphate (ATP) increased normalized current (nPo) in 48% of inside‐out patches containing Cl‐ channels from unstimulated tubules and in 63% of patches from forskolin‐treated CTAL tubules. The non‐hydrolysable ATP analogue, adenosine 5'‐adenylyl imidodiphosphate (AMP‐PNP) did not increase channel activity. 5. Adding the catalytic subunit of protein kinase A to the bath in the presence of ATP increased the activity of the small channel in 58% of inside‐out patches from unstimulated tubules, but it had no effect on the 45 pS channel. 6. The Cl‐ channel blockers 5‐nitro‐2‐(3‐phenylpropylamine)‐benzoic acid (NPPB), 4,4'‐diisothiocyanatostilbene‐2,2'‐disulphonic acid (DIDS) or glibenclamide, all at 0.1 mmol l‐1, and diphenylamine‐2‐carboxylic acid (DPC), at 1 mmol l‐1, inhibited the small channel activity by 80‐100% in inside‐out patches. 7. These results indicate that two Cl‐ channels with contrasting properties mediate the basolateral step of NaCl absorption in the thick ascending limb of the loop of Henle.
Excitability of human upper limb motoneurones during rhythmic discharge tested with transcranial magnetic stimulation.
Authors: Olivier E , Bawa P , Lemon R N
Published: December 2014

1. The activity of thirty‐one single motor units (SMUs) was recorded from forearm and hand muscles of three volunteers. The excitability of the rhythmically firing motoneurones supplying these SMUs was examined after voluntary discharge using transcranial magnetic stimulation (TMS). 2. The magnetic stimulus was delivered either at a fixed delay (range: 1‐60 ms) after SMU discharge (triggered mode) or at random with respect to voluntary SMU discharge (random mode). Post‐stimulus time histograms (PSTHs) of responses to 50‐100 stimuli were constructed for each experimental condition. 3. In the triggered mode, the probability of response to TMS progressively decreased as the spike‐to‐stimulus interval was shortened. Shortening of the interval also resulted in redistribution of responses within the different subpeaks characterizing the short‐latency response of motor units to TMS: the relative response probability of the first subpeak decreased with the shorter spike‐to‐stimulus intervals. 4. In the triggered mode, the probability of SMU responding to TMS was significantly higher when the firing rate of the motor unit was increased from a slow rate (< 10 impulses s‐1) to a faster rate (> 12 impulses s‐1), irrespective of the spike‐to‐stimulus interval. In contrast, in the random mode, the response probability was greater at the slower discharge rate. 5. The higher excitability of motoneurones at the fast rate in the triggered mode is consistent with findings in cat motoneurones suggesting a shallower after‐hyperpolarization, but other mechanisms could contribute. Furthermore, our results suggest that there is an asymptotic recovery in the excitability of slow firing motoneurones towards the end of the interspike interval.
Fractional calcium currents through recombinant GluR channels of the NMDA, AMPA and kainate receptor subtypes.
Authors: Burnashev N , Zhou Z , Neher E , Sakmann B
Published: December 2014

1. Simultaneous fluorescence and whole‐cell current measurements using the calcium indicator dye fura‐2 were made in HEK 293 cells expressing recombinant glutamate receptor (GluR) channels, and fractional Ca2+ currents (the proportion of whole‐cell current carried by Ca2+; Pf) were determined. 2. Cells expressing N‐methyl‐D‐aspartate receptor (NMDAR) channels showed glutamate activated Ca2+ inflow in the voltage range ‐60 to 40 mV in normal extracellular solution. Ca2+ inflow decreased in a voltage‐dependent manner at membrane potentials more negative than ‐30 mV due to Mg2+ block. Voltage dependence of block at negative potentials was stronger in cells expressing the NR1‐NR2A as compared with cells expressing NR1‐NR2C subunits. 3. Fractional Ca2+ currents through NMDARs were independent of extracellular Mg2+ and varied between 8.2% (NR1‐NR2C subunits) and 11% (NR1‐NR2A subunits) in normal extracellular solution (1.8 mM Ca2+) at ‐60 mV membrane potential. Pf values increased with increasing [Ca2+]o in the range of 0.5‐10mM [Ca2+]o in a saturating fashion. 4. In cells expressing alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate receptor (AMPAR) subunits which were unedited at the Q/R site of the putative transmembrane segment TM2 (Q‐form), or in cells coexpressing unedited and edited subunits (R‐form), the glutamate‐evoked Ca2+ inflow increased from 20 to ‐80 mV in an almost linear way. 5. Fractional Ca2+ currents through AMPAR channels depended on subunit composition. Pf values of Q‐form homomeric channels at ‐60 mV and 1.8 mM [Ca2+]o were between 3.2 and 3.9%. They were slightly voltage dependent and increased with [Ca2+]o in the range 1.8‐10mM. Pf values in cells co‐expressing Q‐ and R‐form subunits were almost one order of magnitude smaller (0.54%). 6. Relative concentrations of Q‐form and R‐form GluR‐B subunit‐specific cDNAs used for cell transfection determined the expression of functionally different heteromeric AMPARS. Pf decreased with increasing relative concentration of R‐form encoding CDNAs from 3.4 to 1.4%, demonstrating that editing of the Q/R site of GluR‐B subunits decreases Ca2+ inflow through heteromeric AMPARs. 7. Cells expressing the GluR‐6 subunit of the kainate receptor (KAR) family were characterized by Pf values which depended on the editing in the TM1 and TM2 segments. Pf values were largest for the Q‐form (1.55‐2.0%) and lowest for R‐form channels (< 0.2%), suggesting that Q/R site editing also decreases Ca2+ inflow through KAR channels. Cells co‐expressing both subunit forms showed an intermediate value (0.58%).(ABSTRACT TRUNCATED AT 400 WORDS)
An assessment of central‐peripheral ventilatory chemoreflex interaction using acid and bicarbonate infusions in humans.
Authors: Clement I D , Pandit J J , Bascom D A , Dorrington K L , O'Connor D F , Robbins P A
Published: December 2014

1. The object of this study was to investigate the effect of central chemoreceptor stimulation on the ventilatory responses to peripheral chemoreceptor stimulation. 2. The level of central chemoreceptor stimulation was varied by performing experiments at two different levels of end‐tidal CO2 pressure (PCO2). Variations in peripheral chemoreceptor stimulus were achieved by varying arterial pH (at constant end‐tidal PCO2) and by varying end‐tidal O2 pressure (PO2). 3. Two protocols were each performed on six human subjects. In one protocol ventilatory measurements were made during eucapnia, when the arterial pH was lowered from 7.4 to 7.3. The variation in pH was achieved by the progressive infusion of acid (0.1 M HCl). In the other protocol ventilatory measurements were made during hypercapnia, when the arterial pH was increased from 7.3 to 7.4. The variation in pH was achieved by the progressive infusion of 1.26% NaHCO3. In each protocol ventilatory responses were measured during euoxia (end‐tidal PO2, 100 Torr), hypoxia (end‐tidal PO2, 50 Torr) and hyperoxia (end‐tidal PO2, 300 Torr), with end‐tidal PCO2 held constant. 4. The increase in ventilatory sensitivity to arterial pH induced by hypoxia (50 Torr) was not significantly different between protocols (acid protocol, ‐104 +/‐ 31 l min‐1 (pH unit)‐1 vs. bicarbonate protocol, ‐60 +/‐ 44 l min‐1 (pH unit)‐1; mean +/‐ S.E.M.; not significant (n.s.)). The ventilatory sensitivity to hypoxia at an arterial pH of 7.35 was not significantly different between protocols (acid protocol, 14.7 +/‐ 3.3 l min‐1 vs. bicarbonate protocol, 15.6 +/‐ 2.4 l min‐1; mean +/‐ S.E.M.; n.s.). The results provide no evidence to suggest that peripheral chemoreflex ventilatory responses are modulated by central chemoreceptor stimulation.
Presynaptic metabotropic glutamatergic regulation of inhibitory synapses in rat cerebellar slices.
Authors: Llano I , Marty A
Published: December 2014

1. The effects of the metabotropic glutamate agonist trans‐ACPD (t‐ACPD) were investigated in various locations of the inhibitory network made by GABAergic interneurones in the molecular layer of rat cerebellar slices. 2. t‐ACPD exerted complex effects on spontaneous IPSCs in Purkinje cells. IPSC frequency was transiently inhibited during short (< 1 min) applications, and enhanced upon washing. During prolonged exposure to t‐ACPD, IPSCs became organized in high‐frequency bursts interspersed with periods of deep inhibition. 3. In interneurones, the frequency of spontaneous IPSCs was enhanced by t‐ACPD. As in Purkinje cells, spontaneous IPSCs had a tendency to cluster in bursts in the presence of t‐ACPD. 4. Evoked IPSCs recorded either in interneurones or in Purkinje cells upon stimulation of presynaptic interneurones were reversibly inhibited by t‐ACPD. 5. Miniature IPSCs (mIPSCs) were recorded in the presence of tetrodotoxin both in Purkinje cells and in interneurones. t‐ACPD did not alter the mean amplitude of mIPSCs in either cell type. It reduced the frequency of mIPSCs in Purkinje cells, but did not alter their rate in interneurones. 6. In cell‐attached recordings on interneurone somata, t‐ACPD was found to induce clustering of action potentials and to enhance the mean rate of firing. These results apply whether t‐ACPD was tested in normal saline, in the presence of glutamatergic ionotrophic blockers, or in the presence of a mixture of glutamatergic and GABAergic blockers. 7. The results suggest that t‐ACPD has at least two different modes of action. One effect is to alter the intrinsic firing rate of interneurones, presumably through an action on somatic conductance mechanisms. The other is to decrease the efficacy of the interneurone‐interneurone and interneurone‐Purkinje cell synapses, presumably through an action on axonal conductance systems and/or vesicle release mechanisms.
Alpha 1‐ and alpha 2‐adrenoreceptor actions of phentolamine and prazosin on breathing movements in fetal sheep in utero.
Authors: Giussani D A , Moore P J , Bennet L , Spencer J A , Hanson M A
Published: December 2014

1. We studied the effects of systemic administration of the alpha 1‐ and alpha 2‐adrenoreceptor antagonist phentolamine and the selective alpha 1‐adrenoreceptor antagonist prazosin on fetal breathing movements (FBM) and electrocortical activity (ECoG) in fetal sheep. In one group of fetuses (group I; n = 7) the effects of phentolamine were measured during normoxia and hypoxia. In the second group of fetuses (group II; n = 8) the effects of either phentolamine, or combined phentolamine and prazosin, or prazosin alone, were measured during normoxia. 2. In group I fetuses, the incidence of FBM increased after phentolamine treatment. An increase in the incidence and mean episode duration of low‐voltage ECoG (LV‐ECoG) was also measured after phentolamine treatment. These effects of phentolamine persisted during hypoxia. 3. In group II fetuses a pronounced decrease in the incidence of FBM occurred after administration of prazosin following either phentolamine or saline pretreatment. These effects of prazosin on FBM were independent of an effect on ECoG activity. 4. We conclude that catecholamines have a stimulatory role on FBM mediated via an alpha 1‐adrenoreceptor mechanism. Phentolamine leads to an increase in FBM by preferentially antagonizing presynaptic alpha 2‐adrenoreceptors over postsynaptic alpha 1‐adrenoreceptors. This influence of phentolamine on FBM may be secondary to its effect on ECoG. Promotion of LV‐ECoG by catecholamines is mediated via an alpha 1‐independent mechanism.
Properties and roles of an intramembranous charge mobilized at high voltages in frog skeletal muscle.
Authors: Shirokova N , González A , Ma J , Shirokov R , Ríos E
Published: December 2014

1. Membrane Ca2+ currents (ICa), intramembranous charge movement currents and changes in intracellular Ca2+ concentrations were recorded in voltage clamped cut skeletal muscle fibres of the frog. Intra‐ and extracellular solutions, designed to prevent ionic current, and use of the saponin‐permeabilization procedure made possible the measurement of transfer of intramembranous charge up to high positive potentials. 2. Substantial charge moved at positive potentials. This charge was shown to be intramembranous in four tests of charge conservation, demonstrating that the total displacement of charge depended only on the initial and final voltages, and not on the history or pathway of intermediate voltages. 3. On average, in twenty‐three cells, the charge moved at 50 mV was 31 +/‐ 1.9 nC microF‐1 (mean +/‐ S.E.M.), and at 0 mV was 25 +/‐ 1.5 nC microF‐1. Approximately one‐fifth of the total charge moved above 0 mV. 4. The charge that moved at high voltage could be fitted, in most cases, with a Boltzmann distribution function. In twenty of twenty‐three cells, the total charge distribution could be fitted as the sum of two Boltzmann terms; the high voltage term was centred at 11 +/‐ 3.9 mV, with a steepness factor of 12 +/‐ 1.6 mV and a magnitude of 8.6 +/‐ 1.1 nC microF‐1. The low voltage term was centered at ‐43 +/‐ 2.1 mV, with a steepness factor of 7.7 +/‐ 0.6 mV and a magnitude of 22 +/‐ 1.8 nC microF‐1. Thus, the high voltage component comprised about one‐quarter of the mobile charge. In four cells it was possible to fit the sum of three Boltzmann terms to the distribution of mobile charge; the parameters of the high voltage term then were similar to those found by fitting the sum of two Boltzmann terms to the same data. 5. The voltage dependence of activation of ICa was determined in a buffered 2 mM Ca2+ external solution, from the tails of ionic current at ‐30 mV, after activating pulses to various voltages, the duration of which was sufficient to reach the peak of inward current. The voltage dependence was described by a Boltzmann function centred at 2.6 +/‐ 6.9 mV (n = 6), with a steepness factor of 20 +/‐ 1.4 mV. The voltages at which the high voltage charge moved were roughly the same as those at which ICa was activated. 6. Calcium release from the sarcoplasmic reticulum was determined from the Ca2+ transients. Calcium release continued to increase at potentials above 0 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
Synaptic input from CA3 pyramidal cells to dentate basket cells in rat hippocampus.
Authors: Kneisler T B , Dingledine R
Published: December 2014

1. Excitatory inputs from CA3 pyramidal cells to dentate basket cells were examined using the whole‐cell recording technique in neonatal (10‐16 days) rat hippocampal slices to characterize this unexpected feedback pathway. 2. Minimal electrical stimulation of the CA3 pyramidal layer evoked in basket cells short latency (5.2 +/‐ 0.4 ms) glutamate receptor‐mediated excitatory postsynaptic currents (EPSCs) with fast rise times (at ‐70 mV, 0.9 +/‐ 0.2 ms), fast decay time constants (3.6 +/‐ 0.6 ms), and small amplitudes (‐14 +/‐ 3.4 pA). Minimal electrical stimulation evoked monosynaptic EPSCs in only 48 +/‐ 9.2% of the trials suggesting that the CA3 pyramidal cell to basket cell pathway was unreliable. 3. CA3 pyramidal cell layer stimulation did not antidromically or synaptically activate granule cells but did evoke polysynaptic IPSCs in granule cells, suggesting that the net effect of CA3 pyramidal cell firing on the dentate gyrus was granule cell inhibition. 4. Stimulation of the CA3 pyramidal cell layer evoked both monosynaptic and polysynaptic EPSCs in basket cells, which were eliminated by a knife lesion separating CA3 from the dentate gyrus. The latencies of the EPSCs evoked in 0.6 mM extracellular calcium were the same as the earliest latencies of EPSCs in 1.5 mM calcium, suggesting that those EPSCs were monosynaptic. The polysynaptic input was more prominent in the presence of 10 microM bicuculline, implying that inhibitory GABAergic circuits normally limit this feedback from CA3 to basket cells. 5. In recordings from 103 pairs of CA3 pyramidal cells and dentate basket cells from 11 slices, two polysynaptic connections were found that were active only when the presynaptic CA3 pyramidal neuron fired in bursts. No monosynaptic connections between CA3 pyramidal cells and basket cells were identified indicating that connections between the two cell types may be sparse. 6. Raising the external potassium concentration from 3.5 to 8.5 mM, which elicited burst firing in CA3 pyramidal cells, resulted in a barrage of EPSCs and action potentials in basket cells. In contrast, granule cells neither fired action potentials nor exhibited increased EPSC frequency in elevated potassium but instead received a higher frequency of bicuculline‐sensitive IPSCs, consistent with interneuron firing. The CA3 pyramidal cell to basket cell monosynaptic pathway exhibited paired‐pulse facilitation as manifested by an increased probability of release, which supports the idea that basket cells were better activated by short trains of action potentials than by single inputs.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of stimulation of hindlimb flexor group II afferents during fictive locomotion in the cat.
Authors: Perreault M C , Angel M J , Guertin P , McCrea D A
Published: December 2014

1. This study examines the effects of electrical stimulation of hindlimb flexor nerves on the fictive locomotion pattern. Locomotion was initiated by stimulation of the mesencephalic locomotor region in the decerebrate paralysed cat and monitored by recording the electroneurogram from selected hindlimb flexor and extensor muscle nerves. Flexor nerves were stimulated using short trains (20‐50 stimuli at 100 Hz) during either the flexor or the extensor phase of the fictive locomotor cycle. 2. Stimulation of tibialis anterior (TA), posterior biceps and semitendinosus (PBSt) or sartorius (Sart) nerves at 5 times threshold (T) during the flexor phase of the fictive locomotor cycle terminated on‐going activity in flexor nerves and initiated activity in extensors. Thus, flexor nerve stimulation during flexion shortened the locomotor cycle by resetting to extension. The failure of lower intensity (2T) stimulation of PBSt or Sart nerves to reset the step cycle to extension suggests that group II afferents are responsible for these actions. Resetting evoked by 2T stimulation of the TA nerve may be due to a high proportion of group II afferents with low electrical threshold. 3. During extension, stimulation of TA and PBSt nerves at 5T did not perturb the locomotor rhythm whereas Sart stimulation prolonged the locomotor cycle. 4. Stimulation of cutaneous or knee joint afferents failed to produce effects similar to those evoked by stimulation of flexor muscle nerves at group II strength. These findings are at odds with those obtained elsewhere in the acute spinal, DOPA fictive locomotion preparation. The possibility that group II resetting during fictive locomotion is not mediated by flexion reflex pathways but by previously unknown pathways released in the present preparation is discussed. 5. Since many of the flexor afferents recruited by 5T electrical stimulation are the length‐sensitive group II fibres, spindle secondaries may act to regulate the duration and onset of flexor and extensor activity during real locomotion. The resetting from flexion to extension also suggests that unexpected or enhanced activity of flexor secondaries during swing would promote a switch of the step cycle to stance.
Evidence for limbic system activation during CO2‐stimulated breathing in man.
Authors: Corfield D R , Fink G R , Ramsay S C , Murphy K , Harty H R , Watson J D , Adams L , Frackowiak R S , Guz A
Published: December 2014

1. The role of supra‐brainstem structures in the ventilatory response to inhaled CO2 is unknown. The present study uses positron emission tomography (PET), with infusion of H2(15)O, to measure changes in relative regional cerebral blood flow (rCBF) in order to identify sites of increased neuronal activation during CO2‐stimulated breathing (CO2‐SB) in awake man. 2. Five male volunteers were scanned during CO2‐SB (mean +/‐ S.E.M.; end‐tidal PCO2, 50.3 +/‐ 1.7 mmHg; respiratory frequency, 16.4 +/‐ 2.7 min‐1; tidal volume, 1.8 +/‐ 0.2 l). As control, scans were performed during ‘passive’ isocapnic (elevated fraction of inspired CO2) positive pressure ventilation (end‐tidal PCO2, 38.4 +/‐ 1.0 mmHg; respiratory frequency, 15.5 +/‐ 2.2 min‐1; tidal volume, 1.6 +/‐ 0.2 l). With CO2‐SB, all subjects reported dyspnoea. 3. The anatomical locations of the increases in relative rCBF (CO2‐SB versus control) were obtained using magnetic resonance imaging. 4. Group analysis identified neuronal activation within the upper brainstem, midbrain and hypothalamus, thalamus, hippocampus and parahippocampus, fusiform gyrus, cingulate area, insula, frontal cortex, temporo‐occipital cortex and parietal cortex. No neuronal activation was seen within the primary motor cortex (at sites previously shown to be associated with volitional breathing). 5. These results suggest neuronal activation within the limbic system; this activation may be important in the sensory and/or motor respiratory responses to hypercapnia in awake man.
Estimated potassium reflection coefficient in perfused proximal convoluted tubules of the anaesthetized rat in vivo.
Authors: Wareing M , Wilson R W , Kibble J D , Green R
Published: December 2014

1. As yet there is no definitive description of the mechanism and route by which K+ reabsorption is achieved in the proximal convoluted tubule (PCT). We have assessed the contribution of convective K+ transport to net potassium ion flux (JK) by estimating the reflection coefficient of K+ (sigma K) in the proximal tubule of anaesthetized rats previously prepared for in vivo microperfusion. 2. Alterations in the luminal concentration of the impermeant solute raffinose in single‐perfused (lumen only) and double‐perfused (lumen and capillaries) PCTs were found to change fluid reabsorption in a predictable fashion. 3. Net potassium ion flux (JK) in single‐ and double‐perfused tubules was significantly correlated with net fluid flux (Jv), suggesting that convective K+ transport may be a significant factor in overall K+ transport by the PCT. 4. Estimates of sigma K in single‐ and double‐perfused tubules were very similar (0.14 +/‐ 0.06 and 0.13 +/‐ 0.05, respectively), even though K+ diffusion was not strictly controlled in the former group. The maximum effect of ‘pseudo‐solvent’ drag in double‐perfused tubules was estimated to give a sigma K of 0.40. This low value for sigma K suggests that true convection/solvent drag may be an important driving force for the reabsorption of K+ from the PCT of the rat.
Mechanism for reflex reversal during walking in human tibialis anterior muscle revealed by single motor unit recording.
Authors: De Serres S J , Yang J F , Patrick S K
Published: December 2014

1. A reversal in the sign of a cutaneous reflex during walking was recently described in the human. Such reversals were most clearly seen in muscles that were active in two parts of the step cycle, such as the tibialis anterior (TA). The current study determined whether the reversal resulted from differential activation of a single group of motor units. 2. Single motor units were recorded from the TA muscle of healthy human subjects while they walked on a treadmill with a splint that limited motion of the ankle joint. The majority of motor units from which recordings were made (43 out of 46) were active in both the swing phase and the transition from swing to stance, indicating that the two bursts of activity from the TA muscle do not represent the activity of two separate populations of motor units. 3. The firing behavior of three motor units was observed during walking steps when stimuli were applied to the posterior tibial nerve during either the swing phase or the transition from swing to stance. The post‐stimulus time histograms indicated that the same motor unit was excited during the swing phase, and inhibited during the transition from swing to stance. 4. The results support the hypothesis that there are parallel excitatory and inhibitory pathways from cutaneous afferents to single motoneurones of the TA muscle. A shift in balance between the two pathways as a function of the step cycle most probably generates the reflex reversal observed.
The mechanism of inhibitory action of secretin on gastric acid secretion in conscious rats.
Authors: Shimizu K , Li P , Lee K Y , Chang T M , Chey W Y
Published: December 2014

1. Secretin has been recognized as an important enterogastrone. In order to investigate the mechanism of secretin‐induced inhibition of gastric acid secretion, the effects of both anti‐somatostatin antibody and indomethacin on acid secretion were examined in conscious rats with gastric cannulas. 2. Secretin given intravenously at 5.6 pmol kg‐1 h‐1 inhibited profoundly the acid secretion stimulated by pentagastrin at 0.3 microgram kg‐1 h‐1. 3. When a rabbit antisomatostatin serum was given intravenously, it not only abolished the secretin‐induced inhibition on the pentagastrin‐stimulated acid secretion, but also augmented both basal and pentagastrin‐stimulated acid secretion. 4. Indomethacin also significantly augmented basal acid secretion, starting 45 min after the drug delivery began. It reversed the secretin‐induced inhibition but it did not augment the pentagastrin‐stimulated acid secretion. 5. Neither antisomatostatin serum influenced prostaglandin E2‐induced inhibition of the pentagastrin‐stimulated acid secretion, nor did indomethacin affect the inhibition by somatostatin, suggesting strongly that the inhibition by somatostatin is not mediated by endogenous prostaglandins, nor is that by prostaglandins E2 mediated by endogenous somatostatin. 6. It is concluded that the inhibitory action of secretin on pentagastrin‐stimulated gastric acid secretion is mediated by both somatostatin and prostaglandins in conscious rats. The two inhibitors do not seem to interact endogenously for the inhibition of acid secretion. While endogenous somatostatin exerts a tonic inhibitory effect on both basal and pentagastrin‐simulated acid secretion, prostaglandins augment basal acid secretion only.
The effects of anaemia on heart, placenta and body weight, and blood pressure in fetal and neonatal rats.
Authors: Crowe C , Dandekar P , Fox M , Dhingra K , Bennet L , Hanson M A
Published: December 2014

1. Reports that maternal anaemia in pregnancy is associated with a greater placental: birth weight ratio, which predisposes towards high postnatal blood pressure in the human, led us to examine the effects of maternal anaemia during pregnancy on placental size, fetal and neonatal growth, and blood pressure development in the rat. 2. Nutritional anaemia was induced in female rats prior to mating and maintained throughout pregnancy and up until weaning of the pups. Fetuses were studied at 20 days of gestation (E20). Pups were studied on postnatal days 20 (P20) and 40 (P40), having been weaned onto normal rat chow at 21 days. 3. In the anaemic group placental: fetal body weight ratios were lower compared with controls. Body weights at all ages were lower in the anaemic group than in controls, despite a greater rate of growth in the anaemic group between P20 and P40. 4. At P20 heart weights of the anaemic group were almost twice that of controls, suggesting an alteration in their cardiovascular development. However, paradoxically, the systolic blood pressure of the anaemic group was lower than that of controls. 5. By P40 the systolic blood pressure of the anaemic group (136 +/‐ 3 mmHg) had increased and was greater than that in control pups (126 +/‐ 3 mmHg). 6. In conclusion, we have shown that there is a pronounced postnatal rise in systolic blood pressure associated with maternal anaemia during pregnancy, which is not related to a greater placental: birth weight ratio. Before weaning, anaemic pups have a lower systolic blood pressure than controls and there is an important association between the rate of postnatal growth and blood pressure.
Na+ current and Ca2+ release from the sarcoplasmic reticulum during action potentials in guinea‐pig ventricular myocytes.
Authors: Sipido K R , Carmeliet E , Pappano A
Published: December 2014

1. Ca2+ release from the sarcoplasmic reticulum (SR) was examined in enzymatically isolated single guinea‐pig ventricular myocytes by monitoring [Ca2+]i with fura‐2 during whole‐cell recording of action potentials at room temperature (23‐25 degrees C). Modulation of Ca2+ release by the Na+ current (INa) was studied by manipulating Na+ influx through the Na+ channel. 2. For a comparable Ca2+ loading of the SR, brief hyperpolarizing currents applied at the peak of the action potential increased Ca2+ release, while depolarizing pulses had the opposite effect. Similar currents applied before the action potential did not affect Ca2+ release. 3. Application of tetrodotoxin (TTX; 60 microM) moderately reduced Ca2+ release from the SR, but this effect was delayed in comparison with the immediate block of INa. An early effect of TTX was to increase Ca2+ release. 4. Replacement of Na+ with Li did not reduce Ca2+ release, but led to a progressive increase in Ca2+ release, resulting in spontaneous activity. 5. Ca2+ channel blockers (CdCl2, 100 microM; nisoldipine, 20 microM; or nifedipine, 20 microM) drastically reduced Ca2+ release from the SR. 6. Voltage clamp experiments confirmed that TTX blocked INa and its associated [Ca2+]i transient during voltage steps from ‐90 to ‐50 mV. INa and its associated [Ca2+]i transient were equally suppressed following replacement of Na+ with N‐methyl‐D‐glucamine (NMDG+), but the [Ca2+]i transient was not suppressed following replacement of Na+ with Li+. 7. The INa‐associated transient was sensitive to Ca2+ channel blockers. During steps from ‐50 to 0 mV, it appeared that the dihydropyridine antagonists often did not provide full block of the calcium current (ICa). 8. During current clamp stimulation at 1 Hz in the presence of TTX (60 microM), the Ca2+ content of the SR was decreased, due to the changes in action potential configuration and to changes in [Na+]i. 9. Our experiments indicate that the Ca2+ entry coupled to Na+ influx via the Na+ channel does not contribute substantially to the trigger for Ca2+ release from the SR during action potentials (23‐25 degrees C). However, INa modulates Ca2+ release by affecting the Ca2+ load of the SR.
Evidence that cell surface charge reduction modifes capillary red cell velocity‐flux relationships in hamster cremaster muscle.
Authors: Vink H , Wieringa P A , Spaan J A
Published: December 2014

1. From capillary red cell velocity (V)‐flux (F) relationships of hamster cremaster muscle a yield velocity (VF = 0) can be derived at which red cell flux is zero. Red cell velocity becomes intermittent and/or red blood cells come to a complete standstill for velocities close to this yield velocity, and, at the same time, capillary tube haematocrit becomes very low. 2. We have tested whether the net negative charge of red blood cells (RBCs) contributes to the magnitude of VF = 0. Velocity‐flux relationships were measured for normal cells, normal cells labelled with the fluorescent dye calcein (LRBCs), and red cells treated with hexadimethrine to mask negative charge and labelled with calcein as well (HDM‐LRBCs). Measurements were done in a hamster cremaster muscle preparation applying video in vivo microscopy. 3. Hexadimethrine treatment reduced the net negative surface charge of red cells to 20% of control as estimated from transmission electron microscopy using a ferritin tagging technique. The values of VF = 0 found for normal red cells and HDM‐LRBCs were 86 +/‐ 15 and 31 +/‐ 17 microns s‐1, +/‐ S.E.M., n = 12, respectively, which were significantly different (P < 0.05). For normal cells and cells labelled with calcein only, VF = 0 values were 63 +/‐ 14 and 65 +/‐ 13 microns s‐1, n = 8, respectively, which were not significantly different. The effect of HDM treatment did not alter filterability of the red cells as estimated from transit times through 5 microns pores. 4. The present findings demonstrate that the net negative charge of RBCs contributes significantly to the yield velocity for red blood cells entering capillaries and flowing through them. HDM treatment reduced the net negative charge of red blood cells and may have caused cells to enter capillaries more easily owing to reduced electrostatic repulsion at the capillary entrance. In addition, HDM treatment may have lowered intracapillary flow resistance by a reduction in electrostatic repulsive forces between red blood cells and negatively charged (macromolecules on) capillary endothelial cells at sites of irregular capillary cross‐sectional shape, without significantly affecting the lubricating properties of the capillary endothelial glycocalyx and/or associated plasma macromolecules.
On the origin of low‐frequency blood pressure variability in the conscious dog.
Authors: Just A , Wagner C D , Ehmke H , Kirchheim H R , Persson P B
Published: December 2014

1. Baroreceptor denervation increases blood pressure variability below 0.1 Hz. This study was undertaken to determine to what extent these fluctuations originate from the central nervous system or from cardiovascular sources. 2. Blood pressure was recorded at a rate of 10 Hz for approximately 3.5 h in conscious, resting dogs. Power density spectra were calculated from all 2(17) points of each recording session and integrated between 0.0002 and 0.1 Hz. 3. Blockade of the afferent limb of the baroreceptor reflex by surgical denervation of sinoaortic and cardiopulmonary afferents (Den; n = 6) significantly increased integrated power more than sixfold compared with a control group (n = 11). 4. Impairment of the efferent limb in non‐deafferented dogs by either alpha 1‐adrenergic blockade with prazosin (Praz; n = 7) or ganglionic blockade with hexamethonium (Hex; n = 6) failed to raise variability. 5. Both prazosin (n = 6) and hexamethonium (n = 3) reduced the increased variability in denervated dogs. 6. In non‐deafferented dogs receiving hexamethonium, elevation of mean blood pressure to the hypertensive level of the Den group, by a continuous infusion of noradrenaline (n = 4), did not change the variability. 7. It is concluded that in the absence of changes in posture, most of the increased blood pressure variability after baroreceptor denervation is derived from the central nervous system. 8. Direct comparison of power spectra of the Den (total variability) and Hex groups (variability derived from the cardiovascular system only) suggests that the central nervous system is also the prevalent source of low‐frequency blood pressure variability in intact animals.
Kinetic characterization of the voltage‐gated currents possessed by Xenopus embryo spinal neurons.
Authors: Dale N
Published: December 2014

1. Using the whole‐cell patch clamp technique, the voltage‐gated currents of neurons acutely isolated from the Xenopus embryo spinal cord were studied. 2. The spinal neurons possessed a very fast Na+ current, which activated with time constants that ranged from 0.1 to 0.25 ms. It was also subject to rapid inactivation with time constants ranging from 0.3 to 8 ms. This current could only be fitted with Hodgkin‐Huxley equations once the rapid inactivation that occurs by the time of the peak current had been taken into account. 3. Xenopus embryo neurons also possessed a mixture of kinetically similar Ca2+ currents, which activated with time constants that ranged from 0.3 to 0.8 ms. Sometimes the Ca2+ currents showed very slow inactivation at more positive voltages (> 20 mV). The Ca2+ current was modelled as a single non‐inactivating current. 4. As might be expected, the embryonic neurons possessed a mixture of outward currents that were hard to separate either pharmacologically or through differences in voltage dependence. The delayed rectifier seemed to consist of varying proportions of two currents: a fast‐activating K+ current (with time constants of activation ranging from 0.6 to 2 ms) and a slow K+ current (with time constants of activation ranging from 5 to 25 ms). The slow current was occasionally seen in isolation. 5. For the Ca2+, fast K+ and slow K+ currents the rate of deactivation was faster than would be predicted from the kinetics of activation. This was modelled by allowing the closing rate constant of the channels to be described by one of two different functions of voltage that between them covered the whole range of transmembrane voltage. Although this was done for empirical reasons, it could be interpreted to suggest that the channels have more than one open state and predominantly close from a state that is distinct from the one to which they originally opened.