bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of a facilitating calcium current in pace‐maker neurones of the snail, Helix pomatia.
Authors: Heyer C B , Lux H D
Published: December 2014

1. Simultaneous measurements of local voltage clamp currents from patches of soma membrane and K activity at the soma surface were used to analyse the time and voltage dependence of the slow inward current in bursting pace‐maker neurones of the snail (Helix pomatia). 2. At low levels of depolarization (less than or equal to mV) a net inward current is recorded simultaneously with an efflux of K ions from the cell. 3. With larger depolarizations (20‐170 mV from holding potential of ‐50 mV) the deficit in net outward charge transfer compared with K efflux and the appearance of inward‐going tail currents following repolarization, reveal a persistent inward‐going current also under these conditions. This inward current is carried primarily by Ca ions, as demonstrated by its voltage dependence (a minimum at about + 115 mV) and its disappearance in Co‐Ringer. It is identified with the slow inward Ca current Iin slow (Eckert & Lux, 1976). 4. The inward current predicted from comparisons of current trajectories reaches a maximum at 15‐20 msec (for depolarizations from ‐50 to 0 mV) and gradually declines with sustained depolarization. 5. Partial inactivation is removed by repolarization to ‐50 mV and the Ca dependent deficit is greater in the sum of repeated voltage clamp pulses than during sustained depolarization. It is largest for pulses of 25‐100 msec duration, decreasing as pulse duration increases. 6. Responses to repeated activation with 100 msec pulses with different repolarization intervals reveal a minimum Iin slow at short intervals (e.g. 20 msec) due to failure to remove partial inactivation. At intermediate intervals (e.g. 200‐400 msec) Iin slow shows facilitation. This is revealed in calculations of the net charge transfer and current deficits and is also shown in the tail currents following repolarization. The deficit increases progressively with repetitive stimulation. With longer intervals (e.g. 800‐1000 msec) defacilitation during repeated stimulation after the first two pulses is revealed in calculations of deficits, current trajectories and in the tail currents. 7. Although facilitation depends on duration of repolarization between pulses, increasing intermediate hyperpolarizations from the holding potential of ‐50 mV are usually ineffective in increasing Iin slow. Strong preceding hyperpolarization can even decrease the magnitude of Iin slow and prevent its facilitation with repetitive stimulation,whereas preceding depolarizing pulses can increase Iin slow without preventing its facilitation with repetitive stimulation. 8. The properties of Iin slow are contrasted with previously described membrane conductances and compared with properties attributed to Ca fluxes in other systems.
The viscosity of mammalian nerve axoplasm measured by electron spin resonance.
Authors: Haak R A , Kleinhans F W , Ochs S
Published: December 2014

1. The microviscosity of the axoplasm of can sciatic nerve was determined by an in vitro electron spin resonance (e.s.r.) method using the spin label tempone. To identify the spin label signal as one arising only from within the axoplasm, Ni2+ was used as a line broadening agent. In one series of experiments in nerves with sheath intact the Ni2+ ion was shown to eliminate the tempone signal arising from the surface water, and in another series of experiments, with the sheath slit, to eliminate the signal from the extracellular space as well. 2. A microviscosity of less than 5 centipoise (cP), i.e. 5x that of water, was determined for the axoplasm. Changes in the viscosity of the nerve axoplasm as a function of temperature over a range of 38 degrees down to 2 degrees C were seen to follow closely the viscosity change found for a water solution. 3. The microviscosity of nerve axoplasm and its change with temperature were related to axoplasmic transport of material in nerve fibres. The results were used to exclude a large increase in viscosity at low temperatures as the cause for the cold‐block of fast axoplasmic transport.
Manganese‐dependent propagated action potentials and their depression by electrical stimulation in guinea‐pig myocardium perfused by sodium‐free media.
Authors: Ochi R
Published: December 2014

1. Propagated action potentials were recorded in right ventricular papillary muscles from guinea‐pig heart while exposed to Na‐free, Ca‐free and Mg‐free solutions containing Mn. 2. When Na was totally replaced by 95 mM‐Mn the overshoot was about 45 mV while the resting potential was about ‐90mV. 3. The overshoot of action potentials was increased by about 20‐30 mV per tenfold increase of Mn concentration over the range of 2‐50 mM. 4. Similar increases of overshoots with increasing of Mn concentration also occurred in the presence of 0‐6 mM‐Ca. Increasing of Ca from 5 to 20 mM had little influence on the overshoot but shortened the duration of the Mn‐dependent action potential in the presence of 5 mM‐MN. 5 Mn‐dependent action potentials were not depressed by 3 X 10(5) M tetrodotoxin but by La. 6. These results suggest that Mn passes through the slow inward current channel to generate the action potential seen under the Na‐free condition. 7. The overshoot and duration of the Mn‐dependent action potential decreased with stimulation. At stimulus frequencies (Hz) of 0‐5, 0‐2, 0‐1, 0‐017 and 0‐0033 the overshoot of action potential in 5 mM‐Mn Tyrode decreased by 0‐5‐1 mV per an action potential. This depression of the action potential is explained by assuming intracellular accumulation of Mn.
Afferent sympathetic nerve fibres with aortic endings.
Authors: Malliani A , Pagani M
Published: December 2014

1. We recorded the electrical impulse activity of thirty‐five single afferent fibres with aortic endings isolated from the third to the sixth left thoracic sympathetic rami communicantes of anaesthetized cats. The endings of each fibre were localized by mechanical probing of the opened aorta at the end of each experiment. 2. Twenty‐four fibres had a single aortic receptive field. Eleven fibres had several and distinct receptive fields (from two to four): they were usually located in nearby aortic areas or, in addition, in other proximal portions of the arterial tree or in the adjacent pleura and connective tissue. 3. Twenty‐nine fibres had conduction velocities ranging between 5 and 27 m/sec (Group Adelta), while six fibres had conduction velocities between 0‐2 and 1‐2m/sec (Group C). 4. The spontaneous impulse activity was in phase with the aortic pressure pulse and consisted of not more than one impulse per pressure pulse. It was increased during increases in aortic pressure and, conversely, decreased during decreases in aortic pressure. In vivo and post mortem studies showed that these mechanoreceptors had an impulse activity which rapidly adapted during sustained stimuli. They thus seem to signal pulsatile aortic stretch. 5. These aortic sympathetic afferents are likely to be part of a nervous pathway through which pressor reflexes, exhibiting positive feed‐back characteristics, can elicited.
Birefringence signals from surface and t‐system membranes of frog single muscle fibres.
Authors: Baylor S M , Oetliker H
Published: December 2014

1. When the tonicity of Ringer is increased above 2‐5 times normal and a single fibre stimulated externally, the large, early birefringence signal preceding twitch tension (Baylor & Oetliker, 1975, 1977 a,b) is sufficiently reduced and delayed so as to reveal a small but distinct signal ('1st component") preceding it. For an average‐sized fibre, the deltaI/I of the 1st component was (minus) 1 to 2 x 10‐5. 2. The time course of the 1st component superimposed with the surface action potential simultaneously recorded by an internal micro‐electrode. The polarity of the 1st component reversed with compensation. 3. From these characteristics, the 1st component is thought to arise from a small change in optical retardation of the surface membrane due to the action potential. 4. When a fibre was impaled with two micro‐electrodes, retardation changes accompanying small hyperpolarizing and depolarizing current steps were detected. In some cases the polarity of the observed signal was opposite in sign to that expected for a retardation change only from the surface membrane. 5. Because the anatomical orientation of the T‐system appears to be primarily transverse rather than longitudinal, these signals of opposite polarity are probably, on balance, due to retardation changes from the membranes of the T‐system. 6. The possible origin of the large birefringence signal preceding contraction is discussed.
The influence of activity on muscle size and protein turnover.
Authors: Goldspink D F
Published: December 2014

1. The effects of the loss of normal activity can be studied in muscles held in a shortened position by immobilizing the ankle in a plaster cast. Since the innervation remains intact with this procedure, removal of the restraining case allows normal activity to be restored. The soleus and plantaris muscles grew as a function of time after the return of normal activity and these changes in tissue size are explained by changes in the average rates of protein synthesis and protein break‐down as measured by sensitive in vitro techniques. Activity stimulates protein synthesis and inhibits protein break‐down of the soleus muscle, thus enabling the tissue to accumulate protein. Blockage of de novo synthesis of RNA, but not DNA, severely restricted the normal, rapid enhancement of protein synthesis after thr return of activity. 2. The return of isotonic activity to the extensor digitorum longus muscle after immobilization in a lengthened position failed to fully compensate for the loss of the growth‐promoting influence of stretch and the tissue gradually returned to the size of the control muscle. During the recovery process the higher rate of protein turnover and RNA concentrations of the immobilized muscle returned to the lower values of the control.
The influence of the lymph node on the protein concentration of efferent lymph leaving the node.
Authors: Quin J W , Shannon A D
Published: December 2014

1. Experiments have been performed in sheep to determine the contribution of lymph formed within a lymph node to the total protein output in lymph leaving the node. 2. The lymphatic duct leaving the popliteal lymph node was cannulated and the protein and lymphocyte output in efferent lymph determined. The afferent lymph flow to the popliteal node was then diverted and lymph formed only within the lymph node collected from the efferent cannula. It appeared from the results that the popliteal lymph node forms lymph at the rate of approximately 1 ml. per hour and may contribute 30‐50% of the protein output observed in efferent lymph. 3. The importance of lymph formation within the lymph node varied between nodes found in different regions of the body. This was due in part to the different protein concentrations in the afferent lymph to the different nodes. 4. A positive correlation was found between the protein and lymphocyte concentrations in efferent lymph from the popliteal lymph node in seven out of eleven sheep and in lymph formed within the popliteal lymph node in two out of three sheep. It is suggested that this relationship may be due to an increased transfer of plasma proteins through the post‐capillary venules in the lymph node accompanying the continual traffic of lymphocytes across the wall of these vessels. The results indicated that the protein transfer across the post‐capillary venules was not an indiscriminate transfer of plasma per se but a selective transport from the blood plasma compartment based on molecular size.
The effect of ambient temperature upon the secretion of thyroxine in the young pig.
Authors: Evans S E , Ingram D L
Published: December 2014

1. Fluctuations in the rate of secretion and metabolism of thyroxine in the pig were observed whilst the ambient temperature was reduced from 32 to 8 degrees C. The quantity of food supplied was either maintained constant or doubled when the animals were exposed to the lower temperature. 2. It was found that the rate of disappearance of [125I]thyroxine did not change when the animal was exposed to the cold, unless the animal's food intake was altered. 3. The secretion of thyroxine increased temporarily after exposure to the cold. This was shown by a rise in the concentration of thyroxine in the plasma and a simultaneously increased loss of 131I from the thyroid gland. The increase in secretion of thyroxine was not maintained throughout the exposure to cold when the food intake of the animal was kept constant.
The production of denervation‐like changes in rat muscle by colchicine, without interference with axonal transport or muscle activity.
Authors: Cangiano A , Fried J A
Published: December 2014

1. Rat extensor digitorum longus (EDL) muscles were examined after colchicine treatment of the sciatic nerve. Colchicine was applied in one of two ways: (i) a single sub‐epineural injection; (ii) a chronically implanted silicone cuff. 2. After the sub‐epineural injection, the entire membrane of muscle fibres became sensitive to iontophoretically applied acetylcholine and the muscle action potentials became resistant to tetrodotoxin. However, the majority of these fibres were found to be normally innervated. 3. These effects were not restricted to the EDL muscle of the colchicine injected side but were also found in the EDL muscle of the contralateral side, indicating that the action of colchicine was systemic. 4. In the treated sciatic nerve there was a partial block of axonal transport of 3H‐labelled proteins, which correlated with a partial paralysis of the ipsilateral leg. However, axoplasmic transport was found to be normal in the contralateral sciatic nerve and the contralateral limb was not paralysed despite the supersensitivity of the investigated muscle on that side. 5. When colchicine was applied with a silicone cuff, denervation‐like changes were confined to the ipsilateral EDL muscle. However, impulse conduction block at the level of the cuff was usually observed. 6. It is concluded that (i) colchicine can produce denervation‐like changes in normally active muscle without blocking axoplasmic transport, through an action probably exerted directly on the muscle membrane, and (ii) that colchicine‐cuff experiments failed to provide unambiguous evidence in support of the existence of neurotrophic influences on the muscle membrane.
The release of vasopressin by nicotine: further studies on its site of action.
Authors: Castro de Souza E , Rocha E Silva M
Published: December 2014

1. In cats anaesthetized with chloralose the release of vasopressin in response to nicotine injections was examined. This release was measured by assaying the hormone in samples of venous blood. 2. Nicotine injections were given by three different routes, namely intravertebral, intracarotid and intravenous. The first two represent close arterial routes to the medulla and to the hypothalamus, respectively, the effects of which could be compared to those following intravenous, i.e. systemic, administration. 3. Nicotine was found to increase vasopressin secretion by all three routes of administration. The potency of intracarotid injections was found to be no greater than that of intravenous injections, in sharp contrast to intravertebral injections, which were 4‐5 times more potent. 4. In terms of vascular effects, intracarotid and intravenous injections of nicotine were found to increase blood pressure, whereas intravertebral injections of low doses of nicotine were always followed by a fall in blood pressure. Higher doses of intravertebral nicotine produce mixed results, pressor or depressor, in different animals. 5. The vasodepressor effect of intravertebral nicotine was part of a cardiovascular response which included a lowering of total peripheral resistance and of stroke work, whereas the cardiac output, the heart rate and the stroke volume remained essentially unchanged. 6. These results clearly indicate that a medullary area, which has been previously described, is the most sensitive site for the vasopressin releasing action of nicotine and that systemic administration of the drug induces vasopressin secretion by virtue of its action on the medulla, rather than directly on the supraoptic nucleus. 7. The results also indicate that the vasodepressor effect which follows the application of nicotine on the medulla is chiefly due to vasodilator effects on systemic blood vessels, with practically no action on cardiac function. The significance of these results is discussed.
The sensitization of high threshold mechanoreceptors with myelinated axons by repeated heating.
Authors: Fitzgerald M , Lynn B
Published: December 2014

1. Seventy high threshold mechanoreceptor units (HTMs) with myelinated axons were isolated from the sural nerves of cats and rabbits. Thirteen cat and forty‐two rabbit HTMs were testec by controlled, repeated heating of the skin of the foot or lower leg to noxious levels. 2. Many of the units (77% in the cat and 40% in the rabbit) fired to heating. Only six (11%) of these fired to the first brief heating to 50‐55 degrees C. The rest required 2‐6 heat trials before responding. 3. Heat responding units always became more sensitive with repeated heat stimulation but their mechanical sensitivity showed no comparable changes when heat sensitization occurred. 4. If these results are applicable to man, they suggest that HTMs play little role in generating the first pain that follows skin heating but that they may be involved in the increased sensitivity to heat pain (hyperalgesia) shown by skin previously injured by heating.
The effects of hypothalamic temperature variation and intracarotid cooling on behavioural thermoregulation in sheep.
Authors: Baldwin B A , Yates J O
Published: December 2014

1. Shorn‐sheep, placed in cold environments, have been trained to turn on infra‐red heaters. The effect, on this thermoregulatory behaviour, of warming and cooling the hypothalamus by means of a thermode has been examined. 2. At ambient temperatures of 5, 15, 25 and 35 degrees C; cooling the anterior hypothalamus by means of a thermode, for periods of 20 min, resulted in a marked increase in the rate of using the heaters. 3. At ambient temperatures of 5 and 15 degrees C, warming the anterior hypothalamus for periods of 20 min caused a considerable reduction in the rate of using the radiant heaters. 4. At an ambient temperature of 10 degrees C, a 2 hr period of hypothalamic cooling resulted in an increase in the rate at which the heaters were used for the first 70 min, but after this the effect was reduced and the reduction coincided with a rise of deep body temperature of about 0‐75 degress C. 5. At an ambient temperature of 10 degress C, a 2 hr period of hypothalamic warming resulted in a reduction in the rate of operating the heaters during the first 85 min, but after this period the use of the heaters increased and this increase coincided with a fall of about 0‐75 degrees C in deep body temperature. 6. At ambient temperatures of 15, 25 and 35 degrees C, the cephalic region was cooled by intracarotid injections of cold saline for periods of 15 min. This procedure lowered hypothalamic temperature by about 1 degree C and produced increases in the rate at which the heaters were used similar to those seen when the thermode was cooled. To elicit marked increases in the rate at which the heaters were used it was not necessary to lower hypothalamic temperature outside the normal range.
Substrate‐limited function and metabolism of the isolated perfused rat kidney: effects of lactate and glucose.
Authors: Cohen J J , Kook Y J , Little J R
Published: December 2014

1. The objective of this study was to determine the separate contributions of exogenous substrate and of kidney tissue to the support of function and metabolism in the isolated perfused rat kidney. The effects of the addition of L(+) [U‐14C]lactate or D[U‐14C]glucose either to a specially prepared substrate‐free albumin (SFA) or to Fr. V bovine serum albumin (Fr. V‐BSA) were compared. The Fr. V‐BSA has significant quantities of lactate, citrate and free fatty acids associated with it. 2. Perfusion of the rat kidney with the Krebs‐Ringer bicarbonate solution containing SFA, without addition of exogenous substrate, resulted in a lower % Na+ reabsorption (approximately 43%) than when the perfusions contained Fr. V‐BSA (approximately 80%). Thus, kidney tissue can support at most 45% of Na+ reabsorption, while the substrates associated with the Fr. V‐BSA can support approximately 30% of Na+ reabsorption. When the initial concentration of L(+)lactate in the perfusate containing SFA was progressively raised from 0 to 10 mM, % Na+ reabsorption increased to between 85 and 90%. 3. The apparent Km (0‐59 mM) and the Vmax (0‐67 micronmole g‐1. min‐1) for lactate oxidation in the presence of SFA were both significantly lower than when Fr. V‐BSA was present (Km = 2‐0 mM; Vmax = 1‐1 micronmole g‐1. min‐1). The lower Km is interpreted as being due to the removal of substances from the Fr. V‐BSA which competitively inhibit either the uptake or oxidation of lactate; the lower Vmax is considered to be related to the lower rate of Na+ reabsorption when SFA is present. 4. Addition of glucose enhanced gomerular filtration rate in the presence of both types of albumin. The resulting increase in the filtered load of Na+ in the presence of glucose was associated with either no change (Fr. V‐BSA) or an increase (SFA) in fractional Na+ reabsorption. Although absolute Na+ reabsorptive rate was greater in the presence of glucose than in the presence of lactate, the oxidation rate of glucose, on a carbon‐atom basis, was less than 50% of the oxidation rate of lactate. 5. The metabolism of glucose may regulate the permeability characteristics of the glomerulus and the tubular epithelium: by contrast, the high oxidation rate of lactate suggests it can provide direct support for a major fraction of the Na+ actively absorbed.
Facilitation of transmitter secretion from toad motor nerve terminals during brief trains of action potentials.
Authors: Balnave R J , Gage P W
Published: December 2014

1. End‐plate potentials produced by brief trains of action potentials (5‐7 at 50‐100 Hz) were recorded at toad sciatic‐sartorius neuromuscular junctions. When transmitter secretion was depressed in solutions containing magnesium, the increase in amplitude (growth pattern) of successive end‐plate‐potentials was greater than could be accounted for by arithmetic summation of facilitation (arithmetic model) as proposed by Mallart & Martin (1967). 3. With e.p.p.s of normal quantral content or in solutions in which the calcium concentration was lowered, growth patterns were occasionally reasonably close to those predicted by the arithmetic model but there was always some degree of disparity. 4. A simple, two‐step, kinetic model is described which is more consistent with the varied growth patterns of end‐plate potentials that have been recorded. The model can predict growth patterns of e.p.p.s with high or low quantal content.
Relative capabilities of sarcoplasmic reticulum in fast and slow mammalian skeletal muscles.
Authors: Briggs F N , Poland J L , Solaro R J
Published: December 2014

1. The calcium uptake capabilities of the sarcoplasmic reticulum (SR) of the fat‐twitch muscles extensor digitorum longus (EDL) and tibialis anterior (TA) of the rat and the extensor digitorum longus of the cat have been compared with the same capabilities of the slow‐twitch soleus muscles of the rat and cat. 2. For the ra the Vmax values of sarcoplasmic reticulum from tibialis anterior, extensor digitorum longus and from soleus muscles were 50, 51, and 10 micronmole Ca2+/g per minute, respectively. 3. For the extensor digitorum longus and soleus muscles of the cat the Vmax values were 34 and 5‐6 micronmole Ca2+/g per minute, respectively. 4. These data were compared with mechanical data as reported in the literature for the same muscles. The relative calcium uptake capabilities of sarcoplasmic reticulum from slow and fast muscles corresponded closely to the relative rates of relaxation of these muscles.
Types of intra‐ and extrafusal muscle fibre innervated by dynamic skeleto‐fusimotor axons in cat peroneus brevis and tenuissimus muscles, as determined by the glycogen‐depletion method.
Authors: Barker D , Emonet-Dénand F , Harker D W , Jami L , Laporte Y
Published: December 2014

1. The types of intra‐ and extrafusal muscle fibre innervated by dynamic skeleto‐fusimotor (beta) axons were determined by using a modification of the glycogen‐depletion method of Edström & Kugelberg (1968) combined with histochemical tests for various enzyme reactions. A single beta axon was prepared in each of the experiments, which were carried out on six peroneus brevis and two tenuissimus muscles. 2. The intrafusal distribution of dynamic beta axons is almost exclusively restricted to bag1 fibres. The bags fibre was depleted in each of twenty‐four beta‐innervated spindle poles; the only fibres of a different type depleted intrafusally were a bag2 fibre in one pole and a long chain in another. 3. Depletion in the bag1 fibres was usually restricted to one zone in one pole, generally in a mid‐polar location. 4. The extrafusal muscle fibres depleted by dynamic beta axons belong to the slow oxidative type as defined by Ariano, Armstrong & Edgerton (1973). The number of such fibres in each motor unit could not be accurately determined, but is almost certainly small. 5. The slow oxidative muscle fibres innervated by dynamic beta axons were not depleted over their entire length. Since there is no reason to assume that they are not twitch fibres, it would seem that the localized depletions result from the conditions required to obtain glycogen depletion, i.e. long periods of motor stimulation applied during the occlusion of the muscle's blood supply. Under similar experimental conditions depletion of glycogen was also restricted to portions of fibres in fast oxidative‐glycolytic motor units, but extended over most of the length of the fibres in fast glycolytic units.
Site and mode of adrenaline action on chloride transport across the rabbit corneal epithelium.
Authors: Klyce S D , Wong R K
Published: December 2014

1. Membrane events accompanying adrenaline‐stimulated Cl secretion by the isolated rabbit corneal epithelium were investigated with micro‐electrodes. 2. Pulses of adrenaline (5 X 10(‐10) M final concentration) delivered to either side of the epithelium produced a transient decrease in epithelial resistance occuring at the outer membrane of the squamous cell. This response was reversible and could be blocked completely by total Cl substitution with SO4. 3. Adrenaline generally produced a small transient increase in epithelial potential occuring also at the squamous cell outer membrane. Reversal potentials obtained for the adrenaline response were 45‐1 mV for corneal potential and 22‐8 mV for outer membrane. 4. Adrenaline always hyperpolarized epithelial potential when the tear side was bathed in Cl‐free solution. Reversing the gradient (Cl‐free on the stromal side) slowly and consistently changed the response to a depolarization which reached a steady level after 2 hr. 5. The reversal potential of the outer membrane for the adrenaline response was found to be a semilogarithmic function of the tear side Cl concentration over a broad range with a slope of 56 mV/decade. The reversal potential was zero at a tear side Cl concentration of 41‐5 mM, which value may be taken to be representative of cell Cl concentration. 6. After abolishing the adrenaline response by perfusing both sides of the tissue with Cl‐free solution, reintroduction of Cl to the stromal side led to a recovery of the epithelial potential response in the hyperpolarizing direction. The recovery of the response was inhibited by ouabain (10(‐5) M). 7. The results supported the following model for the influence of adrenaline on anion transport in the epithelium: Cl is transported against an electrochemical potential gradient into the cells from the stromal side by an active process linked to Na‐k activated ATPase. Normally a slight gradient exists from cells to tears favouring the passive outward diffusion of Cl. This latter process is enhanged by adrenaline, which increases cell cyclic AMP, in turn increasing the passive Cl permeability of the outer cellular membrane.
Reduction of the duration of isovolumic relaxation in the ejecting left ventricle of the dog: residual volume clamping
Authors: Suga Hiroyuki , Yamakoshi Ken-Ichi
Published: December 2014

1. The individual effects of stroke volume and speed of ejection on the duration of the isovolumic relaxation phase were analysed in the canine left ventricle with a constant end‐systolic residual volume.

2. A new technique was employed to maintain the ventricular end‐systolic residual volume at a desired constant value regardless of wide changes in stroke volume and speed of ejection in a given inotropic background.

3. The duration of isovolumic relaxation, which was defined to be the time taken for ventricular pressure to fall from its end‐systolic level to its 75, 50 and 25% levels, markedly decreased with increases in stroke volume. The reduction amounted to as much as 30‐50% when stroke volume was increased from zero (isovolumic) to 20‐25 ml.

4. The degree of shortening of the duration of isovolumic relaxation was largely independent of changes in speed of ejection which ranged from about 100‐800 ml./sec at a constant stroke volume of 15 ml.

5. It was therefore concluded that stroke volume itself could be a major determinant of the duration of isovolumic relaxation.

6. It was speculated that the mechanism of the observed phenomenon might be a manifestation of the uncoupling effect of muscle shortening on contractile state.
Kinetics of luminal acidification in cortical tubules of the rat kidney.
Authors: Giebisch G , Malnic G , De Mello G B , De Mello Aires M
Published: December 2014

1. Some kinetic aspects of renal tubular acidification were studied in proximal and distal tubules of the rat kidney by combining stationary microperfusion methods and continuous measurements of luminal pH changes of phosphate or bicarbonate buffers by means of antimony electrodes. The analysis included the measurement of steady‐state pH, steady‐state buffer concentrations and acidification half‐times. From these data, net rates of tubular bicarbonate reabsorption and of H ion secretion were obtained since it was shown that the rate of phosphate acidification provides a realistic estimate of H ion secretion. 2. Experiments were performed in control rats, in animals undergoing metabolic acidosis or alkalosis and in control and acidotic rats receiving the carbonic anydrase inhibitor Diamox. 3. In all experiments, the rates of tubular bicarbonate reabsorption and of phosphate acidification (H ion secretion) were proportional to luminal buffer levels. The changes of luminal acid concentrations followed first‐order kinetics. 4. Steady‐state transepithelial pH differences were reduced in metabolic alkalosis and after diamox but augmented during metabolic acidosis. 5. Acidification half‐times were prolonged in metabolic acidosis and after Diamox but remained similar to control levels in metabolic alkalosis. 6. From the observation that both bicarbonate reabsorption and phosphate acidification are similarly affected by these experimental manoeuvres, it is concluded that H ion secretion plays a key role in both transport processes.
Supporting effects of myoepithelial cells in submandibular glands of dogs when acting against increased intraluminal pressure
Authors: Emmelin N. , Garrett J. R. , Gjörstrup P.
Published: December 2014

1. In dogs under chloralose‐urethane anaesthesia secretion from the submandibular gland was recorded with the outflow at gland level and at heights of up to 50 cm above the gland.

2. With the outflow level increased, secretion elicited by sympathetic nerve stimulation was far better maintained before than after injection of the α‐adrenoceptor blocking agent dihydroergotamine.

3. When the outflow level was raised while no secretion occurred, fluid flowed into the gland. Part of this amount was returned on lowering the outflow to gland level. This volume was assumed to have been accommodated in the distended luminal system, whereas some fluid was obviously lost into the gland tissues.

4. Both these fractions of the fluid flowing into the gland when the outflow level was high could be reduced by injecting the α‐receptor agonist phenylephrine. Bradykinin, which like phenylephrine is known to contract salivary myoepithelial cells, had the same effect on the two inflow volumes.

5. It is concluded that myoepithelial contraction reduced the distensibility of the luminal system and in addition supported the acini, thereby diminishing backflow into the glandular tissues and enabling the gland to discharge saliva against a high pressure.

6. Morphologically it was found that in resting glands PAS‐positive saliva was displaced from the ductal system when the outflow cannula was raised, but it was preserved in the lumina under similar conditions when the myoepithelial cells were being stimulated by phenylephrine or bradykinin.

7. Although sympathetic secretion could be maintained against a head of pressure, so long as it was accompanied by myoepithelial contraction, the increased force caused by the secretion led to disruptive damage of striated ducts which are the first part of the luminal system not supported by myoepithelial cells.

8. The morphological findings reinforce the belief that contraction of myoepithelial cells gives active support to the underlying parenchyma.
Muscarinic, alpha‐adrenergic and peptide receptors regulate the same calcium influx sites in the parotid gland.
Authors: Putney J W
Published: December 2014

1. Carbachol, phenylephrine and substance P were each capable of producing a transient release of K (86 Rb) from rat parotid slices in the absence of extracellular Ca. 2. Each of the agonists was also capable of producing "cross‐receptor inactivation"; that is, if a transient response was elicited by any one of the agonists then no transient response could be obtained by either of the other two. 3. Removal of carbachol from muscarinic receptors with atropine did not reverse the cross‐receptor inactivation of the substance P response unless Ca was added with substance P or unless Ca was present when atropine was added. 4. It is concluded that the K release response in the parotid gland is mediated by receptor‐controlled Ca influx sites. These influx sites also bind Ca at a location inaccessible to EGTA and release the bound Ca upon receptor activation. 5. It is also conlcuded that all three receptors (muscarinic, alpha‐adrenergic, and peptide) appear to regulate the same Ca influx sites.
Inhibition of cuneate neurones: its afferent source and influence on dynamically sensitive ‘tactile’ neurones
Authors: Bystrzycka E. , Nail B. S. , Rowe Mark
Published: December 2014

1. Responses were recorded in decereberate, unanaesthetized cats from individual cuneate neurones in order to determine firstly, the afferent sources of inhibition on cuneate neurones and secondly, the influence of afferent‐induced inhibition on those response features of dynamically sensitive tactile neurones which determine their capacity to code information about parameters of tactile stimuli.

2. For all cuneate neurones which displayed afferent‐induced inhibition from areas surrounding or within their excitatory receptive field (71% of the sample) it was consistently found that 300 Hz vibration at low amplitudes (< 25‐50 μm) which selectively engages Pacinian corpuscles was an effective source of inhibition. In contrast, steady indentation which activates slowly adapting tactile afferents was quite ineffective, as was low frequency vibration (30 Hz) at amplitudes of < 50‐100 μm. The latter stimulus can be used to engage rapidly adapting receptors either within glabrous skin (presumed to be Meissners corpuscles) or in association with hair follicles. It is concluded that afferents from Pacinian corpuscles are the dominant or exclusive source of afferent‐induced inhibition of cuneate neurones.

3. For dynamically sensitive neurones responsive to low frequency cutaneous vibration (30 Hz) there was a reduction in the slope of stimulus—response relations with afferent‐induced inhibition, but no expansion of the range of stimulus amplitudes over which the neurone responded.

4. The influence of afferent‐induced inhibition on the phase‐locking of impulse activity to a cutaneous vibratory wave form was examined by constructing post‐stimulus time histograms and cycle histograms. Measures of dispersion of impulse activity around the preferred point of firing in the vibratory waveform indicated that the capacity of individual cuneate neurones to code information about the frequency of the cutaneous vibration was not systematically changed in the presence of afferent‐induced inhibition.
Ia afferent activity during a variety of voluntary movements in the cat
Authors: Prochazka A. , Westerman R. A. , Ziccone S. P.
Published: December 2014

1. Implanted dorsal root electrodes were used to record discharge trains of single spindle primary afferents (Ia's) of the cat's hind limb during different types of movement.

2. The length of the ipsilateral ankle extensors was continuously monitored by an implanted length gauge. Length changes occurring during active stepping were subsequently passively reproduced during brief anaesthesia.

3. A comparison of the Ia responses in active and simulated step cycles revealed that moderate fusimotor drive to ankle extensor spindles probably occurred mainly, if not exclusively, during the E1, E2 and E3 phases of active stepping.

4. A temporal advance in the Ia response to passive stretching in the F‐phase was attributed to the after‐effects of fusimotor activity in the extension phases.

5. Light thrust applied to the animal's back evoked a potent fusimotor response. This load compensation effect may provide an explanation for the apparently higher degree of α‐γ co‐activation seen in the mesencephalic locomotor preparation.

6. Ankle extensor Ia discharge decreased during falls, despite an increase in extensor e.m.g. This is seen as a clear example of independent α and γ control.

7. Placing reactions during walking were consistent with the notion that cutaneous inputs dominate over proprioceptive inputs in these movements.

8. α and Ia discharge during paw‐shaking showed many of the characteristics of that in decerebrate and spastic clonus. The present results suggest that movements resembling clonus may be part of the animal's normal repertoire.

9. Isometric co‐contraction of agonists and antagonists was found to involve α‐γ co‐activation.

10. Hamstring Ia discharge behaviour during stepping further highlighted the increases in firing rate which normally occur during passive muscle stretching in ‘pre‐programmed’ movements.
Sensory deprivation during development decreases the responsiveness of cricket giant interneurones
Authors: Matsumoto S. G. , Murphey R. K.
Published: December 2014

1. The effect sensory deprivation, early in development, has on the adult response properties of identified neurones was studied in the abdominal nervous system of the cricket Acheta domesticus.

2. Neural activity in the cercal‐to‐giant interneurone system was lowered by blocking the movement of the mechanosensitive hairs, located on each cercus, with a facial cleansing cream.

3. When specimens were treated unilaterally one of a pair of homologous neurones exhibited drastically altered response properties. The neurone which received its afferent input from the treated receptors was much less sensitive to tones. Its threshold was increased approximately 20 db with respect to its untreated homologue.

4. Bilateral treatment lowered the responsiveness of both of the bilaterally homologous neurones.

5. Increased levels of inhibition impinging on the treated neurones accounts for part of the altered responsiveness. The inhibitory pathway is activated by the untreated mechanoreceptors.

6. Control experiments demonstrate that the sensory apparatus is not injured or modified by the treatment.

7. The results suggest that normal development of some invertebrate neural pathways may be more dependent on experience during ontogeny than has previously been assumed.
The physiologically relevant information regarding systemic blood pressure encoded in the carotid sinus baroreceptor discharge pattern.
Authors: Arndt J O , Morgenstern J , Samodelov L
Published: December 2014

1. The objective was to find out what kind of informatioon regarding systemic blood pressure is transduced by baroreceptors in vivo and how this information is coded in the receptor discharge. 2. Carotid sinus pressure, e.c.g., and receptor action potentials were recorded for fifty‐two single fibre carotid sinus receptors found in twenty decerebrated unanaesthetized cats. 3. The inflation and gradual deflation of an intraaortic catheter tip balloon manipulated the blood pressure in the carotid sinus in a way as to define the full in vivo stimulus‐response curve for each receptor. 4. Correlation coefficients were computed between stimulus and response variables for several points on the response curve of each receptor and for every possible combination of stimulus and response variables defined. 5. Stimulus variables were (a) systolic, (b) diastolic,, (c) mean, (d) pulse pressures and (e) peak positive dP/dt. Response variables were (a) average discharge rat, (b) peak instantaneous frequency, and (c) average burst frequency. 6. For every fibre in the sample only the correlations between systolic, diastolic and mean pressures vs. average discharge rate were consistently high and positive. All other correlations were numerically low and/or negative. 7. It was concluded that in vivo baroreceptors signal mainly pressure level (systolic, diastolic or mean) as opposed to pulse pressure or dP/dt, and that the average discharge rate is their best index of information content.
The binding of labelled saxitoxin to the sodium channels in normal and denervated mammalian muscle, and in amphibian muscle.
Authors: Ritchie J M , Rogart R B
Published: December 2014

1. The binding of [3H]saxitoxin to innervated and denervated rat diaphragm muscle, and to normal frog muscle, has been measured. 2. A saturable component of saxitoxin binding, which was inhibited by tetrodotoxin, was detected in all preparations, as well as a component of non‐saturable binding. The values for the maximum saturable capacity, M, and the equilibrium binding constant, K, for normal rat diaphragm muscle were: M = 24‐4 f‐mole.mg wet‐1, and K = 3 ‐8 NM. 3. Denervation of rat diaphragm muscle reduced the maximum binding capacity per unit weight to 16‐5 f‐mole.mg‐1. The value of K remained virtually unchanged at 4‐2 nM. 4. It is suggested that the decrease in density per unit weight does not reflect any change in the density of sodium channels per unit area of membrane. 5. Two varieties of the same species of frog, Rana pipiens, were examined. In one variety (Southern) the value of M was 25‐6 f‐mole.mg‐1 and the value of K was 4‐3 nM. In the Northern variety the maximum binding capacity was less, M being 14‐6 f‐mole.mg‐1; the value of K was 3‐8 nM.
The effect of prostaglandin synthesis inhibitors on renal blood flow distribution in conscious rabbits.
Authors: Beilin L J , Bhattacharya J
Published: December 2014

1. We have studied the effects of two prostaglandin synthesis inhibitors on renal cortical blood flow distribution in conscious rabbits. 2. Renal blood flow distribution was estimated by means of radioactive microspheres injected into chronically implanted left atrial cannulae. Cardiac output was measured by a thermodilution technique. 3. Measurements were made in groups of animals treated with either indomethacin, meclofenamate or control injections of phosphate buffer. 4. A method of microtome slicing of the renal cortex was developed to standardize measurements. Microtome sections were grouped into inner, middle and outer zones. After both indomethacin and meclofenamate there was a reduction in total renal blood flow with a redistribution of flow from inner to outer cortex. 5. Estimated renal vascular resistance rose in all three cortical zones. 6. The data support the hypothesis that renal prostaglandin synthesis is necessary for maintaining flow to the deep cortex. It is suggested that renal prostaglandins may also influence flow in more superficial zones. 7. Estimated total systemic vascular resistance was increased both with meclofenamate and indomethacin, suggesting an inhibiting effect of prostaglandins on arteriolar tone throughout a major part of the systemic circulartion.
Adaptation of the human carotid baroreceptor‐cardiac reflex.
Authors: Eckberg D L
Published: December 2014

1. Four intensities of neck suction were applied for 5 sec in healthy young men to determine the time course of decay of carotid baroreflex sinus node inhibition. 2. Peak responses occurred at about 1‐25 sec after the onset of baroreceptor stimulation and were proportional to the intensity of stimulation. 3. Responses declined steadily during the remaining period of stimulation; the rate of decay of sinus node inhibition was decribed well by a power function and was proportional to the intensity of baroreceptor stimulation. 4. beta‐adrenergic blockade did not alter the rate of decay of abroreflex sinus node inhibition. 5. These results suggests that adaptation of the integrated baroreceptor‐cardiac reflex occurs in man and follows the same time course as adaptation of individual baroreceptor units an experimental animals.
The relation between surface tension and area in the alveolar lining film
Authors: Pattle R. E.
Published: December 2014

1. The properties of the rat alveolar lining film have been studied by observing the behaviour in a hanging drop, under reduced or increased ambient pressure, of bubbles derived from the lung.

2. When such a bubble, covered by a metastable film of surfactant, is made to shrink, the material displaced from the surface usually remains in a form in which it can be re‐adsorbed to the surface and retains its surpellic properties.

3. When an excess of surfactant is available for adsorption to the surface of such a bubble in water, an increase in area to about 1.25 (ϕ) times the metastable area is both necessary and sufficient for additional adsorption to the surface to take place.

4. No significant variation of the ratio ϕ with temperature between 22 and 37° C has been found.

5. It is concluded that during quiet breathing (involving a twofold change in lung volume in the rat) the variation in alveolar surface area is less than 25%. This finding is compatible with the extant morphometric data, but not with any assumption that the surface area is proportional to the 2/3 power of the gas volume.

6. The behaviour of the bubbles in blood serum is similar to that in water. In a 2% solution of the detergent Tween 80, further adsorption of surfactant to the bubble surface does not take place.

7. The fact that bubbles obtained from the lung by instillation of a solution of Tween 80 have surfactant linings similar to those of bubbles obtained with water or saline demonstrates that the bubble lining layer consists of the original alveolar lining layer detached.

8. When a metastable bubble is stretched, it sometimes behaves as if some or all of its surfactant had been lost from the surface. The causes of this are unknown.

9. The amount of surfactant associated with metastable bubbles freshly squeezed from a fragment of lung varies from bubble to bubble; the amounts found have ranged from 1 to 4.5 times (mean, 2) that required to cover the original bubble area with a metastable film. This would be compatible with an alveolar lining film of very uneven thickness.

10. The maximum surface tension reached in the early stages of expansion of a lung bubble from the metastable state is about 34 mN/m.