bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient outward current in adult rat supraoptic neurones with slice patch‐clamp technique: inhibition by angiotensin II.
Authors: Nagatomo T , Inenaga K , Yamashita H
Published: December 2014

1. Outward potassium currents were recorded from microscopically identified supraoptic neurones of adult Wistar male rats using the whole‐cell patch‐clamp technique in thin‐slice preparations. The basic characteristics of transient outward current (IA or A‐current) and the effects of angiotensin II (AII) on the currents were studied. 2. IA was isolated by subtracting outward currents elicited by stepping from two different holding potentials to a test potential or by applying 4‐aminopyridine (4‐AP) at 5 mM. The isolated IA had a threshold for activation between ‐55 and ‐65 mV and was characterized by fast activation and inactivation. Values of the time to peak and the inactivation time constants for current decay at different test potentials were voltage dependent. 3. Normalized currents for activation and steady‐state inactivation of IA were fitted to the Boltzmann function. The mid‐points and the slope factors were, respectively, ‐35.0 and ‐14.3 +/‐ 0.40 mV (n = 5) for the activation curve, and ‐72.0 and 7.0 +/‐ 0.68 mV (n = 5) for the inactivation curve. 4. The time course of recovery from inactivation was best fitted to a single exponential function with the time constant of 37.8 +/‐ 6.6 ms (n = 6). 5. The effects of AII on IA and delayed rectifier current (IK) were investigated. According to their responses to AII, cells were classified into two groups, sensitive and low‐sensitive. Bolus injection of AII (10 microM, 100 microliters) decreased the IA amplitude by 25.1 +/‐ 2.4% in seven (53.8%) of the thirteen neurones tested (sensitive group), whereas the other six neurones (low‐sensitive group) changed by only 2.2 +/‐ 0.8%. Perfusion of AII (0.1 microM) decreased the IA amplitude by 21.3 +/‐ 3.1% in six (54.5%) of eleven neurones tested (sensitive group), whereas the other five neurones (low‐sensitive group) changed only by 1.7 +/‐ 0.8%. Bolus injection of AII (10 microM, 100 microliters) decreased the IK amplitude 9.6 +/‐1.6% mV in five (45.5%) of the eleven neurones tested (sensitive group), whereas the other six neurones (low‐sensitive group) changed only by 0.46 +/‐ 0.27%. In the sensitive groups, the reduction of IA by AII was significantly larger than that of IK (P < 0.05). 6. Application of saralasin at 1 microM, an AII antagonist, blocked the effects of AII on IA. 7. These results suggest that the excitatory action of AII on supraoptic neurosecretory cells is mediated at least in part through suppression of IA.
Power spectral analysis of respiratory responses to pharyngeal stimulation in cats: comparisons with eupnoea and gasping.
Authors: Tomori Z , Fung M L , Donic V , Donicova V , St John W M
Published: December 2014

1. Based on similarities between properties of gasping and the aspiration reflex, we hypothesized that this reflex activates the central pattern generator for gasping. To evaluate this hypothesis, we have analysed high‐frequency oscillations in phrenic and hypoglossal neural activities. These oscillations, analysed by power and coherence spectra, are considered as signatures of the central pattern generators for automatic ventilatory activity. 2. In decerebrate, vagotomized, paralysed and ventilated cats, the aspiration reflex was elicited in eupnoea and gasping by mechanical stimulation of the pharynx and electrical stimulation of the glossopharyngeal nerve. 3. Compared with eupnoeic values, the peaks in the power spectra occurred at higher frequencies in spontaneous gasping. Peaks in the coherence spectra showed identical changes. 4. Power and coherence spectra of inspiratory neural activities during the aspiration reflex differed markedly from those of eupnoea, but were similar to those in gasping. 5. We conclude that mechanical stimulation of the pharynx or electrical stimulation of the glossopharyngeal nerve activates a reflex by which the central pattern generator for eupnoea is depressed, and that for gasping is activated. Our results also support the concept that separate brainstem mechanisms generate ventilatory activity in eupnoea and gasping.
Response of C fibre nociceptors in the anaesthetized monkey to heat stimuli: estimates of receptor depth and threshold.
Authors: Tillman D B , Treede R D , Meyer R A , Campbell J N
Published: December 2014

1. Responses to ramped or stepped temperature stimuli were obtained from fifty‐three cutaneous C fibre mechano‐heat nociceptors (CMHs) in the hairy skin of the pentobarbitone‐morphine anaesthetized monkey. A three‐layer heat transfer model was developed to describe the temperature distribution within the skin and to estimate receptor depth and heat threshold. 2. Surface heat threshold, defined as the surface temperature when the first action potential occurs, increased as: (a) the rate of temperature rise for the ramped stimuli increased from 0.095 to 5.8 degrees C s‐1; (b) the duration of stepped heat stimuli decreased from 30 to 1 s; and (c) the base temperature of stepped heat stimuli decreased from 38 to 35 degrees C. These results suggest that the heat threshold for CMHs is determined by the temperature at the depth of the receptor. 3. Receptor depth estimates from responses to ramped stimuli ranged from 20 to 570 microns with a mean of 201 microns. The estimated mean receptor heat threshold was 40.4 +/‐ 2.2 degrees C (+/‐ S.D.). No correlation was observed between depth and thermal or mechanical threshold. The average receptor depth and threshold, estimated from the responses to stepped heat stimuli, were 150 microns and 40.2 degrees C, respectively. 4. We conclude that: (a) the receptor endings of CMHs occur in the epidermis and dermis; (b) temperature at the level of the receptor determines threshold; (c) temperature at the receptor ending is much lower than skin surface temperature at threshold; and (d) the tight distribution of receptor heat thresholds suggests a uniform transducer mechanism for heat in CMHs.
Block of native Ca(2+)‐permeable AMPA receptors in rat brain by intracellular polyamines generates double rectification.
Authors: Koh D S , Burnashev N , Jonas P
Published: December 2014

1. The influence of intracellular factors on current rectification of different subtypes of native alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazoleproprionate receptors (AMPARs) was studied in rat brain slices by combining fast application of glutamate with patch pipette perfusion. 2. The peak current‐voltage (I‐V) relation of the AMPARs expressed in Bergmann glial cells of cerebellum and dentate gyrus (DG) basket cells of hippocampus was weakly rectifying in outside‐out patches and nystatin‐perforated vesicles, but showed a doubly rectifying shape with a region of reduced slope between 0 and +40 mV in nucleated patches. The I‐V relation of AMPARs expressed in hippocampal CA3 pyramidal neurones was linear in all recording configurations. 3. Intracellular application of 25 microM spermine, a naturally occurring polyamine, blocked outward currents in outside‐out patches from Bergmann glial cells and DG basket cells in a voltage‐dependent manner, generating I‐V relations with a doubly rectifying shape which were similar to those recorded in nucleated patches. AMPARs in CA3 pyramidal cell patches were unaffected by 25 microM spermine. 4. The half‐maximal blocking concentration of spermine at +40 mV was 0.3 microM in Bergmann glial cell patches and 1.5 microM in DG basket cell patches, whereas it was much higher (>> 100 microM) for CA3 pyramidal cell patches. Spermidine also affected current rectification, but with lower affinity. The block of outward current by polyamines following voltage jumps developed within < 0.5 ms. 5. We conclude that current rectification, rather than being an intrinsic property of the Ca(2+)‐permeable AMPAR channel, is generated by polyamine block.
Voltage‐dependent calcium currents are enhanced in dorsal root ganglion neurones from the Bio Bred/Worchester diabetic rat.
Authors: Hall K E , Sima A A , Wiley J W
Published: December 2014

1. Whole‐cell, high‐threshold, voltage‐dependent calcium currents (ICa) were enhanced in acutely dissociated, capsaicin‐sensitive dorsal root ganglion neurones from diabetic Bio Bred/Worchester (BB/W) rats, compared with those from age‐matched, non‐diabetic controls. The magnitude of the enhancement increased with the duration of diabetes, and reached significance at diabetic durations of 6 months (diabetic: 6.3 +/‐ 0.4 nA; current density (CD), 157 +/‐ 12 pA pF‐1; means +/‐ S.E.M., n = 9, P < 0.01; control: 3.9 +/‐ 0.6 nA; CD, 116 +/‐ 11 pA pF‐1; n = 18) and 8 months (diabetic: 7.6 +/‐ 0.4 nA; CD, 177 +/‐ 25 pA pF‐1; n = 11, P < 0.005; control: 5.1 +/‐ 0.5 nA; CD, 111 +/‐ 26 pA pF‐1; n = 15). Low‐threshold, voltage‐dependent ICa were also enhanced in neurones from animals diabetic for 8 months (diabetic: 2.5 +/‐ 0.7 nA, n = 4, P < 0.05; control: 0.7 +/‐ 0.5 nA, n = 6). 2. The ICa enhancement was prevented by long‐term treatment of diabetic animals with an aldose reductase inhibitor (ARI; peak ICa at 6 months: 4.41 +/‐ 0.48 nA, n = 2; at 8 months: 4.32 +/‐ 0.60 nA, n = 9). 3. The ICa enhancement was not due to a shift in the voltage dependence of either the current‐voltage relationship or steady‐state inactivation. 4. The L channel antagonist nifedipine and preferential N channel antagonist omega‐conotoxin GVIA (omega‐CgTX) caused a greater inhibition of high‐threshold ICa in diabetic neurones compared with controls (nifedipine: control: 25 +/‐ 3%, n = 26; diabetic: 36 +/‐ 7%, n = 11; omega‐CgTX: control: 40 +/‐ 4%, n = 21; diabetic: 50 +/‐ 7%, n = 7). Diabetic neurones also demonstrated a significantly greater residual current (2.44 +/‐ 0.34 nA, n = 7) in the presence of both antagonists vs. controls (1.28 +/‐ 0.30 nA, n = 8, P < 0.05), suggesting that N‐, L‐ and additional non‐N‐, non‐L‐type high‐threshold ICa were enhanced.
Reduced effect of pH on skinned rabbit psoas muscle mechanics at high temperatures: implications for fatigue.
Authors: Pate E , Bhimani M , Franks-Skiba K , Cooke R
Published: December 2014

1. Inhibition of actomyosin function by decreased pH has been proposed to account for much of the depression of muscle function during fatigue. The clearest support for this hypothesis has been from studies of skinned skeletal muscle fibre mechanics at low temperatures (< or = 15 degrees C). 2. We re‐examined the effect of decreased pH (7.0‐6.2) on skinned mammalian skeletal fibre mechanics at low (10 degrees C) and high (30 degrees C) temperatures, using recently developed protocols that allow reproducible mechanical data to be obtained at higher temperatures. 3. At 10 degrees C we duplicated previous observations of a significant inhibition of maximum shortening velocity (Vmax) and isometric tension (Po) by acidosis. In contrast, at the higher temperature, we found only a very minimal effect of acidosis on Vmax and a threefold reduction in the decrease in Po. 4. Thus at temperatures only slightly below physiological for mammalian skeletal muscle systems, pH plays a much less important role in the process of muscle fatigue at the cross‐bridge level than has been suggested by data obtained at physiologically unrealistic temperatures.
Involvement of neurokinin receptors in the induction but not the maintenance of mechanical allodynia in rat flexor motoneurones.
Authors: Ma Q P , Woolf C J
Published: December 2014

1. Intrathecal (i.t.) injections of the (tachykinin) NK1 receptor agonist, substance P methyl ester (SPME; 20 pmol), or the NK2 receptor agonist, neurokinin A (NKA; 20 pmol), substantially decreased the cutaneous mechanical threshold and markedly enhanced the touch‐evoked response of posterior biceps femoris‐semitendinosus (PBF‐ST) spinal flexor motoneurones in decerebrate‐spinal rats. This cutaneous mechanical reflex allodynia was prevented by pretreatment with the NK1 antagonist RP 67580 (2.28 nmol, i.t.) and the NK2 antagonist MEN 10376 (0.7 nmol, i.t.), respectively. 2. Electrical stimulation of the sural nerve at C fibre strength or cutaneous application of the irritant, mustard oil, produced prolonged cutaneous mechanical allodynia in PBF‐ST motoneurones (15 min and > 1 h, respectively). Pretreatment with RP 67580 but not MEN 10376 prevented this, but when RP 67580 was administered 25 min after the application of mustard oil, the established hypersensitivity of the flexor motor reflex was not reversed. The enantiomer of RP 67580, RP 68651 was without effect. 3. Injection of bradykinin (60 microM, 80 microliters) into the gastrocnemius muscle increased the cutaneous mechanical hypersensitivity of PBF‐ST flexor motoneurones for 40‐50 min. MEN 10376, but not RP 67580, prevented this, but only when administered prior to the bradykinin injection. 4. These results suggest that the induction, but not the maintenance, of cutaneous mechanical allodynia in flexor motoneurones is NK receptor dependent, with cutaneous C fibre conditioning inputs acting via NK1 and muscle C fibre conditioning inputs via NK2 receptor subtypes.
A slowly activating Ca(2+)‐dependent K+ current that plays a role in termination of swimming in Xenopus embryos.
Authors: Wall M J , Dale N
Published: December 2014

1. Acutely isolated Xenopus spinal neurons possess a slowly activating Ca(2+)‐dependent outward current which was revealed either by removal of external Ca2+ or by the addition of the Ca2+ channel blocker, 150 microM Cd2+. 2. The Ca(2+)‐sensitive current was very slow to activate and had a mean time constant of activation of 437 ms at 0 mV. The current also had very long tail currents which were blocked by Cd2+. The rate of decay of the slowest component of the Ca(2+)‐dependent tail currents was insensitive to membrane potential suggesting that the relaxation of the Ca(2+)‐dependent current may only be weakly voltage dependent. 3. The reversal potential of the Ca(2+)‐sensitive tail currents depended on the concentration of external K+ in a manner predicted by the Nernst equation. Thus the Ca(2+)‐sensitive current was carried by K+. 4. The toxin apamin (10 nM to 2 microM) selectively blocked the Ca(2+)‐dependent K+ current without affecting voltage‐gated K+ currents. This current may be analogous to a small‐conductance Ca(2+)‐dependent K+ (SK) current; however, unlike some SK currents, the Ca(2+)‐dependent K+ current was also sensitive to 500 microM tetraethylammonium chloride (TEA). 5. Applications of 10 nM apamin to spinalized embryos did not perturb the motor pattern for swimming. However, the cycle periods over which the locomotor rhythm generator could generate appropriate motor activity were lengthened by about 10% and the mean duration of swimming episodes was increased by approximately 40%. 6. We therefore propose that the Ca(2+)‐dependent K+ current plays an important role in the self‐termination of motor activity.
Carbonic anhydrase and control of breathing: different effects of benzolamide and methazolamide in the anaesthetized cat.
Authors: Teppema L , Berkenbosch A , DeGoede J , Olievier C
Published: December 2014

1. The effect of inhibition of erythrocyte carbonic anhydrase on the ventilatory response to CO2 was studied by administering benzolamide (70 mg kg‐1, i.v.), an inhibitor which does not cross the blood‐brain barrier, to carotid body denervated cats which were anaesthetized with chloralose‐urethane. 2. In the same animals the effect on the ventilatory response to CO2 of subsequent inhibition of central nervous system (CNS) carbonic anhydrase was studied by infusing methazolamide (20 mg kg‐1), an inhibitor which rapidly penetrates into brain tissue. 3. The results show that inhibition of erythrocyte carbonic anhydrase by benzolamide leads to a decrease in the slope of the normoxic CO2 response curve, and a decrease of the extrapolated arterial PCO2 at zero ventilation. 4. Inhibition of CNS carbonic anhydrase by methazolamide results in an increase in slope and alpha‐intercept of the ventilatory CO2 response curve. 5. Using a mass balance equation for CO2 of a brain compartment, it is argued that inhibition of erythrocyte carbonic anhydrase results in a decrease in slope of the in vivo CO2 dissociation curve, which can explain the effects of benzolamide. 6. The changes in slope and intercept induced by methazolamide are discussed in relation to effects on neurones containing carbonic anhydrase, which may include central chemoreceptors.
The functional expression of a pontine pneumotaxic centre in neonatal rats.
Authors: Fung M L , St John W M
Published: December 2014

1. Our purpose was to determine whether a pneumotaxic centre could be localized to the rostral pons in newborn rats. We recorded efferent activity of the phrenic nerve in decerebrate, paralysed, vagotomized and ventilated rats, whose age varied from the day of birth to 22 days. 2. The rostral pontine tegmentum was ablated by aspiration and electrolytic lesions. Neuronal activities were blocked by microinjections of the glutamate antagonist MK‐801 and were destroyed by the neurotoxins kainic acid and domoic acid. 3. Unilateral ablation or lesions of the pontine tegmentum caused a significant prolongation of the duration of the phrenic burst in animals of all ages. This duration increased further following contralateral destruction and apneusis was established. The period between phrenic bursts increased in most rats whereas peak phrenic height was not consistently altered. 4. Similar changes to those following physical ablations or lesions were recorded after microinjections of MK‐801 or neurotoxins. 5. A common region of ablation, lesion and microinjection was the parabrachialis and Köllicker‐Fuse nucleus. 6. Exposure to anoxia resulted in an alteration from apnoeusis to gasping. 7. We conclude that from the day of birth, rostral pontine pneumotaxic mechanisms play a significant role in the definition of eupnoea. Moreover, from the day of birth, rats can exhibit the classical ventilatory patterns of eupnoea, apneusis and gasping.
Effects of hypobaric hypoxia on antioxidant enzymes in rats.
Authors: Nakanishi K , Tajima F , Nakamura A , Yagura S , Ookawara T , Yamashita H , Suzuki K , Taniguchi N , Ohno H
Published: December 2014

1. The present study was undertaken to investigate the effects of hypobaric hypoxia, equivalent to an altitude of 5500 m, on antioxidant enzymes in rats. 2. Malondialdehyde levels in serum, heart, lung, liver and kidney of hypobaric‐hypoxic rats were all significantly higher than in control rats by day 21 of exposure (P < 0.05), indicating increased oxidative stress. 3. Superoxide dismutase (SOD) catalyses the conversion of the superoxide anion to H2O2 and O2. The concentration of immunoreactive Mn‐SOD in the serum of hypobaric‐hypoxic rats was raised significantly from day 5 onwards, whereas in liver and lung, it had decreased significantly by day 21 (P < 0.05). 4. Glutathione peroxidase (GSH‐Px) catalyses H2O2 and certain lipid peroxides. By day 21, GSH‐Px activity had increased significantly in the heart and lungs, but decreased significantly in the liver (P < 0.05). 5. Catalase catalyses H2O2. Catalase activity in the liver and kidney of hypobaric‐hypoxic rats was significantly decreased on day 1 (P < 0.05) though levels then recovered. 6. Mn‐SOD mRNA in the liver of hypobaric‐hypoxic rats was induced during the experiment, the effect being exceptionally marked, especially during the first 3 days of exposure to hypobaric hypoxia. 7. These results suggest that the liver may be more vulnerable than the other organs tested to oxidative stress under hypobaric hypoxia.
Amplitude and time course of evoked and spontaneous synaptic currents in rat submandibular ganglion cells.
Authors: Callister R J , Walmsley B
Published: December 2014

1. Excitatory postsynaptic currents (EPSCs) were recorded in rat submandibular ganglion cells in vitro using the two‐electrode voltage clamp technique. 2. The peak amplitude of EPSCs evoked by nerve impulses in single presynaptic fibres varied between 1.2 and 9.8 nA in different cells (mean = 4.6 +/‐ 2.6 nA; n = 23; ‐80 mV membrane potential; 22‐25 degrees C). 3. Experiments were performed to re‐investigate a previous hypothesis that different mechanisms underlie the generation of evoked versus spontaneous quantal EPSCs in submandibular cells. This hypothesis was based on the observation of different time courses of evoked and spontaneous EPSCs. 4. In agreement with previous studies, the time course of the decay phase of evoked EPSCs was described by the sum of two exponentials, with time constants tau 1 and tau 2 of 6.9 +/‐ 0.7 and 34.4 +/‐ 7.7 ms, respectively (n = 23; ‐80 mV membrane potential). 5. The double‐exponential decay of evoked EPSCs persisted when transmitter release was reduced by bath addition of 100 microM cadmium chloride to the level of failures, one or several quanta. 6. Spontaneous EPSCs exhibited mean amplitudes of 81 +/‐ 24 pA (n = 5 cells; ‐80 mV membrane potential), and displayed an extremely wide range of peak amplitudes in the same cell (mean coefficient of variation (c.v.) = 0.37 +/‐ 0.09; n = 5 cells). In contrast to a previous report (see below), the decay phase of spontaneous EPSCs was found to exhibit a double‐exponential time course with time constants similar to those of the evoked EPSC recorded in the same cell. 7. These results indicate that evoked and spontaneously released quanta of transmitter most probably act on the same population of postsynaptic receptors in submandibular ganglion cells. There is a large variability in the peak amplitudes of quantal EPSCs recorded in the same cell. This large variability is not due to electrotonic effects, since these cells lack dendrites.
Regulation of L‐arginine transport and nitric oxide release in superfused porcine aortic endothelial cells.
Authors: Bogle R G , Baydoun A R , Pearson J D , Mann G E
Published: December 2014

1. We have investigated whether changes in extracellular ion composition and substrate deprivation modulate basal and/or bradykinin‐stimulated L‐arginine transport and release of nitric oxide (NO) and prostacyclin (PGI2) in porcine aortic endothelial cells cultured and superfused on microcarriers. 2. Saturable L‐arginine transport (Km = 0.14 +/‐ 0.03 mM; Vmax = 2.08 +/‐ 0.54 nmol min‐1 (5 x 10(6) cells)‐1) was pH insensitive and unaffected following removal of extracellular Na+ or Ca2+. 3. Cationic arginine analogues, including L‐lysine and L‐ornithine, inhibited L‐arginine transport, whilst 2‐methylaminoisobutyric acid, beta‐2‐amino‐bicyclo[2,2.1]‐heptane‐2‐carboxylic acid, L‐phenylalanine, 6‐diazo‐5‐oxo‐norleucine, L‐glutamine, L‐cysteine and L‐glutamate were poor inhibitors. 4. Deprivation of L‐arginine (30 min to 24 h) reduced intracellular free L‐arginine levels from 0.87 +/‐ 0.07 to 0.40 +/‐ 0.05 mM (P < 0.05) and resulted in a 40% stimulation of L‐arginine, L‐lysine and L‐ornithine transport. 5. L‐arginine and NG‐monomethyl‐L‐arginine (L‐NMMA), but not N omega‐nitro‐L‐arginine methyl ester (L‐NAME), trans‐stimulated efflux of L‐[3H]arginine. 6. Depolarization of endothelial cells with 70 mM K+ reduced L‐arginine influx and prevented the stimulation of transport by 100 nM bradykinin, but agonist‐induced release of NO and PGI2 was still detectable. 7. Basal rates of L‐arginine transport and NO release were unaffected during superfusion of cells with a nominally Ca(2+)‐free solution. Bradykinin‐stimulated L‐arginine transport was insensitive to removal of Ca2+, whereas agonist‐induced NO release was abolished. 8. Although bradykinin‐stimulated NO release does not appear to be coupled directly to the transient increase in L‐arginine transport, elevated rates of L‐arginine influx via system y+ in response to agonist‐induced membrane hyperpolarization or substrate deprivation provide a mechanism for enhanced L‐arginine supply to sustain NO generation.
Two different constituents of plasma increase cytosolic calcium selectively in neurons or glia of primary rat cerebellar cultures.
Authors: Nuñez L , García-Sancho J
Published: December 2014

1. The ability of several serum fractions to increase the cytosolic calcium concentration ([Ca2+]i) was tested in rat cerebellar cells maintained in primary culture. 2. Serum filtered through an ultrafiltration membrane with 3000 Da molecular mass cut‐off (filtered serum, FS) selectively stimulated neurons whereas dialysed serum (DS) selectively stimulated glia. 3. The effects of FS were due to glutamate as they were reproduced by N‐methyl‐D‐aspartate (NMDA), blocked by NMDA receptor antagonists and prevented by enzymatic removal of glutamate. 4. The effects of DS on glia were not reproduced by platelet‐activating factor, thrombin or bradykinin. They were not lost on heating or extraction with diethyl ether. They were reproduced by a methanol‐chloroform‐HCl extract from DS and by several commercial fraction V plasma albumins. 5. These [Ca2+]i‐increasing factors present in blood could contribute to brain damage during ischaemia if they reached the brain interstitium on disruption of the blood‐brain barrier.
Mechanism of lactate‐induced relaxation of isolated rat mesenteric resistance arteries.
Authors: McKinnon W , Aaronson P I , Knock G , Graves J , Poston L
Published: December 2014

1. The effects of the sodium salt of the weak acid lactate on tension and intracellular pH (pH1) were studied in rat mesenteric small arteries mounted on a wire myograph. Sodium lactate was substituted iso‐osmotically for sodium chloride. 2. At a concentration of 50 mM, both L‐ and D‐stereoisomers of lactate markedly relaxed arteries preconstricted with noradrenaline (NA) within 10 min. The concentration‐response relationship for L‐lactate showed that the NA contracture was relaxed by 50% at approximately 26 mM. L‐Lactate did not, however, relax arteries preconstricted with high‐K+(45 mM) solution. 3. L‐Lactate did not alter extracellular pH (pHo) but caused a small but significant decrease in pH1, measured using the pH‐sensitive fluorochrome, 2',7'‐bis(carboxyethyl)‐5‐(6)‐carboxyfluorescein (BCECF). Relaxation to L‐lactate was unaffected when this change in pHi was offset by the simultaneous addition of NH4Cl to the solution. 4. Sodium pyruvate (50 mM) caused a significant intracellular acidosis but did not relax arteries preconstricted with NA. 5. L‐Lactate‐induced relaxations were unaffected by removal of the endothelium or when the synthesis of nitric oxide (NO) was inhibited by 10(‐4) M N omega‐nitro‐L‐arginine methyl ester (L‐NAME). 6. The potassium channel blockers glibenclamide (10 microM), 4‐aminopyridine (3 mM) and tetraethylammonium chloride (10 mM) did not affect L‐lactate‐induced relaxation in arteries preconstricted with NA. Inhibition of guanylate cyclase with Methylene Blue, or cyclooxgenase with indomethacin, also did not affect relaxation to L‐lactate. 7. The Rp stereoisomer of adenosine‐3',5'‐cyclic monophosphothioate (Rp‐cAMPS), an analogue of cAMP which inhibits competitively stimulation of protein kinase A, reduced significantly L‐lactate‐induced relaxation at a concentration of 25 microM. Rp‐cAMPS also significantly reduced forskolin‐induced relaxation of the NA contracture. 8. It is concluded that L‐lactate‐induced relaxation in this vascular bed is pHi‐1 endothelium‐, and nitric oxide‐independent. It is not mediated by inhibition of voltage‐gated Ca2+ channels, opening of K+ channels, prostacylin or cyclic GMP. cAMP may however play a role in L‐lactate‐induced relaxation.
Neuronal nicotinic alpha 7 receptor expressed in Xenopus oocytes presents five putative binding sites for methyllycaconitine.
Authors: Palma E , Bertrand S , Binzoni T , Bertrand D
Published: December 2014

1. The recently isolated compound methyllycaconitine (MLA) is a plant toxin which is a competitive inhibitor of nicotinic acetylcholine receptors (nAChRs). We found that homomeric alpha 7 receptors display a very high sensitivity to MLA with an IC50 in the picomolar range. 2. The competitive nature of the alpha 7 MLA blockade was reinforced by the observation that this compound has no action on wild‐type serotoninergic receptors (5‐HT3), whereas it is a powerful antagonist of chimaeric receptors alpha 7‐5‐HT3. 3. The time course of MLA inhibition of the wild‐type (WT) alpha 7 follows a monotonic exponential decay whose time constant is proportional to the MLA concentration and could be described by a bimolecular mechanism with a forward rate constant (k+) of 2.7 x 10(7) S‐1 M‐1. In contrast, recovery from MLA inhibition displays an S‐shaped time course that is incompatible with a simple bimolecular reaction. 4. Given the pentameric nature of the neuronal nicotinic receptors, a linear chain model, including five putative MLA binding sites corresponding to the homomeric nature of alpha 7, is proposed. 5. Both onset and recovery data obtained on the alpha 7 wild‐type receptor are adequately described by this model assuming that a single MLA molecule is sufficient to block receptor function. 6. Analysis of MLA blockade and recovery of reconstituted heteromeric alpha 4 beta 2 receptors reveals, as expected, a time course compatible with only two binding sites for the toxin and, thus, further supports the validity of our model.
Evidence for cutaneous and corticospinal modulation of presynaptic inhibition of Ia afferents from the human lower limb.
Authors: Iles J F
Published: December 2014

1. Presynaptic inhibition of soleus muscle Ia afferent fibres, produced by stimulation of group I afferents in the common peroneal nerve, was assessed from changes in the H reflex at long conditioning intervals, in six normal subjects. 2. Stimulation of the ipsilateral sural nerve at the malleolus, just before stimulation of the common peroneal nerve at the head of the fibula, decreased the presynaptic inhibition. This effect was strongest during voluntary plantar flexion and weaker during dorsiflexion or at rest. 3. Stimulation of other cutaneous nerve branches serving the dorsum of the ipsilateral foot, and also the contralateral sural nerve, decreased presynaptic inhibition. Adequate stimulation of low threshold cutaneous mechanoreceptors by light brushing of both distal dorsal and plantar surfaces of the ipsilateral foot decreased presynaptic inhibition. 4. Stimulation of the ipsilateral plantar nerves increased presynaptic inhibition, but this action is attributed to activation of group I afferents from the intrinsic muscles of the foot. 5. Transcranial magnetic stimulation of the lower limb area of the contralateral motor cortex decreased presynaptic inhibition. This effect was strongest during voluntary plantar flexion and weaker during dorsiflexion or at rest. 6. The actions of cutaneous and corticospinal pathways completely occluded each other. However, when both effects were adjusted to be liminal, a spatial facilitation between them was observed. 7. It is concluded that in man, as in the cat, cutaneous and corticospinal axons converge on interneurones that inhibit the machinery of presynaptic inhibition of group Ia afferents. These actions may be responsible for the modulation of presynaptic inhibition which has been observed to precede and accompany a wide range of human movements.
ATP‐activated cation conductance in a Xenopus renal epithelial cell line.
Authors: Mori M , Nishizaki T , Kawahara K , Okada Y
Published: December 2014

1. Using a whole‐cell voltage‐clamp technique and fura‐2 fluorescence measurements, the actions of extracellular adenosine 5'‐triphosphate (ATP) in single cells of an epithelial cell line (A6), were investigated. 2. ATP (0.1‐1000 microM) induced currents in cells held under voltage clamp. The sequence of purinergic agonist potency in activating the currents (2‐methylthio ATP > adenosine 5'‐diphosphate (ADP) > ATP > alpha, beta‐methylene ATP) was consistent with that of P2y receptors. 3. Reversal potentials (Erev) of the currents under various ionic conditions suggest that potassium channels and non‐selective cation channels were responsible for the ATP‐activated conductance, which was permeable to calcium. 4. ATP activated the currents in a calcium‐free extracellular solution. In the presence of extracellular calcium, the currents were completely inhibited with 10 mM EGTA in the pipette. 5. ATP (10 microM) increased the intracellular calcium concentration ([Ca2+]i) whether cells were bathed in a solution containing calcium or not. 6. These results indicate that ATP evoked a calcium‐dependent cation conductance, permeable to calcium, through P2y receptors by releasing calcium from intracellular stores in A6 cells.
A non‐inactivating K+ current sensitive to muscarinic receptor activation in rat cultured cerebellar granule neurons.
Authors: Watkins C S , Mathie A
Published: December 2014

1. Whole‐cell recordings were made from cultured cerebellar granule neurons using perforated patch clamp techniques. The primary cultures were prepared using 6‐ to 9‐day‐old Sprague‐Dawley rats. 2. Neurons in culture for less than 48 h possessed resting membrane potentials of ‐29 mV. However, neurons in culture for 7 days had much more hyperpolarized resting membrane potentials (‐89 mV). Over the same period, these neurons developed an additional component of outward current. 3. This non‐inactivating current was activated by depolarization, exhibited outward rectification and reversed close to the potassium equilibrium potential. The kinetics of activation and deactivation were very rapid. 4. Muscarine ((+)‐muscarine chloride) reversibly inhibited the current with an EC50 of 0.17 microM. The inhibition by muscarine was unaffected by pre‐incubation for 17‐20 h with 120 micrograms ml‐1 pertussis toxin. 5. The current and its inhibition by muscarine were unaffected by 100 microM Cd2+. In Ca(2+)‐free conditions, the current was significantly larger than in 0.5 mM Ca2+, but inhibition by 10 microM muscarine was significantly reduced. 6. The standing outward current was not obviously affected by 50 microM 5‐HT, 50 microM noradrenaline, 50 microM 2‐chloroadenosine or 5 mM tetraethylammonium. It was reduced by 10 microM La3+, 10 microM Zn2+ and 1 mM Ba2+. 7. Muscarinic agonists increased the input resistance of neurons and shifted the zero current level in the depolarized direction when voltage clamped. This enhanced excitability was evident under current clamp, where 10 microM muscarine depolarized granule neurons such that action potentials became evident.
Ca2+ transients associated with openings of inositol trisphosphate‐gated channels in Xenopus oocytes.
Authors: Parker I , Yao Y
Published: December 2014

1. The mechanisms underlying inositol 1,4,5‐trisphosphate (InsP3)‐induced Ca2+ liberation were studied in Xenopus oocytes by using scanning and stationary‐point confocal fluorescence microscopy to record Ca2+ signals evoked by photorelease of InsP3 from a caged precursor. 2. Fluorescence measurements from confocal images showed that increasing [InsP3] evoked three distinct modes of Ca2+ liberation: a diffuse ‘pacemaker’ signal, localized transient puffs, and propagating waves. Peak free Ca2+ concentrations during waves and puffs (respectively, 2‐5 microM and 100‐200 nM) varied only slightly with [InsP3], whereas the pacemaker amplitude varied over a wider range (at least 1‐30 nM Ca2+). 3. The improved resolution provided by confocal point recording revealed discontinuous Ca2+ ‘blips’ during pacemaker release. These events were resolved only at particular locations and had time courses similar to the puffs (rise, approximately 50 ms; decay, a few hundred milliseconds) but with amplitudes one‐fifth or less of puff amplitudes. 4. We conclude that blips may arise through opening of single InsP3‐gated channels, whereas puffs reflect the concerted opening of several clustered channels due to local regenerative feedback by Ca2+.
Selective depletion of spinal monoamines changes the rat soleus EMG from a tonic to a more phasic pattern.
Authors: Kiehn O , Erdal J , Eken T , Bruhn T
Published: December 2014

1. To assess the role of descending monoaminergic pathways for motor activity long‐lasting EMG recordings were performed from the adult soleus muscle before and after selective depletion of spinal monoamines. 2. Rats were chronically implanted with an intrathecal catheter placed in the lumbar subarachnoid space and gross‐EMG recording electrodes in the soleus muscle. EMG recordings were performed in control conditions and at different times after intrathecal administration of either 40‐55 micrograms 5,6‐dihydroxytryptamine (5,6‐DHT) and 40‐55 micrograms 6‐hydroxydopamine (6‐OHDA) or 80 micrograms 5,7‐dihydroxytryptamine (5,7‐DHT) alone. The depletions were evaluated biochemically in brains and spinal cords after recordings. 3. In agreement with previous studies the intrathecal administration of neurotoxins caused a reduction of the noradrenaline (NA) and serotonin (5‐HT) content of the lumbar spinal cord to about 2‐3% of control, with little or no changes in the monoamine content of the cortex. 4. In non‐treated chronically catheterized rats the integrated rectified gross EMG displayed long‐lasting EMG episodes composed of phasic high‐amplitude events and tonic segments of varying duration and amplitude. 5. After intrathecal administration of neurotoxins the number of long‐lasting gross‐EMG episodes, the mean episode duration, and the total EMG activity per 24 h, were reduced. These changes were accompanied by a simultaneous increase both in the number of short‐lasting EMG episodes and the total number of EMG episodes per 24 h period. The changes were apparent 5‐6 days after drug administration and fully developed after 2‐3 weeks. 6. No changes in general movement ability were observed, except that the denervated animals had a tendency to a less errect posture. 7. These results indicate that descending monoaminergic pathways are important for the maintained motor output in tonic hindlimb muscles.
Modulation of inwardly rectifying currents in rat sympathetic neurones by muscarinic receptors.
Authors: Wang H S , McKinnon D
Published: December 2014

1. Intracellular recordings were made from rat sympathetic neurones in isolated superior cervical ganglia (SCG), coeliac ganglia (CG), and superior mesenteric ganglia (SMG). 2. Following classification of the firing properties of these neurones as either ‘phasic’ or ‘tonic', single‐electrode voltage‐clamp recordings of the inwardly rectifying current were performed. The inward rectifier conductance was 6.4 times larger in tonic neurones than in phasic neurones. 3. The basic features of the inward rectifier in sympathetic neurones were similar to those of the classic inward rectifier described in several neuronal and non‐neuronal preparations. The properties of the native channel were also similar to a subset of recently cloned inwardly rectifying channels. The reversal potential and the slope conductance were both dependent on external potassium ion concentration. The conductance was blocked by low concentrations of external Ba(2+) and Cs(+) ions. 4. A striking feature of the inward rectifier in sympathetic neurones was its modulation by muscarine. Application of 20 microM muscarine produced a mean 78 +/‐ 1.4% inhibition of the current. From dose‐response curves for muscarine a mean dissociation constant of K(D) = 1.95 +/‐ 0.2 microM was determined. Schild plot analysis using the competitive antagonists pirenzepine and himbacine indicated that the effect of muscarine was mediated by the M(1) class of muscarinic receptors. 5. The inward rectifier was also inhibited by repetitive nerve stimulation which produced a block of the conductance similar to that seen in response to bath‐applied muscarine. The onset of inhibition was relatively slow, 20‐30 s, suggesting that it is mediated by a soluble second messenger pathway.
Unloaded shortening velocities of rabbit masseter muscle fibres expressing skeletal or alpha‐cardiac myosin heavy chains.
Authors: Sciote J J , Kentish J C
Published: December 2014

1. Some rabbit masseter fibres express the alpha‐cardiac myosin heavy chain (MHC). To compare the biochemical and physiological properties of these fibres with other skeletal fibre types, we examined the histochemical and immunohistochemical staining characteristics, maximum velocity of shortening (V(zero)) and MHC isoform content of fibres from rabbit masseter and soleus muscles. 2. The fibre‐type composition of muscle sections was determined with MHC antibodies and myofibrillar ATPase histochemistry. Fibres we designated ‘type alpha‐cardiac’ were different from type I and type II fibres in that they stained positively with the alpha‐cardiac MHC antibody and they maintained. ATPase reactivity after acid and alkali pre‐incubations. Samples of superficial masseter contained a few type I fibres, with the majority of fibres classified as either type IIA or type alpha‐cardiac. Soleus samples contained type I, IIA and IIC fibres. 3. The V(zero) of chemically skinned fibres was determined by the slack‐test method. Each fibre was subsequently characterized as type I, IIA, IIC or alpha‐cardiac from MHC identification using gel electrophoresis (SDS‐PAGE). In masseter fibres the V(zero) values were (in muscle lengths s‐1): type I, 0.54 +/‐ 0.05 (mean +/‐ S.D., n = 3); type IIA, 1.23 +/‐ 0.34 (n = 27); type alpha‐cardiac, 0.78 +/‐ 0.08 (n = 9). In soleus fibres V(zero) values were: type I, 0.55 +/‐ 0.06 (n = 14); type IIA, 0.89 +/‐ 0.04 (n = 8); type IIC, 0.73 (n = 2). 4. We conclude that the rabbit masseter muscle contains an ‘alpha‐cardiac’ fibre type that is distinct from other skeletal fibres. This fibre type expresses only the alpha‐cardiac MHC, has unusual myofibrillar ATPase reactivity and has a V(zero) intermediate between type I and type II fibres.
Chronic volume expansion in the rat: proximal tubular Na+ transport and Na+ pump inhibition.
Authors: Györy A Z , Salipan‐Moore N , Reddy S
Published: December 2014

1. The lesser natriuresis of chronic volume expansion (ChVE) compared with that of acute volume expansion (AcVE) implies different homeostatic mechanisms. Because little information is available in the literature on proximal tubular (PT) Na+ transport and intracellular electrolyte concentrations, these were investigated in a rat model of ChVE. 2. Haematocrit was significantly lower and urine volume and Na+ excretion were significantly higher in ChVE rats compared with control rats. 3. Proximal tubular Na+ transport with artificial PT fluid was normal (3.67 +/‐ 0.09 x 10(‐4) mm3 mm‐2 s‐1; mean+/‐S.E.M.), while with endogenously harvested tubular fluid it was reduced to 2.78 +/‐ 0.07 x 10(‐4) mm3 mm‐2 s‐1 in ChVE rats (P < 0.0001). 4. Intracellular Na+ was significantly elevated from 18.0 +/‐ 0.7 mmol (kg wet wt)‐1 in control rats to 20.2 +/‐ 0.8 mmol (kg wet wt)‐1 in ChVE rats (P = 0.044). The cells showed residual swelling, with dry weight and phosphorus values decreasing significantly compared with controls (19.5 +/‐ 0.4 to 18.5 +/‐ 0.03% and 130.4 +/‐ 3.7 to 117.8 +/‐ 2.8 mmol (kg wet wt)‐1, P = 0.04 and 0.006, respectively). 5. The results demonstrate that in ChVE a tubular factor inhibits PT Na+ transport associated with an inhibition of the Na+ pump and this resembles one mechanism defined in AcVE.
Changes in muscle strength, relaxation rate and fatiguability during the human menstrual cycle.
Authors: Sarwar R , Niclos B B , Rutherford O M
Published: December 2014

1. The effect of the different phases of the menstrual cycle on skeletal muscle strength, contractile properties and fatiguability was investigated in ten young, healthy females. Results were compared with a similar group on the combined (non‐phasic) oral contraceptive pill (OC). Cycle phases were divided into the early and mid‐follicular, mid‐cycle (ovulatory) and mid‐ and late luteal. Cycle phases were estimated from the first day of the menstrual bleed. 2. Subjects were studied weekly through two complete cycles. Measurements included quadriceps and handgrip maximum voluntary isometric force and the relaxation times, force‐frequency relationship and fatigue index of the quadriceps during percutaneous stimulation at a range of frequencies from 1 to 100 Hz. 3. In the women not taking the OC there was a significant increase of about 11% in quadriceps and handgrip strength at mid‐cycle compared with both the follicular and luteal phases. Accompanying the increases in strength there was a significant slowing of relaxation and increase in fatiguability at mid‐cycle. No changes in any parameter were found in the women taking the OC. 4. The changes in muscle function at mid‐cycle may be due to the increase in oestrogen that occurs prior to ovulation.
Analysis of gamma rhythms in the rat hippocampus in vitro and in vivo.
Authors: Traub R D , Whittington M A , Colling S B , Buzsáki G , Jefferys J G
Published: December 2014

1. We have shown previously, with experimental and computer models, how a ‘40 Hz’ (gamma) oscillation can arise in networks of hippocampal interneurones, involving mutual GABAA‐mediated synaptic inhibition and a source of tonic excitatory input. Here, we explore implications of this model for some hippocampal network phenomena in the rat in vitro and in vivo. 2. A model network was constructed of 1024 CA3 pyramidal cells and 256 interneurones. AMPA (alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid), NMDA (N‐methyl‐D‐aspartate), GABAA and GABAB receptors were simulated on pyramidal cells and on interneurones. 3. In both model and experiment, the frequency of network oscillations, in the gamma range, depended upon three parameters: GABAA conductance and decay time constant in interneurone‐‐>interneurone connections, and the driving current to the interneurones. 4. The model of gamma rhythm predicts an average zero phase lag between firing of pyramidal cells and interneurones, as observed in the rat hippocampus in vivo. The model also reproduces a gamma rhythm whose frequency changes with time, at theta frequency (about 5 Hz). This occurs when there is 5 Hz modulation of a tonic signal to chandelier and basket cells. 5. Synchronized bursts can be produced in the model by several means, including partial blockade of GABAA receptors or of AMPA receptors on interneurones, or by augmenting AMPA‐mediated EPSCs. In all of these cases, the burst can be followed by a ‘tail’ of transiently occurring gamma waves, a phenomenon observed in the hippocampus in vivo following sharp waves. This tail occurs in the model because of delayed excitation of the interneurones by the synchronized burst. A tail of gamma activity was found after synchronized epileptiform bursts both in the hippocampal slice (CA3 region) and in vivo. 6. Our data suggest that gamma‐frequency EEG activity arises in the hippocampus when pools of interneurones receive a tonic or slowly varying excitation. The frequency of the oscillation depends upon the strength of this excitation and on the parameters regulating the inhibitory coupling between the interneurones. The interneurone network output is then imposed upon pyramidal neurones in the form of rhythmic synchronized IPSPs.