bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dichroic components of Arsenazo III and dichlorophosphonazo III signals in skeletal muscle fibres
Authors: Baylor S. M. , Chandler W. K. , Marshall M. W. 
Published: December 2014

1. Absorbance changes were measured following stimulation of single muscle fibres injected with the metallochromic indicator dye Arsenazo III. Two dye‐related signals can be clearly resolved: (1) an early, transient isotropic signal that appears to be due to the formation of Ca2+:dye complex and (2) a slower, transient signal that is ‘dichroic’ in nature. The dichroic signal is obtained by taking the difference between absorbance changes measured with light plane polarized along the fibre axis (0° light) and at right angles to the axis (90° light).2. The time course of the dichroic signal is the same at all wavelengths employed, suggesting that a single underlying process is involved. The wavelength dependence of the magnitude of the signal is similar to that obtained for dye absorbance in a resting fibre.3. At 570 nm, near the isosbestic wavelength for changes in H+:dye, Mg2+:dye and Ca2+:dye, the dichroic signal is near maximal. The absorbance change with 0° light is positive and is about twice as large as the change with 90° light, which is negative. This finding is consistent with the idea that the dichroic signal arises from dye molecules which change their orientation in the radially symmetric muscle fibre. The direction of the change is for the dye's transition moment to become more aligned with the fibre axis during activity.4. During a train of ten action potentials the (isotropic) Ca2+ transient increases in magnitude three‐fold, whereas the dichroic waveform reaches a plateau value only 30‐40% larger than the single twitch value.5. Replacing H2O in Ringers with D2O causes a slight reduction in the Ca2+ signal, reduces the dichroic signal to 0·4 times normal, and reduces tension to 0·1 times normal. Qualitatively similar reductions were found to accompany an increase in osmolality of H2O Ringer from 1 × to 2·5 × normal.6. Dichroic signals are also observed in fibres injected with Dichlorophosphonazo III. These are similar in many respects to the Arsenazo III dichroic signals.7. With Arsenazo III, the dichroic signal probably arises from a reorientation of some dye molecules which are bound to one of the oriented structures in muscle. The reorientation lags the Ca2+ transient and may be due to a change which occurs in the oriented structure itself. Using this idea, the Arsenazo III dichroic signal can be fitted by assuming that Ca2+ ions bind to receptor sites and that this binding induces the required change in the oriented structure. The analysis indicates that the hypothetical receptors have a dissociation constant for Ca2+ equal to 0·1‐1 times the peak value of myoplasmic free [Ca2+] during a twitch and an ‘off’ rate constant equal to 10‐30 sec−1 at 15 °C.
Properties of single calcium‐activated potassium channels in cultured rat muscle
Authors: Barrett J. N. , Magleby K. L. , Pallotta B. S. 
Published: December 2014

1. Properties of the Ca‐activated K channel were studied in excised patches of surface membrane from cultured rat muscle cells using single channel recording techniques.2. Increasing the concentration of calcium at the intracellular membrane surface [Ca]i, increased both the frequency and effective duration of channel openings. Ca at the extracellular membrane surface was not sufficient to activate the channels.3. An approximate third power relationship (slope = 2·7) was observed between [Ca]i and the percentage of time the channels spent in the open state.4. Both the frequency and effective duration of channel openings increased as the intracellular membrane surface was made more positive; the percentage of time spent in the open state increased e‐fold for a 15 mV depolarization for low levels of activity.5. The percentage of time spent with 1, 2,...n channels open in membrane patches with n channels was described by the binomial distribution, suggesting that the channels opened and shut independently of one another.6. Single channel conductance (144 mM‐K on both sides of the membrane) was essentially independent of membrane potential (‐50 to +50 mV) and [Ca]i (0·1 μM ‐1 mM), but did increase with temperature, from 100 pS at 1 °C to 300 pS at 37 °C.7. Channel activity occurred in apparent bursts, with the duration of the apparent bursts increasing with increasing [Ca]i.8. Two exponentials were required to describe the distribution of observed channel open times, suggesting two different open channel states of apparently normal conductance. The observed mean channel open time of these states at +30 mV was 0·34 and 2·2 msec with 0·1 μM‐Cai and was 0·47 and 6·9 msec with 0·5 μM‐Cai.9. The channel occasionally entered an apparent third open channel state with a single channel current amplitude about 40% the amplitude of the normally observed single channel currents. The reduced conductance state was immediately preceded and followed by a normal conducting state.10. While the kinetics of the Ca‐activated K channel appear complex, its large conductance and high Ca and voltage sensitivity suggest that it is uniquely suited to resist depolarizations of the cell membrane potential that are accompanied by increases in intracellular Ca.
Voltage‐activated and calcium‐activated currents studied in solitary rod inner segments from the salamander retina
Authors: Bader C. R. , Bertrand D. , Schwartz E. A. 
Published: December 2014

1. Solitary rod inner segments were obtained by enzymatic dissociation of the tiger salamander (Ambystoma tigrinum) retina. Their membrane currents were studied with the single‐pipette voltage‐clamp technique. Individual currents were isolated with the aid of pharmacological agents.2. Extracellular caesium blocked a current activated by hyperpolarization from ‐30 mV. Changing external sodium and potassium concentrations altered the value of the reversal potential in a manner consistent with the current being carried equally by both ions.3. Extracellular tetraethylammonium (TEA) blocked a current activated by depolarization from ‐70 mV. In normal medium this current had a reversal potential of ‐72 mV. Changing the external potassium concentration altered the value of the reversal potential in a manner consistent with the current being carried predominantly by potassium.4. Extracellular cobalt blocked a current activated by depolarization that had an initial inward and a later outward component.5. After EGTA was injected into an inner segment the outward component was suppressed. Cobalt then blocked an inward current. This current is believed to be carried predominantly by calcium. The conductance increased with depolarization from ‐45 mV and reached a maximum at approximately 0 mV. Following a step of depolarization the current activated rapidly (< 20 msec) and then remained constant for at least several seconds without evidence of inactivation.6. Injecting caesium into an inner segment eliminated a calcium‐activated outward current believed to be carried by potassium ions.7. After the injection of caesium there remained another calcium‐activated current with a reversal potential of ‐17 mV. Changing extracellular chloride concentration altered the value of the reversal potential in a manner consistent with chloride carrying at least 70% of the current. Another anion may carry the balance.8. When the five currents mentioned in items 2, 3, 5, 6 and 7 were blocked, the membrane resistance between ‐90 and ‐25 mV was linear, time‐independent, and had a high value (2·1 GΩ).9. The five identified currents can all be activated in the physiological range of voltage in which salamander rods normally operate.
Blocking kinetics of the anomalous potassium rectifier of tunicate egg studied by single channel recording
Authors: Fukushima Yasuo 
Published: December 2014

1. The kinetics of the anomalous K current produced by blocking cations Na, Cs and Sr were analysed by single channel recording in the tunicate egg cell.2. The open—close kinetics in a single channel with the presence of blocking cation were consistent with the blocking kinetics of the total anomalous K current. The open—close kinetics in a single anomalous K rectifier channel could be regarded as the first order transition between the open and closed states.3. The closing rate constants of the single channel for the first order transition increased almost linearly on a semilogarithmic scale as the membrane potential became more negative, while the opening rate constants decreased and then increased, showing the minimum at a certain potential level. The latter indicated that the channel was released from the blocking by excessive hyperpolarization.4. The opening rate constant increased in spite of the fixed concentration of the blocking cation (10 μM‐Cs), when the external K concentration was raised from 200 mM to 400 mM. This result suggested that there are interactions within the channel between the blocking cation and the K ion.5. When there were two kinds of blocking cations such as Na and Cs, the kinetic properties in a single channel indicated that the two kinds of blocking cations blocked the single channel independently.6. The single channel conductance of the anomalous K rectifier in 200 mM‐Na‐containing 200 mM‐K solutions was about 1·5 times larger than that in Na‐free 200 mM‐K solutions.7. The single channel conductances in 100, 200 and 400 mM‐K solution with 10 μM‐Cs were 5·0, 7·1 and 12·3 pS respectively, being roughly proportional to the square root of the K concentration.8. The density of the anomalous K rectifier channel in the tunicate egg cell was 0·039/μm2.9. The amplitude of the single channel current increased with the rise of temperature, the Q10 being 1·5.
Closely coupled excitation of γ‐motoneurones by group III muscle afferents with low mechanical threshold in the cat
Authors: Ellaway P. H. , Murphy P. R. , Tripathi Anita 
Published: December 2014

1. The reflex responses of γ‐motoneurones to discharges of muscle receptors innervated by Group III axons have been examined in hind‐limb muscles of decerebrated and spinal cats.2. Electrical stimulation of the gastrocnemius medialis nerve at a strength sufficient to excite Group III axons caused excitation of gastrocnemius lateralis or soleus γ‐motoneurones. The excitation was more prominent in the spinal animal.3. Excitation of either silent or tonically firing γ‐motoneurones was a secure, driven type of response consisting of one or two spikes occurring at fairly fixed latency in response to a single stimulus. Eighteen out of thirty‐nine γ‐motoneurones studied showed such excitation.4. Subtracting peripheral conduction times of the γ‐motoneurone impulse and the earliest component of the Group III volley from the latency of reflex excitation gave a range of central delays of 1·8‐4·8 msec (mean 3·0 msec).5. Inhibitory Group III effects were also seen but were less pronounced than the excitation.6. The origin of the receptors connected to the Group III axons whose discharge causes driven excitation of γ‐motoneurones was investigated.7. Isometric twitch contractions of a muscle caused pronounced facilitation or excitation of homonymous and heteronymous γ‐motoneurones. Excitation occurred close to the peak or during relaxation of the twitch with a range in latency of 30‐110 msec. The muscles studied were triceps surae, flexor digitorum and hallucis longus.8. Pressure or light taps applied to the gastrocnemius medialis muscle caused an increase in discharge frequency in twenty out of twenty‐eight γ‐motoneurones of the same muscle (four were inhibited). The response to a steady stimulus adapted but could outlast it by many seconds. Pressure was more effective when applied to the proximal or distal parts of the muscle.9. Fifteen out of thirty‐eight gastrocnemius medialis receptors having Group III axons (conduction velocities 5‐27 m/sec) were found to discharge one, or occasionally two, spikes to twitch contractions of the parent muscle at latencies of 30‐80 msec.10. Eight out of ten receptors with Group III axons that responded to contraction had low thresholds to pressure and taps, whereas the majority of the twenty‐three Group III units which were insensitive to contraction had high thresholds to such stimuli. Receptive fields of all Group III units were confined to either the proximal third or distal third of gastrocnemius medialis or, in a few instances, the Achilles tendon.11. We conclude that discharges in Group III axons from receptors which respond to non‐noxious, low threshold mechanical stimuli cause a tightly coupled excitation of γ‐motoneurones. The likely contribution of this reflex to the control of movement is discussed.
The influence of the sympathetic nervous system on individual vessels of the microcirculation of skeletal muscle of the rat
Authors: Marshall Janice M. 
Published: December 2014

1. Direct observations have been made on the responses of individual vessels of the microcirculation of rat spinotrapezius muscle to stimulation of the sympathetic paravascular nerve fibres and to topically applied catecholamines.2. All arteries and arterioles were constricted by sympathetic stimulation, the maximum response occurring at a stimulus frequency of 8‐10 Hz. Primary and secondary arterioles (13‐50 μm internal diameter) showed the greatest percentage change in diameter and remained constricted throughout the 1 min stimulation period whilst terminal arterioles (7‐13 μm internal diameter) constricted initially but then returned towards their control diameter before the stimulus ceased.3. By contrast the venules and veins showed no response to sympathetic stimulation.4. In accord with these observations, fluorescence histochemical studies revealed a network of noradrenergic nerve fibres on all arterial vessels but showed no innervation of any venous vessels.5. Topically applied noradrenaline or adrenaline (10−10‐10−8 g/ml.) dilated the majority of arteries and arterioles while higher concentrations of either agent produced dose‐dependent constrictor responses. In addition, many venules dilated in response to adrenaline (10−9 g/ml.) while others constricted, but concentrations of either noradrenaline or adrenaline greater than 10−8 g/ml. produced dose‐dependent constriction of all venules and veins.6. The behaviour of the more proximal and more distal arterioles during sympathetic stimulation is in accord respectively with the changes in muscle vascular resistance and in capillary surface area recorded in previous studies during sympathetic stimulation.7. The observation that venous vessels are not influenced by sympathetic nerve fibres contrasts with the established view that venous vessels of skeletal muscle are strongly constricted during sympathetic stimulation. However, reappraisal of the evidence used to support this view indicates that such results may have been misinterpreted, while other available evidence supports the proposal that the present findings may be representative of skeletal muscle vasculature in general.
The inhibitory effect of the olivocerebellar input on the cerebellar Purkinje cells in the rat†
Authors: Montarolo P. G. , Palestini M. , Strata P. 
Published: December 2014

1. In rats under Nembutal anaesthesia the inferior olive region has been reversibly inactivated by applying a cooling probe to the ventral surface of the medulla. Simple and complex spike activity has been recorded from Purkinje cells of the cerebellar cortex.2. Following cooling of the inferior olive of one side we have observed a remarkable increase of the simple spike activity in all the twenty‐two Purkinje cells, showing a disappearance of the complex spike activity.3. In some rats two Purkinje cells were recorded simultaneously from each side of the cerebellar cortex. Following cooling of the left inferior olive the effect on the Purkinje cell was observed only or predominantly on the contralateral cerebellar cortex.4. In a group of animals the inferior olive has been destroyed by 3‐acetylpyridine 4‐221 days before the recording session. Cooling of the inferior olive region was not accompanied by any significant and consistent increase in the spike activity of presumed Purkinje cells of the contralateral cerebellar cortex.5. These results indicate that the remarkable increase of the simple spike frequency following cooling of the inferior olive region is due specifically to the suppression of the activity of the olivocerebellar neurones.6. Only a small amount of the simple spike frequency increase is attributable to the removal of the post‐climbing fibre pause.7. In some lesioned rats recording was made from Purkinje cells, which showed complex spikes due to the few surviving inferior olive cells. In these Purkinje cells cooling of the inferior olive region was accompanied by a disappearance of the complex spike and by a small increase of the simple spike frequency of discharge. Such an increase is mainly attributable to the removal of the post‐climbing fibre pause.8. These results suggest that a given Purkinje cell is not only under the inhibitory influence of its own climbing fibre, but also of other olivocerebellar neurones, probably through climbing fibre collaterals to the cerebellar cortical interneurones.9. It is suggested that one role of the olivocerebellar system is to exert a powerful tonic inhibitory action on the Purkinje cells and consequently to exert a significant control on the excitability of the subcerebellar centres.
Effect of barbiturates on the GABA receptor of cat primary afferent neurones
Authors: Higashi H. , Nishi S. 
Published: December 2014

1. The effects of the barbiturate anaesthetics, pentobarbitone and thiopentone, on the membrane properties and the γ‐aminobutyric acid (GABA)‐induced responses of cat primary afferent neurones were studied with intracellular recording and voltageclamp techniques.2. At low concentrations (10−7‐10−5 M) both barbiturates slightly enhanced and prolonged GABA‐induced depolarizations or currents without affecting the membrane properties. At these concentrations, barbiturates have no effect on the apparent dissociation constant of the GABA‐GABA receptor interaction or the reversal potential for GABA‐induced depolarizations or currents.3. At high concentrations (10−4‐10−3 M) barbiturates produced a few millivolts reduction in the resting membrane potential. Voltage‐clamp analysis revealed that the depolarization was associated with one of the three types of conductance change, i.e., an initial increase followed by a decrease (40% of neurones examined), only an increase (40%) and only a decrease (20%).4. Analysis in different ionic media indicated that the depolarization with a reduced membrane resistance is associated with an increased chloride conductance and that the one with an increased membrane resistance is accompanied by a reduction in potassium conductance. Bath‐application of GABA (10−3 M) or picrotoxin (10−5 M) inhibited the increase in chloride conductance but not the reduction in potassium conductance.5. Barbiturates at these high concentrations initially caused a marked augmentation and prolongation of GABA responses; this was followed by a depression. The depressant action did not appear to be voltage‐dependent. These actions of barbiturates were not accompanied by changes in the apparent dissociation constant of the GABA‐current dose—response curve or the reversal potential for GABA currents. In addition, the single exponential decay of GABA current was not changed despite a marked prolongation of its decay time.6. Picrotoxin (10−5 M) antagonized the depressant effect of barbiturates at high concentrations on GABA currents, and barbiturates (5 × 10−6 M) reduced the inhibitory action of picrotoxin (5 × 10−6 M) on the GABA‐currents.7. From all these results, it is suggested that the site of barbiturate actions on GABA‐responses is mainly the allosteric site (the ionic conductance regulatory subunit) but not the agonist recognition site or the chloride channels linked with GABA receptors.
Mechanisms involved in irreversible anoxic damage to the in vitro rat hippocampal slice
Authors: Kass Ira S. , Lipton Peter 
Published: December 2014

1. We have studied the effects of anoxia on the recovery of neural transmission between the perforant path and the dentate granule cells in the in vitro rat hippocampal slice. There is almost no recovery of the evoked population spike following 10 min of anoxia in slices from adult rats.2. A 2 h exposure of slices to creatine markedly improves the recovery of the population spike (80% vs. 5%). The creatine pre‐incubation builds up phosphocreatine levels in the slice and prevents the large fall in ATP during anoxia; ATP falls to 7·9 rather than 3·6 nM/mg protein. The intracellular pH of both groups falls to the same level during anoxia.3. If calcium concentration in the medium is reduced to 0 while magnesium concentration is raised to 10 mM during anoxia the evoked response recovers to about 65%.4. The data suggest that an attenuation of the fall in ATP or entry of calcium during anoxia protects the tissue against irreversible transmission damage. Thus both of these factors participate in the generation of this damage. It is not yet clear if they act independently or if one acts by altering the other.5. In the post‐anoxic recovery period the intracellular concentration of potassium is reduced by about 25%. However, it is still much higher than in slices that show only partial block of the evoked response when treated with ouabain. Therefore a fall in intracellular potassium 1 h after anoxia cannot explain the lack of recovery of the evoked response in adult tissue.6. ATP levels in the post‐anoxic recovery period are reduced from their pre‐anoxic levels (9·7 vs. 13·9 nM/mg protein). However when azide or antimycin A are used to directly reduce ATP to the level found 1 h after anoxia the evoked response is reduced by only about 45%. Thus the reduced post‐anoxic ATP levels are not sufficient to explain the loss of the evoked response in adult tissue.7. The data show that the irreversible loss of transmission is not due to decreased cell ATP or to decreased cell K/Na levels 1 h after the anoxic period.8. Since creatine pre‐incubation protects against irreversible transmission loss this compound or one closely related to it may prove useful in attenuating irreversible brain damage in situ.