bluuebunny/crossref_metadata_2025 huggingface dataset:
The responses of aortic arch and right subclavian baroreceptors to changes of non‐pulsatile pressure and their modification by hypothermia
Authors: James Jennifer E. Angell
Published: December 2014

1. A method is described for isolation of the aortic arch and right subclavian—carotid angle in situ in the rabbit and perfusion with Krebs—Henseleit solution or blood under controlled conditions of pressure and temperature.

2. The characteristics of the baroreceptors of the aortic arch and right subclavian—carotid angle were studied by recording from single or few‐fibre preparations of the left and right aortic nerves respectively. Curbes were plotted to show the relationship between the frequency of baroreceptor impulse activity and intra‐aortic pressure during non‐pulsatile perfusion under steady‐state conditions.

3. The aortic arch and right subclavian—carotid angle baroreceptors were found to have similar characteristics. Three types of response of the baroreceptors at the threshold pressure to a steady intra‐aortic pressure are described.

4. Increasing the intra‐aortic pressure increased the frequency of impulses in fibres previously active and caused recruitment of other fibres in multi‐fibre preparations. The relationship was linear at low pressures and a point of inflexion occurred at higher pressures in the majority of fibres.

5. Lowering the temperature of the perfusate reduced the impulse frequency at any given pressure.

6. The curves obtained during stepwise increases and decreases in intra‐aortic arch pressure were dissimilar, particularly at the lower end of the pressure range. This phenomenon is probably due to properties of the arterial wall.

7. When the aortic arch preparation was excised, changes occurred in the shape of the impulse frequency—pressure curves from baroreceptors in both areas. The point of inflexion was elevated and a higher percentage of fibres failed to reach a point of inflexion in the pressure range studied.
The effects of ethacrynic acid and other sulphydryl reagents on sodium fluxes in frog muscle
Authors: Erlij D. , Leblanc G.
Published: December 2014

1. Ethacrynic acid (2 m
M) increased the sodium efflux from freshly dissected frog sartorius muscles. This increase was not observed in muscles previously treated with strophanthidin.

2. In strophanthidin‐treated muscles, the addition of ethacrynic acid (2 m
M) caused a reduction of sodium efflux. The value of efflux reached in these muscles is similar to that observed in muscles immersed in sodium‐free solutions containing strophanthidin.

3. Ethacrynic acid reduced sodium influx into strophanthidin‐treated muscles. Potassium influx was not affected by this substance. These findings suggest that the inhibitor blocks an exchange of sodium for sodium.

4. The increase in sodium efflux caused by ethacrynic acid did not result from depolarization nor from an increase in [Na]i.

5. Ethacrynic acid caused only a reduction of sodium efflux in muscles previously loaded with sodium by prolonged immersion in potassium‐free solutions at low temperatures.

6. A derivative of ethacrynic acid that lacks the ability to combine with sulphydryl (SH) groups did not reduce sodium efflux from muscles treated with strophanthidin.

7. Para‐chloromercuribenzoic acid (PCMB) reduced sodium efflux from control and strophanthidin‐treated muscles. This reduction seems to be restricted to the sodium dependent component of the efflux.

8. The inhibition of the sodium‐dependent component of sodium efflux caused by ethacrynic acid and PCMB appears to have a similar mechanism, namely, the combination with SH groups.
Ionic dependence of protein transport across the new‐born pig intestine
Authors: Smith M. W.
Published: December 2014

1. The everted small intestine of the new‐born pig transports albumin to its serosal surface at rates which depend on the ionic composition of the bathing medium.

2. Albumin transport takes place most rapidly at sodium and potassium concentrations of 120 and 6 m
M respectively. Increasing the concentration of sodium or potassium, or decreasing the concentration of sodium, reduces the net transfer of albumin.

3. Albumin can increase the serosal transfer of sodium, potassium and water. The calculated ionic composition of fluid transported in the presence of albumin closely resembles that presented to the mucosal surface over a wide range of sodium and potassium concentrations.

4. Lowering the concentration of sodium reduces water transfer but only if albumin is present in the mucosal medium. Albumin‐stimulated water transfer is only seen when the external concentration of sodium is high.

5. Raising the concentration of potassium reduces water transport, whether or not albumin is present, but this reduction is too small to account for the inhibitory effect of potassium on albumin transport.

6. The mutual interaction that exists between the transport of albumin and sodium is probably responsible for the increased potassium transport seen at low external concentrations of potassium. Higher concentrations of potassium appear directly to inhibit the interaction between the transport of sodium and albumin.
Membrane properties of the smooth‐muscle fibres of the guinea‐pig portal vein
Authors: Ito Y. , Kuriyama H.
Published: December 2014

The membrane activities and the various characteristic constants of the smooth‐muscle membrane of the guinea‐pig portal vein were investigated with the micro‐electrode technique.

1. The mean membrane potential was −37 mV. Spontaneous discharges appeared as regular bursts of short trains of spikes alternating with silent periods, as a mixture of single spikes and bursts of spikes appearing continuously, or as regular spikes with low frequency.

2. Spontaneous spikes with overshoot were frequently observed. The maximum rate of rise of the spike was 3·7 V/sec. The shapes of the spikes were classified into three different types, i.e. pace‐maker type of spike, monophasic spike and spike with a hump during the falling phase.

3. Tetrodotoxin (10−5 g/ml.) did not influence the patterns of the spontaneous train discharges nor the shape of the spike.

4. Extracellularly applied outward current elicited spikes which were either monophasic or had a hump on the falling phase. Inward current elicited break excitation of the spike.

5. Current—voltage relations, produced by application of inward current pulses to the tissue and measured at various distances from the stimulating partition, were linear.

6. The smooth‐muscle membrane of portal vein showed cable‐like properties. The mean space constant of the membrane was 0·52 mm; the mean time constant of the membrane calculated from the electrotonic potential was 330 msec.

7. Conduction velocity of the spike measured by insertion of two micro‐electrodes was 0·58 cm/sec.

8. The time constant of the foot of the propagated spike was 27 msec. The time constant of the membrane calculated from the time constant of the foot of the spike and the conduction velocity was 310 msec.

9. The membrane properties of longitudinal smooth muscle of the portal vein were discussed in comparison with other veins and various visceral smooth muscles.
The effect of potassium and chloride ions on the volume and membrane potential of single barnacle muscle cells
Authors: Mobley Bert A. , Page Ernest
Published: December 2014

1. In single barnacle skeletal muscle cells cell diameter has been measured as a function of external osmolality, and cell diameter and membrane potential have been measured during changes of external K and Cl concentrations ([K]o and [Cl]o) like those described in frog muscle by Hodgkin & Horowicz (1959). The diameter was monitored microscopically with a precision of 0·2–0·4% (
S.D.). [K]o was varied from 1 to 18 m
M, a range of concentrations which does not cause contracture.

2. At pH 8·0 the Cl permeability was so low that net KCl and water movements were absent. Such net movements were present at pH 4·5, corresponding to a change in the ratio (Cl conductance/K conductance) from approximately 1/12 at pH 8·0 to 1/2 at pH 4·5.

3. Characteristically long time constants were observed for membrane potential responses to a change in [K]o and/or [Cl]o, even at constant [K]o.[Cl]o. This phenomenon is attributed to a delayed equilibration by diffusion within the system of sarcolemmal invaginations and T‐tubules. The delay in the response was increased by introducing polyvinylpyrrolidone (PVP) into this system, presumably because PVP raises intratubular viscosity.

4. At pH 4·5 anomalous rectification for net movements of K was demonstrated by measurements of cell diameter and of membrane potential.
The isoenzymes of carbonic anhydrase: tissue, subcellular distribution and functional significance, with particular reference to the intestinal tract
Authors: Carter M. J. , Parsons D. S.
Published: December 2014

1. The total carbonic anhydrase activity in some guinea‐pig tissues has been measured using a pH‐stat procedure. Stomach, gall bladder, proximal colon and caecum all possess more carbonic anhydrase activity per unit amount of protein than does whole blood.

2. The carbonic anhydrase activity of the small intestine is low. Reasons are given for supposing that activity found there is not entirely due to contamination by whole blood, and it is suggested that in this tissue the enzyme may be localized in some cell type other than the columnar absorbing cells.

3. Evidence is presented which indicates that heavy metals interfere with the activity of the enzyme as measured in tissue homogenates.

4. The distribution and concentration of the two major isoenzymes of carbonic anhydrase have been measured in different tissues. Blood and proximal colon contain both isoenzymes in comparable concentrations, the ratio of the concentration of the ‘low activity’ isoenzyme to that of the ‘high activity’ being about 2. The gastric mucosa contains much ‘high activity’ carbonic anhydrase, but only a negligible amount of the ‘low activity’ isoenzyme. In the caecal mucosa, the ‘low activity’ isoenzyme is predominant, the ratio of its concentration to that of the ‘high activity’ isoenzyme being about 9. It is also found that more than 1·5% of the protein in the caecal mucosa is accounted for as carbonic anhydrase enzymes.

5. It is found that some 45% of the total carbonic anhydrase activity of sucrose homogenates of the guinea‐pig colon is bound to particles. The activity is located mainly in the nuclear and microvillous fraction and in the ‘high‐speed supernatant’ fraction. The form of enzyme bound is largely of the ‘high activity’ variety. When the tissue is homogenized in potassium chloride solutions less than 4% of the total activity is recovered in particulate fractions. The amount of activity which is bound to particulate fractions increases as the ionic strength or pH of the homogenate is lowered.

6. The findings are discussed in relation to the possible physiological roles of the isoenzymes in tissues other than blood. Possible relationships between the presence of the enzymes and the metabolism and transport of ammonium and fatty acids are considered.
The maintenance of resting potentials in glycerol‐treated muscle fibres
Authors: Eisenberg R. S. , Howell J. N. , Vaughan P. C.
Published: December 2014

1. A modification of a previously published method for the disruption of the T‐tubules of frog skeletal muscle is described. The modification permits the disruption of the T‐tubules without the decline in resting potentials which was reported previously.

2. The method for the disruption of the T‐tubules involves the washout of glycerol following loading in a 400 m
M glycerol Ringer solution. The modification consists of elevating the concentration of divalent cations in the Ringer used for glycerol washout.

3. The optimum concentrations are 5 m
M‐Ca2+ and 5 m
M‐Mg2+ added as their chloride salts. Neither 10 m
M‐Ca2+ nor 10 m
M‐Mg2+ are as effective as the combination of each at 5 m
M. Other concentrations gave less satisfactory results.

4. The use of the modified technique provides a preparation which maintains 85–90 mV resting potentials for up to 6 or 8 hr but which will not contract in response to membrane depolarization.
Effects of Ba2+ and tetraethylammonium on cortical neurones
Authors: Krnjević K. , Pumain R. , Renaud L.
Published: December 2014

1. Ba2+, applied by micro‐iontophoresis, excites most cortical neurones that are excitable by ACh; other neurones tend to be depressed.

2. The discharges evoked by Ba2+ resemble those evoked by ACh, but they have an even slower time course and are characterized by firing in high frequency bursts.

3. The excitatory action of Ba2+, unlike that of ACh, is not abolished by muscarine antagonists; but it can be prevented with dinitrophenol.

4. The depolarizing effect of Ba2+ is associated with a rise in membrane resistance and it has a reversal level 24 mV more negative than the resting potential.

5. These observations suggest that, as in other tissues, Ba2+ reduced the K+ conductance by a direct action on the cell membrane. Some diminution in Na+ inactivation is indicated by the repetitive firing at high frequency.

6. TEA has a predominantly depressant effect on all neurones tested. Like Ba2+, it often increases greatly the duration of spikes, but there is no regular change in resting membrane resistance and no tendency to repetitive firing. TEA probably reduces only the delayed K+ current.

7. Even in large doses neither Ba2+ nor TEA interferes with the conductance increase that generates the typical prolonged IPSPs recorded in cortical neurones.
Disturbances of rod threshold forced by briefly exposed luminous lines, edges, disks and annuli
Authors: Hallett P. E.
Published: December 2014

1. When the dark‐adapted eye is exposed to a brief duration (2 msec) luminous line the resulting threshold disturbance is much sharper (decay constant of ca. 10 min arc) than would be expected in a system which is known to integrate the effects of light quanta over a distance of 1 deg or so.

2. When the forcing input is a pair of brief duration parallel luminous lines the threshold disturbance falls off sharply at the outsides of the pattern but on the inside a considerable spread of threshold‐raising effects may occur unless the lines are sufficiently far apart.

3. The threshold disturbance due to a briefly exposed edge shows an overshoot reminiscent of ‘lateral inhibition’.

4. If the threshold is measured at the centre of a black disk presented in a briefly lit surround then (a) the dependence of threshold on time interval between test and surround suggests that the threshold elevation is due to a non‐optical effect which is not ‘metacontrast’; (b) the dependence of threshold on black disk diameter is consistent with the notion that the spatial threshold disturbance is progressively sharpened as the separation of luminous edges increases.

5. If the threshold is measured at the centre of briefly exposed luminous disks of various diameters one obtains the same evidence for an ‘antagonistic centre‐surround’ system as that produced by other workers (e.g. Westheimer, 1965) for the steadily light‐adapted eye.

6. The previous paper (Hallett, 1971) showed that brief illumination of the otherwise dark‐adapted eye can rapidly and substantially change the extent of spatial integration. The present paper shows that brief illumination leads to substantial ‘inhibitory’ effects.

7. Earlier approaches are reviewed: (a) the linear system signal/noise theory of the time course of threshold disturbances (Hallett, 1969b) is illustrated by the case of a small subtense flash superimposed on a large oscillatory background; (b) the spatial weighting functions of some other authors are given.

8. A possible non‐linear model is briefly described: the line weighting function for the receptive field centre is taken to be a single Gaussian, as is customary, but the line weighting function for the inhibitory surround is bimodal.
Effects of CO2 on transmembrane potentials of rat liver and muscle in vivo*
Authors: Williams J. A. , Withrow C. D. , Woodbury D. M.
Published: December 2014

1. The effects of increasing the inspired CO2 concentration on the transmembrane resting potential (RP), intracellular electrolytes, and cell pH of rat liver and muscle were studied.

2. Elevation of CO2 produced a rapid reversible fall in hepatic RP. This effect is mediated by a decrease in plasma pH and is in part due to hypoxia.

3. The decrease in hepatic RP could not be accounted for by shifts in electrolytes, and an effect on membrane permeability is suggested.

4. The hepatic RP was also found to be decreased by hypoxia and increased by hyperoxia.

5. Muscle RP showed no immediate change in response to CO2 but after 60 min there was significant depolarization. This effect could be accounted for on the basis of electrolyte shifts between cells and plasma, by use of the Goldman equation.

6. Cell pH data showed that liver is buffered approximately threefold more than skeletal muscle.

7. While intracellular pH fell in response to CO2 the H+ gradient remained constant in muscle and increased in liver.
The influence of deep body temperatures and skin temperatures on peripheral blood flow in the pig
Authors: Ingram D. L. , Legge K. F.
Published: December 2014

1. The rate of blood flow through the tail of the pig has been measured by means of venous occlusion plethysmography using a mercury in rubber strain gauge. Conscious animals were used in all experiments because previous work had demonstrated that anaesthetics interfere with the animal's ability to vasoconstrict.

2. Graded changes in the temperature of the hypothalamus were imposed by means of an implanted thermode. It was found that the change in blood flow depended on the extent of the change in hypothalamic temperature and on the ambient temperature. Below 20° C ambient temperature, heating the hypothalamus did not cause vasodilatation and at 30° C ambient temperature, cooling the hypothalamus caused only slight vasoconstriction, but at 25° C ambient temperature, changes in hypothalamic temperature caused changes in blood flow from full vasoconstriction to full vasodilatation.

3. The skin temperature on the trunk was changed by means of water circulated through tubes sewn into a coat worn by the pig. Blood flow in the tail, which was outside the coat, depended on the skin temperature of the trunk, the ambient temperature, and the temperature of the hypothalamus, all of which were varied separately.

4. A thermode was implanted in the epidural space in the cervical region of the spinal cord. The change in blood flow in the tail which accompanied a change in thermode temperature was found to depend on the temperature of the thermode and the ambient temperature. Cooling the spine while the hypothalamus was being heated to 43° C resulted in a decrease in blood flow, but when the spine was heated while the hypothalamus was being cooled the increase in blood flow was only slight.

5. Local stimulus to the tail in the form of infra‐red heat, or increased air movement was followed by changes in blood flow even when deep body temperature remained stable.
Formation of saliva and potassium transport in the perfused cat submandibular gland
Authors: Petersen O. H.
Published: December 2014

1. In the cat submandibular gland perfused with modified Locke solutions, salivary secretion during acetylcholine (ACh) infusion and K uptake from the perfusion fluid after the ACh‐induced K loss were measured.

2. Strophanthin G (10−5
M) abolished K uptake, whereas salivary secretion was unaffected.

3. Ethacrynic acid (10−4‐2 × 10−4
M) hardly affected K uptake whereas salivary secretion was severely inhibited.

4. During perfusion with Ca‐free solution K uptake was unaffected, whereas salivary secretion was severely reduced.

5. The presence or absence of CO2/HCO3 in the perfusion fluid was of no importance for the secretory process and the K uptake. Acetazolamide (2 × 10−4‐10−3
M) did not inhibit these transport processes.

6. It is suggested that two kinds of Na transport occur in the acinar cells of the salivary glands: a Na extrusion coupled with K uptake, responsible for the maintenance of the concentration gradients across the cell membrane; and a Na transport coupled with Cl transport into the acinar lumen, responsible for the formation of the primary secretion.
Effects of nerve cross‐union on rat intracellular potassium in fast‐twitch and slow‐twitch rat muscles
Authors: Hoh J. F. Y. , Salafsky B.
Published: December 2014

1. Electrolytes of normal, self‐innervated and cross‐innervated extensor digitorum longus and soleus muscles of rats have been determined.

2. [K]i was 173 m‐equiv/l. for both normal and self‐innervated extensor digitorum longus. In cross‐innervated extensor digitorum longus it was reduced to 159 m‐equiv/l.

3. For normal and self‐innervated soleus, [K]i was 150 m‐equiv/l. and 154 m‐equiv/l. respectively. In cross‐innervated soleus it was increased to 182 m‐equiv/l.

4. The content and distribution of most other electrolytes of cross‐innervated soleus, as well as its weight, were not significantly different from those of controls. On the other hand, cross‐innervated extensor digitorum longus weighed about half as much as controls and contained markedly elevated Na+, Cl− and extrafibre water and reduced non‐collagenous protein and intrafibre water.

5. It is concluded that [K]i of fast‐twitch and slow‐twitch muscle fibres are under neural regulation. Possible mechanisms for this regulation are discussed.
The heat of shortening during the plateau of tetanic contraction and at the end of relaxation
Authors: Aubert X. , Lebacq J.
Published: December 2014

1. The net thermal effect of shortening on the heat production of the sartorius muscle of Rana temporaria has been studied at 0° C in tetanic contractions of either 1·2 or 2·0 sec analysed up to the end of relaxation.

2. Three types of contractions have been compared: isometric at the standard length (lo); isometric at a shorter length (lo minus 4·27 mm); and rapid shortening at constant velocity between those two lengths during the plateau of tetanic activity, the work being collected by an ergometer of the Levin—Wyman type. After the end of the shortening, stimulation was continued long enough to allow a complete recovery of tension before relaxation started.

3. In those conditions, shortening heat appears clearly by comparison with the isometric contractions, and most of its effect persists up to the end of relaxation. However, a reduction of the net thermal effect, of the order of 15–25%, is observed during relaxation.

4. The net supplement of heat is the same whether the shortening occurs in the beginning (0·4 sec) or towards the end (1·2 sec) of the contraction period; the reduction of the effect during relaxation is more important in the pelvic part than in the tibial part of the muscle.

5. This small reduction of the thermal effect of the shortening is fully accounted for by the fact that the tension redeveloped after the end of the movement remains always below the tension developed in a tetanus at the same final length, but isometric from the start.

6. As the greater part of the net thermal effect of the shortening persists at the end of relaxation, shortening heat cannot be part of a cyclic process reversed during relaxation; it must derive from some chemical source of energy.
Catecholamines and 5‐hydroxytryptamine in nervous tissue of cephalopods
Authors: Juorio A. V.
Published: December 2014

1. Catecholamines and 5‐hydroxytryptamine were measured fluorimetrically in nervous tissue of cephalopod molluscs.

2. The only catecholamines found present in nervous tissue of Eledone, Octopus and Sepia were dopamine and noradrenaline. The highest concentrations were found in the optic lobes and in the superior buccal lobe. The concentrations of dopamine and noradrenaline were smaller in other regions of the nervous tissue taken.

3. 5‐Hydroxytryptamine was also found in most of the regions investigated. The highest concentration was found in the inferior buccal ganglia and in the optic lobes.

4. The administration of reserpine produced a marked decrease in the concentration of catecholamines and 5‐hydroxytryptamine in octopod nervous tissue.

5. These findings suggest that dopamine, noradrenaline and 5‐hydroxytryptamine may function as neurotransmitters in cephalopod molluscs.
Effects of abrupt load alterations on force—velocity—length and time relations during isotonic contractions of heart muscle: load clamping
Authors: Brutsaert D. L. , Claes V. A. , Sonnenblick E. H.
Published: December 2014

1. Abrupt alterations in load (load‐clamping) have been imposed on cat papillary muscles during the course of isotonic shortening, between the onset of shortening and peak shortening.

2. For any given total load, whether imposed during the course of shortening or before stimulation, the velocity of shortening is determined solely by the instantaneous length, and not by the sequence of length and tension changes through which it arrived at that length.

3. This unique force—velocity—length relation is independent of time from just after the onset of shortening until just prior to peak shortening.

4. These results suggest that a steady state exists for the maximum intensity of active state in heart muscle over a major portion of the time during which isometric force is rising, and that heart muscle always senses total load while shortening.
The effect of temperature change upon transmitter release, facilitation and post‐tetanic potentiation
Authors: Hubbard J. I. , Jones S. F. , Landau E. M.
Published: December 2014

1. End‐plate potentials (e.p.p.s) and miniature end‐plate potentials (m.e.p.p.s) were intracellularly recorded from rat diaphragm phrenic nerve preparations in vitro at temperatures between 7° and 40°C.

2. The quantal content of e.p.p.s and the frequency of m.e.p.p.s showed broadly similar relationships with temperature, with maxima about 20° and above 39°C.

3. Analysis of the change in e.p.p. quantal content showed that the maximum about 20°C was accompanied by a similar maximum of p, the probability of release of quanta. The maximum above 39°C was associated with a rise in n, a presynaptic store of material needed for release.

4. The rate at which transmitter could be mobilized was linear in an Arrhenius plot with an apparent activation energy of 25 kcal deg−1.

5. Facilitation and post‐tetanic potentiation (PTP) were shown to be entirely attributable to changes in p.

6. It is suggested that facilitation and PTP have a common basis and that the (temperature‐dependent) rate of Ca removal from intracellular sites at which it exerts its action is as important a determinant of the magnitude of quantal release as is the amount of Ca combining with these sites.
Catecholamine secretion by the adrenal medulla of the foetal and new‐born foal
Authors: Comline R. S. , Silver Marian
Published: December 2014

1. The content and output of adrenaline and noradrenaline from the equine adrenal medulla has been investigated under different conditions in foetuses, foals and adult mares.

2. In the foetus only small amounts of both amines were secreted in response to stimulation of the peripheral ends of the splanchnic nerves to the gland; during anoxia the adrenal discharge was far greater and was independent of any nervous mechanism.

3. Whereas in the ruminant a direct adrenal response to low PO2 is confined to the noradrenaline cells during foetal life only, the adrenal medulla of the foetal foal secreted both adrenaline and noradrenaline during asphyxia, and the direct response persisted for some days after birth. Noradrenaline was the amine predominantly released during asphyxia in the foetus.

4. Catecholamine output from the equine adrenal medulla changed with age, in that there was a gradual increase in both the absolute and relative amount of adrenaline released, irrespective of the stimulus applied, although at any given stage of development a higher proportion of adrenaline was secreted in response to stimulation of the splanchnic nerves than during anoxia.

5. The relative proportions of the two amines in the effluent blood bore little resemblance to those found in the glands, removed after prolonged asphyxia, in either foetuses or foals. Preliminary observations have indicated that more noradrenaline is present in the glands when the foetus remains relatively undisturbed within the uterus.

6. The possible significance of the larger adrenal response to asphyxia in the foetal foal in comparison with other species is discussed in relation to the development of the innervation and the growth of the adrenal cortex.
The permeability of mammary ducts
Authors: Linzell J. L. , Peaker M.
Published: December 2014

1. The permeability of the teat mucosa of the goat has been studied in vitro and, as an isolated teat pouch, in vivo. In vivo the mucosa was found to be impermeable to radioactive Na, K, Cl and Rb isotopes and to labelled lactose, but permeable to 3HOH, and to a lesser extent, urea.

2. The permeability of the intramammary ducts has been assessed by comparison of the rates of passage from the blood of ions and urea relative to 3HOH into various fractions of milk in different parts of the gland.

3. Negligible quantities of ions were detected in the milk present in large ducts after an
I.V. infusion or during a close arterial infusion to keep the venous blood concentrations constant. However, after approximately 25 min, milk in the alveoli had fully equilibrated with 3HOH, and 24Na+ and was almost fully equilibrated with urea but not with 42K+ and 36Cl−.

4. The quantity of milk in a fraction of milk was directly related to the amount of 3HOH present in that fraction but not to the amounts of the other indicators (urea, labelled Na, K, Rb and Cl). Comparison of the concentration of these substances with 3HOH in different milk fractions indicates that the mammary ducts are probably impermeable to ions and only slightly permeable to urea.

5. The injection of [14C]lactose into the teat showed that after 10 and 20 min, 7 and 14% respectively of the radioactivity had reached the residual (alveolar) milk. Thus diffusion within the milk in the ducts could account for the small quantities of labelled ions found in milk within the ducts following intravascular injection.

6. It is concluded that the large and medium‐sized ducts in the mammary gland are impermeable to lactose and to the monovalent ions studied.

7. In non‐lactating animals, the ducts are more permeable to Na+ and Cl− than in the lactating animals.

8. The relative rates of passage of ions into residual (alveolar) milk was Na > Cl > K.
The effects of oxytocin and milk removal on milk secretion in the goat
Authors: Linzell J. L. , Peaker M.
Published: December 2014

1. When goats were milked each hour after being given a dose of synthetic oxytocin within the range thought to be released by the pituitary, there was a progressive rise in milk yield becoming statistically significant by 5 hr. The effect was reduced if the milk was not removed from the gland each hour.

2. Milking transplanted glands each hour without injecting oxytocin also increased milk yield. The yield of the unmilked glands on the same animals was not affected. Massaging the transplanted glands had no effect on the milk yield.

3. Oxytocin treatment and, to a lesser extent, frequent milking without oxytocin, altered milk composition. [Na], [Cl] and [non‐casein protein] increased; [K] and [lactose] decreased.

4. Oxytocin infusions permitted the leakage of [14C]lactose from milk to plasma and [14C]sucrose from plasma to milk.

5. In some goats very small doses of oxytocin caused changes in milk composition and in one such animal these changes were mimicked by the close arterial infusion of bradykinin.

6. Reasons are given for believing that the changes in composition are incidental to the main action of oxytocin in expelling milk and could be caused by a small number of leaks between the tight junctions connecting secretory cells.

7. The increase in the rate of milk secretion following milk removal is probably of greater physiological significance than the small changes in milk composition and supports Levy's idea of a local negative feed‐back via a chemical component of milk.
The membrane properties of the smooth muscle of the guinea‐pig portal vein in isotonic and hypertonic solutions
Authors: Kuriyama H. , Ohshima K. , Sakamoto Y.
Published: December 2014

The membrane properties of the longitudinal smooth muscle of the guinea‐pig portal vein were investigated under various experimental conditions.

1. In isotonic Krebs solution, the membrane potential (−48·7 mV), the maximum rates of rise and fall of the spike (4·6 and 2·3 V/sec respectively), the space constant (0·61 mm), the conduction velocity of excitation (0·97 cm/sec) and the time constant of the foot of the propagated spike (18·4 msec) were measured.

2. The various parameters of the muscle membrane in the isotonic solution were compared with those in the hypertonic solution prepared by the addition of solid sucrose (twice the normal tonicity).

3. When the muscles were perfused with hypertonic solution, marked depolarization of the membrane and increased membrane resistance occurred. These were probably due to reduction of the K permeability, increased internal resistance of the muscle and shrinkage of the muscle fibre.

4. The membrane potential in isotonic and hypertonic solutions was analysed into two components, i.e. the metabolic (electrogenic Na‐pump) and the ionic (electrical diffusion potential) component in the various environmental conditions.

(a) In isotonic and hypertonic solutions, the membrane was depolarized by lowering the temperature or by removal of K ion from the solutions. When the tissues were rewarmed or on readdition of K ion, the membrane was markedly hyperpolarized. These hyperpolarizations of the membrane were suppressed by treatment with ouabain (10−5 g/ml.), by warming to only 20° C and by K‐free solution.

(b) The relationships between the membrane potential and the [K]o in isotonic Krebs, in the hypertonic (sucrose) Krebs, in the Na‐free (Tris) Krebs and in the Cl‐deficient (C6H5SO3) Krebs were observed. The maximum slopes of the membrane depolarization against tenfold changes of [K]o were much lower than that expected if it behaved like a K electrode.

(c) In Na‐free (Tris) solution, the membrane was not depolarized in isotonic condition but it was depolarized in hypertonic condition.

5. The low membrane potential in hypertonic solution (−37 mV) compared with isotonic solution (−49 mV) was thought to be mainly due to suppression of K permeability of the membrane and not due to suppression of the metabolic component.

The electrogenic Na‐pump and the membrane potential of the portal vein was discussed in relation to other excitable cell membranes.
The Florida retinal densitometer
Authors: Hood C. , Rushton W. A. H.
Published: December 2014

1. In Part I the principles of reflexion densitometry are discussed in relation to the measurements of visual pigments in man.

2. In Part II the new Florida densitometer is described in some detail, and records are shown of the instrument's performance with pigment in equilibrium or changed by bleaching.

3. With an artificial eye the fluctuations are of the order to be expected from quantum noise and limit the precision of one measurement to 0·0035 of ‘double density’ which corresponds to some 2% of total pigment.

4. Part III treats of the reliability and significance of the measurements in living man. It needs ten repeated measurements to attain the reliability of 1 with the artificial eye.

5. The measuring light used bleaches cone pigments by 0·4% in the 6 sec required to make a measurement.

6. The interpretation of the measurements is briefly discussed.
Stiles—Crawford effect and the bleaching of cone pigments
Authors: Coble J. R. , Rushton W. A. H.
Published: December 2014

1. The efficiency of light entering the eye through various points in the pupil (Stiles—Crawford effect) was studied using two criteria: (a) visual brightness judged by flicker fusion and (b) the rate of cone pigment bleaching measured by reflexion densitometry.

2. Both measurements were made in the same apparatus with the same geometry of presentation and both gave the same Stiles—Crawford effect.

3. This suggests that the densitometer measures pigment deep in the outer segments of the cones where light is absorbed for vision.

4. Foveal cones seem all to point in the same direction, since the fraction of pigment bleached by light entering the pupil at any one point is the same when measured by light entering anywhere.
Electrogenic sodium pump in smooth muscle cells of the guinea‐pig's taenia coli
Authors: Casteels R. , Droogmans G. , Hendrickx H.
Published: December 2014

1. The changes of the membrane potential, of the K equilibrium potential, and of the membrane conductance during K accumulation by K‐depleted tissues have been studied. Three subsequent characteristic periods can be described.

2. Readmission of 5·9 m
M‐K after complete depletion results in a rapid extrusion of Na and uptake of K, and in a rapid hyperpolarization of the cells. Initially the time course of the K equilibrium potential and the membrane potential are similar except in propionate solution. This initial period is characterized by a high membrane conductance. No change of membrane potential occurs if 10−5
M ouabain is present.

3. After 5‐7 min the membrane potential becomes more negative than the K equilibrium potential. The difference between both values is larger in solutions containing propionate or in hypertonic solutions. This second phase of the recovery period is characterized by a progressive decrease of the membrane conductance.

4. In a third phase both the membrane potential and the membrane resistance return to their steady‐state value.

5. If the external K concentration in the recovery solution is increased, the maximal hyperpolarization is less and has a shorter duration. A decrease of the temperature of the recovery solution results in a slower initial rate of repolarization and in a decrease of the maximal value of the hyperpolarization.

6. These observations demonstrate the existence of an electrogenic sodium pump in smooth muscle cells during stimulation of the Na pump. An analysis of the experimental data obtained under steady‐state conditions in normal Krebs solution suggests that also under these conditions an electrogenic Na pump might take part in the maintenance of the resting potential.
Different types of extrafusal muscle fibres in snake costocutaneous muscles
Authors: Ridge R. M. A. P.
Published: December 2014

1. Tonic and twitch muscle fibres were identified physiologically in m. costocutanei superiores and inferiores of garter snakes and grass snakes.

2. Tonic fibres were multiterminally innervated and showed s.j.p.s in response to nerve stimulation. They did not show propagated A.P.s. They were innervated by motor axons with lower conduction velocities than those to twitch fibres, and often gave a contraction and developed tension in response to a single shock to the nerve. Intracellular square pulse analysis showed that Cm = 1 μF/cm2 and Rm = 40,000 Ω cm2.

3. Twitch fibres showed a conducted action potential in response to nerve stimulation, and focal, as opposed to diffuse, innervation. They showed a variety of isometric twitch contraction times (times‐to‐peak of about 30–65 msec). Groups of similar motor units contained fibres of approximately similar contraction times. Slow twitch (and tonic) fibres often appeared silvery under dark field illumination, while faster twitch fibres appeared clear. No difference in Cm, Rm or λ was found between faster and slow twitch fibres. Values were approximately 3‐4 μF/cm2, 3000–4000 Ω cm2 and 2 mm respectively.
The resting membrane potential of the somatic muscle cells of Ascaris lumbricoides
Authors: Brading Alison F. , Caldwell P. C.
Published: December 2014

1. The resting membrane potential of Ascaris muscle fibres, which is normally relatively insensitive to ion changes in the medium, has been measured under a wide variety of conditions.

2. The results have been interpreted in terms of a form of the constant field equation containing additional terms for the contribution of ions and charged groups other than potassium, sodium and chloride.

3. Normally the contribution of the additional terms is large and tends to outweigh the contributions of potassium, sodium and chloride.

4. The contribution of the additional terms is considerably reduced in the absence of sodium and in the presence of γ‐amino butyric acid and acetylcholine.

5. It is suggested that the additional terms may represent the contribution of an electrogenic active transport mechanism to the factors determining the membrane potential.
The form and distribution of the receptive fields of Pacinian corpuscles found in and around the cat's large foot pad
Authors: Lynn Bruce
Published: December 2014

1. Firing thresholds of Pacinian corpuscles situated within or close to the large pad of the cat's hind foot have been determined following step displacements applied to various points on the pad surface.

2. The most sensitive positions on the receptive fields of thirty‐one corpuscles were distributed unevenly over the pad. About half were situated close to the interlobular crease lines, and most of the others were at the edge of the pad.

3. Threshold receptive fields were usually of complex form, with more than one region of low threshold.

4. The approximate locations of a number of Pacinian corpuscles whose fields had been mapped were determined by dissection.

5. The most sensitive position on the pad was usually at the closest point to the corpuscle. If the corpuscle was situated outside the pad itself, it was therefore usually most easily excited from some point at the edge of the pad. However, a minority of Pacinian corpuscles were most easily stimulated from some region other than that closest to them.

6. It is suggested that previous estimates of the ability of this population of receptors to transmit information about the positions of stimuli (Gray, 1966) must be re‐evaluated in the light of the non‐uniform distribution and asymmetry of their cutaneous receptive fields.
The responses of frog muscle spindles and fast and slow muscle fibres to a variety of mechanical inputs
Authors: Brown M. C.
Published: December 2014

1. The tension in the iliofibularis muscle of frogs was recorded while the muscle was stretched or released. At the same time recordings were made from single spindle afferents in dorsal root filaments. Either large or small motor nerve fibres were stimulated in split ventral root filaments.

2. While small motor nerve fibres were stimulated the discharge from muscle spindle afferents was greatly increased by stretching, and greatly reduced by shortening the muscle. This sensitivity to movement was shown even if the movements were small, so that a stretch of 0·2% of the muscle length was sufficient to cause a pronounced increase in the afferent discharge.

3. In contrast, during stimulation of the large motor nerve fibres the spindle was much less sensitive to movements with the result that even stretches or releases of the muscle by 1 mm did not cause very large changes in the discharge frequency.

4. The tension in slow extrafusal muscle fibres in many ways mirrored the spindle discharge during the stimulation of small motor nerve fibres, for the tension was greatly increased by stretching, even through small distances, and greatly reduced by releasing the muscle. The tension in fast extrafusal muscle fibres was much less changed by such movements, and thus was rather like the spindle discharge during stimulation of large motor nerve fibres.

5. As the extrafusal muscle fibres do not directly pull on and excite the spindle afferents, the simplest explanation for the similarities between the muscle tension and the spindle discharge is that the mechanical properties of the intrafusal muscle fibres innervated by the large motor nerve fibres are like those of fast extrafusal muscle fibres, and that the mechanical properties of the small intrafusal fibres are similar to those of slow extrafusal muscle fibres.

6. It is shown that the cross‐bridge sliding filament mechanism of muscle contraction provides a ready explanation for the differences found between fast and slow muscles, and it is concluded that a most important functional difference between the two sorts of intrafusal muscle fibres is the speed of their contractions, for it is this which determines their contrasting actions on the spindle.

7. It was also found that low rates (< 4/sec) of small motor nerve fibre stimulation were often very effective in exciting the spindles. These rates produced rather little extrafusal tension.
Effect of electrical stimulation on the fluorescence intensity of catecholamine‐containing tuberal nerve cells*
Authors: Lichtensteiger W.
Published: December 2014

1. By means of a microfluorimetric technique, the intensity of the catecholamine fluorescence was measured in nerve cells of the arcuate and periventricular hypothalamic nuclei of ovariectomized rats pre‐treated with oestrogen and progesterone. In such animals the fluorescence intensity is in the range of the lowest intensities that were observed during the oestrous cycle.

2. Unilateral intermittent electrical stimulation of the arcuate nucleus or of the medial preoptic area induced an acute increase of the fluorescence intensity in the cell bodies of the tuberal catecholamine‐containing nerve cell group. The change was already manifest 5 min after the onset of stimulation and within 10 min the mean fluorescence intensity reached levels that are among the highest so far observed in this cell group. Prolonged stimulation of the medial preoptic area led to a biphasic response, as shown by a decrease in intensity between 30 and 60 min of stimulation.

3. The increase in fluorescence intensity caused by stimulation of the arcuate nucleus was completely prevented by pre‐treatment with the tyrosine hydroxylase inhibitor α‐methyl‐tyrosine. Thus, the effect appears to be due to an enhancement of amine synthesis.

4. The intensity values found after synthesis inhibition were used for a preliminary estimation of the catecholamine turnover time in the nerve cell bodies of the arcuate nucleus.

5. In conclusion, electrical stimulation appears to induce a characteristic type of concentration change in the nerve cell body, at least under certain experimental conditions. It is compared with similar responses to physiological changes such as the reaction to acute cold exposure.
Selective effects of an octopus toxin on action potentials
Authors: Dulhunty Angela , Gage Peter W.
Published: December 2014

1. A lethal, water soluble toxin (Maculotoxin, MTX) with a molecular weight less than 540, can be extracted from the salivary glands of an octopus (Hapalochlaena maculosa).

2. MTX blocks action potentials in sartorius muscle fibres of toads without affecting the membrane potential. Delayed rectification is not inhibited by the toxin.

3. At low concentrations (10−6‐10−5 g/ml.) MTX blocks action potentials only after a certain number have been elicited. The number of action potentials, which can be defined accurately, depends on the concentration of MTX and the concentration of sodium ions in the extracellular solution.

4. The toxin has no post‐synaptic effect at the neuromuscular junction and it is concluded that it blocks neuromuscular transmission by inhibiting action potentials in motor nerve terminals.