bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of picrotoxin and strychnine on rabbit retinal ganglion cells: changes in centre surround receptive fields.
Authors: Caldwell J H , Daw N W
Published: December 2014

1. The effects of picrotoxin and strychnine on the centre surround types of ganglion cell (X, Y, sluggish sustained and sluggish transient with on or off centres, and colour coded) were studied in the rabbit retina. 2. Picrotoxin changed the centre surround balance in favour of the centre for Y cells and sluggish transient cells but not for X cells or sluggish sustained cells. 3. Inhibition by a moving radial grating was abolished by picrotoxin for off centre Y cells, but not for on centre Y cells. 4. Picrotoxin abolished the surround response for six on centre sustained cells. These were hybrid cells with conduction velocities and receptive field properties characteristic of more than one of the X, Y and sluggish categories. The surround was not abolished by picrotoxin for any of the cells which fell in the standard X, Y and sluggish categories. 5. Strychnine did not affect the centre surround balance substantially in any of the cells tested. Strychnine did effect the transients: in general strychnine shortened or abolished them, while picrotoxin made them larger.
Plasma adrenaline, noradrenaline and dopamine in man and different animal species
Authors: Bühler H. U. , Prada M. Da , Haefely W. , Picotti G. B.
Published: December 2014

1. The catecholamines adrenaline (A), noradrenaline (NA) and dopamine (DA) were determined in plasma samples of man and various animal species using a highly sensitive radioenzymatic method.

2. Basal values were determined under conditions producing virtually no physical or psychic stress in blood obtained through acutely inserted venous catheters in human volunteers, rabbits and cows, through chronic indwelling catheters in cats and rats, and by cubital venipuncture in trained dogs.

3. Basal values (pg/ml.) for A, NA, and DA were respectively 64, 203 and 98 in man, 73, 609 and 276 in cats, 166, 392 and 216 in rabbits, 56, 152 and 91 in cows, 204, 376 and 173 in dogs, and 175, 509, and 84 in SPF rats. The NA concentrations were always higher than those of A and DA.

4. Gentle handling of rats for 30 sec greatly increased the levels of all catecholamines, especially of A. Even more marked rises were observed during and up to 5 min after restraint stress.

5. Blood from the trunk of decapitated rats contained about 20 times more A and 3‐4 times more DA and NA than venous blood from catheters in the absence of handling.

6. Basal values of plasma catecholamines in small animals can only be obtained through indwelling catheters and in the absence of handling. Most of the previously reported values are too high and are experimental artifacts.
Effects of diethylstilboestrol and ovarian steroids on the contractile responses and calcium movements in rat uterine smooth muscle.
Authors: Batra S , Bengtsson B
Published: December 2014

1. The synthetic oestrogen diethylstilboestrol had a potent inhibitory effect on the mechanical responses of the rat uterus. The spontaneous contractions were reduced in amplitude by 2 microgram and were completely abolished by 20 microgram diethylstilboestrol. The amplitude of contractions induced by acetylcholine (ACh) was also considerably reduced in the presence of 20 microgram of the compound. 2. Oestradiol (oestradiol‐17 beta) had a weaker, and progesterone a negligible, effect on the spontaneous contractions. 3. In the depolarized (induced by high potassium) uterus, the log concentration response curve for contraction induced by Ca was sigmoidal and reached its maximum at about 1 mM‐Ca. These responses to Ca were greatly depressed by oestradiol and progesterone and were again completely abolished by diethylstilboestrol. All three compounds were also able to induce a relatively rapid relaxation in preparations contracted by Ca. 4. Inhibition of the ACh contraction in the depolarized uterus by diethylstilboestrol, oestradiol and progesterone had the characteristic of blocking the second, and relatively slow, phase of the contraction without influencing the first rapid response. A similar pattern of inhibition was observed in the presence of D‐600 or EGTA. 5. The lanthanum method gave only an approximate measure of cellular Ca in the rat uterus, since La failed to block 45Ca efflux and was unable effectively to displace extracellular 45Ca. 6. Diethylstilboestrol reduced the influx of 45Ca both in normal and depolarizing media but did not affect 45Ca efflux. 7. These results indicate that oestrogens and progesterone are able to decrease Ca entry into the uterine cells, which probably accounts for their inhibitory effect on the contractile activity. The mechanism by which these agents induce relaxation of a contracted uterus also seems to depend on the inhibition of Ca influx.
Properties of twitch motor units in snake costocutaneous muscle
Authors: Hammond G. R. , Ridge R. M. A. P.
Published: December 2014

1. Single motor units of twitch muscle fibres were studied in isolated nerve—muscle preparations of m. costocutanei inferiores from grass and garter snakes. Preparations were superfused with Ringer solution at a controlled temperature of 22 °C.

2. The peak and time‐to‐peak tension (contraction time) were measured for isometric twitches of forty‐seven whole muscles and 83 motor units. The sample of motor units was drawn from an estimated total population of 213‐355 twitch units. Peak tetanic tensions were also measured. The measurements were made at muscle lengths at which the twitch tension was maximal, and this length was not always the same for whole muscle and unit twitches. In fifty‐nine cases 1 and in twelve cases 2 motor units were isolated from each muscle.

3. Whole muscle contraction times ranged from 22‐61 msec (mean ±
S.D. = 40·3 ± 9·8 msec) and those for units from 18‐92 msec (mean ±
S.D. = 46·9 ± 15·9 msec). The wide range for whole muscles is discussed.

4. The percentage of the whole muscle tetanic tension contributed by each unit (unit size) was calculated. Contraction time was inversely related to unit size.

5. Twitch—tetanus ratios were calculated and found not to be related to unit contraction time.

6. The conduction velocities of axons innervating 23 motor units were calculated from latency measurements at two points along the length of the nerve. They ranged from 1·9 to 10·4 m/sec. Axon conduction velocity was inversely related to unit contraction time, and directly related to unit size.
Post‐tetanic potentiation of twitch motor units in snake costocutaneous muscle.
Authors: Hammond G R , Ridge R M
Published: December 2014

1. Isometric twitch responses of single motor units in snake costocutaneous muscle have been recorded before and after conditioning tetanic stimulation. 2. Most units showed post‐tetanic potentiation of twitch tension, associated with increased maximal rate of rise of twitch tension, and in some cases also associated with prolongation of twitch contraction time. A few units showed a short phase of actual depression of the post‐tetanic twich responses, followed by potentiation. 3. The time course and magnitude of post‐tetanic changes of twitch tension and maximal rate of rise of tension could be described by the sum of three processes which are assumed to be maximal close to the end of the conditioning tetanus: (i) a rapidly declining potentiation (called here early potentiation, which lasted less than 2 sec) which may have a purely mechanical origin; (ii) a much slower‐declining potentiation (called here prolonged potentiation, which lasted up to 15 min); and (iii) a process which lasted up to 60 sec during which twitch potentiation was reduced. The latter process (called here depressed potentiation) was usually apparent as a marked trough in the plots of twitch amplitude versus time after the conditioning tetanus, and occassionally was evident as an actual transient depression of twitch amplitude after the tetanus compared with that before. 4. The effects of the prolonged potentiation and the depressed potentiation on the maximal effect of each process close to the end of the tetanus were extracted by fitting single exponential equations to different portions of the data, using a computer program. 5. Twitch potentiation associated with increased maximal rate of rise of tension seemed to be a separate phenomenon to that associated with prolongation of contraction time, seen when conditioning tetani of higher frequency and numbers of stimuli were employed. The depressed potentiation of twitch tension tended to be partly masked in cases where contraction time was prolonged, but this did not affect the depressed potentiation of maximal rate of rise of tension. 6. The post‐tetanic potentiation shown by a unit was related to the contraction time of the unit, in addition to the well known relationship to the initial twitch‐tetanus ratio. The depressed potentiation may correlat more closely with the initial twitch‐tetanus ratio than with the unit contraction time. 7. The magnitude of maximal depressed potentiation shown by a unit may be directly correlated to that of maximal prolonged potentiation. 8. The time constant of decay for prolonged potentiation of twitch tension tended to be related inversely to unit contraction time and directly to unit size and the maximal value of prolonged potentiation oftwitch tension. The time constant of decay for prolonged potentiation of maximal rate of rise of tension tended to be related to unit size and initial twitch‐tetanus ratio, and the time constant of decay for depressed potentiation of rate of rise of tension tended to be related to unit size. 9...
Nucleoside transport in sheep erythrocytes: genetically controlled transport variation and its influence on erythrocyte ATP concentrations.
Authors: Young J D
Published: December 2014

1. The permeability of sheep erythrocytes to purine and pyrimidine nucleosides was investigated. Erythrocytes from most sheep (nucleoside‐impermeable) were almost completely impermeable to 5 mM inosine whereas cells from approximately 5% of the animals studied (nucleoside‐permeable) showed a rapid inosine uptake. Cells from both types of animal were permeable to 5 mM adenosine, although transport was slower in nucleoside‐impermeable erythrocytes. 2. Two distinct nucleoside transport routes were present in nucleoside‐permeable erythrocytes; a high affinity (apparent Km congruent to 0.2 mM) facilitated diffusion system which transported both purine and pyrimidine nucleosides, and a non‐saturable uptake route selective for adenosine. The high affinity system was the major route of adenosine transport at physiological concentrations. 3. Transport by the high affinity system was completely inhibited by micromolar concentrations of dipyridamole and nitrobenzylthioinosine. Dipyridamole had no effect on the non‐saturable component of adenosine uptake. 4. The transport differences between nucleoside‐permeable and impermeable erythrocytes were due to the absence of the high affinity system from nucleoside‐impermeable cells. 5. Nucleoside‐permeable cells had a higher intracellular ATP concentration than nucleoside‐impermeable erythrocytes, suggesting that the high affinity transport system participates in the energy metabolism of the cell.
Liquid‐sensitive laryngeal receptors in the developing sheep, cat and monkey.
Authors: Harding R , Johnson P , McClelland M E
Published: December 2014

1. Action potentials were recorded from single afferent units of the superior laryngeal nerves in neonatal and adult sheep, cats and monkeys when liquids were passed over the laryngeal mucosa. 2. Two types of mucosal receptors, sensitive to water but not to isotonic saline, were found in each species from birth. The most common type of unit responded after a short latency (less than 1 sec), discharged maximally in the first 1‐3 sec and became inactive when the stimulus was withdrawn. The other type responded only after several seconds, the discharges gradually increasing in frequency and continuing after removal of the stimulus. 3. Reproducible responses were elicited by tactile stimulation of the laryngeal mucosa over the receptive field of each of the long‐latency units. Fewer than 50% of the short‐latency units were excited, the remainder responding only unreproducibly to firm pressure. 4. Short‐latency, but not long‐latency, units responded to milks, gastric contents, saliva and isotonic solutions of sugars. 5. The responses of long‐latency units to water were often modified by, but rarely dependent on, reflexly evoked activity in laryngeal muscles. 6. The conduction velocities of afferent fibres of water sensitive units ranged from 22 to 49 m/sec, and differed little from those of water‐insensitive laryngeal mechanoreceptors. 7. Histological examination of the laryngeal mucosa showed that taste buds were present in lambs from birth whereas they developed post‐natally in kittens and monkeys. The evidence suggests that taste buds were not associated with water‐sensitive units.
A time‐resolved X‐ray diffraction study of muscle during twitch.
Authors: Matsubara I , Yagi N
Published: December 2014

1. A position sensitive X‐ray counter was connected to a data‐collection system which registered the outputs of the counter as a function of time. This enabled us to study time‐dependent changes in the intensities of the equatorial reflexions from frog sartorius muscle during an isometric twitch. 2. The intensity ratio of the 1.0 and 1.1 equatorial reflexions (I1,0/I1,1) decreased during a twitch. The time at which the intensity ratio started to decrease coinsided approximately with the onset of tension development. No detectable change in the intensity ratio occurred during the latency relaxation. 3. The intensity ratio reached a minimum level approximately 90 msec before the peak of tension, and stayed at that level until the peak tension. 4. The intensity ratio returned to the 'resting' value 0.7‐‐1.1 sec after the twitch tension had fallen to zero. 5. The observed decrease in the intensity ratio was interpreted as being caused by radial movements of the myosin projections from the vicinity of thick filaments to that of thin filaments. This leads us to conclude that, early in the rising phase of twitch tension, the number of myosin projections in the vicinity of thin filaments reaches the value obtained during a maximum isometric tetanus.
Blocking effects of barium and hydrogen ions on the potassium current during anomalous rectification in the starfish egg.
Authors: Hagiwara S , Miyazaki S , Moody W , Patlak J
Published: December 2014

1. The blocking effects of Ba+ and H+ on the inward K current during anomalous rectification of the giant egg membrane of the starfish, Mediaster aequalis, were studied using voltage clamp techniques. 2. External Ba2+ at a low concentration (10‐‐100 micron) suppresses the inward K current; the extent of suppression, expressed as the ratio of currents with and without Ba2+, can be described by a conventional bimolecular adsorption isotherm, K/(K + [Ba2+]o), K being an apparent dissociation constant. 3. The dissociation constant, K, decreases as the membrane potential V becomes more negative and can be expressed by K(V) = K(0) exp (zmuFV/RT), where K(0) is the K at V = 0, z is the charge of the blocking ion, and mu is a parameter for the membrane potential dependence of Ba2+ blockage. The value of mu ranges between 0.64 and 0.68. 4. Upon a sudden change in membrane potential the change in the blocking effect of Ba2+ follows first order kinetics; the forward rate constant is membrane‐potential‐dependent whereas the backward constant is potential‐independent. 5. The blocking effect of Ba2+ appears to be independent of the activation of K channels during anomalous rectification. 6. The blocking effect of Ba2+ depends on V alone, in contrast to the activation of the K channel during anomalous rectification which depends on V‐‐VK. 7. In these respects, the effect of Ba2+ is equivalent to the introduction of inactivation into the anomalous rectification. 8. SI2+ and Ca2+ show small but observable blocking effects only at much higher concentrations (about 10‐‐20 mM). 9. The inward K current is suppressed when the external pH is reduced below 6.0. The blocking effect of H+ shows no significant potential dependence. The concentration dependence suggests that three H+ ions simultaneously titrate the acidic groups of each channel (pK = 5.3‐‐5.4). 10. The implications of these results are discussed in terms of molecular models of the potassium channel of anomalous rectification and possible mechanisms of K channel inactivation.
Fever and survival: the role of serum iron.
Authors: Grieger T A , Kluger M J
Published: December 2014

1. The effects of bacterial infection and temperature on serum iron levels were investigated in the lizard Dipsosaurus dorsalis. 2. Changes in body temperature from normal (38 degrees C) to febrile (41 degrees C) did not alter serum iron levels. Injection with Aeromonas hydrophila led to a significant reduction in serum iron levels, comparable to that found in mammals. This reduction in serum iron level was independent of the lizard's body temperature. 3. When grown in vitro, A. hydrophila grew equally well at afebrile (38 degrees C) and febrile (41 degrees C) temperatures. When the iron levels of the growth medium were reduced, the bacterial growth was diminished at the febrile temperature but was not significantly affected at the afebrile temperature. 4. The addition of iron supplements to bacterially infected lizards led to an increase in the percent mortality. 5. These results indicate that one of the mechanisms behind the beneficial, or adaptive value of fever in D. dorsalis is the decrease in iron available to the pathogenic micro‐organisms.
Responses and pharmacological properties of preoptic/anterior hypothalamic neurones following medial forebrain bundle stimulation.
Authors: Perkins M N , Whitehead S A
Published: December 2014

1. The responses of neurones in the anterior hypothalamic and preoptic areas (POA/AHA) to stimulation of the medial forebrain bundle (MFB) have been studied in urethane anaesthetized female rats. Extracellular unit recordings have been made from 150 neurones which were responsive to a single stimulus applied to the MFB at the level of the mammillary nucleus. 2. Forty‐five per cent of these cells were orthodromically activated with latencies ranging from 7.5 to 100 msec. However, the majority of cells responded with latencies of less than 40 msec. 3. Marked inhibition of spontaneous activity was observed in 41.5% of the units. Response latencies of up to 40 msec were observed in these cells, the inhibitory periods lasting up to 150 msec. 4. A small proportion of cells (13.5%) were antidromically activated and the average conduction velocity of these neurones in the POA/AHA with axons passing down to the mid‐brain was estimated to be 0.3 m sec‐1. It is suggested that they represent part of the descending MFB. 5. The experiments did not show any discrete topographical organization of cells in the POA/AHA which could be driven by MFB stimulation although the units tended to be located in more lateral rather than medial areas. 6. The responses to iontophoretically applied dopamine (DA) or noradrenaline (NA) was tested on sixty‐one cells. These amines suppressed the activity of the majority of both orthodromically activated and inhibited units; the remaining cells were unresponsive. 7. These results provide electrophysiological evidence for both a direct and indirect input of MFB fibres to cells in the POA/AHA and that these inputs can be either excitatory or inhibitory. The data also indicate that a small number of fibres in the descending MFB originate from cells in the POA/AHA. 8. The sensitivity of these units to NA and DA suggests an inhibitory aminergic input, although this evidence is as yet indirect. 9. These connexions of the MFB, with neurones in the POA/AHA may be part of the neural circuits important for extra‐hypothalamic modulation of gonadotrophin secretion.
Ouabain and regulation of cellular volume in freshly prepared slices of rabbit renal cortex.
Authors: Cooke K R
Published: December 2014

1. Changes in the water and ion contents of rabbit renal cortical slices, which had been bathed, immediately after slicing, in air‐equilibrated media at room temperature ('freshly prepared slices'), were followed during subsequent incubation at 25 degrees C in oxygenated media of the same composition as the initial bathing medium. 2. In comparison with conventional 'equilibrated' slices (slices incubated at 25 degrees C in oxygenated ordinary medium immediately after slicing) these 'freshly prepared' slices had increased tissue water, sodium and chloride contents and low tissue potassium contents. 3. Control freshly prepared slices incubated at 25 degrees C in oxygenated ordinary medium recovered within 4 min to the tissue water content that is usual for rabbit renal cortical slices incubated in oxygenated ordinary medium at 25 degrees C. Freshly prepared slices incubated at 25 degrees C in oxygenated media containing 1 mM‐oubain took 75 min or more to recover to this usual tissue water content. Thus the presence of 1 mM‐oubain in both bathing and incubation media produced a marked inhibition of the volume recovery observed when freshly prepared slices are incubated in oxygenated media at 25 degrees C. 4. Reduction of the ouabain concentration reduced the inhibition of cell volume recovery. 5. Replacement of medium glucose by 3‐O‐methylglucose did not inhibit cell volume recovery in the absence of ouabain. 6. The oxygen consumptions of slices that were bathed and incubated in 1 mM‐ouabain media were similar to those of slices initially bathed and incubated in ouabain‐free media and then incubated in ouabain media. Thus the effect of ouabain in inhibiting cell volume recovery was unlikely to be secondary to inhibition of cellular energy production. 7. The tissue potassium content of slices incubated aerobically in 1 or 10 mM ouabin fell to an apparently stable value of approximately 100 m‐mole/kg dry wt., which corresponds to a calculated concentration ratio of 10:1 across the cellular membrane, suggesting that some residual potassium uptake may still have been occurring. 8. These results indicate that in freshly prepared rabbit renal cortical slices ouabain‐sensitive mechanisms play a major role in cell volume recovery. They are not in accord with the postulate that renal cortical cells possess a separate ouabain‐insensitive mechanism regulating cell volume.
Mammary function and its control at the cessation of lactation in the goat.
Authors: Fleet I R , Peaker M
Published: December 2014

1. The changes in mammary function following cessation of milking during declining lactation have been studied in conscious goats. 2. No significant changes in the rate of milk secretion, mammary blood flow or metabolism occurred in the first 24 h after cessation of milking. After then, secretory rate, mammary blood flow, oxygen consumption, glucose uptake and acetate uptake decreased markedly over the next 3 days. Up to the time of maximum udder distension on day 3, there were no major changes in milk composition. 3. It was found that the rate of milk secretion declined when the calculated pressure within the alveoli became positive. 4. After 3 days, mammary volume and intramammary pressure decreased, and the composition of milk changed slowly to resemble that of extracellular fluid, i.e. [Na+], [Cl‐], [HCO3‐] and pH increased while [K+], [lactose] and [citrate] decreased. During this time [lactose] and [K+] were positively correlated, and [lactose] and [Na+], and [lactose] and [Cl‐] negatively correlated. 5. It is suggested that the changes in milk composition, the decreases in mammary volume and in intramammary pressure after day 3 are due to the loss of integrity of the mammary epithelium. 6. By about 7 weeks after the cessation of milking the udder volume was less than the empty udder volume before milking was stopped, indicating a loss of mammary tissue as well as the resorption of fluid. 7. When milking of an autotransplanted gland was stopped, while milking of the control gland in situ was continued, the rate of secretion in the transplant fell while that of the control did not change. 8. In goats milked normally but in which a volume of isosmotic lactose equal to the volume of milk removed at that milking was injected into the lumen of one gland at each milking, the rate of secretion of that gland, but not that of the other, decreased.
Branched afferent nerves supplying tooth‐pulp in the cat.
Authors: Lisney S J , Matthews B
Published: December 2014

1. Recordings have been made from nerve terminals in canine and third incisor teeth of cats. 2. Ninety‐three tooth‐pulp units in ten cats could be excited either by mechanical or electrical stimulation of adjacent mucous membrane or by electrical stimulation of the pulp of a nearby tooth. 3. Section of the trigeminal nerve centrally did not abolish these responses. 4. Results for twelve out of thirteen units tested with collision techniques indicated that the nerves were branched.
The role of the autonomic nervous system in the control of pancreatic endocrine responses to milk ingestion in the calf.
Authors: Bloom S R , Edwards A V , Hardy R N
Published: December 2014

1. Pancreatic endocrine responses to ingestion of milk have been investigated in conscious unweaned calves, 3‐5 weeks after birth. Passage of gastric content from abomasum to small intestine was prevented by means of a cannula placed in the duodenum adjacent to the pylorus and food was witheld for at least 22 h in order to deplete liver glycogen. 2. Under these conditions ingestion of milk was followed by a prompt rise in the concentrations of pancreatic glucagon, PP and gastrin in the arterial plasma but the usual rises in plasma glucose and insulin concentration were absent. 3. Evidence was obtained to show that absorption of glucose from the small intestine occurs sufficiently rapidly to account for the initial rise in plasma glucose concentration after feeding in normal animals. However, the rise in plasma glucagon concentration was sufficient to contribute to alimentary hyperglycaemia by promoting hepatic glycogenolysis in calves with abundant liver glycogen. 4. None of the neuroendocrine responses to ingestion of milk was affected by prior section of the splanchnic nerves whereas each was blocked by atropine (0.2 mg/kg), showing that all depend upon muscarinic, parasympathetic rather than sympathetic activity, in the absence of extraneous stress.
The effect of intravenous infusion of angiotensin II on drinking in the Australian marsupial Trichosurus vulpecula
Authors: Young C. E. , McDonald I. R.
Published: December 2014

1. When marsupial brush‐tailed possums were maintained on a normal fruit and vegetable diet with access to water ad libitum,
I.V. infusion of synthetic angiotensin II at rates of 0·035‐3·5 μg/kg. min caused short‐latency drinking in up to seven of eleven animals tested. These rates also had significant pressor effects.

2. There was a positive correlation between the rate of angiotensin infusion and the percentage of tested animals which responded by drinking, as well as the amount of water drunk by such animals. The amount drunk during a second infusion 1 hr later was reduced. There was a negative correlation between the rate of infusion and the latency to drinking.

3. Of six animals given access to both water and 1·8% sodium chloride solutions, five drank some saline during maintenance and control periods and all responded with short‐latency drinking of water to infusion of angiotensin II at 0·35 μg/kg. min.

4. Withdrawal of 10% of blood volume, known to stimulate renin production in the possum, caused an increase in water intake in only one of six possums.

5. Infusion of isoprenaline
I.V. at 20 μg/kg. min, which caused a profound fall in
B.P., had no effect on drinking by all six possums.

6. It is concluded that these marsupials share with eutherian mammals responsiveness to a dipsogenic action of angiotensin II, which appears to be inhibited by preceding ingestion of water and potentiated by preceding ingestion of hypertonic saline. The physiological significance of this effect is uncertain.
Maintenance of low sodium and high potassium levels in resting muscle cells.
Authors: Ling G N
Published: December 2014

1. Previous work has shown that a frog sartorius muscle consists of parallel cells running all the way from one end of the muscle to the other and that amputation of one end of the muscle is not followed by regeneration of a new cell membrane. If now only the cut end of the amputated muscle is exposed to a Ringer solution in which the solutes 42K and 22Na act as radioactive labels and the rest of the cell is suspended in air, we have what is described as an effectively membraneless open‐ended cell or EMOC preparation. In this case the only remaining anatomically intact plasma membrane and pumps are made nonfunctional by the removal of 'sources' for inward pumps and 'sinks' for outward pumps. 2. The healthy region of a frog sartorius muscle EMOC preparation continues to accumulate labelled K+ to a level higher than that in the Ringer solution and to exclude labelled Na+ to a level below that in the Ringer solution, much as a normal uncut muscle does in its normal environment. The differences were reduced by inclusion of ouabain in the medium. 3. The diffusion coefficient of Na+ in the normal muscle cytoplasm at 25 degrees C was measured using two methods. The average diffusion coefficient measured was 2.07 X 10(‐6) cm2/sec, roughly 1/6 that of the diffusion coefficient of Na+ in a 0.1 N‐NaCl solution. 4. The data obtained are discussed in terms of the association‐induction hypothesis. In this theory asymmetrical solute distribution, basically an expression of a non‐energy consuming metastable equilibrium state, is the result of specific combinations of two opposing mechanisms: adsorption which raises the level of the intracellular solute; and exclusion from cell water which tends to lower it.
A potential‐ and time‐dependent blockade of inward rectification in frog skeletal muscle fibres by barium and strontium ions.
Authors: Standen N B , Stanfield P R
Published: December 2014

1. A three‐electrode voltage clamp method was used to investigate the effects of Ba and Sr ions on the inwardly rectifying K conductance of resting frog sartorius muscle fibres. 2. When Ba2+ (0.01‐5 mM) was added to the control (115 mM‐K+) solution the inward currents recorded during hyperpolarizing voltage steps turned off exponentially with time as the blockade by Ba2+ developed. Outward currents showed no time‐dependence. 3. Ba2+ ions reduced both the instantaneous and the steady‐state values of currents recorded on hyperpolarization. The blockade was potential‐dependent, steady‐state currents being increasingly reduced with increasing hyperpolarization. 4. The concentration‐effect relation for the blockade of instantaneous currents by Ba2+ could be fitted assuming 1:1 binding of Ba2+ to a receptor, with the block being proportional to the number of Ba2+‐filled receptors. The apparent dissociation constant at the holding potential (‐5 mV) was 0.65 mM. Concentration‐effect relations were shifted along the concentration axis to lower concentrations by hyperpolarization. The apparent dissociation constant was reduced e‐fold for a 16.8 mV change in potential. 5. Increasing the [Ba]o increased the rate of onset of the blockade at a given potential. 6. The rate of onset of the blockade had a high temperature dependence (Q10 = 3.15 +/‐ 0.08). 7. When [K]o was doubled to 230 mM, under conditions where [K]i was also doubled, [Ba]o had to be raised approximately fourfold to produce the same degree and rate of onset of blockade. Similarly, when [K]o was decreased, the degree and rate of onset of blockade were increased for a given [Ba]o. 8. The blockade could be readily removed by removal of Ba2+ from the bathing solution. In addition the blockade which develops on hyperpolarization is removed exponentially on return to the holding potential. 9. The blockade which exists at the holding potential may be removed by a depolarizing prepulse. 10. Sr causes a similar potential‐dependent blockade to that by Ba2+, but is around 400 times less effective. 11. The results have been fitted with a model assuming that the permeability mechanism is an aqueous pore with a site which binds one Ba2+ ion or two K+ ions. The site must have affinity for Ba2+ and a low affinity for K+.
Type A atrial receptors in the cat: effects of changes in atrial volume and contractility.
Authors: Recordati G M
Published: December 2014

1. Action potentials were recorded from filaments of the right cervical vagus in anaesthetized, paralysed cats. Right atrial receptors with type A (twelve units) and Intermediate type (two units) patterns of spontaneous discharge were selected and their responses to changes in atrial volume were analysed. 2. Changes in atrial volume of similar magnitude were produced under four different conditions: a, innervated hearts; b, denervated hearts; c, depression of atrial muscle contractility induced after cardiac denervation and d, non‐beating hearts. 3. In innervated hearts the systolic discharge of each receptor showed a characteristic response to changes in atrial volume. Cardiac denervation and depression of atrial contractility markedly altered this response in terms of frequency of discharge threshold and 'sensitivity'. 4. During increments in atrial volume all the receptors but one assumed an Intermediate pattern of discharge. The diastolic firing rate was, however, higher for any given atrial pressure, in innervated hearts than under conditions b, c and d. 5. In innervated hearts the response of the receptors to atrial systole was characterized by a higher frequency of discharge and a lower threshold with respect to the responses of the same receptors to atrial filling. These differences were minimized at high atrial volumes and during depression of atrial contractility. 6. The results indicate that the responses of the receptors to atrial systole are mainly dependent upon the state of contraction of atrial muscle and that the differences between systolic and diastolic discharge are mainly due to the high dynamic component of the stretch during atrial contraction.
Influence of the autonomic nervous system on the release of vasoactive intestinal polypeptide from the porcine gastrointestinal tract.
Authors: Fahrenkrug J , Galbo H , Holst J J , Schaffalitzky de Muckadell O B
Published: December 2014

1. The release of vasoactive intestinal polypeptide from the gastrointestinal tract in response to stimulation of the vagus nerves, the splanchnic nerves and to intra‐arterial infusion of acetylcholine (ACh) was examined in pigs. 2. Stimulation of the vagus nerves caused an abrupt increase in the release of vasoactive intestinal polypeptide. The amount of the peptide released depended on the frequency at which the nerves were stimulated. Maximum release was obtained at 8 Hz. 3. Atropine and beta‐adrenergic blocking agents failed to diminish the vagally induced release of vasoactive intestinal polypeptide, while the response was completely blocked by hexamethonium and increased after alpha‐adrenergic blockade and after splanchnicotomy. 4. Intra‐arterial infusion of ACh closely imitated the response to vagal stimulation, but the release of vasoactive intestinal polypeptide induced by ACh was abolished by atropine. 5. Stimulation of the splanchnic nerves caused a decrease in the release of vasoactive intestinal polypeptide, an action which was annulled by alpha‐adrenergic blockade, but still present after the adrenal glands were isolated from the circulation. The inhibitory effect of splanchnic stimulation significantly diminished the vagally induced release of vasoactive intestinal polypeptide. 6. The results demonstrate a dual innervation with opposing effects on the neurones containing vasoactive intestinal polypeptides. The possible physiologic implication of this finding is discussed.
Extrajunctional acetylcholine sensitivity of inactive muscle fibres in the baboon during prolonged nerve pressure block.
Authors: Gilliatt R W , Westgaard R H , Williams I R
Published: December 2014

1. Nerve‐evoked muscular activity was abolished in the small hand muscles of the baboon for 1‐2 months by a 3 hr period of nerve compression from a pneumatic tourniquet inflated round the forearm. In the large diameter nerve fibres, this produced either a prolonged conduction block due to local myelin damage at the site of compression, or (in 10‐30% of the large fibres) Wallerian degeneration. 2. At varying intervals after nerve compression the extrajunctional acetylcholine (ACh)‐sensitivity of innervated but inactive muscle fibres in the fourth lumbrical muscle was measured. Observations were also made on lumbrical muscle fibres at similar intervals after surgical denervation. 3. The ACh sensitivity of nerve‐blocked muscle fibres started to develop later than in denervated muscle fibres (10 vs. 7 days) and remained at a lower level (40‐80 mV/nC, median ACh‐sensitivity) than that of denervated muscle fibres (200‐437 mV/nC) from 21 to 63 days after nerve block or denervation. 4. In stimulation experiments on four muscles, extrajunctional ACh‐sensitivity of both denervated and innervated but inactive fourth lumbrical muscle fibres was reduced by muscular activity. 5. In four animals mild compression was used in the lower limb to produce persistent nerve block without Wallerian degeneration. With one exception (in which some Wallerian degeneration had occurred) recording with a co‐axial needle from abductor hallucis showed no spontaneous fibrillation up to 28 days after compression, although the extrajunctional ACh‐sensitivity of the muscle fibres appeared to reach levels similar to those observed in the forelimb. All four muscles developed a slight increase in insertion activity after 1‐2 weeks. 6. It may be concluded that both muscular activity and some other neural influence, independent of muscular activity, are able to influence extrajunctional muscle properties in the baboon. The neural influence appears to be more effective in preventing spontaneous fibrillation than in preventing a rise in ACh sensitivity of the extrajunctional muscle membrane.
A transition temperature for acetylcholine channel conductance in chick myoballs.
Authors: Fischbach G D , Lass Y
Published: December 2014

1. The temperature dependence of ACh channel conductance (gamma) and channel open time (tau) was determined by analysing ACh induced membrane current fluctuations in voltage clamped chick myoballs. 2. gamma decreased from 25‐30 pmho at 37 degrees C to less than 5 phmo at 10 degrees C. An Arrhenius plot of gamma vs. temperature exhibited a clear break or 'transition temperature' at 20 degrees C. 3. tau increased from 2 msec at 37 degrees C to 16 msec at 10 degrees C. The Arrhenius plot of tau vs. temperature was linear. No transition temperature was detected. 4. Submicellar concentrations of the non‐ionic detergent, Triton X‐100 reversibly blocked ACh respnses. The effect was all‐or‐none at the molecular level. 5. These results are consistent with the possibility that the fluidity of membrane lipids in the ACh receptor micro‐environment may influence the degree to which the channel can open.
Regulation by patterned preganglionic neural activity of transmitter stores in a sympathetic ganglion.
Authors: Birks R I
Published: December 2014

1. The effect of patterned preganglionic stimulation on acetylcholine (ACh) stores was studied in the superior cervical ganglion of the cat. 2. Patterns of stimulation based on 0.5 and 1.0 s trains at frequencies from 10 to 80/s and intervals between trains of 2‐180 s increased ACh stores, over periods of 1‐3 h stimulation, to the same extent (30‐70%) as found earlier to result from continuous stimulation. 3. If the mean frequency of the overall pattern was greater than 5/s the increase in stores developed after termination of the stimulation. If the mean frequency was less than 5/s the increase developed progressively during stimulation and it was then maintained without accommodation over 7 h of stimulation. 4. The magnitude of the increase in ACh stores was linearly related to the frequency within the trains from 10 to 40/s, decreasing with further increase in frequency, and absent below 6‐7/s. 5. The ACh stores were increased by patterns of stimulation that mimicked discharging of preganglionic neurones driven by the central respiratory drive under hypercapnic or asphyxial stress; and were increased similarly in animals respired with hypercapnic or partially asphyxial gas mixtures when the preganglionic innervation was intact, but not when it was severed. 6. The variance between ACh stores of ganglia from different animals was reduced in animals held in a controlled environment for 1‐2 weeks before experimentation. 7. It is concluded that patterning of preganglionic inputs into high frequency trains is a code for the ongoing modulation of transmitter stores in a sympathetic ganglion. 8. The findings are discussed in relation to current knowledge of ganglionic transmission and to after‐hyperpolarization in mammalian unmyelinated nerve fibres.
Multiple innervation of normal and re‐innervated parasympathetic neurones in the frog cardiac ganglion.
Authors: Dennis M J , Sargent P B
Published: December 2014

1. Multiple innervation of parasympathetic neurones was examined in normal and re‐innervated frog cardiac ganglia. The number of synaptic inputs impinging upon individual ganglion cells was determined by recording intracellularly and stimulating the vagosympathetic nerves. 2. In unoperated cardiac ganglia most neurones (93%) received a large, suprathreshold synaptic input. Some ganglion cells received additional, small synaptic inputs. Roughly equal numbers of cells encountered were singly and doubly innervated, and only 8% received more than two inputs. 3. Re‐innervation of cardiac ganglion cells began three weeks after bilateral crush of the vagosympathetic nerves. By 7 weeks more than 90% of the ganglion cells were re‐innervated. At this stage the pattern of multiple innervation was significantly different than normal: doubly innervated neurones outnumbered singly innervated ones, and 31% of the cells encountered received more than two inputs. This pattern was stable for at least a year. 4. These results indicate that polyneuronal innervation of cardiac ganglion cells is more widespread after re‐innervation than it is normally and, furthermore, that synapse elimination does not occur during re‐innervation of these cells.
Enhancement of mechanical performance by stretch during tetanic contractions of vertebrate skeletal muscle fibres.
Authors: Edman K A , Elzinga G , Noble M I
Published: December 2014

1. Single fibres from the semitendinosus muscle of Rana temporaria were stretched during fused tetanic contractions and tension and sarcomere length (laser diffraction) responses were recorded. 2. Stretch of the fibres caused proportional increases in length of the sarcomeres. The force increased to a plateau value which was maintained during stretch or increased to a plateau value which was maintained during stretch or increased slightly. 3. The plateau value of force during stretch was dependent upon the velocity of stretch, was independent of the amplitude of stretch and was not proportional to overlap of thick and thin filaments. 4. There was enhancement of force after stretch compared with that produced at the same sarcomere length during isometric tetani. This force enhancement was independent of the velocity at which the stretch had been applied. 5. At sarcomere lengths between 1.9 and 2.3 micrometer, the force enhancement after stretch declayed rapidly, was independent of amplitude of stretch above approximately 25 nm per sarcomere not associated with a shift of the force‐‐velocity curve. At sarcomere lengths above 2.3 micrometer the force enhancement after stretch decayed very slowly and was still present after 4 sec in long tetani. 6. At sarcomere lengths above 2.3 micrometer, force enhancement after stretch increased with amplitude of stretch and increased for any given stretch amplitude with sarcomere length. The force recorded after stretch was thus not proportional to overlap of thick and thin filaments. 7. At sarcomere lengths above 2.3 micrometer, the force enhancement after stretch was associated with a shift towards higher force value of the force‐‐velocity curve. The velocity of shortening and zero load (V max) derived by hyperbolic extrapolation of the force‐‐velocity curve was not affected. 8. Tension enhancement during and after stretch has a stabilizing effect in preventing dispersion of sarcomere length, particularly on the descending limb of the length‐‐tension curve.
Quantal analysis of transmitter release at an inhibitory synapse in the central nervous system of the leech.
Authors: Nicholls J , Wallace B G
Published: December 2014

The quantal nature of transmitter release has been analysed at central inhibitory synapses in the leech nervous system between an interneurone (HN) and a motoneurone (HE) that regulate the heartbeat. 1. Ganglia were bathed in leech Ringer fluid containing 20 mM‐Mg and 1.8 mM‐Ca and the membrane of the presynaptic HN interneurone was hyperpolarized by current injection. Under these conditions successive inhibitory potentials in the HE motoneurone, evoked by impulses in the HN interneurone, showed striking fluctuations in amplitude. 2. Assuming a Poisson distribution of the i.p.s.p.s and estimating the number of failures from the amplitude histograms of the observed responses, the mean size of the quantal unit was estimated as 0.25 +/‐ 0.015 mV (S.E. of mean, n = 26). When m, the mean number of quanta released per trial, was varied by changing the membrane potential of the presynaptic HN cell (Nicholls & Wallace, 1978), the experimentally observed amplitude distributions could be predicted by the Poisson theory. 3. An independent estimate of the unit size was obtained by noise analysis. A long subthreshold depolarizing pulse applied to the presynaptic HN interneurone evoked a sustained hyperpolarization of the HE motoneurone, apparently caused by an increase in the rate of on‐going release of quanta by the HN cell terminals. From the mean change in membrane potential and the increase in variance, the size of the unit was calculated as 0.21 +/‐ 0.039 mV (S.E. of mean, n = 11). For ten pairs of cells an estimate of unit amplitude was made both from the Poisson analysis and the analysis of variance, again with good agreement. For these cells the estimated unit sizes were 0.24 +/‐ 0.023 mV (S.E. of mean, n = 10) from the failures and 0.21 +/‐ 0.043 m V (S.E. of mean, n = 10) from the noise. 4. A similar analysis was made of the inhibitory synaptic potentials evoked in one HN interneurone by stimulation of its contralateral homologue. Transmission again appeared to be qualtal; the mean unit amplitude from Poisson analysis was 0.31 +/‐ 0.022 mV (S.E. of mean, n = 19) and from the noise 0.29 +/‐ 0.027 mV (S.E. of mean, n = 3). 5. We conclude that transmitter is released from the terminals of the HN interneurone in quantal units that evoke miniature i.p.s.p.s of about 0.25 mV in the post‐synaptic cells. Furthermore, modulation of transmission proudced by variation in the presynaptic resting potential and during presynaptic inhibition results from changes in the mean number of quanta released by each impulse.