bluuebunny/crossref_metadata_2025_split huggingface dataset:
The responses of chemoreceptors at reduced temperatures
Authors: Paintal A. S. 
Published: December 2014

1. The responses of aortic chemoreceptors and pulmonary stretch receptors of cats were studied by recording impulses in individual fibres at normal body temperatures and thereafter at various temperatures down to 24–26° C while cooling the cat with ice.2. Reduction of metabolism by lowering the temperature did not obviously slow the PO2 sensing mechanism of chemoreceptors but it greatly slowed the development of excitation after circulatory arrest. It also greatly reduced the excitatory effect of hypoxia.3. The Q10 for the frequency of discharge of chemoreceptors (during maximal activity) was estimated by comparing the activity of the endings at normal body temperature after circulatory arrest (i.e. at a local PO2 of 0 mm Hg) with similar activity at reduced body temperatures. This averaged 2·5 in nine endings. The Q10 for the peak frequency of discharge also averaged 2·5 in seven endings. These values are similar to those of some mechano‐receptors.4. Apart from the reduction in the frequency of discharge (Q10 = 2·6) lowering the temperature did not alter the stimulus—response relationship of pulmonary stretch receptors.5. The poor responses to ACh at lower temperatures indicate that ACh is not likely to be a transmitter at chemoreceptors.
The volume of the T‐system and its association with the sarcoplasmic reticulum in slow muscle fibres of the frog
Authors: Flitney F. W. 
Published: December 2014

1. A study has been made of the T‐system and sarcoplasmic reticulum (SR) in slow muscle fibres of the frog, Rana temporaria.2. The size of the T‐system was measured by an autoradiographic method, using tritium‐labelled albumin as a marker. Its volume, expressed as a fraction of that of the fibre, was found to be 1·8 × 10−3, as compared with a figure of 3·9 × 10−3 for the T‐system in a twitch fibre.3. The spatial distribution of the T‐tubules, and their association with the SR, was studied with the electron microscope, employing ferritin and the enzyme peroxidase as markers. The observations show (a) the tubules form a three dimensional, rather than transverse, network and (b) the area of triadic (and diadic) contact with the SR is 5‐10 × smaller than in a twitch fibre.4. The possibility that the T‐system and SR of the slow fibre participate in linking membrane excitation with contraction is discussed in the light of these findings.
Membrane potential of smooth muscle cells in K‐free solution
Authors: Casteels R. , Droogmans G. , Hendrickx H. 
Published: December 2014

1. The changes of the ion content, the membrane potential and of the membrane permeability of taenia coli cells have been studied during exposure to K‐free solutions. The relative value of the total membrane conductance was determined by measuring the electrotonic potential during constant current pulses with an intracellular electrode. The PK values were calculated from 42K‐efflux in K‐free solutions.2. In solutions containing penetrating anions the cells initially depolarize. Thereafter they hyperpolarize to about − 85 mV and again depolarize after 90 min to − 5 mV. These potential changes are much smaller if large anions are used as chloride substitutes. Moreover, the final depolarization is only reached after 4‐5 hr. This hyperpolarization is not inhibited by 10−5
M ouabain.3. These potential changes are accompanied by a progressive exchange of intracellular K by Na. In solutions containing chloride or nitrate the relative value of the total membrane conductance increases to a maximal value, corresponding to the peak value of the calculated PK. Such changes of the membrane conductance and of PK do not occur in K‐free solutions containing large anions.4. It is proposed that the initial depolarization is probably caused by an inhibition of an electrogenic Na pump. In chloride or nitrate solution the hyperpolarization is due to an increase of the [K]i/[K]o ratio and to an increase of the K permeability. In the presence of large anions the hyperpolarization remains small because this increase of PK does not occur.
Variation in the permeability properties of the inhibitory post‐synaptic membrane of the crayfish neuromuscular junction when activated by different concentrations of GABA
Authors: Takeuchi A. , Takeuchi Noriko 
Published: December 2014

1. The membrane conductance of the crayfish muscle was measured with intracellular micro‐electrodes. Increase in the membrane conductance induced by various concentrations of γ‐amino butyric acid (GABA) was measured in the Br−, NO3−, I− and CNS− solutions and compared with that in Cl− solution. When the membrane was activated by lower concentrations of GABA, the resulting membrane conductance in NO3− and I− solutions was larger than in Cl− solution, while the membrane conductance activated by higher concentrations in NO3− and I− solutions were smaller than in Cl− solution. The membrane conductance activated by GABA was larger in Br− solution and smaller in CNS− solution than the membrane conductance activated in Cl− solution, throughout the concentration range of GABA examined.2. The reversal potential of inhibitory junctional potentials (i.j.p.s) was measured shortly after replacing Cl− by foreign anions: Br−, NO3−, I− and CNS−. In I− solution the i.j.p.s produced by lower stimulation frequencies showed a reversal potential at a more hyperpolarized level than those produced by higher stimulation rates.3. Shortly after replacing Cl− by I−, the GABA potential induced by iontophoretic application showed a triphasic potential change at the ‘reversal’ potential. The reversal level of the GABA potential produced by smaller doses was at a more hyperpolarized level than that produced by larger doses.4. Possibilities of a concentration effect of GABA are discussed. It is suggested that the relative permeability of the crayfish inhibitory membrane to anions changes depending on the concentration of GABA.
Changes in body temperature of the unanaesthetized monkey produced by sodium and calcium ions perfused through the cerebral ventricles
Authors: Myers R. D. , Veale W. L. , Yaksh T. L. 
Published: December 2014

1. In the unanaesthetized Rhesus monkey, solutions containing sodium, calcium, potassium or magnesium in excess of the normal concentration of extracellular fluid were perfused from a lateral to the fourth ventricle through chronically implanted cannulae.2. Sodium (11·0–88·0 m
M in excess of the physiological concentration) perfused through the ventricles, caused an immediate rise in body temperature which was accompanied by vasoconstriction, piloerection and shivering. The latency of the hyperthermia was related directly to the rate of perfusion and the concentration of sodium, whereas the magnitude of the response depended upon the concentration only. When the perfusion was terminated, shivering ceased and the temperature of the monkey returned to the base line level.3. When calcium ions were perfused in concentrations 2·5–47·9 m
M in excess of that of extracellular fluid, a fall in the temperature of the animal occurred. The magnitude of the decreases depended upon the concentration of calcium in the perfusion fluid. Vasodilatation, sedation and a reduction in withdrawal reflexes accompanied the calcium‐induced hypothermia. After the perfusion ended, the temperature continued to fall until the monkey began to shiver and vasoconstriction was observed in many skin areas.4. The perfusion through the cerebral ventricles with modified Krebs solution alone or with the Krebs solution which contained potassium or magnesium ions in concentrations five to ten times normal had virtually no effect on the temperature of the monkey.5. Since the temperature of the monkey was unchanged as long as the physiological ratio of sodium to calcium in the perfusion fluid remained constant, we conclude that the balance between these two essential cations within the brain stem could determine the neural mechanism whereby the set‐point for body temperature of the primate is established.
Rectification in instantaneous potassium current—voltage relations in Myxicola giant axons
Authors: Binstock L. , Goldman L. 
Published: December 2014

1. Measurements of the instantaneous K current, under voltage clamp, were obtained using paired de‐ and hyperpolarizing clamp pulse sequences. The instantaneous potassium current—voltage relations so obtained showed constant field type rectification.2. The zero current potential of the instantaneous K current—voltage relation, when examined as a function of the K concentration, [K]o, behaved like a Nernst concentration cell potential for K. It was concluded that during the generation of the delayed current, the membrane shows substantial selectivity for K.3. The equivalent of the ‘Frankenhaeuser—Hodgkin space’ in Myxicola was found to be more difficult to load with K ions than in squid. The thickness of the space may be taken as effectively about seven times larger than in squid.4. Myxicola axons were found to show little or no long time constant delayed current inactivation as has been described for squid.5. In high [K]o a negative steady‐state conductance was observed which was predictable from the independence principle with a suitable scaling factor.
Human thyroxine‐binding globulin and thyroxine‐binding pre‐albumin: dissociation rates
Authors: Hillier A. P. , Balfour W. E. 
Published: December 2014

1. A simple method is described for estimating the rate of thyroxine dissociation from binding sites in plasma.2. At tracer concentrations in human plasma thyroxine dissociates at two distinct exponential rates. These are due to the two thyroxine‐binding proteins present in human plasma.3. The t½ for thyroxine dissociation from thyroxine‐binding globulin is 8·1 ± 0·7 (
S.E.) min at room temperature and 38·6 ± 2·1 sec at 37° C.4. The t½ for thyroxine dissociation from thyroxine‐binding pre‐albumin is 53 ± 5·0 sec at room temperature and 7·9 ± 0·3 sec at 37° C.5. Dissociation of thyroxine from both proteins is a single exponential process, suggesting that each protein has only one type of specific binding site.6. These results indicate that the minute pool of free thyroxine in plasma is turning over about 100 times each second, with about two thirds of this flux being due to release and binding of the hormone by pre‐albumin.
Ionic permeability changes induced by some cholinergic agonists on normal and denervated frog muscles
Authors: Feltz Anne , Mallart Alberto 
Published: December 2014

1. The reversal potential of responses to iontophoretic application of acetylcholine, carbamylcholine and decamethonium has been measured at junctional and extrajunctional sensitive areas of the normal sartorius muscle of the frog.2. The values obtained with any one of the drugs at junctional spots were similar to those previously reported for the end‐plate potential (about — 16 mV).3. On the other hand, at extrajunctional areas the reversal potential of responses to these agonists was found to have a mean value of — 42 mV. The muscle‐tendon responses to acetylcholine reversed at — 51 mV.4. The response to decamethonium was used to determine the nature of the ionic permeability changes mediated by the extrajunctional receptors. The results obtained show that extrajunctional responses are due to an increase in conductance to Na+ and K+ but not to Cl−.5. The reversal potential of acetylcholine responses in denervated frog sartorius was — 42 mV both at former junctional spots and at non‐neural sensitized regions.6. These different values of the reversal potential can be due either to effects of receptor density on the ionic selectivity of the membrane or to regional variations in the extracellular ionic accumulation during the transmitter action.
Ionic effects on spindle adaptation
Authors: Husmark I. , Ottoson D. 
Published: December 2014

1. Effects of changes in ionic environment on the receptor potential were studied in isolated frog spindle. Particular attention was focused on the action of potassium removal on the early adaptive decline of the response.2. Removal of potassium caused a reduction and final disappearance of the dynamic overshoot of the receptor potential. The static phase of the response was also reduced although to less extent. The repolarization phase of the response following release of phasic or maintained stretch was greatly prolonged.3. Increased potassium concentration caused a reduction of the response, but did not change its general time course. The amount of reduction was related to the potassium concentration.4. Removal of sodium caused a marked diminution of the response, the static phase being in general more affected than the dynamic phase.5. It is suggested that the effects of potassium removal are caused by a delay in sodium inactivation and a partial depolarization of the endings. It is concluded that the greater part of the early adaptation of the spindle proper may be attributed to ionic mechanisms in the transducer membrane.
Participation of the anterior hypothalamus in the baroreceptor reflex
Authors: Hilton S. M. , Spyer K. M. 
Published: December 2014

1. On the basis of discrete electrical stimulation in the pre‐optic region and anterior hypothalamus of anaesthetized cats, a depressor area has been defined, stimulation of which elicits a fall of arterial blood pressure of 30–50 mm Hg and a bradycardia of some 25%, caused by inhibition of sympathetic vasomotor tone and by vagal activation respectively. These are accompanied by a reduction in rate and depth of respiration.2. The depressor area, from which this pattern of response is elicited, lies ventral and caudal to the anterior commissure, and extends caudally in the dorsal hypothalamus, dorsal to the fornix.3. The pattern of response elicited from identified points in the depressor area was shown to be indistinguishable from that to baroreceptor afferent stimulation.4. A lesion destroying the hypothalamic depressor area bilaterally reduced the response to baroreceptor afferent stimulation. Lesions in the medullary depressor area which spared a large part of the nucleus of the tractus solitarius also reduced, but did not abolish, the baroreceptor reflex response. The two lesions combined abolished the reflex.5. It is concluded that the whole brain‐stem depressor area, from the hypothalamus through the mid‐brain to the medulla, constitutes a functional unit which integrates the response to baroreceptor afferent stimulation.
Distribution of magnesium in the arterial wall
Authors: Palatý Vladimír 
Published: December 2014

1. The Mg, Ca, Na and K content were determined in the rat tail artery in vitro under various experimental conditions.2. The arterial Mg could be varied selectively at a constant [Mg]o by altering the content of intracellular compounds capable of forming complexes with Mg2+ such as nucleoside‐5′‐triphosphates or citrate.3. The release of tissue Mg during incubation in Mg‐free solutions was found to consist of a fast and a slow component. The size of the fast component was dependent on the original [Mg]o. The size of the slow component was dependent on the content of intracellular compounds forming complexes with Mg2+. The rate of efflux of the slow component could be increased by increasing [Mg2+]i, by removing external Ca, or by making the artery metabolically inactive.4. The results seem to indicate that [Mg2+]i in metabolically active vascular smooth muscle cells is maintained at a level of ca. 10−4
M.
Muscle spindle response at the onset of isometric voluntary contractions in man. Time difference between fusimotor and skeletomotor effects
Authors: Vallbo Å. B. 
Published: December 2014

1. Impulses in single muscle afferents were recorded from the median nerves of waking human subjects with percutaneously inserted tungsten needle electrodes. During isometric voluntary contractions, unitary discharges were analysed from muscle spindle endings in the wrist and finger flexor muscles and the electromyographic activity from these muscles was recorded simultaneously.2. When the subject activated the muscle portion in which a spindle was located, the afferent discharge increased in spite of the mechanical unloading effects of the skeletomotor contraction indicating a concomitant fusimotor activation. This was valid for slowly rising contractions as well as small fast rising twitches.3. The time of onset of spindle acceleration was determined in relation to the time of onset of the electromyographic activity for thirty‐one units studied altogether in more than seven hundred contractions. It was found that spindle acceleration regularly occurred after the onset of the electromyographic activity.4. There was a considerable variation from one test to the other, for the individual units, with regard to the exact time of onset of spindle acceleration, although spindle acceleration occurred mostly within 0·5 sec after the onset of the electromyographic activity in sustained contractions and within 0·1 sec in small fast rising twitches. It was not possible to assess to what extent this variation was accounted for by variations in the mechanical unloading effects of the skeletomotor contraction or variations in the timing of the fusimotor outflow.5. For many units, spindle acceleration did not occur until 10–50 msec after the onset of the skeletomotor contraction. This time is of the same order of magnitude as the time difference in latency from the spinal cord to the recording points in the two systems, as estimated from reasonable assumptions.6. It was concluded that the fusimotor system does not participate in the initiation of voluntary contractions in man, but that the skeletomotor activity is initiated by descending impulses from supraspinal structures and their effects on the neuronal organization within the spinal cord.7. The fact that fusimotor activation occurs also in very small and short lasting twitches, when spindle acceleration must have a negligible influence on the skeletomotor outflow, suggests that the fusimotor and the skeletomotor systems are rigidly co‐activated in voluntary contractions.8. The finding that spindle acceleration does not occur until 10–50 msec after the onset of the electromyographic activity suggests that there is an approximately simultaneous onset of the fusimotor and the skeletomotor outflows from the spinal cord.
Sodium and rubidium fluxes in rat red blood cells
Authors: Beaugé L. A. , Ortíz Olga 
Published: December 2014

1. The Na content of rat red cells was found to be 4·40 m‐mole/l. cells. When incubated in K(Rb)‐free Na this value was doubled in 1 hr, whereas in K(Rb)‐free choline it was reduced to about 35% in the same period of time.2. In cells with elevated Na (13·70 m‐mole/l.) the activation curve of Rb influx by external Rb reached the same Vmax in sodium as in choline. The shape of the curve was sigmoid in the first case (Km about 1·05 m
M) and hyperbolic in the second (Km about 0·20 m
M).3. The activation curve of rubidium influx by internal sodium was linear at least up to 12 m‐mole/l. cells with a slope of 0·84. From this concentration it could increase more steeply, though the data is insufficient to assure it.4. In normal cells the efflux of Na in K(Rb)‐free Na Ringer was 5·64 m‐mole/l. cells. hr, and it was reduced to 4·32 m‐mole by 10−4
M ouabain. This was accompanied by a reduction of Na influx by 4·14 m‐mole, representing then a Na‐Na ouabain‐sensitive exchange mechanism.5. At a concentration of 5 m
M, external Rb increased Na efflux in 2·32 m‐mole/l. cells. hr above the K(Rb)‐free levels, and reduced Na influx by 2·13 m‐mole.6. It is proposed that the Na pump is able to operate even in the absence of external K(Rb), though at reduced rate and on a Na‐Na exchange basis (Na is the only monovalent cation in the bathing solution). External K(Rb) would have two actions: to increase the rate of shuttling of the carrier (catalytic effect) and to switch the Na‐Na to a Na‐K(Rb) exchange.7. These results raise a question of the real significance of the Na/K(Rb) ‘coupling’ ratio and the K‐free effect on the Na pump mechanism.
Changes in the physiology and fine structure of the taenia of the guinea‐pig caecum following transplantation into the anterior eye chamber
Authors: Burnstock G. , Gannon B. J. , Malmfors T. , Rogers D. C. 
Published: December 2014

1. The taenia of the guinea‐pig caecum has been used as a model to study the re‐establishment of autonomic innervation following transplantation into the anterior eye chamber. The ultrastructure, the histochemical localization of noradrenaline and acetylcholinesterase and the pharmacology of transmission to the taenia have been examined 1 day to 16 weeks following transplantation. Both ganglion‐free strips of the taenia and caecal wall segments including the underlying Auerbach's plexus were used.2. Caecal wall preparations: nerve fibres from intramural ganglion cells retracted during the first 2 days following transplantation, but reappeared in the muscle soon afterwards. Adrenergic nerves from the iris formed terminals about ganglion cells at about 2‐4 weeks. Both cholinergic excitatory and non‐adrenergic (‘purinergic’) inhibitory transmission to the muscle was re‐established by 2‐4 days following transplantation.3. Taenia strip preparations: both adrenergic and cholinergic nerve fibres were demonstrated histochemically in muscle bundles by 2‐4 weeks. Non‐adrenergic inhibitory and cholinergic transmission was not re‐established until 2‐4 weeks following transplantation. There was an abnormally dense re‐innervation of the muscle by adrenergic nerve fibres by about 8 weeks which is compared with the innervation of aganglionic bowel in Hirschsprung's disease.4. The origin of non‐adrenergic inhibitory responses in the transplanted taenia is discussed and the results considered in relation to the re‐innervation of transplants of the vas deferens and of intestine during early development.
Excitation—contraction coupling in frog ventricle: evidence from voltage clamp studies
Authors: Morad M. , Orkand R. K. 
Published: December 2014

1. Membrane potential, tension and membrane current were simultaneously recorded from frog ventricular strips in a modified sucrose‐gap which enabled control of membrane potential by voltage clamp.2. Shortening the frog ventricular action potential by repolarizing the membrane to the resting potential terminates contraction.3. Depolarization to the level of the normal action potential plateau for longer than about 80–100 msec (up to 30 sec) produces and maintains tension for the duration of the depolarization.4. Depolarizations less than about 80 msec in duration generate no tension but can facilitate the tension response to subsequent depolarizations. The facilitating effect of a short depolarizing pulse persists for no longer than 0·5 sec.5. The mechanical threshold is about −50 mV; the relation between membrane potential and tension is fairly linear from about +5 to +80 mV.6. Variation of holding potential, below the mechanical threshold, has no effect on the tension—voltage relation. The absolute membrane potential rather than pulse amplitude determines the developed tension.7. Increasing external calcium increases the slope of the voltage—tension relation.8. Contraction of the frog ventricle is directly controlled by the electrical activity of the surface membrane.