bluuebunny/crossref_metadata_2025_split huggingface dataset:
Amino acid transport in Myxicola giant axon: stability of the amino acid pool, taurine efflux, and trans effect of sodium
Authors: Horn Lyle W. 
Published: December 2014

1. The giant axon of Myxicola infundibulum was assessed for its suitability as a model preparation for study of amino acid transport mechanisms.2. The amino acid composition of axoplasm was measured and compared with those of coelomic fluid, muscle and axon sheath. The axoplasmic composition is unique. Axoplasm/coelomic fluid concentration ratios are all much larger than 1. The axoplasmic amino acid concentrations are (mmol/kg plasm): cysteic acid (104), aspartic acid (75), glutamic acid (10), taurine (64), serine (5), glycine (191) and alanine (5). Other amino acids or primary amines, if present, must have concentrations of less than 1 m
m.3. The size of the sheath amino acid pool is 12% or less of the axoplasmic pool.4. The amino acid pool of axons soaked in sea water for up to 24 h is stable. Removal of Na from sea water causes a large increase of net efflux and net production of amino acids.5. Net amino acid production can not be detected in sheath. Metabolic production occurs in axoplasm with little accumulation. Time scales for production and net efflux are therefore similar.6. The Myxicola axon has a vigorous amino acid metabolism and transport systems capable of relatively large fluxes. Homeostasis is strongly linked to Na and may involve Na‐coupled co‐transport. Conservation of transmembrane amino acid gradients could be promoted in part by trans inhibition of efflux by external Na.7. Taurine is a useful model substrate because it is not catabolized in Myxicola and its net efflux is sensitive to Na. [3H]taurine efflux was measured from injected axons. Fluxes and internally recorded action potentials are stable for up to 6 h.8. Axon sheaths take up [3H]taurine from 10 m
m‐taurine sea water with an apparent half‐time of 5 h. [3H]taurine washout from the apparent extracellular space has a half‐time of 5 min. Washout from sheath cells has a half‐time of 2‐3 h. Sheath is not an important parallel compartment for taurine fluxes in the axon.9. Taurine efflux has a Q10 of 1·8.10. Taurine efflux is insensitive to external taurine concentrations up to 10 m
m.11. Taurine efflux is sensitive to external Na, but only if internal Na is high.12. Taurine is transported by a low‐affinity Na‐dependent system in Myxicola axon. Results could be explained by a carrier which is more mobile in the empty state than in the substrate‐loaded state. Trans inhibition of taurine efflux by external Na is an important property of the system, and contributes to conservation of axoplasmic taurine.
The mechanical activity of chick embryonic myocardial cell aggregates
Authors: Clusin William T. , Hamilton W. E. , Nelson D. V. 
Published: December 2014

1. Simultaneous recordings of membrane potential and edge movement were obtained in spontaneously beating chick embryonic myocardial cell aggregates, which are known to behave as an isopotential syncytium.2. The time course of edge movement was similar in different aggregates, and in different regions of the same aggregate.3. Peak amplitude was increased by 10−6
m‐ouabain, and by rapid reduction of the external sodium concentration.4. Peak amplitude was decreased during single premature action potentials, but sustained rapid pacing produced an ascending staircase.5. Depolarizing current pulses increased both the amplitude and duration of the contraction, and caused potentiation of the next spontaneous beat. Edge displacement during a series of pulses was a monotonic function of membrane potential.6. Edge movement between action potentials (diastolic movement) was well fitted by an exponential with a mean time constant of 69 msec. Diastolic edge movement was due to a weak, slowly decaying contractile force, which was demonstrated in cells grown on a linear‐elastic nylon bristle.7. The time course of diastolic edge movement remained constant, or nearly constant, during variations in peak amplitude that resulted from prematurity of the action potential, exposure to 10−6
m‐ouabain, spontaneous mechanical alternans, or prolongation of the action potential by current pulses.8. In contrast, reduction of the external sodium concentration produced marked, selective slowing of the diastolic edge movement. Similar slowing occurred during cooling and during staircase. Diastolic edge movement was selectively accelerated when the preceding interbeat interval was prolonged by a hyperpolarizing current pulse.9. The above observations are consistent with the hypothesis that edge displacement is a monotonic function of contractile force.10. The slow relaxation between action potentials probably reflects removal of intracellular calcium across the surface membrane in exchange for sodium. Changes in the rate of calcium removal may play a role in the regulation of contractility in this tissue.
Tension responses of chemically skinned fibre bundles of the guinea‐pig taenia caeci under varied ionic environments
Authors: Iino M. 
Published: December 2014

1. Thin fibre bundles (about 100 μm in width and 1.5 mm in length) were dissected from taenia caeci of the guinea‐pig, and were mounted in an apparatus to record isometric tension mainly at 25 °C.2. Fibre bundles were chemically skinned by treating with 50 μg saponin/ml. for 20 min in a relaxing solution. Upon application of an activating solution containing 80 μ
m‐Ca2+ the fibre bundles rapidly developed a tension which was comparable in magnitude to that elicited with 10 μ
m‐carbachol before the saponin treatment.3. It was confirmed that skinned fibre bundles develop active tension slowly in the virtual absence of Ca2+ when Mg2+ concentration was raised above 2 m
m in the presence of MgATP. However, this tension was not developed in the presence of an ATP regenerating system.4. Maximum Ca2+ activated tension and Ca sensitivity of skinned smooth muscle fibre bundles were examined using solutions in which pH, ionic strength, and the concentrations of Mg2+ and MgATP2- were varied around supposedly physiological values. An ATP regenerating system was used when necessary.5. Maximum Ca2+ activated tension changed only slightly with alteration in ionic strength (0.15‐0.3
m). It decreased by 40% with increase in pH from 6.4 to 7.2, and decreased by 10‐30% when Mg2+ concentration was either lowered to 0.2 m
m or raised to 2 and 10 m
m from 1 m
m. The tension increased by about 10‐20% as MgATP2- concentration was raised from 0.4 to 4 or 8 m
m.6. Changes in pH, ionic strength, and MgATP2- concentration in the above range had no important effects on the relative isometric tension—pCa relation. Decrease of Mg2+ concentration from 1 to 0.2 m
m had little effect, but increase to 2 and 10 m
m shifted the curve some 0.2 and 0.6 pCa units, respectively, toward a lower pCa. There was not large difference between the relative isometric tension—pCa relation at 25 °C and that at 38 °C.7. The Ca2+ concentration in the smooth muscle cell of taenia during physiological contraction can be estimated from the results obtained and the values for the relevant in vivo ionic constituents given in the literature; the lowest Ca2+ concentration for detectable tension development is between 0.2 and 0.5 μ
m, and tension tends to level off above 10 μ
m‐Ca2+.
Single glutamate‐activated channels recorded from locust muscle fibres with perfused patch‐clamp electrodes
Authors: Cull‐Candy S. G. , Miledi R. , Parker I. 
Published: December 2014

1. Glutamate‐activated single channels have been examined with conventional and internally perfused patch‐clamp electrodes applied to the extrajunctional membrane of locust muscle fibres which were usually treated with concanavalin A to reduce desensitization. Channels opened by glutamate and other agonists have been compared.2. Recording patches were selected where there appeared to be only one active channel under the pipette. The conductance for single glutamate‐activated channels was 150 pS and was not markedly dependent on clamp potential. The lifetimes of the channels were usually exponentially distributed with a mean of τ(glutamate) = 2.3 ± 0.12 msec, T = 23 °C, Vm = ‐60 mV.3. Channels opened by fluoroglutamate had a mean lifetime of τ(fluoroglutamate) = 1.4 ± 0.1 msec; channels opened by quisqualate had a mean lifetime of τ(quisqualate) = 6.4 ± 1.0 msec. The conductances of channels opened by fluoroglutamate, quisqualate and glutamate were not significantly different.4. The behaviour of individual receptor—channel complexes has been examined at various concentrations of glutamate. Drug solutions were applied through an internal perfusion pipette which allowed exchange of the solution in the patch‐electrode tip within 10 sec. The distribution of channel closed times could be fitted with a single exponential. Channel lifetime was not markedly dependent on glutamate concentration (30‐600 μm) whereas the channel closed time decreased with increasing glutamate concentration.5. The reciprocal of channel closed time vs. glutamate concentration had a slope value of 1.85 on logarithmic co‐ordinates. The approximately second power dependence of net forward reaction rate on glutamate concentration suggests that at least two glutamate molecules activate a single receptor—channel complex.6. The apparent dissociation constant for the glutamate—receptor complex is large, being about 300‐500 μM. If the receptors have an equally low affinity for neurally released transmitter, then only a small amount of the transmitter packet is expected to bind to receptors. Quisqualate and glutamate have similar receptor affinities whereas receptor affinity for fluoroglutamate is smaller.
Oesophageal and diaphragmatic activity during sucking in lambs
Authors: Harding R. , Titchen D. A. 
Published: December 2014

1. Buccal, pharyngeal, oesophageal and diaphragmatic movements during swallowing of saliva and sucking from a bottle were studied in lambs by recording electromyograms (e.m.g.s) from the mylohyoid, thyrohyoid and thyroarytenoid muscles, cervical and caudal thoracic oesophagus and vertebral and costal regions of the diaphragm. Buccal and pleural pressure recordings were also made.2. Swallows of saliva characteristically involved contraction of the mylohyoid followed sequentially by contraction of the thyrohyoid, cervical, and finally, caudal thoracic oesophagus.3. Sucking (indicated by the mylohyoid e.m.g.s and buccal pressure) was initially at rates up to 6 sec−1, sustained at up to 4 sec−1 for 30‐45 sec and, once established, accompanied by swallows in a 1:1 association with sucking.4. Respiration ceased during the pharyngeal phase of swallowing. At the time the primary contraction (of swallowing) involved the caudal thoracic oesophagus vertebral fibres of the diaphragm forming the hiatus oesophageus became quiescent, although costal fibres continued to contribute to inspiration.5. During sucking, respiration was shallow and rapid, with diaphragm contractions sandwiched between swallows.6. Towards the end of an episode of sucking, contractions of the diaphragm became more intense and occurred in groups with pressure changes corresponding to both individual contractions and the grouped activity.7. Primary oesophageal contractions occurred only after single swallows or at the end of a series of swallows.8. During periods when sucking and swallowing were frequent, short episodes of oesophageal contraction occurred, each being between thyrohyoid contractions.9. Recording from contiguous sites of the caudal thoracic oesophagus confirmed a caudally progressive character of those short contractions of the oesophagus observed during sucking.10. Factors contributing to these changes in oesophageal activity and consequences of altered diaphragmatic activity in sucking have been discussed.
Roles of stored calcium on the mechanical response evoked in smooth muscle cells of the porcine coronary artery
Authors: Itoh Takeo , Kajiwara Makoto , Kitamura Kenji , Kuriyama Hirosi 
Published: December 2014

Effects of acetylcholine (ACh), caffeine and procaine on the membrane and mechanical properties of the intact and skinned muscle cells of the porcine coronary artery were investigated using the micro‐electrode and isometric tension recording methods.1. ACh (10−8‐10−5
m) had no effect on the membrane potential and membrane resistance, as assessed from the current—voltage relationship.2. Caffeine possessed dual actions on the membrane property, i.e. a low concentration (0·3‐1 m
m) hyperpolarized and a high concentration (over 1 m
m) depolarized the membrane, while caffeine (over 0·3 m
m) consistently increased the ionic conductance of the membrane. Procaine (over 1 m
m) depolarized the membrane and decreased the ionic conductance of the membrane.3. The spike and contraction evoked by outward current pulses in the presence of 10 m
m‐TEA were suppressed by treatment with caffeine (5 m
m) or procaine (3 m
m), but the spike was slightly and the electrically induced contraction was significantly suppressed by ACh (10−6
m) due to the marked increase in resting tension.4. In Ca‐free 2 m
m‐EGTA containing solution, the K‐induced contraction (118 m
m) rapidly ceased, but not the contraction evoked by ACh (10−5
m) or caffeine (5 m
m). The ACh‐induced contraction rapidly ceased in the presence of 1 m
m‐procaine; however, over 5 m
m‐procaine was required to abolish the caffeine‐induced contraction.5. The pCa—tension relationship was measured in saponin‐treated skinned muscles. The minimum concentration of free Ca required to produce contraction was 2 × 10−7
m, while maximum contraction was observed at 10−5
m‐free Ca. The maximum amplitude of Ca‐induced contraction observed in skinned muscles was larger or the same as that evoked by ACh in the intact muscle. ACh (10−5
m), caffeine (5 m
m) and procaine (5 m
m) had no effect on the pCa—tension relationship.6. After Ca has been loaded in skinned muscles, caffeine and replacement of K with choline (116 m
m) in the Ca‐free EGTA containing solution produced the contraction. However, the application of ACh did not result in a release of the stored Ca, and procaine suppressed the release of Ca activated by caffeine.7. The present results indicate that ACh activates the muscarinic receptor distributed on the plasma membrane, thus releasing the stored Ca. However, this mechanism may not be a prerequisite for direct action of ACh on the Ca releasing site. The possible mechanism of ACh action on the Ca releasing site, mainly sarcoplasmic reticulum, was discussed in relation to actions of caffeine and procaine, particularly with regard to the functional relations between plasma membrane and sarcoplasmic reticulum.
Calcium currents in internally perfused nerve cell bodies of Limnea stagnalis
Authors: Byerly Lou , Hagiwara Susumu 
Published: December 2014

1. When K+ is removed from both sides of the somal membrane of Limnea neurones, time‐dependent, voltage‐dependent outward currents are observed at positive potentials. These currents can be carried by Tris+ and tetraethylammonium (TEA+), as well as Cs+, but the Cs currents are several times larger. The Cs currents are not affected by external or internal TEA, but are strongly reduced by 4‐aminopyridine (4‐AP) and all Ca blockers tried.2. The presence of these non‐specific outward currents and their sensitivity to all treatments that eliminate the Ca currents prevent the complete isolation of Ca currents. The non‐specific outward currents are most prominent at large positive potentials and as slow tail currents on stepping back to the holding potential.3. Ca currents are ‘washed out’ in well perfused cells. Typically the Ca current has decayed to less than one tenth of its original size after ½ h of perfusion. This wash‐out is specific for the Ca current; Na and K currents persist for several hours.4. Once the Ca current has completely decayed, it is possible to study one type of non‐specific current without overlapping inward currents. This current activates between 0 and +30 mV and appears to reverse near 0 mV.5. In spite of the probable presence of slowly activating outward currents, the net inward currents measured show little apparent inactivation. In all the cells studied the inward current evoked at +20 mV has never decayed by more than 50% during a 60 ms pulse. So the true inactivation of these Ca currents must be quite slow, with time constants of the order of 100 ms and larger.6. The activation of the Ca current agrees with m2 kinetics. The rate of activation is the same for Ba currents as for Ca currents.7. When the membrane potential is stepped back to the holding level (‐50 mV), the Ca current turns off quite rapidly with a time constant of about 100 μs (25 °C). The time constant for turning off the Ca current is not related to the time constant for turning on the Ca current at the same voltage as expected for m2 kinetics in the Hodgkin and Huxley model. At ‐30 mV the τm for turn‐on is eight times larger than the τm for turn‐off.
The influence of visceral mechanoreceptors on sympathetic efferent discharge in the cat
Authors: Floyd K. , Hick Verity E. , Morrison J. F. B. 
Published: December 2014

1. Recordings have been made from eighty‐three single sympathetic efferent units in the hypogastric nerve in two types of preparation. In all animals the baroreceptors were denervated to exclude changes in sympathetic discharge resulting from any variations in arterial pressure, and the spinal cord was sectioned at the 6th lumbar segment to exclude changes in efferent discharge that might have been due to pelvic nerve afferents from the bladder or other viscera. In some animals the afferent pathways were sectioned from all pelvic and lower abdominal viscera other than the bladder, so that the vesical afferent pathway was the only neural pathway that might mediate reflex events from these viscera. The hypogastric nerve afferent pathway was excited by bladder distension or by bladder contractions induced by electrical stimulation of the sacral cord.2. Approximately half the units gave an increase in spike rate during distension or during contraction of the bladder. Three‐quarters of the units tested also gave an increase in spike rate during colonic distension. In no units that exhibited convergence of afferent input did colonic and vesical stimuli cause responses of opposite sign.3. Approximately 10% of units showed a reduction in discharge rate when the bladder was distended or caused to contract.4. The estimated intravesical pressure thresholds for these reflexes were in the range 8‐56 mmHg which extends beyond that of the mechanoreceptors which form the afferent limb of the reflex.5. These reflex studies indicate that the hypogastric nerve afferents from the bladder can elicit sympathetic reflexes within the physiological range of intravesical pressures, and that vesico‐sympathetic reflexes can be elicited in the absence of pelvic nerve afferent inputs.In 75% of sympathetic efferent units that respond to bladder distension or contraction, there is evidence for convergent inputs with similar actions from the colon.
Time course and extent of recovery in reinnervated motor units of cat triceps surae muscles
Authors: Gordon Tessa , Stein R. B. 
Published: December 2014

1. Nerve and muscle properties were studied in single motor units of triceps surae muscles in the cat using chronic recording techniques and intramuscular microstimulation. Recordings were made before and at intervals up to 18 months after a nerve was sectioned and sutured either to its distal stump (nerve—nerve suture) or to a muscle directly (nerve—muscle suture). Thus, each nerve and muscle served as its own control for recovery after reinnervation.2. Following a delay all muscles recovered their preoperative tension after nerve—nerve suture with a single exponential having a time constant of 1‐2 months. Only half the muscles recovered their preoperative tensions after nerve—muscle sutures. Muscles which did not recover fully also had a slower time course of recovery.3. The estimated number of motor units did not increase significantly later than 2 months after nerve section and suture. Further recovery of muscle tension is due to increased unit tension, rather than increasing numbers of reinnervated motor units. Unit tension recovered completely in all muscles, but did not become enlarged, even when muscles apparently remained partially denervated.4. The latency of compound nerve potentials often recovered completely, although the amplitude of the potential remained depressed. Single motor axonal potentials recovered to control levels after reinnervation of muscle with a time constant similar to that for the recovery of motor unit tension. Therefore, two distinct populations of motor axons contribute to the compound potential: reinnervating axons whose size recovers fully, and disconnected axons which remain atrophic. Incomplete recovery of the compound potential amplitude mainly results from a failure of all axons to remake peripheral connexions.5. Thus, formation of functional nerve—muscle connexions completely reverses the effects of axotomy on nerve and muscle. Reinnervated motor units recovered their preoperative size, whether or not much of the muscle remained denervated.
The nature of the excitatory transmitter mediating X and Y cell inputs to the cat dorsal lateral geniculate nucleus
Authors: Kemp J. A. , Sillito A. M. 
Published: December 2014

1. In experiments examining the possibility that an excitatory amino acid may be an optic nerve transmitter in mammals, excitatory amino acid antagonists have been ionophoretically applied to cells in layers A and A1 of the cat dorsal lateral geniculate nucleus and their effect on the excitatory response to visual stimulation of the receptive field centre has been assessed.2. The antagonists used were D‐α‐aminoadipate (D‐α‐AA), DL‐α‐ε‐diaminopimelic acid (DAP), 1‐hydroxy‐3‐amino‐2‐pyrrolidone (HA‐966) and L‐glutamate diethyl ester (GDEE). The antagonist effects on the visual response were compared with their effect on similar magnitude responses evoked by ionophoretic pulses of selected agonists and a control excitant, generally acetylcholine.3. Both D‐α‐AA and HA‐966 would selectively block or depress the visual response with respect to the response to the control excitant. At the stage the visual input was blocked, responses to the agonists N‐methyl‐D‐aspartate (NMDA), DL‐homocysteic acid (DLH) and glutamate were also greatly reduced or blocked. At dose levels below those causing a significant reduction in the visual response, D‐α‐AA and HA‐966 would selectively depress responses to NMDA and DLH with respect to the response to glutamate.4. GDEE was relatively ineffective in blocking either agonist responses or the visual response and only produced a significant reduction in either at dose levels that caused a similar depression in the response to acetylcholine. DAP would block responses to DLH but produced no significant effect on the visual response or the responses to glutamate and acetylcholine.5. The cholinergic antagonists atropine and dihydro‐β‐erythroidine (DHβE) blocked responses to acetylcholine without significantly reducing either visual driving or the response to DLH.6. The effects were the same for X and Y cells in the dorsal lateral geniculate nucleus (dLGN). There was also no distinctions between ‘on’ and ‘off’ centre types of each of the two groups.7. The significance of these results is discussed. It is argued that they reintroduce the possibility that either L‐aspartate, L‐glutamate or a similar substance may be the transmitter mediating the optic nerve input to the cat dLGN.