bluuebunny/crossref_metadata_2025 huggingface dataset:
Maturation of the cutaneomuscular reflex recorded from the first dorsal interosseous muscle in man.
Authors: Evans A L , Harrison L M , Stephens J A
Published: December 2014

1. Cutaneous reflexes have been recorded from the first dorsal interosseous muscle following electrical stimulation of the digital nerves of the index finger in man. Recordings have been obtained from 127 children, aged from 3 to 18 years while each performed an isometric abduction of the index finger and whole hand grips. 2. In the adult, reflexes recorded while subjects performed an isometric abduction of the index finger consisted of three readily identifiable components within the first 100 ms. These were an initial short spinal latency increase in EMG (E1), followed by a decrease (I1), followed by a prominent longer‐latency increase (E2) which was normally larger in size than the shorter‐latency increase. 3. The configuration of the reflex changed during development. When recorded during an abduction, the E1 component was present in all children and showed a small but progressive reduction in size with age. With increasing age, both the I1 and E2 components were present in an increasing proportion of children and increased in size until the adult configuration was reached at 14‐15 years. 4. Comparison of reflexes recorded during sustained whole hand grips with reflexes recorded during an isometric index finger abduction revealed differences in all three components. When recorded during those grips used in the present study the E1 component was generally significantly larger while the I1 component was generally significantly smaller than when recorded during index finger abduction. At all ages the E2 component was significantly smaller when recorded during a grip. 5. The configuration of the reflex during an isometric index finger abduction was compared with the ability of the child to perform rapid finger movements. Those children who had no E2 component tended not to perform well in the tests of rapid finger movement. However, there was no simple relationship between the size of the E2 component and ability to produce rapid finger movements.
Extracellular H+ inactivation of Na(+)‐H+ exchange in the sheep cardiac Purkinje fibre.
Authors: Vaughan‐Jones R D , Wu M L
Published: December 2014

1. The inhibition of acid extrusion via Na(+)‐H+ exchange caused by reducing pHo (extracellular pH) was examined in the sheep cardiac Purkinje fibre. Intracellular pH (pHi) and intracellular Na+ activity (alpha 1 Na) were recorded using ion‐selective microelectrodes. Acid extrusion via Na(+)‐H+ exchange was estimated from the pHi recovery rate (multiplied by intracellular buffering power, beta) in response to an internal acid load induced by 20 mM‐NH4Cl removal (nominally CO2‐HCO3‐free media). 2. At a given pHi, acid extrusion decreased sigmoidally with decreases of pHo in the range 8.5 to 6.5 (50% inhibition of efflux occurred at a pHo between 7.0 and 7.5). This inhibition was associated with a parallel decrease in Na+ influx as evidenced from a decrease in the rise of alpha i Na measured during acid extrusion, suggesting inhibition of Na(+)‐H+ exchange. 3. The background acid‐loading rate (estimated by adding 1 mM‐amiloride to inhibit Na(+)‐H+ exchange and recording the initial rate of fall of pHi) was found to be unaffected in the steady state by changes of pHo. We therefore conclude that the slowing of pHi recovery at low pHo is due to direct inhibition of Na(+)‐H+ exchange rather than to an increase of background acid loading. 4. Reducing pHo (constant pHi) inhibited acid efflux by producing a parallel shift of the efflux versus pHi relationship to lower values of pHi, consistent with a decrease in the apparent internal H+ ion affinity (pKi) of the system. 5. Raising pHi (constant pHo) also inhibited acid efflux, but this was associated with a rise in the pHo required for 50% maximal inhibition of acid efflux (pKo), consistent with an increase in apparent affinity for external H ions. Thus reduction of pHo reduces pKi (point 4) while reduction of pHi reduces pKo (point 5). 6. Inhibition by elevated Ho+ was not linearly related to the decrease in chemical driving force for Na(+)‐H+ exchange, nor was it related to a reversal of the transmembrane H+ gradient. We found that efflux still occurred when pHo less than pHi. 7. Efflux was not a unique function of the transmembrane H+ ratio (i.e. pHo‐pHi). At appropriate values of pHi and pHo, acid efflux could be kept constant despite a four‐fold change in the transmembrane H+ ratio. 8. Inhibition by low pHo was a saturating function of Ho+ ions with a Hill coefficient of 1.2.(ABSTRACT TRUNCATED AT 400 WORDS)
The influence of oxygen on the ventilatory response to carbon dioxide in man.
Authors: Dahan A , DeGoede J , Berkenbosch A , Olievier I C
Published: December 2014

1. The ventilatory response to isoxic square‐wave challenges in end‐tidal PCO2 was investigated at three levels of end‐tidal PO2 (PET, O2) in nine healthy male subjects. 2. Twenty‐seven responses against a background of mild hypoxia (PET, O2 approximately 10 kPa), sixty‐seven against a background of normoxia (PET, O2 approximately 14.5 kPa) and seventy‐six against a background of hyperoxia (PET, O2 approximately 70 kPa) were collected. 3. The breath‐to‐breath data were partitioned into a fast and a slow ventilatory component using a two‐compartment model. 4. In the normoxic and hypoxic experiments the CO2 sensitivity of the fast component averaged to about 30 and 40% of the total CO2 sensitivity, respectively. In the hyperoxic experiments three subjects had no fast component in their response while in three others the CO2 sensitivity of the fast component averaged to about 24% of the total CO2 sensitivity. In the remaining three subjects the presence of a fast component was doubtful. 5. We argue that the fast component is due to the peripheral chemoreflex loop and the slow component to the central chemoreflex loop. 6. The central CO2 sensitivity and the apnoeic threshold (extrapolated end‐tidal CO2 at zero ventilation in the steady state) were 15% smaller in hyperoxia than those in normoxia and hypoxia. In normoxia and mild hypoxia the central CO2 sensitivities were not significantly different. 7. We argue, that apart from peripheral oxygen‐carbon dioxide interaction, there is evidence for central oxygen‐carbon dioxide interaction in human subjects. 8. We conclude that in general there is a contribution to ventilation of the peripheral chemoreceptors during hyperoxia in man.
GTP‐binding proteins mediate noradrenaline effects on calcium and chloride currents in rat portal vein myocytes.
Authors: Loirand G , Pacaud P , Mironneau C , Mironneau J
Published: December 2014

1. Membrane currents were recorded by a patch‐clamp pipette technique in cultured cells from rat portal vein using the whole‐cell mode. 2. Noradrenaline (NA, 10(‐5) M) and phorbol‐12,13‐dibutyrate (PDBu, 10(‐7) M) produced an increase in voltage‐dependent inward current carried by barium (5 mM), but their effects were not additive. Calcium‐activated chloride current was evoked by NA but not by PDBu. 3. The NA‐induced increase in peak voltage‐dependent inward current was inhibited by intracellular application of GDP‐beta‐S (10(‐3) M) while the effect of PDBu was unchanged. GDP‐beta‐S blocked the NA‐induced chloride current but had no effect on the caffeine‐induced chloride current. 4. Inclusion of GTP‐gamma‐S (10(‐5)‐10(‐4) M) in the pipette solution increased the voltage‐dependent inward current and inhibited the NA‐ or PDBu‐induced increase in peak current. GTP‐gamma‐S potentiated the effect of NA on calcium‐activated chloride current. At higher concentrations (10(‐3) M), GTP‐gamma‐S activated the chloride current and prevented the effects of NA or caffeine on this current. 5. The combination of 10(‐5) M‐aluminium chloride and 10(‐2) M‐sodium fluoride had an effect similar to that of high concentrations of GTP‐gamma‐S on both inward current and calcium‐activated chloride current. In contrast, arachidonic acid (10(‐3) M) had no effect on calcium and chloride conductances activated by NA. 6. Cells responded normally to NA after pre‐treatment for 4‐30 h with 10 micrograms ml‐1 pertussis toxin (PTx). 7. It is concluded that the stimulation of calcium and chloride conductances by NA is mediated through activation of a PTx‐insensitive GTP‐binding protein. This effect may involve activation of phospholipase C enzyme and production of both D‐myo‐inositol 1,4,5‐trisphosphate which depletes calcium stores and diacylglycerol which activates protein kinase C.
Nicotinic cholinergic modulation of voltage‐dependent calcium current in bovine adrenal chromaffin cells.
Authors: Klepper M , Hans M , Takeda K
Published: December 2014

1. The effects of cholinergic agonists on voltage‐dependent calcium current (ICa) were studied in cultured chromaffin cells from bovine adrenal medulla. 2. Application of both acetylcholine (ACh) and nicotine resulted in inward nicotinic current from a holding potential of ‐90 mV, and at the same time reversible decreases in depolarization‐activated ICa. Both of these effects were blocked by d‐tubocurarine, while atropine pre‐treatment was ineffective. 3. Internal accumulation of neither Na+ nor Ca2+ seems likely to explain the nicotinic‐agonist‐dependent decrease in ICa, as the modulation was observed with symmetrical Na+ solutions, with Ca2(+)‐free Ba2(+)‐containing external solutions, from holding potentials of both ‐90 and ‐40 mV, and when the internal Ca2+ buffer capacity was increased. 4. Isodihydrohistrionicotoxin, an open‐channel blocker which does not compete for the agonist binding site, completely inhibited inward cholinergic currents while the agonist‐dependent decrease in ICa was seen in only two of fifteen cells. 5. The nicotinic agonist‐mediated decreases in ICa were not voltage‐dependent. 6. No changes in voltage‐dependent INa were seen with the nicotinic agonists. 7. Muscarine, with or without GTP in the pipette solution, produced neither modulation of ICa nor any changes in steady holding currents. The nicotinic current and the reversible decrease in ICa induced by ACh and nicotine were not affected by including GTP, or the guanine nucleotide analogues GDP‐beta‐S and GTP‐gamma‐S, in the pipette solution. 8. A 10 min pre‐incubation of the cells in a high‐K+ solution optimal for catecholamine secretion did not affect the nicotinic agonist‐mediated decreases in ICa.
The effects of hypoxia and hypercapnia on perceived breathlessness during exercise in humans.
Authors: Lane R , Adams L , Guz A
Published: December 2014

1. The sensation of breathlessness increases when ventilation is reflexly stimulated but it is not clear whether different stimuli have specific effects in the genesis of this sensation. 2. Our aim was to compare subjective assessments of the intensity of breathlessness at the same levels of ventilation induced by different combinations of reflex ventilatory stimuli. 3. Against a background of progressive exercise (maximum workload 170 W) in ‘blinded’ normal naive subjects, normoxic hypercapnia (maximum end‐tidal CO2, PET, CO2, 56 mmHg) or isocapnic hypoxia (minimum O2 saturation 88%) was induced to achieve levels of ventilation (maximum 60 l min‐1) ‘matched’ with those resulting from a higher intensity of exercise alone. Subjective breathlessness was rated with a visual analogue scale. 4. For a given ventilation, compared with exercise alone, breathlessness scores were similar during hypercapnia and were lower during hypoxia. 5. These results do not support the idea that during exercise, hypercapnia or hypoxia has a specific role in the genesis of the sensation of breathlessness. 6. The findings are consistent with the hypothesis that the degree of reflex ventilatory activation, however achieved, is an important determinant of the intensity of perceived breathlessness in healthy humans.
Voltage‐dependent inactivation of catecholamine secretion evoked by brief calcium pulses in the cat adrenal medulla.
Authors: Garrido B , López M G , Moro M A , de Pascual R , García A G
Published: December 2014

1. Inactivation by voltage changes of 45Ca2+ uptake into and catecholamine release from cat adrenal glands perfused at a high rate (4 ml/min) at 37 degrees C with oxygenated Krebs‐Tris solution has been studied. Experimental conditions were selected so that adrenal medullary chromaffin cells were depolarized for different time periods and with various K+ concentrations in the absence of Ca2+, prior to the application of 0.5 mM‐Ca2+ for 10 s in the presence of 118 mM‐K+ to test the rate of secretion (the ‘Ca2+ pulse’). 2. Application of the Ca2+ pulse after perfusion with 5.9 mM‐K+ led to a 100‐fold increase of the basal rate of secretion. However, if the Ca2+ pulse was preceded by a 10 min period of perfusion with 118 mM‐K+, the secretory response was decreased by over 80%. 3. Inactivation of secretion starts 10‐30 s after high‐K+ perfusion and is completed 2‐5 min thereafter. Inactivation is readily reversed by perfusing the glands with normal K(+)‐containing solution; the recovery phenomenon is also gradual and time‐dependent, starting 30 s after repolarization and ending 300 s thereafter. 4. The rate of inactivation is much slower at 35 than at 118 mM‐K+, suggesting that the process is strongly dependent on voltage. 5. Like catecholamine release, Ca2+ uptake into adrenal medullary chromaffin cells is inactivated in a voltage‐dependent manner. This, together with the fact that Cd2+ blocked secretion completely and inactivation was seen equally using Ca2+ or Ba2+ as secretagogues, suggests that inactivation of a certain class of voltage‐dependent Ca2+ channels is responsible for the blockade of secretion. Such channels must be slowly inactivated by voltage and highly sensitive to dihydropyridines, since (+)PN200‐110 (an L‐type Ca2+ channel blocker) enhanced the rate of inactivation and (+/‐)Bay K 8644 (an L‐type Ca2+ channel activator) prevented it, indicating that they might belong to L‐subtype Ca2+ channels. 6. The effects of (+/‐)Bay K 8644 (100 nM) were seen on both the voltage and time dependence of inactivation. At a moderate depolarization (35 mM‐K+), the drug prevented inactivation and caused potentiation of secretion which developed gradually; at strong depolarizations (118 mM‐K+), Bay K 8644 prevented the time‐dependent development of inactivation. (+)PN200‐110 (30 nM) did not suddenly decrease catecholamine release at the earlier times of depolarization; what the drug did was to accelerate the normal rate of inactivation induced by depolarization.(ABSTRACT TRUNCATED AT 400 WORDS)
Muscle injury, cross‐sectional area and fibre type distribution in mouse soleus after intermittent wheel‐running.
Authors: Wernig A , Irintchev A , Weisshaupt P
Published: December 2014

1. It was previously noticed that mouse soleus, but not extensor digitorum longus (EDL) muscles, suffer fibre damage at the onset of voluntary wheel‐running without further injuries thereafter. 2. In CBA/J mice trained continuously for 5 months and rested for periods of 1, 2, 3, 4 and 5 weeks acute muscle damage was found in soleus 7 days after the resumption of wheel‐running. On single cross‐sections damage was present on average in 8.7 +/‐ 3.5% (mean +/‐ S.D., n = 15) of the fibres, but only in 0.47 +/‐ 0.21% (n = 9) and 1.3 +/‐ 1.1% (n = 4) in control animals rested for 0‐6 weeks after continuous running or in untrained controls. 3. Repeated muscle damage occurred when mice exercised for 4 days at intervals of 21‐25 days, and after thirteen running episodes within 12 months marked changes in soleus, but not EDL muscles, were present. In cross‐sections the total number of muscle fibre profiles was significantly larger in soleus of intermittent runners (768 +/‐ 68, n = 6; P less than 0.05), compared to continuous runners (676 +/‐ 54, n = 3) and sedentary animals (683 +/‐ 33, n = 4). This is probably due to incomplete repair which results in 'split fibres'. 4. At the same time total muscle fibre cross‐sectional area was significantly elevated in intermittent runners (P less than 0.05), mainly due to increase in fibre diameters. Net cross‐sectional areas were 0.59 +/‐ 0.069 mm2 (n = 6) in intermittent, 0.53 +/‐ 0.076 mm2 (n = 3) in continuous runners and 0.46 +/‐ 0.031 mm2 (n = 3) in sedentary controls. 5. Tetanic and twitch force were also significantly elevated in soleus of intermittent runners while the ratio force/area remained the same. 6. There was an increase in the proportion of type I fibres in soleus from 75 +/‐ 0.9% (n = 4) in untrained controls to 90 +/‐ 4.4% (n = 6; P less than 0.05) in intermittent runners and 81 +/‐ 5.6% (n = 3; n.s.) in continuous runners. 7. Resistance to block of synaptic transmission in soleus was significantly higher in intermittent runners for two levels of curare, indicating enhanced safety margins. 8. EDL muscles in intermittent runners were not different from sedentary controls in any of the parameters studied. In particular, muscle fibres with signs of previous damage (split fibres, central nuclei) were rare (on average 0.5‐0.6%) and equally frequent in all experimental groups.(ABSTRACT TRUNCATED AT 400 WORDS)
Voltage‐gated potassium channels and the control of membrane potential in human platelets.
Authors: Mahaut‐Smith M P , Rink T J , Collins S C , Sage S O
Published: December 2014

1. Human platelets were studied using a combination of patch‐clamp and fluorescent indicators of membrane potential and [Ca2+]i. 2. Whole‐cell and cell‐attached patch recordings showed voltage‐gated channels selective for K+ (IK(V]. These channels were activated by depolarization at a threshold close to the platelet resting potential and were blocked by the venom charybdotoxin (CTX; 10‐20 nM). Several different conductance states were observed, ranging from 5 to 34 pS, with isotonic KCl in the patch pipette and bath. 3. Measurements with the potential‐sensitive dye 3,3'‐dipropylthia‐dicarbocyanine, diS‐C3‐(5), in platelet suspensions showed that CTX depolarized the resting potential by approximately 25 mV. Thus, CTX‐sensitive, voltage‐gated K+ channels appear to play a major part in setting the resting potential. 4. ADP‐evoked Ca2+ influx, monitored with Fura‐2, was reduced by 10 nM‐CTX. Restoration of a large negative membrane potential with valinomycin reversed this effect of CTX. These results suggest that the Ca2+ influx depends on the negative membrane potential and that K+ channels may be important in maintaining this potential during activation.
pH modulation of the kinetics of a Ca2(+)‐sensitive cross‐bridge state transition in mammalian single skeletal muscle fibres.
Authors: Metzger J M , Moss R L
Published: December 2014

1. The rate constant of tension redevelopment (ktr) following a rapid release and subsequent re‐extension of muscle length has been demonstrated to be Ca2+ sensitive and is thought to reflect the rate‐limiting step in the cross‐bridge cycle leading to the formation of the strongly bound, force‐bearing state. The kinetics of this cross‐bridge state transition were investigated at 15 degrees C over a wide range of Ca2+ concentrations while varying pH from 7.00 to 6.20 in rat slow‐twitch soleus, rat fast‐twitch superficial vastus lateralis (SVL) and rabbit fast‐twitch psoas skinned single fibres. 2. At maximal levels of Ca2+ activation, ktr was unaffected by changes in pH from 7.00 to 6.20 while isometric tension was depressed to 0.60 +/‐ 0.02 P0 (mean +/‐ S.E.M.) at the low pH in fast‐twitch fibres and to 0.78 +/‐ 0.01 P0 in slow‐twitch fibres (P0 is the maximum isometric tension obtained at pH 7.00). 3. At reduced levels of Ca2+ activation, corresponding to pCa (‐log [Ca2+]) greater than 5.0, ktr was markedly depressed in all fibre types when pH was lowered. The Ca2+ sensitivity of steady‐state isometric tension was also reduced in all fibres at pH 6.20 compared to pH 7.00. 4. The results suggest that pH has a modulatory effect upon an apparent rate constant which is rate limiting in terms of the formation of the strongly bound, force‐bearing cross‐bridge state. This effect of altered pH may in part account for the reduction in the Ca2+ sensitivity of isometric force at low pH as well as the depression of the rate of rise of tension in living fibres during fatiguing stimulation.
Presynaptic glutamate receptors depress excitatory monosynaptic transmission between mouse hippocampal neurones.
Authors: Forsythe I D , Clements J D
Published: December 2014

1. Whole‐cell patch‐clamp techniques were used to record the excitatory postsynaptic current (EPSC) in a cultured mouse hippocampal neurone that resulted from electrical stimulation of another neurone in the cell culture. 2. L‐Glutamate (less than 1 microM) reversibly depressed the EPSC amplitude in 67% of the synapses tested. The average amplitude reduction was 40%. The depression by glutamate was not blocked by extracellular magnesium (0.8 mM) or 2‐amino‐5‐phosphonovaleric acid (AP5, 100 microM), indicating that N‐methyl‐D‐aspartate (NMDA) receptors were not involved. 3. The phosphonic derivative of glutamate, L‐2‐amino‐4‐phosphonobutyrate (L‐AP4), also depressed the EPSC amplitude. Neither glutamate nor L‐AP4 induced any detectable inward current at concentrations which produced a potent depression of the EPSC. Statistical analysis of the amplitude fluctuations of evoked synaptic currents showed that the depression induced by both glutamate and L‐AP4 was due to a decrease in the probability of synaptic release, confirming a presynaptic site of action. 4. Kainate and quisqualate also depressed excitatory synaptic transmission, but this action was related to the postsynaptic inward current that they induced. Statistical analysis showed that this action was consistent with a purely postsynaptic site of action. 5. Paired EPSCs separated by 20 ms showed either depression or potentiation of the second synaptic response. There was a strong correlation between those EPSCs which exhibited paired pulse depression and those depressed by glutamate application. 6. gamma‐Aminobutyric acid (GABA) and baclofen also depressed excitatory synaptic transmission. This depression was not blocked by picrotoxin (100 microM). GABA (10 microM) was effective in 85% of cell pairs tested, while baclofen (5 microM) depressed every EPSC tested. A presynaptic site of action for both substances was indicated by the statistical analysis. 7. The results indicate that both glutamate and GABA suppress excitatory synaptic transmission by an action at presynaptic sites. The glutamate‐induced depression may result from activation of a distinct excitatory amino acid receptor for which L‐AP4 is a specific agonist.
Intracellular regulation of enzyme secretion from rat osteoclasts and evidence for a functional role in bone resorption.
Authors: Moonga B S , Moss D W , Patchell A , Zaidi M
Published: December 2014

1. Osteoclasts are known to secrete acid phosphatase, an iron‐containing phosphohydrolase. We have investigated (a) the possibility that acid phosphatase has a functional role in bone resorption and (b) the factors controlling enzyme secretion from isolated rat osteoclasts. 2. Osteoclasts were freshly disaggregated from neonatal rat long bones and dispersed at low densities on devitalized cortical bone slices or on plastic substrate. The levels of acid phosphatase in culture medium were measured spectrophotometrically using 4‐nitrophenyl phosphate as hydrolysable substrate. The total plan area of bone resorbed was quantified by scanning electron microscopy in combination with image processing and analysis. 3. Ninety‐three per cent of the total enzyme activity detected in the supernatant exposed to bone‐osteoclast preparations was resistant to inhibition by D‐tartaric acid and was bound to an antibody known to be highly specific for the osteoclast‐derived isoenzyme, showing that it originated from osteoclasts. 4. A diminution in the level of supernatant enzyme activity achieved by incubating bone‐osteoclast preparations with an antiserum specifically binding the osteoclast isoenzyme, or with a non‐competitive inhibitor, molybdate or with competitive inhibitors, disphosphonates, led to a marked reduction of osteoclastic bone resorption. 5. The rate of the enzyme released into the culture supernatant, whether from resorbing (cultured on bone) or non‐resorbing (cultured on plastic) osteoclasts declined gradually over 22 h, but that from the former was significantly depressed within the first 30 min of incubation. The supernatant enzyme concentration increased linearly up to 3 h; the levels released from resorbing osteoclasts remained consistently lower than those from non‐resorbing cells. 6. Exposure of osteoclasts for 18 h to elevated [Ca2+]o levels produced a concentration‐dependent inhibition of supernatant acid phosphatase levels. In the presence of 20 mM [Ca2+]o enzyme secretion from resorbing osteoclasts was significantly lower than that from non‐resorbing cells. 7. Exposure of bone‐osteoclast preparations to pertussis toxin produced no significant change of acid phosphatase release, while cholera toxin, dibutyryl cyclic AMP and forskolin produced a marked elevation of enzyme secretion. Ionomycin was found to inhibit enzyme release and this was less marked when osteoclasts were incubated on plastic substrate.(ABSTRACT TRUNCATED AT 400 WORDS)
Adenosine is not essential for exercise hyperaemia in the hindlimb in conscious dogs.
Authors: Koch L G , Britton S L , Metting P J
Published: December 2014

1. The contribution of endogenous adenosine to the increase in hindlimb blood flow that occurs during treadmill exercise was evaluated in conscious dogs. We postulated that if adenosine is essential for the hindlimb hyperaemic response, then pharmacological treatment of the animals with adenosine receptor antagonists should decrease hindlimb blood flow during treadmill exercise. 2. A total of twenty‐three dogs were chronically instrumented for measurement of aortic blood pressure and hindlimb blood flow using electromagnetic or Doppler flow probes on the left external iliac artery. Measurements of arterial blood pressure, hindlimb blood flow and heart rate were made during steady‐state treadmill exercise in both the presence and the absence of adenosine receptor antagonists. Four different protocols were performed using different routes of administration of two adenosine receptor antagonists. Aminophylline was used in most of the experiments, and the effects of the more potent antagonist, 8‐phenyltheophylline, were also evaluated. In addition, the dogs exercised at varying intensities ranging from a low level of 5.5 km h‐1 at 0% gradient to a high intensity of 5.5 km h‐1 at 21% gradient. 3. Aminophylline given as a single intravenous dose, or as a constant infusion either intravenously or directly into the hindlimb artery, did not decrease hindlimb blood flow at low, moderate or high intensities of exercise. Likewise, the blockade of adenosine receptors with 8‐phenyltheophylline, given systemically or as a bolus injection administered directly into the hindlimb circulation during moderate exercise, did not attenuate the hindlimb blood flow response. 4. Our data demonstrate that exercise hyperaemia of the hindlimb is not reduced by antagonism of adenosine receptors. These findings are consistent with the hypothesis that adenosine is not an essential mediator of hindlimb vasodilatation during exercise.
Characterization of voltage‐dependent calcium channels expressed in Xenopus oocytes injected with mRNA from rat heart.
Authors: Lory P , Rassendren F A , Richard S , Tiaho F , Nargeot J
Published: December 2014

1. The properties of voltage dependent cardiac Ca channels expressed in Xenopus laevis oocytes after injection of mRNA from rat heart were investigated using the double‐microelectrode voltage‐clamp technique. 2. Endogenous Ba current (IBa,E) and expressed cardiac Ba current (IBa,C) were studied at various external concentrations of barium (Ba2+). These two entities could be distinguished by their amplitude and their pharmacology. IBa,C was more sensitive to the inorganic Ca channel blocker manganese (Mn2+). The contaminant IBa,E presented properties of voltage dependence identical to IBa,C, but was negligible in the presence of a low external Ba2+ concentration (2 mM). 3. In 2 mM‐Ba2+, IBa,C activated at ‐35 mV, peaked at ‐14 mV, and reversed at +26 mV. Steady‐state inactivation properties, in consideration of the half‐inactivation potential of ‐35 mV, were also typical of L‐type Ba currents. However, the decay of IBa,C was very slow (time constant of inactivation near 600 ms). No evidence for the expression of cardiac transient Ca channels (T‐type) was found. 4. IBa,C was enhanced after exposure to the 1,4‐dihydropyridine (DHP) agonist Bay K 8644. The enhancement of IBa,C was voltage dependent (maximum at ‐30 +/‐ 5 mV) and associated with a slowing in current decay. Current‐voltage and concentration‐response curves obtained for various Ba2+ concentrations revealed an antagonism between external Ba2+ and the 1,4‐DHP agonist Bay K 8644. Similar results were found using the (‐)Bay K 8644 pure agonist isomer. 5. We conclude that oocytes injected with mRNA from rat heart expressed only the high threshold, long‐lasting or L‐type Ca channels. The availability of expressed L‐type Ca channels for quantitative pharmacological studies using low Ba2+ concentration has been demonstrated.
Perceptual responses to microstimulation of single afferents innervating joints, muscles and skin of the human hand.
Authors: Macefield G , Gandevia S C , Burke D
Published: December 2014

1. Microneurographic techniques were used to isolate single afferent axons within cutaneous and motor fascicles of the median and ulnar nerves at the wrist in thirteen subjects. Of the sixty‐five identified afferents, eleven innervated the interphalangeal and metacarpophalangeal joints, sixteen innervated muscle spindles, three innervated Golgi tendon organs and thirty‐five supplied the glabrous skin of the hand. 2. Intrafascicular stimulation through the recording microelectrode, using trains of constant‐voltage positive pulses (0.3‐0.8 V, 0.1‐0.2 ms, 1‐100 Hz) or constant‐current biphasic pulses (0.4‐13.0 microA, 0.2 ms, 1‐100 Hz), evoked specific sensations from sites associated with some afferent species but not others. 3. Microstimulation of eight of the eleven joint afferent sites (73%) evoked specific sensations. With four, subjects reported innocuous deep sensations referred to the relevant joint. With the other four, the subjects reported a sensation of joint displacement that partially reflected the responsiveness of the afferents to joint rotation. 4. Microstimulation of fourteen of the sixteen muscle spindle afferent sites (88%) generated no perceptions when the stimuli did not produce overt movement. However, subjects could correctly detect the slight movements generated when the stimuli excited the motor axons to the parent muscle. 5. With seven of the nine rapidly adapting (type RA or FAI) cutaneous afferents (88%) microstimulation evoked sensations of ‘flutter‐vibration’, and with two of eight slowly adapting (type SAI) afferents (25%) it evoked sensations of 'sustained pressure’. Of the eighteen SAII afferents, which were classified as such by their responses to planar skin stretch, the majority (83%) generated no perceptions, confirming previous work, but three evoked sensations of movements or pressure. 6. The present results suggest a relatively secure transmission of joint afferent traffic to perceptual levels, and it is concluded that the human brain may be able to synthesize meaningful information on joint displacement on the basis of impulses in a single joint afferent. This could partly compensate for the low responsiveness of individual joint afferents within the physiological range of joint displacements. Although single muscle spindle afferents can adequately encode joint position and movement, the results suggest that the brain needs the information from more than one muscle spindle afferent to perceive changes in joint angle.
Participation of Ca2(+)‐activated K+ channels in electrical activity of canine gastric smooth muscle.
Authors: Carl A , McHale N G , Publicover N G , Sanders K M
Published: December 2014

1. The hypothesis that Ca2(+)‐activated K+ channels participate in the repolarization of electrical slow waves was tested in isolated cells and intact muscles of the canine gastric antrum. 2. Freshly dispersed cells from the gastric antrum liberally express large conductance channels that were characterized as Ca2(+)‐activated K+ channels by several criteria. 3. Mean slope conductance of these channels in symmetrical 140 mM‐KCl solutions was 265 +/‐ 25 pS and reversal potential was 1.3 +/‐ 3.3 mV. The reversal potential was shifted when K+ was partially replaced with Na+ in a manner consistent with the Nernst equation for the K+ gradient. 4. Open probability was studied in excised patches in solutions containing 10(‐7)‐10(‐6) M‐Ca2+ with holding potentials ranging from ‐100 to +100 mV. Resulting activation curves were fitted by Boltzmann functions. 5. Increasing [Ca2+] from 10(‐7) to 10(‐6) M shifted the half‐maximal activation from +99 to 0 mV. These data suggest that Ca2(+)‐activated K+ channels may be activated in the voltage range and [Ca2+]i occurring during the plateau phase of the slow wave. 6. In intact muscles loaded with the photolabile Ca2+ chelator, nitr‐5, photo‐activated release of Ca2+ during the slow wave cycle produced changes consistent with activation of Ca2(+)‐dependent outward currents. 7. The data are consistent with the idea that Ca2+ build‐up during electrical slow waves shifts the activation voltage of Ca2(+)‐activated K+ channels into the range of the plateau potential. Activation of these channels yields outward current and repolarization. 8. Since the force of contractions depends on slow wave amplitude and duration, regulation of these channels may be important in controlling gastric motility.
Increase in basal firing rate and sensitivity to angiotensin II in subfornical organ neurones of ducks adapted to salt water.
Authors: Matsumura K , Simon E
Published: December 2014

1. The influence of salt adaptation on spontaneous firing rate of subfornical organ (SFO) neurones and on their responsiveness to angiotensin II (AngII) (10(‐10)‐10(‐7) M) were studied in vitro on hypothalamic brain slices taken alternately from ducks kept on either fresh water (FW ducks) or saline of 500 mosmol/kg for 8 weeks (SW ducks) as their only water supply. The animals were of the same age and were housed and fed identically. In SW ducks plasma osmolality and AngII plasma concentrations were typically increased. 2. Recording SFO single‐unit activity in the AngII‐free control perfusion medium disclosed significantly higher spontaneous firing rates in SW than in FW ducks with an average difference of 2.5 spikes/s. 3. With approximate threshold concentrations of AngII for activation of SFO neurones of 10(‐10) M in slices from SW ducks and of 10(‐9) M in slices from FW ducks, the fractions of neurones excited by AngII increased dose dependently in each group and were consistently larger in the slices from SW ducks. Average maximum increases in discharge rate during AngII‐induced excitation also increased dose dependently and were higher at each AngII dose in SFO neurones from SW as compared to FW ducks. 4. Mean latencies of neuronal excitation decreased with increasing AngII doses in both groups of neurones but were significantly shorter in slices from SW than FW ducks. The shorter latencies in SW ducks corresponded to their enhanced sensitivity to AngII. Mean half‐times of the disappearance of AngII‐induced activation were determined after stimulation with 10(‐7) M‐AngII and were identical in SW and FW ducks, indicating no difference in kinetics in AngII‐neurone interaction. 5. AngII‐responsive SFO neurones in slices from SW ducks did not respond to AngIII and activation by AngII was abolished in the presence of the specific antagonist 1Sar‐8Ile‐AngII. 6. In the magnocellular portion of the paraventricular nucleus, the occurrence of AngII‐responsive neurones was as infrequent in SW ducks (2 out of 45) as in FW ducks (0 out of 36). 7. The results indicate that adaptation to salt water in ducks selectively enhanced basal activity and responsiveness to AngII of the SFO neurones. This is a functional correlate of the up‐regulation of AngII‐receptor density observed in the SFO of the same species in the course of adaptation to salt water. Both adaptive adjustments seem to provide tighter coupling between systemic and central control of salt and fluid balance in conditions of chronic salt stress.
Task‐dependent changes in gain of the reflex response to imperceptible perturbations of joint position in man.
Authors: Hore J , McCloskey D I , Taylor J L
Published: December 2014

1. It has been demonstrated recently that, when suitably instructed, subjects could alter the stiffness at the elbow in response to a slowly and imperceptibly changing elastic load. Although evidence was provided in favour of this occurring via changes in gain of the reflex response to stretch, changes in the degree of co‐contraction could not be entirely ruled out. The major objective of the present experiments was to determine if subjects could alter stiffness at the wrist in a similar task, and then to determine whether they retained this ability when co‐contraction was made impossible by anaesthetizing the nerve to the wrist extensors. A second objective was to determine if changes in stiffness could be controlled independently at the wrist and elbow. 2. Subjects, with eyes closed, initially held position constant against a constant force that loaded the flexors. For the wrist, they were instructed: (i) to keep the hand as still as possible (keep position constant) or (ii) to let the hand be moved by the perturbation (keep force constant). The perturbation was an initially imperceptible elastic load whose direction (loading or unloading) could not be predicted. Subjects were also asked to indicate when the perturbation was first perceived. 3. When asked to hold position constant or force constant at the wrist, subjects demonstrated task‐dependent changes in stiffness prior to perception of the perturbation. These changes in stiffness were still achieved when the nerve to the wrist extensors was anesthetized and thus co‐contraction was prevented. 4. Five subjects demonstrated the ability to control stiffness independently at the wrist and the elbow although most subjects had difficulty with the task we employed to demonstrate this. 5. The results demonstrate: (i) that for the wrist, set‐dependent changes in stiffness that occur prior to perception of a slowly developing perturbation can be mediated by changes in gain of reflex responses to those perturbations, and (ii) that stiffness can be controlled independently at the wrist and elbow, presumably in part by changes in gain of stretch reflexes.
Pacemaking in rabbit isolated sino‐atrial node cells during Cs+ block of the hyperpolarization‐activated current if.
Authors: Denyer J C , Brown H F
Published: December 2014

1. Experiments have been carried out using the whole‐cell patch clamp technique to investigate how the spontaneous pacemaker activity of rabbit isolated sino‐atrial (SA) node cells is affected by the block of the hyperpolarization‐activated current if by 1 and 2 mM‐caesium. 2. Two millimolar caesium reduced the amount of if activated at ‐90 mV to less than 10% of the control value. In the pacemaking range of SA node cells, if was often completely blocked by this concentration of Cs+. 3. Two millimolar caesium slowed but did not arrest spontaneous pacemaking in isolated SA node cells. In freely beating non‐patched cells, 2 mM‐CsCl caused a 30% reduction in rate of beating, indicating that in all cells observed if was normally contributing to pacemaking. 4. No increase in instantaneous inward current was seen in response to hyperpolarizing voltage clamp pulses from a holding potential of ‐40 mV when 1 or 2 mM‐CsCl was applied to SA node cells. These concentrations of Cs+ do not therefore induce an ‘extra’ inward current. 5. Neither the inward calcium current (iCa) nor the outward potassium current (iK) showed changes which could be attributed to Cs+ application. 6. Since spontaneous pacemaking continues during Cs+ block of if while other membrane currents show no Cs(+)‐induced changes which could account for this, these experiments provide strong, though indirect, evidence for the presence in SA node of a time‐independent background current, ib, which will contribute to a mode of pacemaking controlled by the decay of potassium conductance (gK). The nature of this inward current has yet to be clarified. 7. The results strongly suggest that the hyperpolarization‐activated current if normally makes an important contribution to the pacemaker depolarization of all SA node cells.
O2 deprivation induces a major depolarization in brain stem neurons in the adult but not in the neonatal rat.
Authors: Haddad G G , Donnelly D F
Published: December 2014

1. In order to study the neuronal response to hypoxia with maturation, hypoglossal neurons from adult and neonatal rat (3‐7, 14‐16, 21 and 28 days) brain stem slices were subjected to O2 deprivation. All neurons depolarized and showed no evidence of hyperpolarization at any time during the hypoxic period. 2. The magnitude of depolarization was about three‐fold larger in adult hypoglossal neurons (mean = 32.0 mV) than in young neonatal neurons (mean = 10.4‐11.2 mV) during hypoxic exposure (15‐20 Torr) of 5 min. During longer periods of hypoxia of 15‐30 min, neonatal cells showed an increase in the magnitude of depolarization reaching a level close to 80% of that in the adult. 3. In the early phase of hypoxia, adult neurons increased peak and steady‐state spike frequency to induced current injections. Later, both spike frequencies decreased and, in 1/2 of adult neurons, there was a depolarization block. Input resistance (RN) of most adult neurons increased during hypoxia (RN = 180% of control after 5 min). Though neonatal neurons increased firing frequency, none had depolarization block and there was no increase in RN. 4. Tetrodotoxin (TTX), tetraethylammonium (TEA), apamin, high Mg2+/low Ca2+ solutions and intracellular ethyleneglycol‐bis‐(beta‐aminoethylether)N,N,N',N'‐tetrac etic acid (EGTA) did not reduce the magnitude of depolarization in hypoglossal neurons of 4‐week‐old and adult rats. Strophanthidin application depolarized hypoglossal neurons but decreased RN. 5. Ion‐selective electrodes used to measure K+ concentrations in the extracellular fluid (Ko+) revealed a major increase in Ko+ (mean = 3.2 mM) in the adult hypoglossal area but not in the newborn tissue (mean = 0.65 mM). This probably reflects a difference in the amount of K+ efflux between neonatal and adult hypoglossal neurons. Shrinkage in the extracellular compartment in the adult may also account for some of the difference. 6. These results suggest that neonatal neuronal tissue is more tolerant to hypoxia than the adult, with the inherent cellular properties being maintained in newborn but not in adult neurons. The difference in membrane depolarization during hypoxia between the neonate and the adult can be attributed, in part, to differences in Ko+. The reason(s) for the difference in Ko+ is not known but could be due, to some extent, to different rates of intracellular ATP depletion and failure of the Na(+)‐K+ pump.
Single‐channel measurement from the cyclic GMP‐activated conductance of catfish retinal cones.
Authors: Haynes L W , Yau K W
Published: December 2014

1. A patch of plasma membrane was excised, in the inside‐out configuration, from the outer segment tip of a catfish cone and recorded electrically with a patch pipette. A solution of 118 mM‐NaCl was present on both sides of the membrane. 2. With the solution outside the pipette containing a low concentration (typically several micromoles per litre) of cyclic GMP and the membrane potential held at a non‐zero level, brief steps of current indicative of the openings of single ion channels could be detected. There was no sign of desensitization to the ligand over a period of tens of seconds. 3. The prominent openings were associated with a conductance near 50 pS and an open‐time constant of 0.5 ms or less. There was also an indication of sub‐state openings. 4. The conductance of the large openings appeared to be invariant between ‐50 mV and +50 mV. However, the macroscopic current‐voltage relation measured at a saturating concentration of cyclic GMP showed a slight upward curvature, which we attribute to a voltage dependence in the open probability of the fully liganded channel. 5. The relation between mean current and cyclic GMP concentration had an average Hill coefficient of about 2.4. The Hill coefficient was not affected by membrane voltage, but the conductance was activated by cyclic GMP slightly more readily at depolarizations; this could be adequately explained by a higher open probability of the fully liganded channel at positive voltages. 6. In several experiments, the membrane patch apparently contained a single cyclic GMP‐activated channel, in that the measured current never rose above that for a single channel even at high concentrations of cyclic GMP. In these cases, a high concentration of the ligand simply engaged the channel in a literally continuous burst of openings, with an open probability of 0.8‐0.9 at between ‐30 mV and +30 mV. The amplitude distribution of the burst under these conditions could be described by a beta distribution, consistent with the channel switching predominantly between a single closed state and a single open state when fully liganded. 7. Estimates of channel density on the cone membrane ranged from about 2 to 130 microns ‐2, with an average of 20 microns ‐2. This observed density is about ten times lower than the density of the homologous channel on rod membrane, being roughly in inverse relation to the tenfold larger surface membrane area of the cone outer segment.(ABSTRACT TRUNCATED AT 400 WORDS)
Permanent release of noradrenaline modulates respiratory frequency in the newborn rat: an in vitro study.
Authors: Errchidi S , Hilaire G , Monteau R
Published: December 2014

1. Respiratory activity was recorded on ventral cervical roots during in vitro experiments performed on superfused newborn rat brain stem‐cervical cord preparations. 2. Eliminating the pontine structures by performing a transection at the level of the ponto‐medullary junction resulted in a sustained increase in respiratory frequency, which suggests the existence of a pontine inhibitory drive impinging on the medullary rhythm generator. 3. Noradrenaline (NA) and drugs affecting NA efficiency were added to the bathing medium and the resulting changes in respiratory frequency were analysed. NA decreased the respiratory frequency, and this effect was potentiated by pargyline (an inhibitor of the NA degradation by monoamine oxidases) and blocked by yohimbine (an alpha 2‐antagonist). 4. Yohimbine or piperoxane (which blocks the alpha 2‐adrenoceptors) increased the resting respiratory frequency to the level reached after ponto‐medullary transection, whereas pargyline or desipramine (which potentiates NA efficiency) decreased the respiratory rate. Since these effects were no longer observed after elimination of the pons, it is suggested that a permanent release of endogenous NA by pontine areas may modulate the activity of the medullary respiratory rhythm generator. 5. When alpha‐methyltyrosine (an inhibitor of NA biosynthesis) was applied to the pons, the respiratory frequency was increased, whereas when tyrosine (a precursor of NA) was applied, the respiratory frequency decreased. This decrease was enhanced by pargyline, suppressed by alpha‐methyltyrosine and blocked by piperoxane. 6. To conclude, it is suggested that the mechanisms underlying NA biosynthesis (i) continue to function under these in vitro experimental conditions and (ii) are responsible for a permanent release of endogenous NA, which slows down the respiratory frequency. These results are discussed as regards the possibility that the medullary respiratory rhythm generator may be modulated via the noradrenergic area A5 in the newborn rat.