bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of motor units in a small foot muscle of Xenopus laevis.
Authors: Ridge R M , Thomson A M
Published: December 2014

1. Extensor digitorum longus IV muscle (EDL IV) of Xenopus laevis was isolated together with its nerve and the 8th and 9th spinal roots. Motor units were functionally isolated and their properties investigated. 2. The motor unit isometric twitch and tetanic tensions, contraction time and axon conduction time and distance were measured. Axon conduction velocity and twitch:tetanus ratio were calculated. 3. The distributions of motor unit properties were continuous and showed no tendency to separate into types. 4. Axon conduction velocity was directly related to unit tetanic tension (expressed as a percentage of whole muscle tetanic tension and to twitch:tetanus ratio and inversely related to contraction time. Unit tetanic tension was directly related to twitch:tetanus ratio and inversely related to contraction time. Contraction time was inversely related to twitch: tetanus ratio. Possible explanations for these relationships are discussed. 5. The units of EDL IV show a greater resistance to fatigue than fast units of other amphibian muscles. There was no separation of units into fatiguable and fatigue resistant types.
Polyneural innervation: mechanical properties of overlapping motor units in a small foot muscle of Xenopus laevis.
Authors: Ridge R M , Thomson A M
Published: December 2014

1. Extensor digitorum longus IV of Xenopus laevis was isolated together with its nerve and the 8th and 9th spinal roots. Motor units were functionally isolated, by splitting and stimulating ventral root filaments. 2. Motor units were stimulated separately and in pairs. Between many pairs, overlap of motor innervation was found (evidence of polyneuronal innervation of muscle fibres). Evidence for overlap was a deficit in the tension developed when the two units were stimulated together compared with the sum of the tetanic tensions developed when the two units were stimulated separately. This provided a measure of the extent of overlap. 3. Polyneuronal innervation was confirmed by intracellular recording from muscle fibres during stimulation of each motor axon. 4. For each motor unit, isometric twitch and tetanic tensions, twitch contraction time and the motor axon conduction time and distance were measured and axon conduction velocity and twitch:tetanus ratio were calculated. 5. The properties of the pairs of motor units found to overlap are reported and marked disparities between the properties of some units in overlapping pairs demonstrated. 6. Frequency distributions for the properties of motor units shown to overlap with others were not significantly different from those for total unit samples., Therefore polyneuronal innervation of muscle fibres occurs throughout the motor unit population of this muscle. 7. In several motor units the isometric twitches of several individual muscle fibres were recorded, each fibre being stimulated by intracellular current injection. It was found that contraction times of single fibres differed by up to 36% between muscle fibres in the same unit and that twitch tension varied by up to 400%.
Anticipation and fusimotor activity in preparation for a voluntary contraction.
Authors: Burke D , McKeon B , Skuse N F , Westerman R A
Published: December 2014

1. Multi‐unit and single‐unit recordings were made of muscle spindle afferent activity from the pretibial muscles of human subjects who were initially relaxed. The muscles were subjected to a stretching perturbation of 1 s duration, occurring irregularly, on average once every 5 s. In test sequences, an auditory or visual warning was provided 1 . 06 s before some of the perturbations. Subjects were required to oppose every perturbation by contracting the receptor‐bearing muscle as rapidly as possible. 2. Following the warning all subjects sometimes tensed the receptor‐bearing muscle unintentionally in preparation for the perturbation. In these contractions, the discharge of a spindle ending accelerated only if the contraction strength exceeded the ending's threshold for activation, established in control voluntary contractions performed under isometric conditions. 3. When the receptor‐bearing muscle did not contract in the interval between warning and perturbation, there was no detectable change in the multi‐unit recordings of spindle activity or in recordings from twelve of thirteen single spindle afferents. The thirteenth spindle afferent discharged prior to the perturbation in the absence of detectable e.m.g. in response to (only) three of twenty‐three warning stimuli. However, this ending had been so responsive during isometric voluntary contractions that a contraction level at which it did not respond could not be established, and it is suggested that the findings with this ending resulted from its low threshold rather than from selective activation of the fusimotor system. 4. When subjects were warned of the perturbations, the dynamic response of spindle endings to the perturbations was not increased in size or altered in latency. 5. The motor response to perturbations without warning generally contained only long‐latency (volitional) e.m.g. activity occurring 107‐‐200 ms after the onset of the perturbation. When a warning was given, short‐latency (reflex) e.m.g. activity was also recorded, beginning 46‐‐76 ms after the onset of the perturbation. 6. It is concluded that anticipation of the need to contract a muscle does not result in selective activation of fusimotor neurones in preparation for the contraction. The change in stretch reflex gain that occurs as a result of ‘anticipation’ occurs through a central process which does not involve the fusimotor system.
Voltage‐clamp experiments in normal and denervated mammalian skeletal muscle fibres.
Authors: Pappone P A
Published: December 2014

1. The vaseline‐gap voltage‐clamp method has been applied to the study of ionic currents in cut pieces from innervated and 5‐‐7 days denervated rat skeletal muscle fibres. 2. Kinetic analysis of sodium currents in innervated rat muscle showed them to be similar to those in frog muscle, except that rat sodium channels are activated at slightly more negative potentials. Peak sodium conductances of 40‐‐50 m‐mho/cm2 were measured, corresponding to values of GNa of 100‐‐120 m‐mho/cm2. 3. The permeability sequence of the sodium channel to several organic and inorganic cations is Li+ greater than Na+ greater than hydroxylammonium greater than hydrazinium greater than guanidinium approximately ammonium greater than K+. TMA+ and Ca2+ were not measurably permeant. 4. Denervation appears to shift activation and inactivation parameters of sodium currents by approximately 10 mV to more negative potentials, but does not appreciably affect the maximum peak sodium conductance or the time constants for activation and inactivation. 5. Dose‐‐response curves for block by tetrodotoxin in innervated fibres are fitted well by assuming binding of toxin to a single population of channels with a dissociation constant of about 5 nM. In denervated fibres there appears in addition a second population of channels with a dissociation constant in the micromolar range. These relatively toxin‐insensitive channels respond less rapidly to potential changes, and can contribute up to 25‐‐30% of the total sodium conductance. 6. The potassium currents of innervated rat muscle were similar to those of frog muscle in their voltage dependence of activation. 7. The time constant for inactivation of the sodium current, tau h, at ‐13 mV showed a temperature dependence measured between 10 and 20 degrees C equivalent to an average Q10 of 2 . 3. The Q10 for the time constant of activation of the potassium current tau n, averaged 2 . 5 between ‐40 mV and +40 mV, measured over the same temperature range.
Intracellular potassium and sodium activities of chick ventricular muscle during embryonic development.
Authors: Fozzard H A , Sheu S S
Published: December 2014

1. The basis of the resting potential of chick embryo ventricular muscle was studied by use of ion‐selective micro‐electrodes. Membrane resting potential hyperpolarized from ‐65 . 4 +/‐ 1 . 1 mV (mean +/‐ S.E.) at age 4 day to ‐75 . 8 +/‐ 0 . 6 mV at age 18 day. Action potential overshoot increased from +19 . 8 +/‐ 0 . 9 at age 4 day to +33 . 1 +/‐ 0 . 6 mV at age 18 day. 2. Intracellular K+ activity measured with ion‐selective micro‐electrodes increased from 71 . 3 +/‐ 1 . 9 mM at age 4 day to 89 . 9 +/‐ 1 . 1 at age 18 day. Intracellular Na+ activity decreased from 12 . 5 +/‐ 0 . 4 to 7 . 0 +/‐ 0 . 3 mM during the same period. The difference between membrane resting potential and the calculated potassium equilibrium potential decreased with development. PNa/PK estimated from the constant field equation decreased from 0 . 012 at age 4 day to 0 . 005 at age 18 day. 3. The hyperpolarization of resting potential and the increased action potential overshoot during development could be explained by a rise in intracellular K+ activity and a fall in intracellular Na+ activity, as if the Na‐‐K exchange pump became more active.
Comparison between the delayed outward current in slow and fast twitch skeletal muscle in the rat.
Authors: Duval A , Léoty C
Published: December 2014

1. A comparison of the delayed outward current of isolated fibres from rat soleus and iliacus muscle has been made using a double sucrose‐gap voltage‐clamp method. 2. The fast and slow components of the outward current were separated using time constants of the tail currents. The results indicate that in both iliacus and soleus fibres there is a shift in reversal potential which depends on the quantity of current that flows during depolarization. 3. The shift is larger in iliacus than in soleus; it is absent in glycerol‐treated muscles. 4. The results obtained in normal and in detubulated fibres show that the shift is due to an accumulation process of potassium ions in the lumen of the T‐tubules. 5. In detubulated soleus fibres the outward current is composed of a fast and a slow component, each with the same reversal potential; in detubulated iliacus the slow component is absent. 6. In both types of muscles TEA produces a dose‐dependent block of the total outward current. 4‐aminopyridine has different effects; it inhibits the total outward current in iliacus fibres and only the fast component in soleus fibres. 7. These results show that in soleus fibres a fast and a slow component participate in the potassium outward current, while only a fast component is present in iliacus muscle.
The variance of sodium current fluctuations at the node of Ranvier
Authors: Sigworth F. J.
Published: December 2014

1. Single myelinated nerve fibres 12‐17 μm in diameter from Rana temporaria and Rana pipiens were voltage clamped at 2‐5 °C. Potassium currents were blocked by internal Cs+ and external tetraethylammonium ion. Series resistance compensation was employed.

2. Sets of 80‐512 identical, 20 ms depolarizations were applied, with the pulses repeated at intervals of 300‐600 ms. The resulting membrane current records, filtered at 5 kHz, showed record‐to‐record variations of the current on the order of 1%. From each set of records the time course of the mean current and the time course of the variance were calculated.

3. The variance was assumed to arise primarily from two independent sources of current fluctuations: the stochastic gating of sodium channels and the thermal noise background in the voltage clamp. Measurement of the passive properties of the nerve preparation allowed the thermal noise variance to be estimated, and these estimates accounted for the variance observed in the presence of tetrodotoxin and at the reversal potential.

4. After the variance σ2 was corrected for the contribution from the background, its relationship to the mean current I could be fitted by the function σ2 = iI—I2/N expected for N independent channels having one non‐zero conductance level. The single channel currents i corresponded to a single‐channel chord conductance γ = 6·4 ± 0·9 pS (S.D.; n = 14). No significant difference in γ was observed between the two species of frogs. The size of the total population of channels ranged from 20,000 to 46,000.

5. The voltage dependence of i corresponded closely to the form of the instantaneous current—voltage relationship of the sodium conductance, except at the smallest depolarizations. The small values of i at small depolarizations may have resulted from the filtering of high‐frequency components of the fluctuations.

6. It is concluded that sodium channels have only two primary levels of conductance, corresponding to ‘open’ and ‘closed’ states of the channel.

7. The fraction pmax of channels open at the time of the peak conductance was found to be 0·59 ± 0·08 (S.D.; n = 5) and 0·9 ± 0·1 (S.D.; n = 3) for depolarizations to ‐5 and +125 mV, respectively. (50 ms hyperpolarizations to ‐105 mV preceded the depolarizations in each case.) These values are similar to those predicted by Hodgkin‐Huxley kinetics.

8. Fluctuations in the firing threshold of neurones are expected from the stochastic gating of sodium channels. A prediction of the size of these fluctuations based on the measured properties of the channels gives a value of about 1% for the relative spread, which agrees with experimental values in the literature.
The role of the vagus and splanchnic nerves in the regulation of intragastric pressure in the ferret.
Authors: Andrews P L , Grundy D , Lawes I N
Published: December 2014

1. The role of the vagus and splanchnic nerves in the regulation of intragastric pressure was investigated by quantifying the effect of nerve section on the response to a standard fluid inflation of the stomach. An opportunity was also taken to compare the responses to a step and physiological ramp inflation of the same volume (50 ml). 2. The peak pressure at the end ot the step inflation (13.6 +/‐ 1.0 cmH2O) was twice that for a ramp inflation (6.2 +/‐ 0.4 cmH2O). 5 min after the peak the pressures were similar (4.8 +/‐ 0.3 cmH2O; 4.7 +/‐ 0.3 cmH2O) for both. 3. Vagotomy produced a significant increase in the intragastric pressure response for both the peak and plateau levels of the step and ramp inflations. 4. Atropine produced a statistically significant decrease in the pressure response to both step and ramp inflation. 5. Splanchnic nerve section produced an increase in the intragastric pressure response to both step and ramp inflations although the values failed to reach the 5% significance level. However, following vagotomy or atropine, section of the splanchnic nerves produced a statistically significant increase in the pressure response to inflation. 6. These results indicate that the vagal cholinergic excitatory and vagal non‐cholinergic, non‐adrenergic inhibitory fibres are activated at physiological levels of gastric inflation and play a role in the regulation of intragastric pressure. The splanchnic nerves also play a role although in the intact animal they are suppressed by the action of the vagus nerve.
Effect of temperature on the anomalous rectification of the membrane of the egg of the starfish, Mediaster aequalis.
Authors: Hagiwara S , Yoshii M
Published: December 2014

1. The effect of temperature upon the anomalous or inward rectification of the K conductance in the immature egg membrane of the starfish, Mediaster aequalis, was studied by using voltage clamp technique. 2. The K conductance decrease with a relatively small Q10 (1.62) down to about 10 degrees C; below 10 degrees C, the Q10 is much greater (5.8 at [K+]o = 25 mM). The smaller Q10 is independent of [K+]o, whereas the larger one depends on [K+]o. 3. The activation of the rectification depends on V‐VK, rather than V alone, at all temperatures at constant internal K concentration. 4. The K conductance at a given V‐VK is approximately proportional to the square root of [K+]o at a fixed [K]i above 10 degrees C while the conductance depends substantially less on [K+]o below this temperature. 5. The logarithm of the activation time constant of the inward rectification depends linearly on the membrane potential at all temperatures. 6. The slope of the relation is strongly temperature dependent above about 10 degrees C whilst the dependence is much less below 10 degrees C; i.e. the Q10 of the activation time constant is membrane potential‐dependent above 10 degrees C. 7. The results suggest that the mechanism of ion permeation during anomalous rectification changes at about 10 degrees C.
Parotid secretion of fluid and amylase in rabbits during feeding.
Authors: Gjörstrup P
Published: December 2014

Saliva has been collected from conscious rabbits in response to feeding pellets and carrots and amylase concentrations and flow‐rates were measured. Saliva was collected from a polythene tube permanently inserted into the main duct, which, in most cases, kept patent for about a fortnight without any obvious decrease in the secretory capacity of the glands. 2. With pellets the flow‐rate varied between 50 and 1250 microliter./min, and the corresponding amylase concentration was relatively constant around 250 units/ml. When carrots were fed, the flow‐rates were about threefold lower, but the amylase concentration was raised to a mean value around 1000 units/ml. In spite of the differences in flow‐rates, the two kinds of food promoted the same maximum output of amylase, and the output for both kinds of food promoted the same maximum output of amylase, and the output for both kinds of food was found to increase with the flow‐rate. 3. The amylase concentration in the saliva decreased after pre‐ or post‐ganglionic sympathetic denervation, reducing the output of amylase by about 50%. However, the amylase concentration was further lowered by beta‐adrenoceptor block, which decreased the output by an additional 25%, suggesting that circulating catecholamines contributed to the secretion of amylase. 4. The fluid secretion in response to pellets and carrots was mainly dependent on parasympathetic activity, and for both kinds of food the range of flow‐rates was unaltered by sympathectomy or beta‐adrenoceptor block. However, at flow‐rates below 50 microliter./min, where 25% of all samples with carrots were obtained, sympathetic activity may have contributed significantly to the fluid secretion. 5. In experiments on anaesthetized rabbits, frequency‐response curves for amylase and fluid secretion in response to parasympathetic and sympathetic activation were obtained. A comparison between these observations and those obtained in the conscious animals during feeding suggests a parasympathetic activity mainly between 1 and 5 Hz and a sympathetic around 1 Hz. 6. It is concluded that both parasympathetic and sympathetic secretory nerves are reflexly activated during feeding, and that the normal secretion during a meal is dependent on an interplay between the nerves. The results suggest that at least two different afferent nervous pathways are involved in the control of the secretory nerves.
Luminal acidification by the perfused rat cauda epididymidis
Authors: Au C. L. , Wong P. Y. D.
Published: December 2014

1. Acid secretion by the rat cauda epididymidis was studied by microperfusion of the epididymal duct and by measuring the pH of the perfusate at a constant pCO2 using a micro pH sensitive electrode. The rate of acidification was expressed as the rate of fall of intraluminal bicarbonate per cm duct per min.

2. When the cauda epididymal duct was perfused with normal bicarbonate solution, the luminal bicarbonate concentration fell at a rate of 0.59 ± 0.39 n‐equiv cm−1 min−1 (mean ±
s.e., n = 22).

3. The rate of luminal acidification was independent of the perfusion rate but was dependent on the concentration of bicarbonate in the perfusion fluid. The rate of fall of luminal bicarbonate increased with increasing bicarbonate concentration and showed saturation at an intraluminal bicarbonate concentration of 25 m‐mole/l.

4. Acidification was abolished in the absence of intraluminal sodium ions. This may suggest a linked sodium reabsorption and hydrogen ion secretion.

5. Acidification of the luminal fluid was studied under different acid‐base conditions. In animals undergoing metabolic acidosis, the rate of acidification was enhanced, and conversely in animals undergoing metabolic alkalosis, the rate was depressed.

6. Intravenous infusion of acetazolamide into rats at a dose rate of 20 mg/kg.hr markedly inhibited the acidification process. This effect was still observed in animals undergoing metabolic acidosis. Acetazolamide (10−5
m) applied luminally was found to have no effect but higher concentration (10−4
m) was found to inhibit acidification by 50%.

7. The role of acidification of the epididymal fluid in sperm maturation was discussed.
Effects of vanadate on the functional properties of the isolated toad bladder.
Authors: Beauwens R , Crabbé J , Rentmeesters M
Published: December 2014

1. Vanadate, considered by some as a candidate for physiological modulation of Na pumping activity, was studied in the isolated toad urinary bladder. It produced a decrease in Na transport activity that was reversible and could be partially antagonized by pretreatment with a disulphonic distilbene derivative, SITS. This suggests an intracytoplasmic site of action for vanadate. Other transition metal salts, prepared from Ta and Nb, produced instead a transient rise in Na transport and this was unaffected by SITS. 2. Comparison between ouabain and vanadate showed clear‐cut differences: inhibition of Na transport by the former, not the latter, was partially overcome by increasing of Na transport by the former, not the latter, was partially overcome by increasing cell Na or serosal K. Unexpectedly intracellular K did not decrease appreciably following vanadate treatment, in contrast to what occurs when ouabain was used instead. 3. Vasopressin‐induced hydro‐osmotic flow was irreversibly inhibited by vanadate but not by ouabain; pretreatment with SITS attenuated this effect. Moreover, vanadate blocked urinary acidification in this epithelium, thus supporting the hypothesis that proton flow occurs through an enzyme distinct from the mitochondrial ATPase, insensitive to vanadate.
Sympathetic modulation of mechanoreceptor sensitivity in frog skin.
Authors: Calof A L , Jones R B , Roberts W J
Published: December 2014

1. Sympathetic effects on the mechanical sensitivity of frogcutaneous mechanoreceptors were examined in vivo. 2. Functionallyidentified units were tested with repetitive mechanical stimuli ofthreshold intensity during electrical stimulation of the sympathetictrunk. 3. Sympathetic activity resulted in increased sensitivity forthree classes of afferents; slowly adapting compression receptors,slowly adapting stroke receptors, and rapidly adapting strokereceptors. Decreased sensitivity was produced in the fourth class,rapidly adapting compression receptors. 4. Preliminary tets of severalpossible modes of sympathetic influence indicated that blood flowchanges, changes in probe‐skin coupling and changes in tissuecompliance could not account for the observed changes in receptorsensitivity. Na+ and Cl‐ ions, secreted by cutaneous mucous glandswere found to be possible contributors to the decreased sensitivity ofrapidly adapting compression receptors. Direct neurotransmitter actionon the receptors, a likely mechanism of sympathetic action, was nottested. 5. The data indicate that systematic changes in cutaneoussensibility occur with modest changes in sympathetic efferentactivity. Possible mechanisms of these sympathetic effects arediscussed.
Effects of calcium and ionic strength on shortening velocity and tension development in frog skinned muscle fibres.
Authors: Julian F J , Moss R L
Published: December 2014

1. The influence of Ca2+ concentration and ionic strength on the maximum velocity of shortening (Vmax) and the tension generating capability of frog skinned muscle fibres has been studied at temperatures between 1 and 10 degrees C. 2. Fibre segments were mounted between a force transducer and servo motor, where they could be viewed and photographed through a microscope. Segments in which the striations became non‐uniform during activation were discarded. 3. Velocity was obtained as a function of load by stepping the tension to values less than the steady isometric tension. Vmax was then determined by an extrapolation technique. Vmax was also obtained using a second, independent method by measuring the times required to take up various amounts of slack imposed on the segments. 4. Vmax was significantly influenced by the Ca2+ concentration, decreasing by about one half when the Ca2+ concentration was reduced to give steady tensions less than half‐maximal. 5. Vmax was not influenced by changes in ionic strength, in the range 0.09‐0.18 M. Steady tension was found to increase as ionic strength was decreased in the same range. 6. These results indicate that the effect of changes in ionic strength is to alter the numbers or stiffness of attached cross‐bridges, while there is no apparent influence of ionic strength on the steady‐state kinetics of the actin‐myosin interaction during unloaded shortening. The mechanism responsible for the influence of Ca2+ on Vmax is unknown, though possible sites of action for Ca2+ are discussed.
The influence of hyaluronidase on urinary and renal medullary composition following antidiuretic stimulus in the rat.
Authors: Law R O , Rowen D
Published: December 2014

1. The influence of urinary hyaluronidase (believed to be predominantly of renal origin) on the urinary concentrating process has been studied in rats subjected to antidiuretic stimulus. 2. Antiserum against a partially purified preparation of this enzyme has been raised in rabbits. Urinary volume, solute excretion and medullary composition have been investigated in rats treated with this antiserum (0.2 ml./100 g body weight, i.v.) before water deprivation for 48 hr or infusion for up to 4 hr with arginine‐vasopressin. Control rats were pre‐treated with normal rabbit serum. 3. Pre‐treatment with antiserum against rat urinary hyaluronidase (AUase) caused water‐deprived rats to excrete urine at a rate significantly greater, and of osmolality significantly lower, than that recorded in control rats. 4. The increase in medullary solute gradient which typically accompanies antidiuresis was significantly reduced in water‐deprived rats pre‐treated with AUase. 5. In rats treated with AUase and infused for 4 hr with arginine‐vasopressin, there was no significant increase in the medullary solute gradient, whereas this increased markedly in control rats. 6. During the first 24 hr of water deprivation there weas an increase in the rate of Ca excretion by control rats which was abolished by pre‐treatment with AUase. 7. The effects of antiserum against a partially purified preparation of rat testicular hyaluronidase (ATase) were studied in water‐deprived rats. No evidence was obtained that this enzyme has any influence on renal function. 8. It is concluded that urinary hyaluronidase, but not testicular hyaluronidase, plays an important role in facilitating the urinary concentrating process following antidiuretic stimulus.
Changes in the recruitment threshold of motor units produced by cutaneous stimulation in man.
Authors: Garnett R , Stephens J A
Published: December 2014

1. The effect of cutaneous stimulation on the recruitment of motor units has been studied during slowly increasing voluntary contractions of human first dorsal interosseous muscle. 2. Continuous electrical stimulation of the index finger at 4 x threshold for perception caused an increase in the recruitment threshold of units normally recruited at contraction strengths less than 1.5 N and a decrease in the recruitment threshold of units normally recruited at contraction strengths greater than 1.5 N. 3. It is concluded that the recruitment order of motor units during gradually increasing voluntary muscle contraction is not fixed but depends in part on cutaneous input.
Influence of external calcium ions on labelled calcium efflux from pancreatic beta‐cells and insulin granules in mice.
Authors: Abrahamsson H , Gylfe E , Hellman B
Published: December 2014

Addition of Ca2+ to a glucose‐free perifusion medium stimulated the efflux of 45Ca from prelabelled pancreatic islets isolated from ob/ob‐mice. This effect differed from that of glucose in being transient, markedly stimulated by previous exposure to a Ca2+‐deficient medium and resulting in mobilization also of substantial amounts of 45Ca incorporated in the absence of glucose. The glucose action on 45Ca efflux reflected the balance between inhibitory and stimulatory components which differed with respect to their chronological order and sensitivity to glucose. The magnitude of the stimulatory phase was related linearly to the extracellular concentration of Ca2+ up to 2.40 mM. The efflux of 45Ca from isolated secretory granules was stimulated by Mg‐ATP. The latter made the 45Ca efflux from the granules sensitive to Ca2+; significant stimulation being seen when increasing the medium Ca2+ from 0.1 to 10 microM. The results support the concept of an efficient Ca/Ca exchange mechanism in the depolarized beta‐cells, emphasizing a role for the secretory granules in this process.
A comparison of the horizontal and vertical vestibulo‐ocular reflexes of the rabbit
Authors: Barmack N. H.
Published: December 2014

1. The gain and phase of the horizontal (H.v.o.r.) and vertical (V.v.o.r.) vestibulo‐ocular reflexes were measured in rabbits. The V.v.o.r. was evoked by sinusoidal rolls about the longitudinal axis of the rabbit. This axis was maintained at different orientations with respect to the earth horizontal axis: V.v.o.r. 0°, prone; V.v.o.r. 90°, ‘nose‐up’; V.v.o.r. 180°, supine; V.v.o.r. 0°L, left side down.

2. In contrast to the H.v.o.r., the V.v.o.r. 0° had a higher gain (eye velocity/head velocity) and a smaller phase lead (eye position + 180° with respect to head position) at low frequencies of sinusoidal vestibular stimulation (± 10 deg, 0·005‐0·05 Hz). At higher frequencies (0·05‐0·8 Hz), the H.v.o.r. and V.v.o.r. 0° were equivalent in both gain and phase.

3. The low‐frequency gain of the V.v.o.r. was smallest in the ‘nose‐up’ orientation. The V.v.o.r. 90° was equivalent in both gain and phase to the H.v.o.r. over the entire range of frequencies tested (0·005‐0·8 Hz). Threshold angular accelerations for the H.v.o.r. and V.v.o.r. 90° were below 0·04 deg/sec2.

4. The compensatory eye movements of the H.v.o.r. were frequently interrupted by anticompensatory re‐setting eye movements. These anticompensatory re‐setting eye movements were present in the V.v.o.r. 90°, but not in the V.v.o.r. 0°.

5. An estimate gain and phase of the otolithic component of the V.v.o.r. 0° was derived by subtraction of the V.v.o.r. 90° (semicircular canal signal) from the V.v.o.r. 0° (semicircular canal signal+otolith signal). This procedure was based on the assumption that the signals from the otolith organs and vertical semicircular canals combine linearly.

6. The V.v.o.r. 180° provided an interesting test of the assumption of linear combination of otolithic and semicircular canal signals by reversing the phase of the modulated otolithic signal. The data indicated that the V.v.o.r. 180° is non‐linear.
L‐proline transport by brush border membrane vesicles prepared from human placenta.
Authors: Boyd C A , Lund E K
Published: December 2014

1. Brush border microvillous plasma membranes were prepared from syncytiotrophoblast of human term placenta by a method of differential centrifugation. 2. Such plasma membranes form closed, osmotically active, right‐side‐out vesicles into which L‐proline (188 microM) is shown to be transported in a time‐dependent manner. There is no detectable metabolism of L‐proline within the vesicles during 30 min of incubation. 3. Transient accumulation of L‐proline to levels of up to three times its equilibrium value occurs in the presence of an inward gradient of sodium chloride. The proline and sodium are shown to have reached electrochemical equilibrium by 30 min, at which stage there is about 100 pmol L‐proline mg protein‐1. 4. This transient accumulation is abolished by the prior equilibration of the sodium chloride gradient, or by the replacement of sodium by inwardly directed gradients of other cations. Entry of the amino acid into the vesicles is also shown to be influenced by the permeability of the anion in the medium and by an imposed potassium diffusion potential. L‐Proline transport across the brush border membrane of human placental syncytiotrophoblast is thus a sodium‐dependent, electrogenic process. 5. Studies of the transport processes indicate saturation at higher concentrations of L‐proline with a ‘Km’ of about 1 mM; Vmax averaged about 2 nmol mg protein‐1 min‐1 varied considerably between preparations. 6. L‐Proline (188 microM) transport is inhibited competitively by the presence of many amino acids and by the dipeptide glycyl‐L‐proline. The Ki for inhibition by methyl AIB is 300 microM. 7. These findings are discussed in relation to the mechanism of transplacental amino acid transfer.
The magnesium dependence of sodium‐pump‐mediated sodium—potassium and sodium—sodium exchange in intact human red cells
Authors: Flatman Peter W. , Lew Virgilio L.
Published: December 2014

1. The magnesium content of human red blood cells was controlled by varying the magnesium concentration in the medium in the presence of the ionophore A23187. The new magnesium levels attained were very stable, which allowed the magnesium dependence of the sodium pump to be investigated.

2. The effects of magnesium were shown to occur at the inner surface of the red cell membrane for the range of magnesium concentrations tested (10−7 to 6 × 10−3
m).

3. At intracellular ionized magnesium concentrations below 0.8 m
m the activation of ouabain‐sensitive sodium—potassium exchange by internal ionized magnesium could be resolved into two or three components: (a) a small component, about 5% of the maximum flux, which is apparently independent of the ionized magnesium concentration below 2 μ
m, (b) a saturating component with a K½ of between 30 and 45 μ
m, and possibly (c) a component which increases linearly with ionized magnesium concentration and which only becomes apparent at concentrations above 0.1 m
m.

4. At intracellular ionized magnesium concentrations below 0.8 m
m, activation of ouabain‐sensitive sodium—sodium exchange by internal ionized magnesium could be resolved into two components: (a) a small component, about 6% of the maximal flux, which is apparently independent of the ionized magnesium concentration below 2 μ
m, and (b) a saturating component with a K½ of about 9 μ
m. At ionized magnesium concentrations between about 0.2 and 0.8 m
m the rate of sodium—sodium exchange remained constant at the maximal level.

5. The intracellular concentration of ATP decreased and the ADP concentration increased as the magnesium content of the cells was reduced from the normal level. A small increase in ATP and a small decrease in ADP was seen when the magnesium content was increased above the normal level. The variation in the ATP: ADP ratio from 2.5 at very low magnesium levels to about 6 at normal magnesium levels can account, at least in part, for the different K½ values of sodium—potassium and sodium—sodium exchange.

6. When the concentration of ionized magnesium was increased above about 0.8 m
m both sodium—potassium and sodium—sodium exchange were inhibited. Sodium—sodium exchange was more strongly inhibited than sodium—potassium exchange.

7. The possible sites of action of magnesium in the sodium pump cycle are discussed.
Role of the intima in cholinergic and purinergic relaxation of isolated canine femoral arteries.
Authors: De Mey J G , Vanhoutte P M
Published: December 2014

1. Experiments were designed to determine the role of the endothelium in relaxations of isolated blood vessels caused by ACh, adenine nucleotides and K+ ions. 2. Paired rings of canine femoral arteries were mounted for isometric tension recording in organ chambers filled with aerated Krebs‐Ringer solution (37 degrees C). One ring served as control; in the other ring the intimal layer was removed mechanically. 3. Removal of the endothelium only slightly depressed the maximal contractile response to noradrenaline, and did not affect the apparent sensitivity to the catecholamine. It depressed the contractile response to 25‐60 mM‐K+ more than that to noradrenaline. 4. In the absence of endothelium, the femoral arteries did not relax on exposure to ACh. 5. Removal of the endothelium did not affect relaxations caused by adenosine and AMP, but markedly reduced those caused by ADP and ATP. 6. The relaxations induced by 5.9 mM‐K+ were comparable in control rings and arteries denuded of their endothelium. 7. These experiments demonstrate that in the canine femoral artery, relaxations induced by ACh, ADP and ATP require the presence of functional endothelial cells, which, when exposed to these substances, initiate an inhibitory signal for the smooth muscle cells of the media. By contrast, relaxations of isolated arteries caused by adenosine, AMP and K+ ions must be due mainly to a direct effect on the vascular smooth muscle cells.
Atropine‐resistant depolarization in the guinea‐pig small intestine
Authors: Bywater R. A. R. , Holman M. E. , Taylor G. S.
Published: December 2014

1. Junction potentials were recorded from the circular muscle cells of the guinea‐pig ileum following transmural stimulation in the presence of atropine at 30 °C.

2. Single stimuli produced a transient hyperpolarization, the inhibitory junction potential (i.j.p.). At high stimulus strengths the i.j.p. was followed by a post‐stimulus depolarization (PSD).

3. During repetitive stimulation the magnitude of the hyperpolarization decreased; however, at the end of the stimulus period the PSD was enhanced and often reached threshold for the generation of action potentials. Thus, the size of the PSD was not directly related to the degree of the preceding hyperpolarization.

4. Hyperpolarization of the circular muscle cells was produced by the application of anodal current using large external electrodes. Rapid cessation of the applied current produced a transient after‐depolarization which was shorter in time course than the PSD following the i.j.p. If the applied anodal current was reduced slowly (at a rate which mimicked the decrease in the hyperpolarization during repetitive nerve stimulation) no after‐depolarization was observed.

5. Conditioning hyperpolarization of the circular muscle cells reduced the amplitude of the i.j.p. The i.j.p. was reversed at membrane potentials greater than approximately ‐90 mV.

6. The PSD did not appear to be due to the extracellular accumulation of potassium ions following the i.j.p. since the PSD persisted even when the i.j.p. was reversed.

7. The neurotoxin apamin reversibly abolished the i.j.p. and unmasked a transient excitatory junction potential (e.j.p.) with a variable latency (350‐900 ms).
Oligosynaptic excitation of motoneurones by impulses in group Ia muscle spindle afferents in the cat
Authors: Jankowska Elżbieta , McCrea David , Mackel Robert
Published: December 2014

1. Intracellular recording from hind‐limb motoneurones was used to investigate whether di‐ and trisynaptic (oligosynaptic) excitatory post‐synaptic potentials (e.p.s.p.s) are evoked from group Ia muscle spindle afferents in those motoneurones in which such potentials are evoked from Ib tendon organ afferents or entire group I afferents. Ia afferents of triceps surae and plantaris were activated either selectively by single brief stretches of these muscles, or together with Ib afferents by electrical stimuli applied to the nerves.

2. Muscle stretches below threshold for Ib afferents (10‐35 μm) evoked e.p.s.p.s which appeared with latencies compatible with disynaptic and trisynaptic coupling between the afferents and the motoneurones. The latencies of a majority of these e.p.s.p.s were too short to allow their mediation by group II afferents, if any were activated by the applied stretches. They were also too short to be compatible with effects attributable to dorsal root reflexes. These e.p.s.p.s are thus attributed to oligosynaptic actions of Ia afferents.

3. Stretch‐evoked di‐ and trisynaptic Ia e.p.s.p.s were found in 83% of motoneurones in which e.p.s.p.s were evoked by stimuli which activated both Ia and Ib afferents; in five motoneurone species they were found in more than 90%. These observations lead to the conclusion that group Ia muscle spindle afferents evoke not only inhibitory but also excitatory actions in parallel with group Ib tendon organ afferents.

4. The distribution of Ia oligosynaptic stretch‐evoked excitation from ankle and toe extensor muscles was compared with the distribution of Ia non‐reciprocal inhibition as described by Jankowska, McCrea & Mackel (1981b). Excitation pre‐dominated in posterior biceps—semitendinosus motoneurones and inhibition in other species of motoneurones investigated, except those of intrinsic foot muscles (tibial motoneurones); similar proportions of the latter showed excitation and inhibition.

5. Occurrence of oligosynaptic e.p.s.p.s as well as inhibitory post‐synaptic potentials (i.p.s.p.s) of Ia origin in some motoneurone species, and in particular in individual motoneurones, is indicative of a number of reflex pathways between group I afferents and these motoneurones. Furthermore, the disappearance of some of the e.p.s.p.s evoked by near‐threshold electrical stimulation following stronger stimuli indicates interactions between various functional groups of interneurones mediating group I actions.
Transient, axotomy‐induced changes in the membrane properties of crayfish central neurones.
Authors: Kuwada J Y , Wine J J
Published: December 2014

1. In crayfish, the normally passive, non‐spiking somata of certain unipolar, efferent neurones became spiking within 36 hr of axotomy. 2. The changes persisted for approximately 2 weeks and then waned. The decline in excitability occurred independently of regeneration, and excitability was not restored by recutting the axon stump. 3. The neuropilar processes also became capable of supporting spikes, but synaptic transmission onto the cells and the spike threshold for orthodromic activation were unchanged, as was the gross structure of the neurone. 4. In somata which normally spike, electrogenicity was nevertheless increased, as evidenced by soma spikes that were larger, faster rising, and easier to evoke. 5. We tested for post‐axotomy excitability changes in a variety of identified neurones. Every type (n = 5) of phasically active efferent we tested responded as above, as did all three phasic interneurones. One class of spontaneously active interneurones and one spontaneously active efferent did not respond to axotomy. 6. Extensive damage to afferents did not initiate changes in efferents of the same ganglion, nor did it interfere with changes induced by axotomy of the efferents. 7. Transection of the larger of the two main branches of the phasic flexor inhibitor induced soma excitability, but cutting the smaller branch did not. However, after the excitability caused by cutting the larger branch waned, transection of the smaller branch then induced excitability. 8. Neurones with longer axon stumps took longer to develop soma excitability.
Ionic and metabolic dependence of axotomy‐induced somatic membrane changes in crayfish.
Authors: Kuwada J Y
Published: December 2014

1. Axotomy induces a transient change in the soma membrane from non‐spiking to spiking in many neurones of the crayfish abdominal C.N.S. The ionic and metabolic dependence of this phenomenon was investigated in one identified neurone. 2. The inward current of axotomy‐induced soma spikes is carried primarily by Na ions. 3. Addition of 50 mM‐tetraethylammonium to the external saline unmasks predominantly Ca‐mediated soma spikes in control cells. The calcium spikes are not affected by axotomy. 4. Axotomy induces a transient increase in delayed rectification of the soma membrane. 5. Membrane potential is dependent on the external potassium concentration as predicted by the Nernst function while external sodium has essentially no effect. This is not changed following axotomy. 6. The inward current of the axon spike is primarily carried by sodium ions both before and after axotomy. The overshoot of the axon spike is not dramatically changed between the time when axotomy‐induced soma spikes are present and when they have disappeared. 7. Following axotomy, both the onset and offset of axotomy‐induced soma spikes occur earlier when the temperature is raised by 10 degrees C. 8. Cycloheximide retards or prevents soma spikes normally seen following axotomy. 9. The results indicate that axotomy induces a transient increase in voltage‐dependent Na and K conductances but not Ca conductance, and that these changes are dependent on axotomy‐inhibited protein synthesis.
Effect of rate‐dependent changes in the transient outward current on the action potential in sheep Purkinje fibres.
Authors: Boyett M R
Published: December 2014

1. The rate of membrane potential change during the initial phase of rapid repolarization of the action potential in sheep Purkinje fibres has been measured by electronic differentiation. 2. Phase‐plane analysis has revealed that the potential dependence of rapid repolarization corresponds to the potential range over which the transient outward current , Ito, is recorded in voltage clamp experiments. 3. The initial rate of repolarization is strongly rate‐dependent and it is markedly reduced at high rates. 4. The effect of high rates of stimulation on the phase‐plane diagram is consistent with a reduction in I. 5. After an increase or decrease in rate there is an abrupt change in the initial rate of repolarization in the first response followed by slower changes over several hundred responses. 6. Recovery of the initial rate of repolarization occurs in two distinct phases after repetitive to activity: there is a rapid, approximately exponential phase of recovery in the first 10 s which is followed by a slower phase of recovery lasting several hundred seconds. 7. The rate‐dependent changes in the initial rate of repolarization are abolished by 4‐aminopyridine, 0.5‐1.0 mmol/l. 8. It is concluded that the rate‐dependent changes in the initial phase of repolarization are due to the similar changes in Ito described in a companion paper (Boyett, 1981). 9. Rate‐dependent changes in peak tension have been measured and they bear no relationship to the changes in the initial rate of repolarization. It is concluded that the major component of the transient outward current in sheep Purkinje fibers is unlikely to be a Ca‐activated current