bluuebunny/crossref_metadata_2025 huggingface dataset:
The projection of joint receptors to the cuneate nucleus in the cat.
Authors: Tracey D J
Published: December 2014

1. Records were made from axons in the dorsal columns and cells in the cuneate nucleus which responded to stimulation of the wrist joint nerve. 2. A sample of twenty‐five axons activated by the wrist joint nerve was recorded in the dorsal columns at the level of the third cervical segment. All twenty‐five were post‐synaptic fibres as judged by response latency, burst length, and maximum frequency of following. Nineteen of the twenty‐five had convergent inputs from the wrist joint nerve and the cutaneous superficial radial nerve. 3. While no primary wrist joint afferent fibres were recorded in the dorsal columns, their presence was demonstrated by recording single units in the wrist joint nerve which were antidromically activated by microstimulation in the cuneate fasciculus. 4. The majority of cells recorded in the cuneate nucleus were activated not only by stimulation of joint afferents, but also by skin and muscle afferent fibres. 5. About half of the cells in the cuneate nucleus responded to wrist movement in animals with partially denervated forelimbs, where the intact wrist joint nerve was the only afferent channel providing information about natural, imposed wrist movements. The majority of the cells had phasic responses, which were weak and irregular in comparison with the responses of primary wrist joint afferents to the same movements. 6. Only two of thirty‐four cells tested could be shown to project directly to the ventrobasal thalamus, using collision of antidromic and peripherally activated impulses as the criterion.
Dual mode of junctional transmission at synapses between single primary afferent fibres and motoneurones in the amphibian
Authors: Shapovalov A. I. , Shiriaev B. I.
Published: December 2014

1. The isolated hemisected frog spinal cord has been used to examine the effects of changes in ionic composition of perfusing medium on the intracellularly recorded e.p.s.p.s produced in single motoneurones by direct stimulation of individual dorsal root fibres through a separate intracellular micro‐electrode.

2. The monosynaptic single‐fibre e.p.s.p.s usually reveal two distinct components, early and late. The early component is resistant to replacement of external Ca2+ by Mn2+ whereas the later is reversibly abolished. It is concluded that the junction between primary afferent fibre and motoneurone provides joint electrical and chemical transmission.

3. The average amplitude of the unitary electrical e.p.s.p. varies at different junctions from 25 to 430 μV, mean 124 ± 17 μV (n = 50). It is relatively stable and changes its amplitude only with changes in the height of presynaptic spike. The individual amplitudes observed in a given cell usually have a normal distribution suggesting that any variability in electrical response is entirely due to noise.

4. The average amplitude of the single‐fibre chemically mediated e.p.s.p. varies from less than 20 μV to 1·7 mV, mean 222 ± 33 μV (n = 71). A positive correlation was found between the amplitudes of chemical and electrical e.p.s.p.s recorded from different motoneurones.

5. Chemical e.p.s.p.s evoked by consecutive impulses in a single presynaptic fibre show statistical fluctuations in amplitude. The fluctuations occur in quantal steps in a manner described by binomial or Poisson statistics. Only in a few cases the deviation from stochastic distribution can be attributed to variable invasion of nerve impulses into the terminal region.

6. The amplitude of the unit e.p.s.p. varies between 33 and 104 μV, mean 66·4 ± 4·3 μV (n = 19). The mean quantum content (m) varies from less than 1 to more than 10. The m is reversibly reduced by Ca2+ lack and by Mn2+ until the chemically mediated response fluctuates according to a Poisson distribution with the unit e.p.s.p. equivalent to the single quantum of transmitter.

7. When paired or repetitive stimuli are applied to the presynaptic fibre the facilitation of the chemically mediated unitary e.p.s.p. can be observed as well as the post‐tetanic potentiation. The amplitude of the electrical e.p.s.p. remains unchanged during the period of post‐tetanic potentiation, suggesting that the latter is attributable to some change restricted to the specific presynaptic mechanism responsible for the transmitter release but not to changes in presynaptic spike height.
The time course of potassium current following potassium accumulation in frog atrium: analytical solutions using a linear approximation.
Authors: DiFrancesco D , Noble D
Published: December 2014

1. Regular perturbation theory was used to obtain analytical solutions for the time course of membrane current decay following voltage‐clamp depolarizing pulses when both time‐dependent K conductance mechanisms and the process of K accumulation in extracellular spaces are present. These solutions apply when the current and K concentration changes are small enough for linear relations to be assumed between current and K concentration. 2. In the case of a single Hodgkin‐Huxley type conductance variable with time constant tau chi the presence of an accumulation process which, by itself, would produce a current decay with time constant tau alpha, induces the appearance of two infinite sets of components with decreasing time constants (1/(n+1/tau chi) and 1/(1/tau alpha + n/tau chi), where n is integer), and decreasing magnitudes. 3. The analytical solutions are used to investigate the range of conditions over which semi‐exponential (curve‐stripping) analysis of current decay tails may give useful information on the kinetics of current change. It is shown that, except at very large decay tail amplitudes, the method may give a good estimate of the true time constants of conductance decay even when the currents are assumed to be strongly dependent on external K concentration. 4. The method introduces error in current amplitude, but over the range in which curve‐stripping gives useful results, the direct distortion of activation curves by variations in external K concentration is fairly small. However, as the current decay becomes grossly distorted in its time course by accumulation, so does the activation curve. The effects are very similar both to those obtained using numerical computation without linearization, and to those obtained experimentally. 5. Even with a large dependence of current on external K concentration the linear model does not reproduce i chi, fast as a perturbation of i chi, slow by K accumulation.
Distribution and pharmacological properties of synaptic and extrasynaptic glutamate receptors on crayfish muscle.
Authors: Onodera K , Takeuchi A
Published: December 2014

1. The distribution of glutamate sensitivity was measured in the opener muscle in the walking legs of the crayfish (Cambarus clarkii). L‐Glutamate was ionophoretically applied under visual control. 2. Bundles of a few muscle fibres were isolated and viewed with Nomarski optics. Two axons, presumably excitatory and inhibitory, branched widely over the surface of individual muscle fibres, forming numerous clusters of boutons or varicosities. 3. Glutamate sensitivity was measured from the slope of the dose‐response curves obtained by ionophoretic application of L‐glutamate and expressed as mV/nC. The highest sensitivities were about 100 mV/nC, obtained at the edge of synaptic boutons. The sensitivity declined to less than 5% about 2 micrometer away from the synaptic terminal. The time course of glutamate potentials was approximately the same as that of spontaneous synaptic potentials. 4. Glutamate depolarization started within 300 microsec after ionophoretic release of glutamate. This time lag was shorter than the synaptic delay of the nerve‐evoked synaptic potential measured with an extracellular micro‐electrode. This indicates that glutamate depolarization results from a direct action on the post‐synaptic receptor. 5. Application of L‐alpha‐kainic acid decreased the amplitude of the glutamate potential produced at the synaptic region, whereas kainate increased the amplitude of the glutamate potential at the extrasynaptic region. It is suggested that the pharmacological properties of the extrasynaptic receptor differ from those of the synaptic receptor. Possible mechanisms for the different actions of kainate are discussed.
Calcium‐dependent electrical activity and contraction of voltage‐clamped frog single muscle fibres.
Authors: Potreau D , Raymond G
Published: December 2014

1. The electrical and mechanical activities of isolated frog muscle fibres have been simultaneously recorded under conditions which allow the development of a calcium permeability (chloride‐free solution containing 72 mM‐calcium levulinate instead of 115 mM‐NaCl). 2. Long‐lasting calcium action potentials and large and sustained contraction occur without inhibition of the potassium permeability. 3. The relationship observed between the slow inward calcium current and the amplitude of the contraction, under voltage‐clamp conditions, resembles that found between IBa and tension in frog skeletal muscle and between ICa and the contraction in frog heart. A part of the mechanical response which is not abolished by manganese seems to be potential‐dependent. 4. Integration of the current traces shows that the threshold of the contraction occurs at [Ca]1 near to 2.10(‐6) M and that the contractile proteins are fully activated at [Ca]1 near to 10(‐4) M, values which are in good agreement with those proposed by other authors. 5. The minimum calcium influx necessary to induce a detectable contraction is close to 4.8 p‐moles/cm2. This value is 10‐20 times larger than the calcium influx measured during a normal action potential. 6. On detubulated fibres the calcium permeability fails to develop: this indicates that this current originates from the T‐system. The close correspondence between ICa and the contraction, and between the time course of the contraction at the end of the depolarizing steps suggests that the potential of the tubular membrane is better clamped than in normal physiological conditions.
Intracellular calcium accumulation during depolarization in a molluscan neurone.
Authors: Gorman A L , Thomas M V
Published: December 2014

1. The bursting pacemaker neurone R‐15 of Aplysia was injected with the Ca2+ sensitive dye arsenzo III. Changes in absorbance were measured with a differential spectrophotometer to monitor changes in free intracellular Ca2+ during membrane depolarization under voltage clamp conditions. 2. Dye absorbance increased linearly for depolarizing pulse durations up to 100 msec and approximately linearly between 100 and 300 msec, but for longer durations the absorbance change decreased. 3. The absorbance change vs. voltage relation increased steeply between ‐20 and 0 mV (e‐fold per 8.5 mV), peaked at +36 mV and declined non‐linearly to an estimated null or suppression potential of about +139 mV. 4. TTX (5 x 10(‐5 M) had no effect on the change in dye absorbance produced by brief or long duration stimuli whereas Ca2+ free ASW abolished all changes in dye absorbance. 5. The absorbance change saturated with increasing external Ca2+ concentrations. The relation between dye absorbance and external Ca2+ concentration was hyperbolic and for a small range of external Ca2+ concentration and membrane potentials could be fitted by a Michaelis‐‐Menten expression where the dissociation constant and the maximum absorbance change are voltage dependent. 6. The absorbance change was reduced by external divalent ions which block the Ca2+ channel (e.g. Cd2+ and Ni2+). The suppression of dye absorbance was increased by membrane depolarization and suggests that there is a voltage dependent site within the Ca2+ channel which binds divalent ions. 7. The decline of the absorbance‐‐voltage relation from its peak to the suppression potential showed a greater nonlinearity when longer duration voltage clamp pulses were used. The non‐linearity can be explained if the accumulation of Ca2+ ions next to the inner surface of the membrane during depolarization reduces the driving force on Ca2+ ions and thus decreases Ca2+ ion influx. 8. The suppression potential estimated from the absorbance‐‐voltage relation increased 29 mV per tenfold change in the external Ca2+ concentration and thus can be used to estimate the Ca2+ equilibrium potential. 9. The change in dye absorbance produced by brief depolarizing voltage clamp steps was inactivated at positive holding potentials (50% inactivation at about ‐14 mV). Our results suggest that the slow decrease in dye absorbance during prolonged depolarization is caused by inactivation of the Ca2+ channel.
Properties of the current if in the sino‐atrial node of the rabbit compared with those of the current iK, in Purkinje fibres.
Authors: DiFrancesco D , Ojeda C
Published: December 2014

1. Properties of the ‘pace‐maker’ current if in rabbit sino‐atrial node have been investigated by voltage clamp of small preparations and compared with those of the iK2 current in the Purkinje fibre. Besides having a similar voltage range of activation and responding in a similar way to adrenaline, if resembles iK2 in other respects. 2. When external Na is reduced, if decreases proportionally. In 25% Na the time‐dependent current change due to if disappears. 3. 20 mM‐Cs completely abolishes it. 4. The time constant of if during a hyperpolarizing voltage‐clamp pulse displays a relatively high temperature dependence. 5. In spite of the similarities between the two current systems, experiments in high K solutions (48 mM) rule out the possibility that the current change seen on a hyperpolarization reflects the decay of a pure K current. 6. From conductance measurements during onset of if it is deduced that if behaves as an inward current activated by hyperpolarizations.
The role of muscle mass in the cardiovascular response to static contractions
Authors: Mitchell J. H. , Payne F. C. , Saltin B. , Schibye B.
Published: December 2014

1. Eleven men performed static contractions with the fingers (digits II and III), forearm (handgrip) and the knee extensors (knee angle 90°) at 40% maximal voluntary contraction (MVC) for 2 min. In seven of the subjects handgrip and knee extension were combined, both contractions held at 40% MVC. At the end of the contraction, cuffs were inflated to 250 mmHg for 3 min around the extremity which had been contracting. Continuous measurements were performed of force, heart rate and intra‐arterial blood pressure (a. brachialis; 20 cm proximally), before and during contraction as well as during the recovery with and without cuffs inflated.

2. Heart rate and blood pressure increased momentarily with the onset of a contraction whereafter a gradual further increase took place. This pattern of response was similar for all muscle groups studied. The increases during the contractions were in the order: fingers, forearm, knee extensors and combined forearm—knee extensors, with the difference between each muscle group contraction being significant.

3. In the recovery period from a contraction with the cuff(s) inflated, heart rate returned to control level. Blood pressure also dropped, but remained elevated above pre‐contraction level until the cuff(s) was released.

4. The present data during contraction are at variance with earlier observations showing that the cardiovascular response to a static contraction is proportional to the% MVC regardless of the muscle mass involved in the contraction. Our findings are in line with the traditional concept of central and peripheral nervous inputs playing a role in the cardiovascular adjustments to exercise, with both the central and the peripheral factors being related to the mass of the muscles engaged in the exercise.
Nitroglycerine and catecholamine actions on smooth muscle cells of the canine coronary artery.
Authors: Ito Y , Kitamura K , Kuriyama H
Published: December 2014

1. The membrane potential of smooth muscle cells of the canine coronary artery was ‐ 52 mV, and cells were electrically quiescent. The length and time constant of the membrane were 0.83 mm and 410 msec, respectively. 2. TEA (> 10(‐3) M) depolarized the membrane, increased the membrane resistance and suppressed the rectifying property of the membrane. In 10(‐2) M‐TEA, an outward current pulse evoked a small active response in the canine coronary artery and a large response in the porcine coronary artery. 3. In the canine coronary artery, the minimum [K]o required for contraction was 11.8 mM (‐48 mV), and the maximum amplitude of the contraction was evoked in 89 mM‐[K]o (‐13 mV). The maximum depolarization produced by a tenfold increase in [K]o was 49 mV. 4. In the canine coronary artery, isoprenaline and a low concentration of phenylephrine reduced the resting tension, and a high concentration of phenylephrine (> 5 x 10(‐5) M) produced a contraction without affecting the membrane properties. 5. Nitroglycerine reduced resting tension, suppressed the amplitude and raised the threshold of contraction evoked by excess [K]o, electrical depolarization or phenylephrine. In the canine coronary artery, the minimum concentration of nitroglycerine required to suppress K‐induced contraction (17.7 mM) was 2.8 x 10(‐12) M nitroglycerine. However, resting membrane properties were not affected by 2.8 x 10(‐5) M nitroglycerine. TEA induced electrical response was only a little depressed by 2.8 x 10(‐5) M nitroglycerine in the porcine coronary artery, while the mechanical response was markedly suppressed. 6. In the canine coronary artery, adenosine (> 10(‐5) M) relaxed the tissue in the presence of 17.7 M‐[K]o without affecting the membrane property. ACh (> 5 x 10(‐5) M) had much the same effects as those observed by treatment with adenosine.
Subthreshold and near‐threshold membrane currents in lobster stretch receptor neurones.
Authors: Gestrelius S , Grampp W , Sjölin L
Published: December 2014

1. The ion currents in the slowly and rapidly adapting stretch receptor neurone of lobster were investigated with respect to their nature and stationary kinetics in sub‐ and near‐threshold voltage regions using electrophysiological and pharmacological techniques. 2. In both neurones the following currents were identified: (a) a tetrodotoxin‐sensitive Na current, (b) a tetraethylammonium and 4‐aminopyridine‐sensitive K current, (c) a Co (or Mn)‐sensitive Ca‐dependent K current, (d) an ouabain‐sensitive pump current and (e) a remaining leak current carried mainly by Na, K and Cl. 3. In suprathreshold voltage regions the balance between the individual membrane currents leads to the formation of a stationary negative conductance (negative slope in the voltage dependence of the ionic current) in the slowly, but not in the rapidly adapting cell. 4. These observations are compatible with the fact that during prolonged suprathreshold stimulation a stationary low frequency impulse during is possible in the slowly adapting cell, whereas in the rapidly adapting cell it is not.
Synaptic action mediating cone responses to annular illumination in the retina of the larval tiger salamander.
Authors: Lasansky A
Published: December 2014

1. Responses of salamander cones to steps of light on their surrounding area were intracellularly recorded through micropipettes filled with 2 M‐potassium acetate or 2 M‐potassium chloride. 2. Using 2 M‐potassium acetate, cone step responses showed a larger relaxation for a 1100 micrometers diameter spot than for a 100 micrometers spot, but dim annular illumination failed to evoke any detectable response. With 2 M‐potassium chloride the larger spot or an anulus evoked responses that were mainly or purely depolarizing, respectively, while the responses to the smaller spot were still hyperpolarizing. 3. The depolarizing response to annular illumination had an increased amplitude immediately after discontinuing the injection of inward current through a micropipette filled with 2 M‐potassium chloride. 4. Depolarization by extrinsic current reversed the polarity of the depolarizing response to annular illumination. 5. It is suggested that the enhancement of the depolarizing influence of the surround is due to an increase in the intracellular concentration of chloride ions, which issue from the electrodes by passive diffusion or electrophoresis. Taking into consideration the effect of depolarizing current, it would follow that surround illumination induces an increase in the chloride conductance of the cone membrane. 6. Preliminary observations on the properties of the enhanced surround response reveal a slow time course and a receptive field of more than 270 micrometers radius.
Renin release from isolated rat glomeruli: seasonal variations and effects of D600 on the response to calcium deprivation.
Authors: Baumbach L , Skøtt O
Published: December 2014

1. The effects of calcium deprivation and D600 on the rate of renin release and seasonal variations in the response were studied on juxtaglomerular cells from a preparation of isolated rat glomeruli superfused in vitro. 2. Reduction of superfusate calcium concentration caused an increase in renin release, which was significantly higher during the summer (May‐August) than during the rest of the year. 3. Addition of D600 (2 X 10(‐4) M) to a calcium‐free medium in the low responsive period caused a markedly increased renin release. In the high responsive period renin release increased more rapidly and to a higher level initially than observed in the control lines without D600. 4. It is suggested that the effect of calcium on renin release predominantly is mediated by changes in calcium bound to the plasma membrane of the juxtaglomerular cell. The sensitivity of this cell to changes in the extracellular calcium concentration seems to be regulated and varies with season, possibly due to regulation of the amount of calcium bound to the membrane.
Conductance of the calcium channel in the membrane of snail neurones.
Authors: Krishtal O A , Pidoplichko V I , Shakhovalov Y A
Published: December 2014

1. Isolated neurones from the snail Helix pomatia were investigated under voltage clamp at 21‐23 degrees C. The cells were internally dialysed and the current through small electrically isolated patches of the membrane was measured. The area of the patches was 30‐500 micrometers 2 (1/1000‐1/100 of the cell surface). The internal resistance of the membrane patches was 10(9)‐10(10) omega. 2. In order to obtain the maximum conductance of the calcium channels an external solution containing 130 mM‐Ba2+ or Ca2+ and an internal solution containing Tris glutamate and 5 mM‐EGTA were used. Fluctuations due to the activity of calcium channels have been detected and analysed. 3. The power density spectra of barium current fluctuations were calculated for conductance values from 3% to 30% of the maximum conductance in the frequency band 1‐1000 Hz. They were fitted to a spectral density function of the Lorentz form. The half‐power frequency of the spectra was 227 +/‐ Hz (S.E.). It did not reveal any distinct voltage dependence. 4. The current flowing through a single calcium channel was calculated from the variance‐to‐mean relationship. Its value for the transfer of Ba2+ ions is iBa = 0.20 +/‐ 0.02 pA (S.E.). Single channel current was not affected by the membrane potential (since the equilibrium potential was high) nor by inactivation. The maximum calcium inward current which flows through a single calcium channel is about 0.1 pA and corresponds to a conductance gamma Ca = 0.5 pS (calculated for an equilibrium potential of 200 mV). This estimate gives an upper limit to gamma Ca. 5. The parameters of calcium channels modified by external EGTA have been evaluated. Measurements were performed in an external solution containing 200 mM‐Na+. The current carried by a single modified calcium channel is iNa = 1.0 +/‐ 0.2 pA (S.E.) (gamma Na approximately 8.0 pS).
Optical recording of development of electrical activity in embryonic chick heart during early phases of cardiogenesis.
Authors: Fujii S , Hirota A , Kamino K
Published: December 2014

1. Developmental changes in the spontaneous action potential were measured using optical signals from early embryonic chick heart stained with a potential sensitive merocyanine‐rhodanine dye. 2. The wave‐length dependence of the dye signal is triphasic in early embryonic chick heart with a decrease in absorption from 525 to 600 nm, an increase from 625 to 720 nm, and a decrease at 750 nm. The signal was largest at 700 nm. 3. The magnitude of the spontaneous absorption signal increased as the development of the embryonic heart proceeded. In addition, the magnitude of the absorption signal differed among the various regions of an early embryonic chick heart and the number of electrically active cells increased dramatically throughout the 7‐9 somite developmental stages. 4. The number of the electrically active cells was largest in the right portion of the ventricle at the 7‐9 somite developmental stages. 5. The shape of spontaneous absorption signals could be classified into four types in the developmental stages between 7 and 9 somites: Signals resembling the cardiac action potential and the pace‐maker potential were not recorded until the 8‐9 somite developmental stage.
A study of pace‐maker potential in rabbit sino‐atrial node: measurement of potassium activity under voltage‐clamp conditions.
Authors: Maylie J , Morad M , Weiss J
Published: December 2014

1. A single sucrose‐gap voltage‐clamp technique was used to control the membrane potential and to measure current in rabbit sino‐atrial (SA) strips. K+ activity in the extracellular space was simultaneously measured using K+‐selective micro‐electrodes. 2. Using double‐barrelled K+ selective micro‐electrodes it was possible to measure the time course of accumulation or depletion of K+ accompanying a single action potential without complications arising from mechanical or electrical artifacts. 3. K+ activity in the extracellular space increased during the action potential and then decreased to base‐line levels during the diastolic depolarization phase. Single beat accumulations of 0.1‐0.4 M could be measured. 4. The magnitude of accumulation or depletion of K+ depended upon the membrane potential such that K+ accumulated at potentials positive to ‐50 mV (K+ efflux greater than K+ uptake) and was depleted from the extracellular space at potentials negative to ‐50 mV (K+ efflux less than K+ uptake). 5. The rate of K+ depletion was fairly constant during the time course of a clamp step within the range of diastolic depolarization (‐55 to ‐75 mV) even though the accompanying membrane current showed marked time‐dependent kinetics. 6. The total membrane conductance measured during the time course of the diastolic depolarization or during the time course of activation of time‐dependent ‘pace‐maker’ current remained fairly constant or increased. 7. No reversal potential for the time‐dependent ‘pace‐maker’ current could be measured at EK in solutions containing 2.7, 5.4 and 8.1 mM‐K+. 8. These results do not support the turn‐off a K+ conductance as the primary mechanisms for the generation of the pace‐maker potential in SA nodal tissue; rather the results are more consistent with the idea that activation of an inward current, with large positive equilibrium potential, is responsible for pace‐making activity.
Variety of functional organization within the monkey motor cortex
Authors: Lemon R. N.
Published: December 2014

1. Single‐unit recordings have been made from 606 neurones in the arm region of area 4 in five conscious monkeys. Their activity during a stereotyped motor task and their responses to passive natural stimulation of the limb have been investigated.

2. 88% of area 4 neurones responsive to natural stimulation received their afferent input from a restricted region of the contralateral arm.

3. The activity and afferent input to cell groups have been determined by comparing the properties of neurones located within 500 μm of each other and recorded in one and the same micro‐electrode penetration. 115 such cell groups containing 344 neurones were investigated.

4. 75/115 cell groups (65%) contained neurones with input from the same arm zone (shoulder, elbow, wrist or hand) and with a similar pattern of task‐related activity. Cell groups containing neurones with identical afferent inputs never showed contrasting behaviour during movement.

5. 40/115 cell groups (35%) contained neurones receiving inputs from more than one arm zone. Twenty‐five cell groups (22%) had two contiguous zones (e.g. wrist and hand) represented and ten groups had input from two discontinuous zones (e.g. elbow and hand). These differences in input within a cell group were usually reflected in contrasting behaviour of its constituent neurones during movement.

6. Pyramidal tract neurones (PTNs) lying immediately adjacent to one another usually received similar inputs and exhibited matching behaviour. PTNs lying further apart in the same penetration often showed different activity and responded to different stimuli.

7. The topographic distribution of afferent input to area 4 revealed multiple representation of input from a single zone combined with considerable intermingling of input from all four zones. Neurones with shoulder and elbow inputs surrounded those with wrist inputs which in turn lay scattered around a central zone. This central zone only contained neurones with hand inputs, although neurones with hand inputs were found outside this central zone.

8. The significance of this complex organization is discussed in terms of motor cortex input and output.
The influence of concanavalin A on glutamate‐induced current fluctuations in locust muscle fibres.
Authors: Mathers D A
Published: December 2014

1. The influence of the plant lectin Concanavalin A (ConA) on the properties of membrane channels opened by 25‐200 microM‐L‐glutamate in voltage‐clamped locust muscle fibres has been studied. Power spectral density plots of membrane current fluctuations were used to estimate the mean lifetime and conductance of glutamate‐induced channels. 2. Exposure to ConA (10 micrograms/ml.) increased the amplitude of the mean current evoked by 200 microM‐glutamate from 7.7 +/‐ 4.7 nA (mean +/‐ S.D.) to 81 +/‐ 57 nA (membrane potential ‐60 mV, temperature 16 degrees C). The mean conductance of glutamate‐induced channels (65 +/‐ 16.8 pS at 16 degrees C) was negligibly affected by the lectin. 3. In normal saline the mean lifetime of glutamate‐induced channels tau noise decreased on membrane hyperpolarization. After treatment with ConA (70 micrograms/ml.), tau noise become totally independent of membrane voltage when studied at potentials in the range ‐60 to ‐120 mV. The value of tau noise at the resting potential was little altered by the lectin.
Impedance of the amphibian lens.
Authors: Duncan G , Patmore L , Pynsent P B
Published: December 2014

1. The electrical resistance of the perfused frog lens was measured using separate internal current passing and voltage measuring electrodes. 2. The resistance values obtained using voltage clamp and direct and alternating current techniques were in good agreement. 3. The voltage transients induced in response to current steps were multi‐exponential in form. Increasing the external K concentration reduced both the amplitude of the voltage response and the rise time. 4. The impedance characteristics were investigated in more detail using alternating current analysis techniques. 5. In an equivalent‐circuit modelling study it was assumed that there were two major pathways for current flow in the lens. The first through the surface membranes and the second through the inner fibre membranes via the narrow extracellular spaces. 6. The experimental impedance loci could not be adequately fitted by a simple two time constant model and a third time constant was introduced which may represent diffusion polarization effects in the extracellular spaces. 7. The three time constant model gave good and consistent fits to impedance data from a number of preparations. 8. The form of the impedance loci was also dependent on the external K concentration, but the only fitted parameter which changed consistently with external K was the surface membrane resistance (Rs).
The effect of local anaesthetics on strophanthidin toxicity in canine cardiac Purkinje fibres
Authors: Bhattacharyya M. L. , Vassalle M.
Published: December 2014

1. Canine Purkinje fibres were superfused in vitro and the electrical and mechanical effects of the local anaesthetics benzocaine and procaine were studied in the absence and in the presence of other agents.

2. Both benzocaine (1 × 10−4‐5 × 10−4
m) and procaine (6 × 10−5‐2·5 × 10−4
m) decreased slightly the amplitude of the upstroke and markedly the duration of the action potential. The plateau was shifted to more negative values and the force of contraction was decreased. These effects were dose‐dependent.

3. The local anaesthetics abolished the spontaneous activity induced by strophanthidin (5 × 10−7
m) by flattening the oscillatory potential in diastole and increased the force of contraction under these circumstances.

4. The local anaesthetics significantly delayed the time of the onset of the spontaneous activity induced by strophanthidin (10−6
m). Also, the intensity of the stimuli had to be increased and the rate of discharge of intoxicated fibres was slower in the presence of local anaesthetics. In contrast, the positive inotropic effect was little affected.

5. The local anaesthetics reduced but did not block the inotropic action of norepinephrine and high Ca; and did not abolish (while Mn did) small action potential in 27 m
m‐K‐depolarized fibres.

6. In fibres treated with local anaesthetics, lowering [Ca]o did not result in a force rebound and administration of caffeine or exposure to low Na resulted in a larger increase in force.

7. In fibres loaded with Ca, local anaesthetics caused an increase in force.

8. Local anaesthetics decreased the force more when the external Na concentration was lower.

9. This work shows that the local anaesthetics alter the mechanical performance of Purkinje fibres and lead to a depression of the strophanthidin induced oscillatory potential. As for the mechanism for these changes, the present experiments support the hypothesis that local anaesthetic agents have an antiarrhythmic action by decreasing intracellular Na and therefore intracellular Ca as suggested by Perry, McKinney & DeWeer (1978) on the basis of experiments on nerve.
Appearance of adenosine triphosphate in the coronary sinus effluent from isolated working rat heart in response to hypoxia.
Authors: Clemens M G , Forrester T
Published: December 2014

1. A working rat heart preparation was used to study the release of adenosine‐5'‐triphosphate (ATP) into the coronary sinus effluent in response to hypoxia. 2. The left ventricle was set to pump against an hydrostatic pressure of 65 cm water; the left atrial filling pressure was kept constant at 10 cm water. The power output of the heart at these pressures was estimated to be approximately one half of the maximum power development. 3. Samples for ATP assay were collected (a) 30 sec before onset of hypoxia, (b) 60‐90 sec after onset of hypoxia, (c) 5 min after restoration of oxygenated buffer solution. Respective concentrations of ATP were (nM +/‐ S.E.) 0.63 (+/‐ 0.18), 4.70 (+/‐ 0.39) and 0.63 (+/‐ 0.06). The total amounts of ATP detected were (p‐mole/min) 5.9 (+/‐ 0.9), 46.1 (+/‐ 6.0) and 5.5 (+/‐ 1.2) respectively. 4. Viability of the hearts was judged to be satisfactory on the following grounds. Alterations in left atrial filling pressure produced typical Frank‐Starling responses of the left ventricle. Oxygen extraction from the perfusate increased in response to increased workload. Coronary blood flow increased immediately upon introduction of hypoxic conditions and mechanical recovery from hypoxia was always complete within 5 min of restoring oxygen. 5. In view of the marked extracellular ATPase activity it is concluded that significant vasodilatory concentrations of ATP are released into the myocardial extracellular space in response to hypoxia. A scheme is proposed describing the possible role of adenine nucleotides in the local control of myocardial blood flow.
Chloride dependence of frusemide‐ and phloretin‐sensitive passive sodium and potassium fluxes in human red cells.
Authors: Chipperfield A R
Published: December 2014

1. In outdated human red blood cells, there was a Ko‐dependent, ouabain‐insensitive efflux of Na that was inhibited by frusemide and phloretin. 2. It was reduced or absent (a) in media containing Ca or Mg, (b) in fresh cells. 3. In media with Cl partly replaced by NO3, Na efflux, and its sensitivity to Ko and frusemide, were reduced. 4. The saturable component of ouabain‐insensitive K influx was dependent on Cl and inhibited by frusemide and by phloretin. 5. Bromide also supported a frusemide‐sensitive, ouabain‐insensitive K influx but acetate and SO4 (like NO3) did not.
Sidedness of the effects of sodium and potassium ions on the conformational state of the sodium—potassium pump
Authors: Karlish S. J. D. , Pick U.
Published: December 2014

1. (Na,K)ATPase from kidney membranes has been reconstituted into proteoliposomes following solubilization in cholate, by the freeze—thaw sonication procedure described by Kasahara & Hinkle (1977). The method is rapid and convenient.

2. Upon addition of ATP to the exterior medium the reconstituted vesicles sustain high rates of active 22Na uptake and 86Rb efflux with many properties similar to those of the Na/K pump in well characterized cells such as erythrocytes.

3. Observations on both active and passive transport of 22 Na and 86Rb indicate that the vesicle population is heterogeneous; about 40 per cent contain Na/K pumps and the remainder seem to be plain lipid vesicles.

4. The major Na+‐ or K+‐stabilized non‐phosphorylated conformational forms of the (Na, K)ATPase, E1. Na and E2. (K) respectively, have been investigated in the proteoliposomes, with particular regard to sidedness of the actions of Na+ and K+.

5. Tryptic digestion of the vesicles reveals the Na+‐ and K+‐stabilized conformations E1. Na and E2. (K) as characterized originally for purified (Na, K)ATPase (Jørgensen, 1975). Controlled trypsinolysis of Tris+‐loaded vesicles in a Na+‐or K+‐containing medium leads to typical biphasic (Na+) or simple exponential (K+) time courses respectively, for loss of ATP‐dependent 22Na uptake (assayed subsequent to the tryptic digestion in the presence of inophores valinomycin plus FCCP). Tryptic digestion of K+‐ or Rb+‐ or Tris+‐loaded vesicles suspended in a Na+ medium results only in the biphasic (E1. Na) pattern of loss of ATP‐dependent 22Na uptake.

6. ATP‐dependent 22Na uptake and 86Rb efflux are reduced by about the same extent following a short tryptic digestion in a Na+‐containing medium.

7. Vanadate ions inhibit ATP‐dependent 22Na uptake into the vesicles, at low concentrations (K0·5 ∼ 2 × 10−7
m), following pre‐incubation together with Mg2+ and K+ ions. K+ ions in the medium are effective, K+ ions within the vesicle are not. Na+ ions in the medium prevent inhibition by vanadate+Mg2+ but do not reverse inhibition in vesicles pre‐incubated with vanadate, Mg2+ and K+ ions.

8. The results show that the conformational forms E1. Na and E2. (K) are stabilized by Na+ or K+ ions respectively, bound to sites on the Na/K pump normally facing the cytoplasm. The significance of this finding is discussed in relation to the cation transport function of the pump.
The effect of insulin upon the influx of tryptophan into the brain of the rabbit.
Authors: Daniel P M , Love E R , Moorhouse S R , Pratt O E
Published: December 2014

1. The effect of hyperinsulinaemia upon the influx of tryptophan into the brain was determined. A raised level of insulin was maintained in the circulation of rabbits for periods of up to 120 min by means of a continuous, programmed intravenous injection of the hormone, given by an electronically controlled variable‐drive syringe. A similar, appropriately programmed, intravenous injection of glucose, given simultaneously with the insulin, maintained the concentration of the blood glucose within normal limits throughout each experiment, so that the results were not vitiated by the development of hypoglycaemia. 2. Raised levels of insulin in the blood affect the supply of tryptophan to the brain in two opposing ways: (a) by increasing the binding of tryptophan to the albumin in the blood, thereby reducing the level of the free tryptophan in the circulation by about a half, which would decrease the influx of tryptophan into the brain; (b) by simultaneously reducing the levels in the blood of six or more of the amino acids which compete with tryptophan for transport carriers into the brain, which would increase the influx of tryptophan. The net result of these two opposing effects is that insulin causes only a slight increase in the influx of tryptophan into the brain. 3. To account in quantitative terms for the effect of insulin upon the influx of tryptophan into the brain it proved necessary to make one assumption. This assumption was that a predictable proportion of the tryptophan which is loosely bound to blood albumin is being stripped off this protein by the transport carrier located on the luminal surface membranes of the endothelial cells during the passage of the blood through the cerebral capillaries. If this assumption is accepted the work reported here explains adequately the effect of insulin on the influx of tryptophan into the brain.
Localization of specialized noradrenaline receptors at neuromuscular junctions on arterioles of the guinea‐pig.
Authors: Hirst G D , Neild T O
Published: December 2014

1. Noradrenaline was applied by ionophoresis to various positions on the surface of an arteriole, and any changes in membrane potential of the arteriolar smooth muscle were recorded. 2. At a proportion of positions noradrenaline produced membrane depolarization. 3. The positions where noradrenaline produced these membrane potential changes were restricted to regions close to the sympathetic nerves which innervated the arterioles.
Amiloride sensitivity of the transepithelial electrical potential and of sodium and potassium transport in rat distal colon in vivo.
Authors: Edmonds C J
Published: December 2014

1. The effect of amiloride within the gut lumen on the transepithelial electrical potential difference (p.d.) and Na and K transport by the distal colon of adrenalectomized (dexamethasone‐maintained), normal, aldosterone‐infused and Na‐depleted groups of rats was examined. 2. Amiloride had no effect in adrenalectomized rats; in normal rats, only the p.d. was significantly reduced. 3. In the group given a short (2 hr) aldosterone infusion, amiloride reduced the elevated p.d. and K secretion rate to normal levels. There was no change in apparent K permeability of the epithelium. 4. In the Na‐depleted group, p.d. and Na absorption were virtually abolished by amiloride but although K secretion was reduced it still remained much above normal levels. Adrenalectomy prevented the effects of Na depletion. 5. P.d. change occurred rapidly when amiloride was added to the perfusate. Increasing the Na concentration in the perfusate reduced the sensitivity to amiloride. Apparent ‘Km’ values estimated from p.d. changes (luminal Na, 50 mM) were similar for aldosterone‐infused (7.6 X 10(‐6) M) and Na‐depleted (5.4 X 10(‐6) M) rats. 6. Aldosterone appears to be essential for the induction of amiloride‐sensitive Na paths in the mucosal plasma membrane of rat colonic epithelial cells. Prolonged aldosterone stimulation, as in the Na‐depleted rats, increases the amiloride‐sensitive Na paths while largely suppressing the amiloride‐insensitive Na paths; in addition, the K/Na clearance rate ratio of the epithelium is increased. AMiloride interacts only with one set of Na paths and does not interact directly with K paths.
Ionized calcium in milk and the integrity of the mammary epithelium in the goat.
Authors: Neville M C , Peaker M
Published: December 2014

1. Injection of citrate or EGTA solutions into the lumen of the mammary gland of goats in quantities sufficient to reduce ionized calcium to less than one‐tenth of normal, led to increases in milk concentrations of Na and Cl and decreases in K and lactose. 2. Subsequent milk yields were decreased in glands treated with citrate but not in those treated with EGTA. 3. Blood‐milk potential difference decreased (i.e. towards zero) in glands in which citrate was present. 4. In goats milked hourly with the aid of oxytocin, milk Na and Cl concentrations increased while K and lactose decreased; there was no apparent decrease in Ca2+ concentration. 5. It is suggested that ionized calcium in milk is essential to preserve the integrity of the mammary epithelium during lactation.
Developmental changes in pancreatic endocrine function in the young calf.
Authors: Bloom S R , Edwards A V
Published: December 2014

1. Pancreatic endocrine responses to 2‐deoxyglucose (1.2 mmol/kg I.V.) known to be mediated via the autonomic innervation, have been investigated in calves 24 h after birth and the results compared with those obtained previously in older calves (Bloom, Edwards & Hardy, 1978). 2. Neurally mediated insulin release was found to be defective in the calf at 24 h, whereas the capacity to release both pancreatic glucagon and pancreatic polypeptide (PP) in response to 2‐deoxyglucose appears to be fully developed at this age. 3. Both the release of glucagon and of PP from the pancreas which occurred under these conditions were suppressed by I.V. infusions of glucose (17 mumol . kg‐1 . min‐1) which raised the arterial plasma glucose concentration of unsuckled 24‐h‐old calves to the level normally encountered in suckled calves of the same age. 4. Closely similar changes in the haematocrit and plasma cortisol concentration occurred in both suckled and unsuckled 24‐h‐old calves in response to 2‐deoxyglucose, suggesting that the intensity of the stimulus to the brain was equipotent and that glucose inhibits the release of glucagon and PP by a direct action on the alpha and PP cells respectively. 5. closely similar changes in plasma PP concentration were observed in suckled and unsuckled 24‐h‐old calves in response to 2‐deoxyglucose, in spite of the higher plasma glucose concentration in the former group. It is concluded that the PP response is potentiated by some unidentified factor in suckled calves.
The direction of growth of differentiating neurones and myoblasts from frog embryos in an applied electric field.
Authors: Hinkle L , McCaig C D , Robinson K R
Published: December 2014

1. Disaggregated single neurones and myoblasts obtained from the neural tube and somites of Xenopus laevis embryos (stages 17‐21) were cultured in the presence of steady small electric fields. 2. Neurites grew preferentially towards the negative pole, or cathode, in field strengths of 7‐190 mV/mm. Many turned through considerable angles to do so. This effect disappeared below a threshold level of about 7 mV/mm. 3. Greater numbers of neurones sprouted neurites in cultures exposed to an electric field compared to control cultures. The difference could be as much as tenfold. The threshold level of this phenomenon was about 6‐8 mV/mm. Other cell types such as pigment cells and fibroblasts were also stimulated to differentiate in culture by an electric field, although to a lesser extent than neurones. 4. Applied electric fields had no effect on the location of the origin of neurites on the cell body. 5. Spherical myoblasts cultured in applied electric fields (36‐170 mV/mm) elongated with a bipolar axis of growth which was perpendicular to the electric field. The response was graded and disappeared at field strengths below 36 mV/mm. 6. It is suggested that in vivo, the direction of neural outgrowth from the neural tube and the strict spatial organization of somites might be under the control, in part, of endogenous electric fields. Possible sources of these are discussed.