bluuebunny/crossref_metadata_2025 huggingface dataset:
Ventilatory response to hyperoxia in newborn rats born in hypoxia‐‐possible relationship to carotid body dopamine.
Authors: Hertzberg T , Hellström S , Holgert H , Lagercrantz H , Pequignot J M
Published: December 2014

1. The influence of postnatal hypoxia on regulation of breathing and turnover rate of carotid body dopamine was examined in newborn rats. The percentage change in frequency, tidal volume and ventilation elicited by transient hyperoxia was assessed by flow plethysmography in unanaesthetized pups. The alteration in ventilation was taken as an index of peripheral chemoreceptor activity. 2. The rats were born and reared in hypoxia. The inspired oxygen fraction (FI,O2) was 0.12‐0.14 until 2 days after delivery when the rats were placed into room air and the ventilatory chemoreflex was tested. At 4 days of age, i.e. 2 days after termination of hypoxia, the rats were tested again. The ventilatory data were compared with those from a previous study in normoxic rats. 3. We found a smaller decrease in ventilation (8.8 +/‐ 3.9%, mean +/‐ S.D.) in the hypoxic rats at 2 days of age compared with normoxic rats (22.7 +/‐ 6.4%; P < 0.001). In contrast, at 4 days of age there was no difference in ventilatory response between the posthypoxic rats (19.2 +/‐ 4.6%) and normoxic pups (18.6 +/‐ 4.9%). 4. The turnover rates of dopamine in carotid bodies were determined at 0‐6, 6‐12, 12‐24 h and 2 days after birth in hypoxic rats and in 2‐day‐old posthypoxic rat pups at different time intervals after termination of hypoxia. Postnatal hypoxia sustained a high turnover rate which decreased after termination of the hypoxia. 5. We propose that the weak chemoreflex in hypoxic rat pups is brought about by a high release of carotid body dopamine.
Muscarinic inhibition of M‐current and a potassium leak conductance in neurones of the rat basolateral amygdala.
Authors: Womble M D , Moises H C
Published: December 2014

1. Voltage‐clamp recordings using a single microelectrode were obtained from pyramidal neurones of the basolateral amygdala (BLA) in slices of the rat ventral forebrain. Slow inward current relaxations during hyperpolarizing voltage steps from a holding potential of ‐40 mV were identified as the muscarinic‐sensitive M‐current (IM), a time‐ and voltage‐dependent potassium current previously identified in other neuronal cell types. 2. Activation of IM was voltage dependent with a threshold of approximately ‐70 mV. At membrane potentials positive to this, the steady‐state current‐voltage (I‐V) relationship showed substantial outward rectification, reflecting the time‐ and voltage‐dependent opening of M‐channels. The underlying conductance (gM) also increased sharply with depolarization. 3. The reversal potential for IM was ‐84 mV in medium containing 3.5 mM K+. This was shifted positively by 27 mV when the external K+ concentration was raised to 15 mM. 4. The time courses of M‐current activation and deactivation were fitted by a single exponential. The time constant for IM decay, measured at 24 degrees C, was strongly dependent on membrane potential, ranging from 330 ms at ‐40 mV to 12 ms at ‐100 mV. 5. Bath application of carbachol (0.5‐40 microM) inhibited IM, as evidenced by the reduction or elimination of the slow inward M‐current relaxations evoked during hyperpolarizing steps from a holding potential of ‐40 mV. The outward rectification of the steady‐state I‐V relationship at membrane potentials positive to ‐70 mV was also largely eliminated. The inhibition of IM by carbachol was dose dependent and antagonized by atropine. 6. Carbachol produced an inward current shift at a holding potential of ‐40 mV that was only partially attributable to inhibition of IM. An inward current shift was also produced by carbachol at membrane potentials negative to ‐70 mV, where IM is inactive. These effects were dose dependent and antagonized by atropine. They were attributed to the muscarinic inhibition of a voltage‐insensitive potassium leak conductance (ILeak). 7. In most cells, carbachol reduced the slope of the instantaneous I‐V relationship obtained from a holding potential of ‐70 mV so that it crossed the control I‐V plot at the reversal potential for ILeak. This was found to be ‐108 mV in 3.5 mM K+ saline, shifting to ‐66 mV in 15 mM K+ saline.(ABSTRACT TRUNCATED AT 400 WORDS)
Control of an external force in leg extensions in humans.
Authors: Jacobs R , van Ingen Schenau G J
Published: December 2014

1. We investigated the hypothesis that mono‐ and bi‐articular muscles perform different functions: the former are chiefly dependent on their mechanical advantage, while the latter are considered to be mainly concerned with controlling the direction of an external force. 2. Seven subjects were asked to exert a constant external force in various directions from three different positions. Feedback was given on the amplitude (300 and 600 N) and direction of the force vector. 3. During each trial the position of the subject was registered. Ground reaction force and muscle activity (EMG) from the main mono‐ and bi‐articular upper leg muscles were recorded. Link segment modelling was used to obtain net moments about the knee and hip joints. For each muscle the mechanical advantage was calculated in each force direction. 4. The task of controlling the ground reaction force was performed with little interindividual variation as reflected by the variability of the different force and EMG variables. 5. A linear relationship between the difference in activity of rectus femoris and hamstrings and the difference in net moment around the knee and hip was found. This relationship showed very high correlation coefficients of 0.96 (300 N) and 0.97 (600 N) and was independent of position. Mean correlations between this activity difference and the angle of the force vector were also high: ‐0.95 (300 N) and ‐0.94 (600 N). 6. The mono‐ as well as the bi‐articular muscles increased in activity when a larger mechanical advantage could be obtained from them, except for the biceps femoris (short head). 7. The results support the hypothesis that bi‐articular muscles have a unique role in controlling the distribution of net moments about the joints, and as a consequence, in controlling the direction of the external force exerted on the environment.
Tension responses of sheep aorta to simultaneous decreases in phosphocreatine, inorganic phosphate and ATP.
Authors: Hardin C D , Wiseman R W , Kushmerick M J
Published: December 2014

1. Tension responses of sheep aortae were investigated when different substrates were included in the superfusing medium. The magnitude of tension development was similar whether or not 5 mM glucose was present in the medium. However, the rate of tension development was greater in the absence of glucose. 2. When 5 mM 2‐deoxyglucose (2DG) was present in the medium, the magnitude of tension generation was 1.6 times that in the absence of exogenous substrate. A second sequential contraction with 2DG generated tension 1.25 times that in the absence of exogenous substrate. The rate of tension development during the first contraction in the presence of 2DG was similar to that in the absence of substrate. However, the second contraction in the presence of 2DG had a substantially increased rate of tension development. 3. 31P nuclear magnetic resonance (NMR) spectroscopy revealed that, at resting tone, in the presence of 2DG, inorganic phosphate (P(i)) and phosphocreatine (PCr) simultaneously decrease while 2‐deoxyglucose‐6‐phosphate accumulates. During contraction‐relaxation cycles, in the presence of 2DG, P(i) and PCr become undetectable while ATP declines to approximately 50% of control values as determined by NMR. During the second contraction in the presence of 2DG, the area of the ADP resonance was similar to that of the alpha‐ATP resonance. 4. The increase in the magnitude of tension generation, during 2DG administration, correlated with a decrease in P(i) levels. The rate of relaxation from a contraction, in the presence of 2DG, was slower than in the presence of glucose or in the absence of exogenous substrate. These results are consistent with the role of P(i) in the release of the proposed ‘latch‐bridge’ state of maintained contraction at low energy demand. 5. The increase in isometric tension generation during contraction in the presence of 2DG appears to be related to the decreased levels of P(i). In the presence of 2DG, the reduction of PCr and of ATP occur to a similar extent to that during hypoxia, yet no inhibition of force takes place. The low levels of ATP and PCr reported with 2DG administration in these studies do not energetically limit the contractile apparatus.
Role of bicarbonate in pH recovery from intracellular acidosis in the guinea‐pig ventricular myocyte.
Authors: Lagadic‐Gossmann D , Buckler K J , Vaughan‐Jones R D
Published: December 2014

1. Intracellular pH (pHi) was recorded ratiometrically in isolated guinea‐pig ventricular myocytes using the pH‐sensitive fluoroprobe, carboxy‐SNARF‐1 (carboxy‐seminaphthorhodafluor). 2. Following an intracellular acid load (10 mM NH4 Cl removal), pHi recovery in HEPES‐buffered Tyrode solution was inhibited by 1.5 mM amiloride (Na(+)‐H+ antiport blocker). In the presence of amiloride, switching from HEPES buffer to HCO3‐/CO2 (pHo of both solutions = 7.4) stimulated a pHi recovery towards more alkaline levels. 3. Amiloride‐resistant, HCO(3‐)‐dependent pHi recovery was inhibited by removal of external Na+ (replaced by N‐methyl‐D‐glucamine), whereas removal of external Cl‐ (replaced by glucuronate, leading to depletion of internal Cl‐), removal of external K+, or decreasing external Ca2+ by approximately tenfold had no inhibitory effect. These results suggest that the amiloride‐resistant recovery is due to a Na(+)‐HCO3‐ cotransport into the cell. 4. The stilbene derivative DIDS (4,4'‐diisothiocyanatostilbene‐2,2'‐disulphonic acid, 500 microM) slowed Na(+)‐HCO(3‐)‐dependent pHi recovery. 5. Intracellular pH increased in Cl(‐)‐free solution and this increase still occurred in Na(+)‐free solution indicating that it is not caused via Na(+)‐HCO3‐ symport and is more likely to be due to Cl‐ efflux in exchange for HCO3‐ influx on a sarcolemmal Cl(‐)‐HCO3‐ exchanger. The lack of any significant pHi recovery from intracellular acidosis in Na(+)‐free solution suggests that this exchanger does not contribute to acid‐equivalent extrusion. 6. Possible voltage sensitivity and electrogenicity of the co‐transport were examined by using the whole‐cell patch clamp technique in combination with SNARF‐1 recordings of pHi. Stepping the holding potential from ‐110 to ‐40 mV did not affect amiloride‐resistant pHi recovery from acidosis. Moreover, following an intracellular acid load, the activation of Na(+)‐HCO3‐ co‐influx (by switching from HEPES to HCO3‐/CO2 buffer) produced no detectable outward current (outward current would be expected if the coupling of HCO3‐ with Na+ were > 1.0). 7. Intracellular intrinsic buffering power (beta i) was assessed as a function of pHi (beta i computed from the decrease of pHi following reduction of extracellular NH4 Cl in amiloride‐containing solution). beta i in the ventricular myocyte increases roughly linearly with a decrease in pHi according the following equation: beta i = ‐28(pHi) +222.6. 8. Comparison of acid‐equivalent efflux via Na(+)‐HCO3‐ symport and Na(+)‐H+ antiport showed that, following an intracellular acidosis, the symport accounts for about 40% of total acid efflux, the other 60% being carried by the antiport.(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of external cation concentration and metabolic inhibitors on membrane potential of human glial cells.
Authors: Brismar T , Collins V P
Published: December 2014

1. The effect on membrane potential (Em) of low external [K+]o, [Na+]o and [Ca2+]o and of metabolic inhibitors was studied in cultured human glial cells (U‐787CG) and human glioma cells (Tp‐483MG and U‐251MG). Whole cells were voltage or current clamped with the tight‐seal recording technique. 2. Em was ‐76 and ‐80 mV in glial and glioma cells (mean values in U‐787CG and U‐251MG, respectively) in a reference external solution with 3.0 mM K+. K(+)‐free external solution caused a rapid and reversible depolarization of these cells by about 26 and 42 mV (respectively). 3. Block of K+ channels with 1 mM Ba2+ in external solution rapidly depolarized the cells (U‐251MG) by about 35 mV. 4. Na(+)‐free solutions caused a delayed depolarization by 40‐50 mV, which was slowly reversible (in 2 min). 5. Ouabain (1 mM) depolarized the cells by about 4 mV. It did not prevent the effect of K(+)‐free solution. 6. Ca(2+)‐free external solution rapidly depolarized the cells to Em about ‐17 mV. The combination of either Na(+)‐K(+)‐free or Na(+)‐Ca(2+)‐free solution transiently repolarized the cell, which indicated that the K+ selectivity of the membrane was decreased in both K(+)‐ and Ca(2+)‐free solutions. 7. Metabolic inhibitors (carbonyl cyanide p‐trifluoromethoxy‐phenylhydrazone (FCCP) and 2,4‐dinitrophenol (DNP)) rapidly and reversibly depolarized the cells. This effect was not prevented by intracellular perfusion of a strong Ca(2+)‐buffering solution. 8. Voltage clamp revealed only minor changes (< 20%) in the leak conductance (g) of cells that were depolarized by the above‐mentioned solutions. 9. Positive polarizing current elicited (in some cells) a regenerative depolarization. The threshold for depolarization was less in low external [K+]o. 10. It is concluded (a) that the resting potential of these glial cells depends on ion channels that are K+ selective only in the presence of external Ca2+ and K+ and (b) that this K+ selectivity may require that Em is near the reversal potential for potassium (EK), and (c) that the action of metabolic inhibitors (DNP and FCCP) is different from that in neurones.
Single voltage‐dependent potassium channels in rat peripheral nerve membrane.
Authors: Safronov B V , Kampe K , Vogel W
Published: December 2014

1. Voltage‐dependent potassium channels were investigated in rat axonal membrane by means of the patch‐clamp recording technique. Three different types of channels (F, I and S) have been characterized on the basis of their single‐channel conductance, activation, deactivation and inactivation properties. 2. The fast (F) channels were activated smoothly at potentials (E) between ‐50 and 50 mV (E50 = 4.6 mV). They had a conductance of 55 pS for inward current and 30 pS for outward current in solutions containing 155 mM K+ (high K+) on both sides of the membrane at 21‐23 degrees C. The F‐channels demonstrated the fastest deactivation, within 1‐2 ms, and inactivated in a few hundreds of milliseconds. The time constant of inactivation was 143 ms at E = +40 mV. 3. The intermediate (I) channels activated steeply between E = ‐70 and ‐50 mV (E50 = ‐64.2 mv) and had a single‐channel conductance of 33 pS for inward and 18 ps for outward currents. The I‐channels deactivated with intermediate kinetics with the time constants of 20.4 ms and 10.1 ms at E = ‐80 mV and E = ‐100 mV, respectively. Complete inactivation of the channels developed over tens of seconds. The time constant of inactivation was 7.4 s at E = +40 mV. 4. The slow (S) channels were active at potentials positive to ‐90 mV. Their conductance was 10 pS for inward currents. The time constant of activation of the S‐channels was strongly potential dependent. At a holding potential of ‐100 mV the channels deactivated during a long time interval between 30 ms and 1 s, producing long‐lasting tail currents. The mean time constant of deactivation for S‐channels was 129 ms. 5. The conductances of F‐ and I‐channels measured under normal physiological conditions (Ringer solution in bath) were 17 and 10 pS, respectively. 6. Tetraethylammonium (TEA), the classic blocker of potassium channels, suppressed F‐, I‐ and S‐channels. It gradually reduced the apparent amplitude of unitary currents in a dose‐dependent manner with IC50 equal to 1.2 mM for F‐channels, 0.6 mM for I‐channels and 1.4 mM for S‐channels. Dendrotoxin (DTX), a toxin from the green mamba snake, considerably inhibited the I tail currents at nanomolar concentrations (IC50 = 2.8 nM) while the amplitudes of single I‐channel currents were not affected. 7. The K+ channels of F, I and S types form the basis of the potassium conductivity in mammalian peripheral myelinated axon.(ABSTRACT TRUNCATED AT 400 WORDS)
The time course of phosphate metabolites and intracellular pH using 31P NMR compared to recovery heat in rat soleus muscle.
Authors: Phillips S K , Takei M , Yamada K
Published: December 2014

1. The recovery time course of changes in phosphate metabolites and pH, after tetanic contractions of 6 and 9 s were studied using 31P NMR with 4 and 16 s resolution, in rat soleus muscles at 20 degrees C. Muscles were at a sarcomere length of 3.15 microns (active), being greater than optimum for force which was 2.88 microns (active). 2. The post‐contraction recovery of chemical changes was compared with the heat production in parallel experiments. Initial and recovery heat production were measured in tetanically stimulated muscles. 3. During recovery from tetanic contractions the changes in phosphocreatine (PCr) matched the changes in inorganic phosphate (Pi). The change in intracellular pH (pHi) was biphasic. The pHi first became more alkaline after contraction and then decreased until it reached a point below the baseline value. There was then a final recovery. 4. The initial heat and recovery heat production were greater than that expected from the PCr hydrolysis estimated during the tetanus and the PCr resynthesis that follows. 5. These data support the presence of ‘unexplained heat’ during a contraction and its related recovery processes in rat soleus muscle.
The action of amyotrophic lateral sclerosis immunoglobulins on mammalian single skeletal muscle Ca2+ channels.
Authors: Magnelli V , Sawada T , Delbono O , Smith R G , Appel S H , Stefani E
Published: December 2014

1. The planar phospholipid bilayer technique was used to study the T‐tubule skeletal muscle dihydropyridine (DHP)‐sensitive calcium (Ca2+) channel. To improve the signal‐to‐noise ratio, Ca2+ channel activity was recorded using both 800‐50 and 500‐50 mM NaCl gradients. 2. Ca2+ channels were characterized by their cation selectivity and pharmacological profile. The mean open time for channels identified by these techniques was increased by the DHP agonist Bay K 8644 (2 microM), while it was decreased by the DHP antagonist nifedipine (5 microM). Nifedipine also reduced Ca2+ channel amplitude levels. 3. Immunoglobulins G (IgG) from three amyotrophic lateral sclerosis (ALS) patients (n = 14 experiments), one myasthenia gravis (MG) patient (n = 3 experiments) and one healthy individual (n = 4 experiments), were tested on Ca2+ channel activity at a final concentration of 3 mg/ml. 4. Channel mean open time, mean closed time and time integral for the current were not modified by normal IgG (n = 4 experiments). Similarly, MG IgG did not reduce channel activity (n = 3 experiments). 5. ALS IgG reduced the mean open time of DHP‐sensitive Ca2+ channel activity in twelve out of fourteen experiments. In addition, in five out of twelve experiments, ALS IgG stabilized the channel to a smaller amplitude level. 6. ALS IgG reduced Ca2+ channel activity in a side‐selective fashion, probably corresponding to the external side of the channel. 7. These results suggest that ALS IgG action on DHP‐sensitive Ca2+ channels is not mediated by second messengers, thus favouring a direct mechanism for interaction with the DHP receptor complex.
The effect of metabolic fuel on force production and resting inorganic phosphate levels in mouse skeletal muscle.
Authors: Phillips S K , Wiseman R W , Woledge R C , Kushmerick M J
Published: December 2014

1. The effect of different metabolic fuels (glucose, pyruvate and lactate) and no exogenous metabolic fuel on force production was studied in isolated mouse soleus and extensor digitorum longus (EDL) muscles. Force was measured, at 25 degrees C, during isometric tetanic contractions and during contractions with isovelocity stretching and shortening. In parallel experiments, measurements were made of the resting phosphorus metabolite levels using 31P NMR. 2. In soleus muscles, the isometric tetanic force was potentiated with pyruvate (20 mM) as metabolic fuel, compared with glucose (11 mM), by 17.8 +/‐ 3.6% (mean +/‐ S.E.M., n = 6). The force was the same with no exogenous metabolic fuel, with glucose, or with lactate as metabolic fuel. The force exerted during shortening was also potentiated by pyruvate and by the same proportion as isometric force. However, during rapid stretching there was no force enhancement with pyruvate. The changes in the force seen with pyruvate are qualitatively similar to those produced when inorganic phosphate (Pi) is lowered in skinned rabbit psoas muscle fibres. 3. We tested whether the Pi content decreased in the presence of pyruvate by measuring resting Pi using 31P NMR spectroscopy. We found that, in soleus muscles, resting Pi was present with glucose and absent with pyruvate as metabolic fuel, and the effect was reversible. 4. EDL muscles produced the same isometric force whether the metabolic fuel was glucose, pyruvate, lactate or if no exogenous metabolic fuel was supplied. EDL muscles already had Pi levels below detectability at rest in glucose. There were no changes in the 31P NMR spectrum with pyruvate as metabolic fuel. 5. It appears therefore that the force potentiation in soleus muscles with pyruvate is due to a lowering of Pi. EDL muscles, which have a very low resting Pi in glucose, therefore have very little potential for force enhancement by this mechanism.
Temporal and spatial summation in the human rod visual system.
Authors: Sharpe L T , Stockman A , Fach C C , Markstahler U
Published: December 2014

1. Absolute and increment thresholds were measured in a retinal region 12 deg temporal from the fovea with 520 nm targets of varying size and duration. Measurements were made under rod‐isolation conditions in two normal observers and in a typical, complete achromat observer who has no cone‐mediated vision. The purpose of these experiments was to determine how the temporal and spatial summation of rod‐mediated vision changes with light adaptation. 2. The absolute threshold and the rise in increment threshold with background intensity depend upon target size and duration, but the psychophysically estimated dark light of the eye (the hypothetical light assumed to be equivalent to photoreceptor noise) does not. 3. The rise in increment threshold for tiny (10 min of arc), brief (10 ms) targets approaches the de Vries‐Rose square‐root law, varying according to the quantal fluctuations of the background light. The slope of the rod increment threshold versus background intensity (TVI) curves in logarithmic co‐ordinates is about 0.56 +/‐ 0.04 (when cones are not influencing rod field adaptation). For large (6 deg) and long (200 ms) targets, a maximum slope of about 0.77 +/‐ 0.03 is attained. 4. The steeper slopes of the rod‐detected TVI curves for large, long targets implies some reduction in temporal or spatial summation. In fact, the change in summation area is much more critical: under conditions where only the rod system is active the TVI curve slope is independent of target duration, suggesting that temporal summation is practically independent of background intensity. 5. The rise in threshold also depends on the wavelength of the background field in the normal observer but not in the achromat, confirming reports that the field adaptation of the rods is not independent of the quantal absorptions in the cones. The cone influence is most conspicuous on long‐wavelength backgrounds and is found for all target sizes and durations, but is greater for large and long targets than for the other conditions.
Kinetic analysis of the denaturation process by alcohols of sodium channels in squid giant axon.
Authors: Kukita F , Mitaku S
Published: December 2014

1. The effects of several aliphatic alcohols on sodium currents were examined in the intracellularly perfused squid giant axon when the same concentration of alcohol was applied on both sides of the membrane. 2. An irreversible suppression of sodium currents, accompanied by anaesthesia at high alcohol concentration, was examined in detail using four aliphatic alcohols, that is, ethanol, 1‐propanol, 1‐butanol and 1‐pentanol. 3. This irreversible effect seemed to be attributable to the sequential denaturation of sodium channels, because the kinetics, the current‐voltage relation and the sodium channel activation‐voltage curve did not change after the sodium current decreased. 4. The time course of the remaining sodium conductance was measured as a function of the sum of the alcohol application time by repeating the process of applying and completely washing out alcohol. The remaining sodium conductance decayed as a function of time in a single exponential manner. This decay time constant depended strongly on the concentration of alcohol and could be assumed to be the denaturation time constant of the sodium channel. 5. The denaturation time constant decreased as the alcohol concentration increased. This time constant is proportional to the Nth power of the alcohol concentration. The N values are 4.3, 4.5, 5.8 and 7.6 for ethanol, 1‐propanol, 1‐butanol and 1‐pentanol, respectively. This implies that alcohol molecules bind to a restricted number of specific sites in the sodium channel protein to cause the denaturation. 6. The concentration of alcohol which caused the same amount of denaturation is related to the exponential function of the carbon number of the alcohol. Considering the partition coefficient of alcohol between lipid and aqueous solution, the concentration of alcohol in the membrane which denatured half of the sodium channels in 2 h can be calculated to be 0.5 M for all alcohols.
The role of bicarbonate in GABAA receptor‐mediated IPSPs of rat neocortical neurones.
Authors: Kaila K , Voipio J , Paalasmaa P , Pasternack M , Deisz R A
Published: December 2014

1. The ionic mechanism underlying the fast, GABAA receptor‐mediated inhibitory postsynaptic potential (IPSPA) was examined in rat neocortical neurones using intracellular recording techniques. Synaptic responses were evoked by orthodromic stimulation applied to the subcortical white matter or to the pial surface. All experiments were carried out at a constant extracellular Cl‐ concentration. 2. The resting membrane potential was ‐76.2 +/‐ 1.0 mV (mean +/‐ S.E.M., n = 32) and in most cells IPSPA was depolarizing. The reversal potential of IPSPA (EIPSP‐A) was ‐70.2 +/‐ 0.9 mV (n = 32) and that of a more slowly developing hyperpolarizing response (IPSPB) was ‐91.4 +/‐ 1.3 mV (n = 28). 3. An examination of the temporal relationships between excitatory postsynaptic potentials (EPSPs) and IPSPAs in different cells suggested that, despite partial overlap of these responses, EPSPs had little influence on the measured values of EIPSP‐A. 4. Application of 20 mM trimethylamine (TriMA), a membrane‐permeant weak base which is expected to produce a rise in pHi (and hence in intracellular HCO3‐), induced a reversible positive shift in EIPSP‐A of up to +9.0 mV (mean + 4.2 mV) at an extracellular pH (pHo) of 7.4. In some experiments, the shift in reversal potential was associated with a change in the polarity of IPSPA from hyperpolarizing to depolarizing. 5. Application of 20 mM lactate (a membrane‐permeant weak acid which is expected to produce a fall in pHi and hence in intracellular HCO3‐) at pHo 7.0 produced a hyperpolarizing shift in EIPS‐A of up to ‐7.5 mV (mean ‐5.6 mV). In some experiments, exposure to lactate changed the polarity of IPSPA from depolarizing to hyperpolarizing. 6. Changes in pHo from 7.4 to 7.0 reduced the effect of TriMA and augmented that of lactate on EIPSP‐A, as could be expected on the basis of the pHo‐dependent change in the fraction of membrane permeable non‐charged weak base or acid. 7. Under control conditions, a change in pHo from 7.4 to 7.0 produced a slight positive shift (< +2 mV) in EIPSP‐A. In the presence of TriMA, a similar change in pHo gave rise to a negative shift (‐1.8 to ‐2.7 mV). 8. The results obtained indicate that HCO3‐ ions contribute significantly to the IPSPA, thereby making EIPSP‐A more positive than the Cl‐ equilibrium potential.(ABSTRACT TRUNCATED AT 400 WORDS)
The regulation of presynaptic inhibition during co‐contraction of antagonistic muscles in man.
Authors: Nielsen J , Kagamihara Y
Published: December 2014

1. The size of the soleus, tibialis anterior and medial gastrocnemius H reflexes were measured at different levels of EMG activity in ankle plantar‐ and dorsiflexors. At similar levels of EMG activity in the agonist muscle, the soleus and tibials anterior H reflexes were found to be smaller during co‐contraction than during an isolated agonist contraction. In contrast to this, the medial gastrocnemius H reflex had the same size during co‐contraction as during an isolated plantarflexion at comparable EMG levels. 2. Peaks occurred at monosynaptic reflex latency in the post‐stimulus time histogram (PSTH) of firing of soleus and tibialis anterior motor units following stimulation of their respective motor nerves. These homonymous Ia peaks were found to be smaller during co‐contraction than during isolated agonist contraction, whereas that of medial gastrocnemius motor units was unchanged. As the monosynaptic peak in the PSTH may give an indirect measure of the size of the monosynaptic EPSP in the motoneurone, it is suggested that these findings reflect a differential control of presynaptic inhibition of soleus and tibialis anterior motor units with respect to medial gastrocnemius motor units. 3. The monosynaptic Ia facilitation of the soleus H reflex evoked by a stimulation of the femoral nerve, was also found to be smaller during co‐contraction of tibials anterior and soleus than during isolated plantarflexion. This suggests that presynaptic inhibition of heteronymous Ia fibres from the quadriceps muscle projecting to soleus motoneurones is regulated in the same way as presynaptic inhibition of homonymous Ia fibres during co‐contraction. 4. The femoral nerve‐induced monosynaptic facilitation of the soleus H reflex was found to decrease with increasing tonic levels of both co‐contraction and isolated dorsi‐ and plantarflexion. The amount of facilitation decreased to the same degree with increasing levels of dorsiflexion and co‐contraction. For the same level of EMG in the dorsiflexors there was thus no difference in the amount of facilitation whether the dorsiflexors were activated separately or in a co‐contraction. 5. Whereas the soleus H reflex increased in size 50 ms prior to the onset of a dynamic plantarflexion, it did not change prior to the onset of a co‐contraction. The femoral nerve‐induced facilitation increased prior to the plantarflexion, but decreased prior to the co‐contraction.(ABSTRACT TRUNCATED AT 400 WORDS)
Identification of vagal sensory receptors in the rat lung: are there subtypes of slowly adapting receptors?
Authors: Bergren D R , Peterson D F
Published: December 2014

1. We studied the characteristics of pulmonary sensory receptors whose afferent fibres are in the left vagus nerve of opened‐chest rats. The activity of these receptors was recorded during mechanical ventilation approximating eupnoea, as well as during deflation, stepwise inflations and constant‐pressure inflations of the lungs. Data were also collected from closed‐chest rats and analysed separately. 2. Ninety‐four per cent of receptors were located in the ipsilateral lung or airways with the remainder in the contralateral lung. 3. Not only were slowly adapting receptors (SARs) the most abundant pulmonary receptors but 21% of them were either exclusively or predominantly active during the deflationary phase of the ventilatory cycle. Deflationary units were found in opened‐ and closed‐chest rats. The average conduction velocity for all fibres innervating SARs averaged 29.7 m s‐1. 4. We found rapidly adapting receptors (RARs) to be extremely rare in the rat. Their activity was sparse and irregular. The conduction velocities of fibres innervating RARs averaged 12.3 m s‐1. 5. Far more abundant than RARs in the remaining population of pulmonary fibres were C fibres. They were observed to have an average conduction velocity of 2.1 m s‐1, base‐level activity which was irregular and a high pressure threshold of activation and were stimulated by intravenous capsaicin injection. 6. Notable differences exist between pulmonary receptors in rats and those reported in other species. The variations include the abundant existence of intrapulmonary SARs with exclusively deflationary modulation and the rarity of RARs. We also encountered C fibres which have not previously been described systematically in the rat.
Effect of medium tonicity on transepithelial H(+)‐HCO3‐fluxes in rat proximal tubule.
Authors: Melis M S , Malnic G , Aires M M
Published: December 2014

1. The effect of luminal and capillary perfusion with hypotonic or hypertonic solutions containing 25 mM NaHCO3 or NaH2PO4 plus NaCl, K+, Ca2+, Mg2+ and acetate at an osmolality of 100 or 500 mosmol kg‐1 on rat proximal H+ secretion was estimated by monitoring luminal pH with Sb microelectrodes. The results were compared to perfusions with the same ionic concentration in which tonicity was adjusted to 300 mosmol kg‐1 with raffinose. 2. The kinetics of acidification of luminally injected bicarbonate buffer permits evaluations of H(+)‐HCO3‐fluxes as well as stationary pH gradients; the kinetics of alkalinization of luminally injected acid phosphate buffer indicates H(+)‐HCO3‐backfluxes from blood to lumen. 3. In alkalinization experiments, luminal perfusion with hypotonic solution during presence of blood in capillaries or hypotonic capillary perfusion leads to a decrease of stationary pH, an increase of alkalinization half‐time and consequently a decrease of passive H(+)‐HCO3‐backflux. 4. In alkalinization experiments, during luminal and/or capillary perfusions with hypertonic solutions, no significant differences in the stationary pH, alkalinization half‐time and H(+)‐HCO3‐backflux were found. 5. During acidification experiments, with both hypo‐ and hypertonic perfusions, no significant differences in stationary pH, acidification half‐time and H(+)‐HCO3‐flux were observed. 6. Luminal perfusion with hypotonic solution increases specific epithelial resistance in the presence of blood in capillaries. Luminal perfusion with hypertonic solution does not change this parameter. 7. Volume changes, measured by the split‐drop method, are slow during the first 30 s and do not explain the increased alkalinization half‐time during luminal perfusion with hypotonic solution, since this is the period of fastest pH change. 8. Luminal perfusion with hypotonic solution decreases apparent H+ permeability in the presence of blood or hypotonic solution in capillaries. Hypertonic solutions in all experimental conditions had no significant effect on this parameter. 9. The data indicate that decrease of tonicity of fluids in contact with proximal tubule epithelium affects passive H(+)‐HCO3‐backflux, which proceeds in part through the shunt path, while acidification (H+ secretion), which is transcellular, is not affected by extracellular tonicity.
The electrical geometry, electrical properties and synaptic connections onto rat V motoneurones in vitro.
Authors: Curtis J C , Appenteng K
Published: December 2014

1. We have developed a tissue slice preparation which allows the study of the actions of single presynaptic neurones onto single trigeminal motoneurones in the immature rat. Our aim in this first stage of the work has been to assess the validity of this preparation as a model for responses obtained in vivo from trigeminal motoneurones in adult rats. We have quantified the integrative properties of the motoneurones and also the variability in transmission at synapses of single presynaptic neurones onto the motoneurones. This data has then been compared to similar published data obtained from adult (rat) trigeminal motoneurones in vivo. 2. Quantitative reconstructions were made of the morphology of three motoneurones which had been labelled with biocytin by intracellular injection. The neurones gave off six to nine dendrites, of mean length 522 microns (S.D. = 160; n = 22), which branched on average 10.5 times to produce 11.45 end‐terminations per dendrite (S.D. = 8.57; n = 22). The mean surface area of the dendrites was 0.92 x 10(4) microns2 (S.D. = 0.67; n = 22), and, for individual cells, the ratio of the combined dendritic surface area to the total neuronal surface area ranged from 98.3 to 99.2% (n = 3). At dendritic branch points the ratio of the summed diameters of the daughter dendrites to the 3/2 power against the parent dendrite to the 3/2 power was 1.09 (S.D. = 0.21; n = 217), allowing branch points to be collapsed into a single cylinder. The equivalent cylinder diameter of the combined dendritic tree remained approximately constant over the proximal 25‐40% of the equivalent electrical length of the dendritic tree and then showed tapering. The tapering could be ascribed to termination of dendrites at different electrical distances from the soma. 3. Electrical properties were determined for a total of eighty‐seven motoneurones, all with membrane potentials more negative than 60 mV (mean = 66.0 mV; S.D. = 5.2) and spikes which overshot zero (mean spike amplitude = 77 mV; S.D. = 10.5; n = 87). The spikes were followed by after‐hyperpolarizations (AHPs) of mean amplitude 2.2 mV (S.D. = 1.7; n = 47), and mean duration 54.1 ms (S.D. = 9.5; n = 47). The mean input resistance of the neurones was 7.5 M omega (S.D. = 2.5; n = 69), the mean membrane time constant was 3.5 ms (S.D. = 2.2; n = 35), and the mean rheobase was 1.6 nA (S.D. = 1.1; n = 56).(ABSTRACT TRUNCATED AT 400 WORDS)
The modulation of N‐methyl‐D‐aspartate receptors by redox and alkylating reagents in rat cortical neurones in vitro.
Authors: Tang L H , Aizenman E
Published: December 2014

1. The properties of sulfhydryl redox modulation of the N‐methyl‐D‐aspartate (NMDA) receptor have been examined in rat cortical neurones in culture. Electrophysiological measurements were performed with the whole‐cell and outside‐out patch variants of the patch‐clamp technique. 2. The disulphide reducing agent dithiothreitol (DTT; 0.1‐10 mM) potentiated 10 microM NMDA‐mediated whole‐cell currents when applied slowly alone via the superfusate. The initial rate of reduction, as well as the degree of potentiation, was dependent on the concentration of DTT although the process was complicated by the fact that a second, large component appeared at a concentration of 10 mM of this agent. 3. DTT (0.1‐10 mM) was also rapidly applied together with the agonist from a perfusion pipette. With this method, the second component was not readily apparent, and the concentration of DTT producing a half‐maximal potentiation of the NMDA response was 1.9 +/‐ 0.3 mM. Two other disulphide reducing agents, ethylene glycol bisthioglycolate and meso‐bis(N,N‐dimethyl)adipamide‐2,5‐dithiol, also potentiated NMDA responses, but were not as effective as DTT. 4. Following a 4 mM DTT treatment, we observed that the NMDA receptor underwent spontaneous oxidation with a half‐time of 1.9 min. In contrast, the sulfhydryl oxidizing agent 5,5'‐dithio‐bis‐(2‐nitro‐benzoic acid) (DTNB; 500 microM) produced a more rapid reversal of the effects of DTT (t1/2 = 0.6 min). The spontaneously oxidized receptor could be further oxidized with DTNB and fully reduced with DTT. 5. After receptor oxidation with 500 microM DTNB, NMDA produced whole‐cell responses with an EC50 of 68.4 +/‐ 9.4 microM, whereas after reduction with 4 mM DTT the EC50 for NMDA was 32.5 +/‐ 3.4 microM. In addition, the maximum response after reduction with DTT was substantially increased over that observed after oxidation. 6. Single channel measurements performed on outside‐out patches revealed that reduction produced a dramatic increase in the number of NMDA‐induced channel openings. We observed a 2.1 +/‐ 0.2‐fold increase in the frequency of openings during reduction with 500 microM DTT when compared to patches which had been exposed to 500 microM DTNB. Small but significant differences were observed in the single channel conductance for the oxidized (34.6 +/‐ 1.1 pS) and reduced (37.6 +/‐ 1.5 pS) states of the receptor. In contrast, no significant changes were seen in the arithmetic mean channel open time between the two redox conditions (5.4 +/‐ 0.3 ms after oxidation, 6.0 +/‐ 0.7 ms after reduction).(ABSTRACT TRUNCATED AT 400 WORDS)
Stretch revealed three components in the hyperpolarization of guinea‐pig coronary artery in response to acetylcholine.
Authors: Parkington H C , Tare M , Tonta M A , Coleman H A
Published: December 2014

1. Membrane potential was recorded with intracellular microelectrodes from the smooth muscle of coronary arteries of guinea‐pigs, and the responses to endothelium‐derived relaxants were studied under a variety of conditions. 2. Stimulation of the endothelium with brief applications of acetylcholine or substance P evoked concentration‐dependent hyperpolarizations that were complex in nature. A transient component, which is likely to result from endothelium‐derived hyperpolarizing factor (EDHF), was followed by a slow component that resulted from the production of nitric oxide (NO) and a prostaglandin. 3. The ability of exogenous and endogenous NO and prostacyclin to hyperpolarize the membrane depended upon the smooth muscle being under stretch. Unstretched preparations responded to acetylcholine with only the transient component of hyperpolarization; NO and prostacyclin were without effect. 4. In stretched preparations exogenous NO and prostacyclin, and its synthetic analogue methyl prostacyclin (Iloprost), evoked hyperpolarization, and the slow component of the response induced by acetylcholine appeared. The amplitudes of these responses reached maximum when the tissues were stretched to the equivalent of approximately 50 mmHg. 5. From a resting membrane potential of ‐61 +/‐ 0.6 mV, exogenous NO and Iloprost hyperpolarized the smooth muscle to around ‐80 mV. The EC50 values for NO‐ and Iloprost‐induced hyperpolarization were 2.6 x 10(‐6) and 1.3 x 10(‐8) M, respectively. 6. Coronary arterial smooth muscles from rats, rabbits and sheep also hyperpolarized in response to exogenous NO, although their sensitivities were less than those of preparations obtained from guinea‐pigs. Iloprost hyperpolarized tissues from rabbits and sheep but not those obtained from rats. 7. It is concluded that the endothelial lining of coronary arteries can release three factors, EDHF, NO and prostacyclin, all of which can hyperpolarize the membrane of the smooth muscle. The relative proportions and significance of each factor depends on the amount of stretch, on the artery and on the species of animal.
Ionic mechanisms of action potential prolongation at low temperature in guinea‐pig ventricular myocytes.
Authors: Kiyosue T , Arita M , Muramatsu H , Spindler A J , Noble D
Published: December 2014

1. We studied the effects of low temperature on the action potentials and membrane currents of guinea‐pig ventricular myocytes, using a tight‐seal whole‐cell clamp technique. 2. The action potential duration at 95% repolarization was prolonged from 146 +/‐ 33 ms (mean +/‐ S.D., n = 6) at 33‐34 degrees C (control temperature) to 314 +/‐ 83 ms at 24‐25 degrees C (low temperature). 3. In whole‐cell clamp experiments, low temperature decreased the calcium current (ICa), the delayed rectifier potassium current (IK), and the inwardly rectifying potassium current (IK1) with ‘apparent’ Q10 (temperature coefficient) values of 2.3 +/‐ 0.6 for ICa, 4.4 +/‐ 1.2 for IK tail current and 1.5 +/‐ 0.3 for IK1 (n = 7). 4. The effect of low temperature on IK was further studied in the presence of 0.6 microM nicardipine to block ICa. The decay phase of the IK tail consisted of two exponential components. The fast but not the slow component was highly sensitive to the temperature change with an apparent Q10 of 4.5. 5. We found that a component of time‐independent current is also sensitive to the temperature. The current had a linear I‐V relationship and remained almost unchanged after inhibition of Na(+) ‐K+ pump in K(+)‐free external solution. 6. Using our mathematical model of the ventricular action potential (a modification from the DiFrancesco‐Noble model), we simulated the action potential at low temperature by modifying some of the membrane currents, namely IK, IK1, ICa and a component of background current. It was shown that simultaneous changes in these currents could reproduce approximately 75% of the action prolongation induced by low temperature.
Nicotinic agonists antagonize quantal size increases and evoked release at frog neuromuscular junction.
Authors: Van der Kloot W
Published: December 2014

1. Previous studies at the frog neuromuscular junction showed that quantal size can be increased two‐ to fourfold by a variety of treatments, including prior exposure to hypertonic solution (which activates protein kinase A) and insulin (which acts via an unknown pathway). Size increases largely because quanta contain more acetylcholine (ACh). 2. Now the effects of cholinergic agonists on the increases in quantal size have been studied. One muscle from a frog was kept for 2 h in hypertonic sodium gluconate solution. The miniature endplate potential (MEPP) sizes were measured in saline: they had increased about fourfold. The paired muscle went through the same experimental sequence, except that an agonist was added to the hypertonic gluconate solution. Again MEPP sizes were measured in saline. The increase in quantal size was significantly depressed by 0.2 microM 1,1‐dimethyl‐4‐phenyl‐ piperazinium (DMPP). The sequence of effectiveness of agonists was: DMPP > carbachol > or = ACh = cytisine > oxytremorine. This sequence suggests that the receptor belongs in the nicotinic class. 3. Quantal size is doubled after 1 h in insulin. One micromolar carbachol largely blocked the size increase. 4. The effects of cholinergic antagonists were tested by keeping the experimental muscle in hypertonic gluconate solution containing 1 microM carbachol plus an antagonist. The controls were paired muscles kept in hypertonic gluconate solution (without carbachol or antagonist). MEPP sizes were measured in saline. The depressing action of carbachol on the increase in MEPP size was blocked by 0.2 microM neuronal‐bungarotoxin (nBTX). The sequence of effectiveness of antagonists was: nBTX > trimethaphan > d‐tubocurarine (dTC). Ten micromolar atropine (without carbachol) depressed the increase in quantal size. Therefore, the antagonist potency of atropine could not be adequately tested. Carbachol action was not blocked by 10 microM hexamethonium or 10 microM mecamylamine. 5. Once quanta are made large they can be converted back to normal size by cholinergic agonists. Muscles in which quantal size had been enlarged were exposed to hypertonic solutions containing the agonist. Quantal size was reduced to a fraction of its former value when the hypertonic solution contained 1 microM carbachol‐ or 1 microM DMPP. One micromolar oxytremorine had no effect. Carbachol still reduced quantal size when applied in low‐Ca2+ solutions, so it does not appear to act by elevating intracellular [Ca2+]. 6. Previous work suggested that the treatments produce a subpopulation of large quanta that are positioned for release.(ABSTRACT TRUNCATED AT 400 WORDS)