bluuebunny/crossref_metadata_2025 huggingface dataset:
Ionic diffusion delays in the transverse tubules of frog twitch muscle fibres
Authors: Caputo Carlo , Dipolo Reinaldo
Published: December 2014

1. The possibility of retarding the diffusional processes in the transverse tubules of frog single muscle fibres was explored by increasing the viscosity of the bathing medium. The viscosity was increased by adding Dextran 15 to the experimental solutions.

2. The criterion used to test this possibility was the speed of repolarization of muscle fibre membranes produced by sudden reduction in [K]o in media of different viscosity.

3. In fibres equilibrated in media containing 15% Dextran 15, and that had been depolarized with 80 m
M‐K for more than 5 sec, the repolarization caused by lowering the [K]o to 40 m
M proceeded more slowly than in fibres in Dextran‐free media.

4. On the basis of the above results, it was deduced that high viscosity solutions would delay the diffusion of Na ions in the transverse tubules. Thus the effect of sudden changes in [Na]o on the twitch tension of single fibres could be studied.

5. The recovery of twitches when the fibres were exposed from a solution containing no Na, to one that contained 46 m
M‐Na, occurred more slowly in high viscosity media.

6. This result can be explained assuming that a Na regenerative process occurs at the level of the membrane of the transverse tubules.
A physiological study of chick myotubes grown in tissue culture
Authors: Harris J. B. , Marshall M. W. , Wilson P.
Published: December 2014

1. A study has been made of some passive and active membrane properties of myotubes of different ages obtained in culture from explants of chick embryo thigh muscle.

2. After 3 days in vitro the mean values for the myotube resting membrane potential and input resistance were ‐ 63·8 mV and 1·30 MΩ respectively. By 13 days these values had fallen to ‐ 51·0 mV and 0·80 MΩ.

3. Current/voltage relations were measured in the presence of tetrodotoxin. The relations were linear for membrane potentials between ‐ 120 and ‐ 35 mV. Further depolarization usually resulted in a delayed increase in conductance which inactivated with time.

4. All myotubes tested using anodal break excitation were capable of generating action potentials. Action potentials were blocked by tetrodotoxin, saxitoxin and procaine.

5. All myotubes were sensitive to iontophoretically applied ACh. The potential change produced by ACh reversed polarity at a membrane potential between 0 and + 10 mV. The depolarization produced by ACh was unaffected by anticholinesterases.

6. The ACh response was blocked by cobra neurotoxin,
D‐tubocurarine and atropine.

7. The electrical properties of the myotubes appear to resemble those of normal adult twitch‐type skeletal muscle fibres.

8. The pharmacological properties of the myotube cholinergic receptor have been compared with those of the neuromuscular junction and the denervated muscle fibre membrane.
Organization of on‐off cells in the retina of the turtle
Authors: Schwartz E. A.
Published: December 2014

1. The organization of central and peripheral responses for one type of spike‐producing cell in the retina of the turtle (Pseudemys scripta elegans) has been studied. These cells produced a short burst of spikes following the onset and offset of a small spot of illumination (i.e.
ON—OFF cells). The effect of increasing the area of illumination was to include a peripheral inhibition. Intracellular
ON and
OFF responses were, however, affected differently.

2.
ON—OFF cells marked intracellularly with Procion Yellow M4R had somata in the inner nuclear and ganglion cell layers.

3. Peripheral inhibition could be evoked without a change in the membrane potential of horizontal cells.

4. Passing 5 nA hyperpolarizing or depolarizing current through a micropipette within a horizontal cell elicited in
ON—OFF cells a transient excitation following the onset and offset of current.

5. It is concluded that inhibition from the periphery of an
ON—OFF cell receptive field is not mediated by luminosity horizontal cells but more probably by peripheral bipolar cells.
The dorsal root potentials produced on both sides of the spinal cord by long‐lasting stimulation of the cutaneous afferents
Authors: Hołobut W. , Niechaj A.
Published: December 2014

1. The dorsal root potentials (DRPs) produced on both sides of the spinal cord by prolonged repetitive stimulation of the alpha cutaneous afferents have been studied in spinal cats lightly anaesthetized by barbiturate.

2. Ipsilateral depolarization produced by long‐lasting stimulation increases rapidly to maximum and then, in spite of a slight decline, it persists throughout the period of stimulation. Contralateral depolarization after its increase to maximum rapidly subsides to zero during continued stimulation.

3. Depression of the contralateral DRP during long‐lasting stimulation depends on its frequency. It occurs at higher frequencies of tetanization (in excess of 20 c/s) while at low frequencies (3–15 c/s) contralateral DRP is maintained till the end of stimulation, displaying the pattern similar to depolarization of the ipsilateral dorsal root.

4. The effect of temporal facilitation on the DRPs is much greater and of longer duration on the contralateral than on ipsilateral side of the spinal cord.

5. After long‐lasting conditioning stimulation there is prolonged depression of the testing DRPs produced by a single volley in the same nerve, Since duration of this depression is prolonged beyond the known duration of presynaptic inhibitory action, it is suggested to be due to homosynaptic depression in interneuronal pathways producing primary afferent depolarization.

6. More severe and prolonged depression of the contralateral DRPs evoked by preceding volleys indicates enhancement of homosynaptic depression on the other side of the spinal cord. It may be assumed that this increase depends on greater complexity of synaptic organization of the pathways producing contralateral depolarization of the primary afferent fibres.
The neural signal of angular head position in primary afferent vestibular nerve axons
Authors: Loe P. R. , Tomko David L. , Werner G.
Published: December 2014

1. The relation between discharge frequency and angular head position was determined for a population of regularly discharging single first‐order vestibular neurones in the eighth nerve of the barbiturate anaesthetized cat.

2. Each axon had a characteristic head position which was maximally excitatory to it, and a diametrically opposed head position which was minimally excitatory.

3. After correction for phase shifts introduced by the orientation of preferred excitability, discharge rate in statoreceptor afferents varied as a power function of the sine of angular head position with exponents ranging from 0·9 to 1·6.

4. Experimentally determined discharge rates were compared with the predictions of a computer simulation model incorporating the idea that shearing force acting on morphologically polarized receptors is the adequate stimulus for macular receptor cells.

5. This approach permitted the identification of a population of first‐order vestibular afferents whose discharge frequency varied with head position as did the magnitude of shear force computed for individual receptors, each most excited in a particular head position.

6. The majority of the spatial orientations of maximal sensitivity defined a surface which is tilted by approximately 30° with reference to the Horsley—Clarke horizontal plane, implying that most statoreceptor afferents are maximally sensitive to position changes when the cat's head is at or near its normal position.
Descending and segmental inhibition of transmission through the spinocervical tract
Authors: Brown A. G. , Kirk E. J. , Martin H. F.
Published: December 2014

1. Micro‐electrode recordings were made from axons of the spinocervical tract in unanaesthetized decerebrate‐spinal cats.

2. The effects of stimulation of (1) descending systems at the level of the upper cervical spinal cord and (2) hind limb cutaneous nerves, on discharges of spinocervical tract neurones were examined.

3. Effects were obtained from bilateral spinal cord regions in the dorsolateral funiculi and the most medial and ventral parts of the ventral funiculi and also from the dorsal columns in the upper cervical region even though the columns had been transected at low thoracic and upper lumbar levels.

4. Stimulation of either descending or segmental systems inhibited spontaneous and evoked responses. Facilitation was not seen. The inhibition had a time course of up to 250 msec, with maximal action at 20–40 msec and was greatest for polysynaptic responses or those evoked from the smaller myelinated cutaneous axons.

5. It is suggested that the descending and segmental systems converge on to common inhibitory interneurones.
Possible screening of surface charges on crayfish axons by polyvalent metal ions
Authors: D'Arrigo J. S.
Published: December 2014

1. The effect of different polyvalent metal ions in the external solution upon the threshold membrane potential for spike initiation in crayfish axons has been studied by means of intracellular micro‐electrodes. The metal ions tested included six divalent cations (Ca2+, Mg2+, Sr2+, Ba2+, Co2+, and Ni2+) and three trivalent cations (La3+, Y3+ and Eu3+).

2. Identical extracellular concentrations of different cations with the same valence had essentially the same effect on threshold membrane potential. However, a very low concentration of trivalent cations (about 225 μ
M) was found to be equivalent to a much higher divalent cation concentration (13·5 m
M) as measured by their effects on threshold potential.

3. Upon a tenfold increase in concentration, the threshold potential for spike initiation was shifted in a positive direction by 30·6 mV with divalent cations and by 20·8 mV with trivalent cations.

4. It is shown that a hypothesis involving screening of negative charges at the axonal membrane surface, based on Gouy—Chapman theory, predicts these various experimental results rather closely.

5. It is concluded that a high negative charge density, sufficient to render a screening mechanism possible, exists at the surface of crayfish axons in the region of the sodium ‘gates’.

6. The density of surface charges is calculated to be approximately 1e−/43 Å2. This calculation is discussed in connexion with the possible molecular identity of the sodium ‘gates’ in crayfish axons and other excitable systems.
Membrane properties and inhibitory innervation of the circular muscle cells of guinea‐pig caecum
Authors: Ito Y. , Kuriyama H.
Published: December 2014

1. The membrane properties of the circular muscle cells of guinea‐pig caecum and nervous factors influencing the muscle activity were studied with micro‐electrodes using partition and field stimulating methods.

2. The mean membrane potential was −52 mV. Spontaneous discharges appeared as regular bursts between silent periods, as regular spikes without silent period, or as regular slow potential changes with superimposed spikes.

3. Spontaneous spikes with overshoot were frequently observed. The mean maximum rate of rise was 5·2 V/sec. The mean conduction velocity of evoked spikes was 5·4 cm/sec.

4. The amplitude of the elctrotonic potential was linearly proportional to the current applied by the partition stimulating method. The spatial decay of the electrotonic potential along the tissue was exponential, with a mean length constant of 1·7 mm.

5. The time constants of the membrane calculated from the electrotonic potential, and from the conduction velocity, length constant and time course of the foot of the spike were about 200 and 100 msec respectively. These results indicate that the circular muscle of guinea‐pig caecum possesses cable like properties.

6. Field stimulation (0·3 msec pulse duration) to the circular muscle evoked three different responses successively, i.e. initial depolarization (initial excitatory junction potential) with or without spike, hyperpolarization (inhibitory junction potential) and delayed depolarization (delayed excitatory junction potential) with or without spikes.

7. These three different potential changes were completely blocked by treatment with tetrodotoxin (5 × 10−6 g/ml.), and both the initial and late excitatory junction potentials were blocked by treatment with atropine (5 × 10−5 g/ml.).

8. The distribution of inhibitory nerves in the circular muscle cells was investigated. The results indicate that inhibitory nerves arise from Auerbach's plexus situated just beneath the taenia coli and the nerve branches spread over the whole distance from one taenia coli to the next along the ciruclar muscle cells, a width of about 3 mm.

9. The mean conduction velocity of excitation of the inhibitory nerves was 16·0 cm/sec. Hexamethonium, in a concentration of 5 × 10−6 g/ml. depolarized the circular muscle membrane and lowered the rate of rise and fall of spike, but did not block the generation of inhibitory junction potentials.
Some further observations on the electrogenic sodium pump in non‐myelinated nerve fibres
Authors: den Hertog A.
Published: December 2014

1. A study has been made of the hyperpolarization that follows a period of electrical activity (post‐tetanic hyperpolarization) and of the hyperpolarization which develops when potassium is readmitted after bathing the desheathed vagus nerve of the rabbit in potassium‐free Locke solution during 15 min (potassium‐activated response).

2. Reduction of the external chloride concentration increases the membrane resistance and the potassium‐activated response without changing the time constant of the response. A linear relation between the amplitude of the potassium‐activated response and the membrane resistance was found. When chloride was replaced completely by isethionate (sodium salt) and by sulphate (other salts) the potassium‐activated response increased by a factor of 5.

3. The membrane resistance is decreased during the post‐tetanic hyper‐polarization elicited in isethionate Locke solution: the decrease is more pronounced after a longer period of electrical stimulation of the nerve.

4. A small increase of the membrane resistance was found during the potassium‐activated response. The changed membrane potential during the response can account for the alteration of the membrane resistance observed.

5. The amplitude of the potassium‐activated response is increased during hyperpolarization and reduced during external depolarization of the nerve, whereas the time constant is not affected. The potassium‐activated response appears to be independent of polarization of the membrane after correction for the changed membrane resistance.

6. The maximum amplitude of the activated response and the external potassium concentration are related following Michaelis—Menten kinetics; the time constant of the response is inversely related to the external potassium concentration.

7. The area of the electrogenic response activated by high potassium concentrations (5·6–20 m
M) is almost constant, but is reduced at lower potassium concentrations. The amplitude and area of the thallium‐activated response are increased (about 1·5 times) compared with the potassium‐activated response.

8. It was concluded that the electrogenic response, reflected by post‐tetanic hyperpolarization, is not directly related to activity of the electrogenic pump, which is probably due to accumulation of potassium in the periaxonal space; that the potassium activated response is produced entirely by activity of the electrogenic sodium pump; and that the current produced by activity of the electrogenic sodium pump is independent of the electrochemical gradient and membrane resistance.
Calcium entry in response to maintained depolarization of squid axons
Authors: Baker P. F. , Meves H. , Ridgway E. B.
Published: December 2014

1. Intracellular aequorin was used to monitor changes in Ca entry in response to maintained depolarization either produced electrically or by exposure to K‐rich solutions.

2. External K concentrations greater than 50 m
M produce a phasic light response. The light rises to a peak in a few sec and then falls in 0·5‐5 min to a new steady level that is always greater than the level in the absence of K.

3. The phasic light response does not result from depletion of available aequorin at the periphery of the axon, but rather seems to reflect a phasic entry of Ca in response to depolarization.

4. Similar phasic responses are produced by prolonged electrical depolarization. These results are consistent with depolarization serving both to activate and also to inactivate Ca entry.

5. Following inactivation and after return to normal sea‐water, there is an appreciable relative refractory period during which the response both to K‐rich sea‐water and electrical depolarization is reduced in size. Complete recovery takes 10–15 min.

6. The response to 410 m
M‐KCl is dependent on the previous treatment of the preparation. Pre‐treatment with 100 or 200 m
M‐KCl reduced the response to 410 m
M‐KCl. The potential for half inactivation was about −25 mV in 112 m
M‐Ca and −40 mV in 20 m
M‐Ca.

7. The rate of onset of inactivation is potential dependent and is faster for depolarizations to zero potential than for smaller ones.

8. The phasic Ca entry produced by K‐rich solutions is insensitive to external tetrodotoxin and internal tetraethylammonium ions, but is blocked by external Mn2+, Co2+ and Ni2+ ions and by the drugs D‐600 and iproveratril. This suggests that the phasic Ca entry involves the late Ca channel.

9. Recovery of the outward K current after a long depolarization is much faster than recovery of the late Ca entry system. This provides further support for the view that the late Ca channel and the K channel are distinct.
Effects of biogenic amines on central thermoresponsive neurones in the rabbit
Authors: Hori T. , Nakayama T.
Published: December 2014

1. Single unit activities were recorded with five‐barrelled micropipettes from the thermo‐responsive neurones in the preoptic area and the mid‐brain reticular formation in urethanized rabbits. 5‐hydroxytryptamine (5‐HT), noradrenaline (NA) and acetylcholine (ACh) were applied micro‐iontophoretically to the immediate vicinity of the recording cells.

2. Out of seventeen warm‐responsive neurones recorded in the preoptic area, fifteen neurones responded to 5‐HT with the increase in firing rate and two showed no response. Thirteen out of seventeen warm‐units decreased their firing rate in response to application of NA and four were not affected. ACh had no effect on any of the warm‐units examined.

3. Six out of seven cold‐units in the preoptic area were depressed by 5‐HT, while NA excited five of six units studied. None of the cold‐units were influenced by ACh.

4. These results are in good agreement with the changes in rectal temperature produced by 5‐HT and NA micro‐injected into the hypothalamus in rabbits.

5. In the mid‐brain reticular formation, 5‐HT excited all of fourteen cold‐responsive neurones. Of these, eight cold‐units were depressed and six were unaffected by NA, while ACh excited six units and had no effect on eight units. All of the five warm‐responsive units were inhibited by 5‐HT and none were influenced by NA. Thus, the responses of reticular thermoresponsive neurones to 5‐HT and NA were opposite to those of the preoptic thermo‐responsive neurones.
Effects of various secretagogues upon 42K and 22Na uptake during in vitro hormone release from the rat adenohypophysis
Authors: Kraicer Jacob , Milligan John V.
Published: December 2014

1. The in vitro uptake of 22Na and 42K was measured simultaneously in rat adenohypophyses during hormone release produced by several secretagogues and during inhibition of hormone release in Ca‐free media.

2. Intracellular adenohypophysial [Na+] and [K+] changed only slightly when the uptake changed. This would indicate that relative permeability changes were the primary effect of the treatments.

3. The uptake of 42K was increased by elevated external [K+], but was unaffected by the presence or absence of Ca2+. Acid extracts of hypothalamus‐stalk—median eminence or cerebellum also increased the 42K uptake.

4. The uptake of 22Na or 24Na was decreased by elevated [K+]. Uptake was increased in Ca‐free Krebs—Ringer bicarbonate; but was unaltered when [K+] was concurrently increased.

5. Neither purified growth hormone releasing hormone, synthetic lysine‐vasopressin, dibutyryl cyclic AMP nor theophylline had an effect on the uptake of either K+ or Na+.

6. The rapid uptake of 22Na and its smaller volume of distribution compared to absolute measurements of intracellular [Na+] suggest that the plasma membrane of adenohypophysial cells is relatively impermeable to Na+.

7. We conclude that changes in the uptake of Na+ and K+ associated with hormone release are incidental to the release process.

8. Hormone release produced by elevated external [K+] is most likely due to a non‐specific increase in permeability of the cell membranes, facilitating Ca2+ entry into the cytoplasm.

9. The results suggest that the low resting transmembrane potentials of adenohypophysial cells may be due to their conjoint relatively high permeability to both K+ and Ca2+, rather than K+ and Na+.
The distribution of sodium and potassium in amphibian embryos during early development
Authors: Slack Christine , Warner Anne E. , Warren R. L.
Published: December 2014

1. Intracellular and intercellular concentrations of sodium and potassium have been measured in pregastrular embryos of Xenopus laevis and Amblystoma mexicanum. Calcium and magnesium contents have also been determined.

2. Between egg and gastrula stages of development the potassium concentration is near to 60 m‐mole/l. embryo. Up to the blastula stage the sodium concentration is near to 50 m‐mole/l. embryo; the amount of sodium in the embryo begins to fall just before gastrulation.

3. Embryo calcium and magnesium concentrations show no significant variations prior to gastrulation. Average calcium concentrations for the different stages range from 5 to 8 m‐mole/l. embryo; magnesium concentrations lie between 12·4 and 17 m‐mole/l. embryo.

4. The intercellular fluid contains 100 m
M sodium and 1 m
M potassium; the majority of the sodium is ionically active. As no net uptake of sodium or potassium occurs before gastrulation these cations must have been transferred from the cells to the cavity.

5. At all developmental stages studied, the intracellular potassium concentration is close to 100 m‐mole/l. cell water. Intracellular sodium falls steadily from 80 m‐mole/l. cell water in eggs to 30 m‐mole/l. cell water at the beginning of gastrulation.

6. The intracellular sodium activity, measured with sodium sensitive intracellular micro‐electrodes, is relatively constant between egg and blastula stages at about 14 m
M. During each cell division cycle the intracellular sodium activity rises transiently by 2–3 m
M.
Intracellular and intercellular potentials in the early amphibian embryo
Authors: Slack Christine , Warner Anne E.
Published: December 2014

1. The sensitivity of the membrane potential of cells of early embryos of Xenopus laevis to variations in the extracellular concentrations of sodium and potassium has been determined.

2. Alterations in the extracellular sodium concentration have little effect on the membrane potential at all pregastrular stages tested.

3. Up to the 32 cell stage an increase in the concentration of potassium in the bathing medium causes a fall in cell membrane potential only when membrane newly synthesized in the furrow during cleavage is exposed at the embryo surface, during the second half of the cell division cycle.

4. Beyond the morula stage (48 cells) a fall in membrane potential on raising external potassium can only be demonstrated when the seal which isolates the intercellular fluid from the bathing medium is broken so that cells lining the inner face of the embryo come into contact with the high potassium solution.

5. The results suggest that the egg membrane has little selective permeability whereas membrane synthesized after fertilization is highly potassium permeable.

6. No evidence could be obtained for any potential difference between the intercellular fluid and the external bathing medium.

7. Dinitrophenol, sodium azide and cyanide prevented normal development only if they were injected into the intercellular cavity. Embryos reared in solutions containing these poisons turned into normal tadpoles.

8. The formation of the intercellular cavity could be halted by injecting ouabain into the cavity while it was still small. Embryos reared in ouabain turned into normal tadpoles.

9. The results suggest that the active transfer of sodium ions from the cells to the intercellular spaces is an integral part of the formation of the intercellular fluid. A hypothesis for the mechanism of formation of the cavity is put forward along these lines.
Biionic potentials in the proximal tubule of Necturus kidney
Authors: Anagnostopoulos Takis
Published: December 2014

1. Biionic potentials were studied in the proximal tubule of the doubly perfused Necturus kidney and subsequently analysed by means of an equivalent electrical circuit.

2. Luminal membrane resistance was found to be at least 3 times greater than peritubular membrane resistance.

3. Potassium contribution to peritubular membrane conductance amounts to at least 75%. Replacement of chloride in peritubular circulation by benzene sulphonate or acetyl glycinate hyperpolarized peritubular membrane.

4. The peritubular membrane is more permeable to choline than to sodium. Indirect evidence suggests that the opposite may apply at the luminal border.

5. The shunt pathway discriminates poorly, if at all, between sodium, potassium and choline, in short term experiments.

6. Chloride permeability across the shunt pathway is about three times as great as combined cationic permeabilities.
Rate of uptake of endogenous cortisol by the left ventricle of the anaesthetized dog during ventilation with ambient air and during hypoxia
Authors: Kolanowski J. , Lammerant J.
Published: December 2014

1. The rate of uptake of endogenous cortisol by the left ventricle was determined in eight dogs as the product of the left ventricular myocardial plasma flow and the coronary arteriovenous difference in plasma cortisol concentration. The arteriovenous difference in hormone concentration in resting skeletal muscle (M. gracilis) was also measured. The values given are means ±
S.E.

2. During ventilation with ambient air (arterial PO2: 85 ± 2 mm Hg), the rate of cortisol uptake by the left ventricle averaged 382 ± 92 ng/100 g.min. The arteriovenous difference in hormone concentration in the vessels of the M. gracilis was more than twice that in the coronary vessels. Assuming a value of 3–4 ml./100 g.min for the blood flow in this muscle, the corresponding rate of cortisol uptake would be in the range of 25–33 ng/100 g.min.

3. During hypoxia (arterial PO2: 35 ± 1 mm Hg), the rate of cortisol uptake by the left ventricle was not significant, averaging 26 ± 113 ng/100 g.min. By contrast, the skeletal muscle still extracted significant amounts of cortisol from the plasma. It is inferred that the suppression of a significant uptake of the hormone by the left ventricle was related, at least in part, to the changes in the mechanical and associated metabolic activity of the heart muscle elicited by the lowering of the arterial PO2.

4. Hypoxia depressed the net uptake of cortisol by the left ventricle rather than the uptake mechanism itself. Indeed, bi‐directional movements of cortisol between the plasma and the heart muscle, with rates of release up to 1150 ng/100 g.min, were observed.
The thermal effects of shortening in tetanic contractions of frog muscle
Authors: Dickinson Valerie A. , Woledge Roger C.
Published: December 2014

1. In tetanic contractions during which shortening has occurred the total heat produced is greater than in isometric controls.

2. The amount of this excess, measured after relaxation, is less than the shortening heat measured before relaxation. In other words relaxation heat is less after contractions with shortening.

3. Only a small part of this reduction in relaxation heat can be explained by the reduced thermoelastic heat and work dissipation due to the lower tension maintained after shortening.

4. In the few experiments in which the full tension is redeveloped after shortening the relaxation heat is still reduced.

5. Decreases in the tension redeveloped after shortening, caused by using shorter tetani, or slower shortening, are not accompanied by decreases in the relaxation heat greater than can be accounted for by the assumed physical results of the lower tension.

6. It is suggested that the reduction in relaxation heat after shortening is due to the occurrence of a reaction in which the exothermic process causing the shortening heat is reversed.
The effect of tetanic and post‐tetanic potentiation on facilitation of transmitter release at the frog neuromuscular junction
Authors: Magleby K. L.
Published: December 2014

1. End‐plate potentials (e.p.p.s) were recorded from frog neuromuscular junctions blocked with high Mg and/or low Ca.

2. Estimates of f(t), the facilitation contributed by each impulse, were obtained during and following repetitive stimulation from the incremental change in e.p.p. amplitudes following step changes in the stimulation rate during the conditioning and testing trains.

3. Estimates of f(t) increased during the conditioning stimulation and returned to control in the post‐tetanic period. This increase in f(t) was proportional to the magnitude of tetanic or post‐tetanic potentiation (PTP) present.

4. These results are described by: [Formula: see text] where h(t)/hc is the e.p.p. amplitude at time t expressed in terms of the control, P(t) is potentiation, F(t) is facilitation and 1 is the base level of transmitter release. Thus, potentiation has a multiplicative (gain) effect on facilitation and the base level of transmitter release.

5. PTP was present immediately following the conditioning train. However, if depression occurred during the conditioning train, PTP developed after a delay.

6. It is suggested that facilitation and potentiation represent increases in two independent factors which act jointly to increase the probability of transmitter release.
An analysis of the cable properties of spinal motoneurones using a brief intracellular current pulse
Authors: Iansek R. , Redman S. J.
Published: December 2014

1. A brief intracellular current pulse, with duration less than 500 μsec, has been applied to lumbosacral motoneurones in anaesthetized cats. The resulting voltage transients have been analysed by the procedure suggested in Jack & Redman (1971b) to obtain the cable parameters for each motoneurone.

2. Forty‐three motoneurone responses were analysed. In all cases the voltage response indicated that the dendrites could be represented as uniform, finite length cables, with either a sealed distal end, or at least a high resistance distal termination. The electrical length of the equivalent uniform dendritic cable ranged from 1·0 to 2·1 space constants, with a mean value of 1·5.

3. The initial decay of the membrane potential following the removal of the current pulse was more rapid than was predicted by the Rall model for the motoneurone, in approximately two thirds of the responses. Consequently a value of dendritic to soma conductance ratio could not be obtained for these motoneurones.

4. The explanation given for the departure from the theoretical response to a brief current pulse is that the specific resistivity of the soma membrane is lower than the specific resistivity of the dendritic membrane. This explanation is complicated by the possibility of the electrode tip not lodging in the isopotential soma region. The contribution that each of these effects has on the early decay phase of the current pulse response has been assessed.

5. It is concluded that the specific resistivity of the soma membrane could be as low as one third of the dendritic membrane resistivity. Tonic inhibitory activity restricted to the soma is suggested as an explanation.
Alterations in secretory patterns following vagotomy in rats with Pavlov or Heidenhain pouches
Authors: Lundell L. , Svensson S. E.
Published: December 2014

1. In conscious rats provided with Pavlov or Heidenhain pouches, the acid and pepsin secretion in response to feeding and infusion of gastrin was established before and after truncal vagotomy. In Pavlov pouches the responses to 2‐deoxy‐
D‐glucose, methacholine and the combination of gastrin and methacholine were also studied.

2. Interdigestive secretion of acid and pepsin after vagotomy was decreased in the Pavlov pouch and increased in the Heidenhain pouch.

3. The acid response to feeding in the Pavlov pouch was substantially reduced after vagotomy, whereas the secretion of pepsin was only slightly diminished.

4. In the Heidenhain pouch after vagotomy, feeding augmented the high interdigestive secretion.

5. After vagotomy, the acid dose—response curve to gastrin was shifted to the right in the Pavlov pouch and to the left in the Heidenhain pouch.

6. In the Pavlov pouch after vagotomy, the acid response to the highest dose of methacholine employed was significantly enhanced.

7. A background infusion of methacholine reestablished in the Pavlov pouch the reduced responsiveness to gastrin following vagotomy.

8. Pepsin secretion was stimulated by gastrin in the Heidenhain pouch and after vagotomy in the Pavlov pouch. The stimulatory effect of methacholine on pepsin secretion in the Pavlov pouch was increased after vagotomy.
The electrical properties of the ectoderm in the amphibian embryo during induction and early development of the nervous system
Authors: Warner Anne E.
Published: December 2014

1. The electrical properties of ectodermal cells have been studied in embryos of the axolotl Ambystoma mexicanum between gastrulation and the closure of the neural tube.

2. At the time of neural induction by the underlying mesoderm the mean membrane potential recorded in ectoderm cells was −30 mV (± 1·5 mV
S.E. of mean) and in presumptive neural cells −27 mV (± 1·6 mV
S.E. of mean).

3. At late neural fold stages, when specification of the neuroectoderm is complete, the membrane potential in presumptive nerve cells was −44 mV (± 1·7 mV
S.E. of mean). This is significantly greater than in cells of the surrounding ectoderm at the same developmental stage (−31 mV ± 1·5 mV
S.E. of mean).

4. Current injected into an ectoderm cell spread freely throughout the neural and lateral ectoderm both before and after neural specification was complete.

5. Voltage—current relations recorded at mid‐neural fold stages in the lateral ectoderm and neural plate rectified in opposite directions. In the neural plate the slope conductance rose as the internal potential was made less negative; in the lateral ectoderm the slope conductance fell with depolarization.

6. At the time of closure of the neural tube ectoderm and presumptive neural cells lose their low resistance connexions with each other. At the same time low resistance contacts are established across the mid line between ectoderm cells originally separated by the neural plate.

7. After the neural tube has closed low resistance connexions remain between presumptive neural cells, although the degree of current spread from one cell to the next is not very great.

8. The voltage—current relation recorded in neural tube cells showed a rise in slope conductance as the cell was depolarized.

9. Occasionally signs of regenerative activity were seen, but the mechanism for generating a fully fledged action potential does not differentiate until after complete closure of the neural tube.
The movement of amino acids between blood and skeletal muscle in the rat
Authors: Baños Guadalupe , Daniel P. M. , Moorhouse S. R. , Pratt O. E.
Published: December 2014

1. The rates of entry of twenty of the blood amino acids into skeletal muscle of living rats were measured directly by means of a technique which ensured that a steady concentration of a radioactively labelled amino acid is reached rapidly and is maintained in the bloodstream.

2. The rates of entry were measured in experiments of short duration to avoid possible artifacts caused by amino acids leaving the muscle or by their metabolism.

3. The entry rate of each amino acid increased in direct proportion to its concentration in the blood plasma over the physiological range.

4. The various amino acids had widely different rates of entry. These rates could not be correlated with the physicochemical properties of the amino acids.

5. Two amino acids,
L‐lysine and
L‐threonine, enter muscle against a concentration gradient, while in the case of a third,
L‐arginine, the blood concentration was raised high enough to induce saturation of the entry mechanism.

6. It is concluded that entry takes place in vivo by means of carrier‐mediated transport processes with a high degree of specificity.

7. When the concentration of an amino acid in the bloodstream was increased to about twice normal the proportion of the additional amino acid that was taken up rapidly by the muscle was large enough, especially for the essential amino acids, to suggest that the tissue constitutes a quantitatively important storage system helping to regulate the concentrations of amino acids in the bloodstream.
The influence of androgens on enzymes (chymotrypsin‐ and trypsin‐ like proteases, renin, kallikrein and amylase) and on cellular structure of the mouse submaxillary gland
Authors: Bhoola K. D. , Dorey Gundula , Jones C. W.
Published: December 2014

1. The effect of age and androgen level on enzyme activity and cellular structure has been determined in the mouse submaxillary gland.

2. A new protease which resembles chymotrypsin in its substrate specificity has been characterized in the gland.

3. Activity of the chymotrypsin‐ and trypsin‐like proteases and renin increased considerably in male mice concomitantly with proliferation of granules in the secretory tubules of the gland.

4. The androgen dependence of the chymotrypsin‐ and trypsin‐like enzymes, renin and the organelles within the secretory tubules was confirmed in castrated male mice. The activity of these enzymes increased and correlated with the appearance of intracellular granules in the secretory tubules when the castrated male mice and in addition female mice were treated with testosterone preparations.

5. Kallikrein, a closely related protease, and amylase increased in activity with age but showed no sex‐linked differences.

6. The results suggest that kallikrein is sequestered in acinar cells whereas the androgen‐dependent enzymes (chymotrypsin, trypsin and renin) are located in the secretory tubules.
The onset of the effects of zinc and tetraethylammonium ions on action potential duration and twitch amplitude of single muscle fibres
Authors: Stanfield P. R.
Published: December 2014

1. Single dissected muscle fibres were used to examine the rates of onset and reversal of the effects of zinc and tetraethylammonium (TEA) ions on the duration of the action potential and the amplitude of the twitch.

2. The increases in fall time (100‐50%) of the action potential and in the amplitude of the twitch resulting from the application of zinc or TEA follow exponential time courses.

3. The time constants for the onset of the effects of 0·1 m
M zinc were 11·03±0·71 sec (six fibres) and 9·24±0·77 sec (sixteen fibres) on action potential and twitch amplitude respectively. The values are not significantly different from each other.

4. The onset of the effect of zinc on action potential duration was speeded up by ‘detubulation’ by glycerol treatment. The time constant was 3·88±0·68 sec (six fibres).

5. The time constants for the onset of the effects of 25 m
M‐TEA were 3·48±0·69 sec (six fibres) and 3·81±0·26 sec (nine fibres) on action potential and twitch respectively. These values are not significantly different from each other.

6. The results are consistent with the idea that zinc and TEA act as twitch potentiators by way of their effect on action potential duration. It seems likely that this effect is, in part at least, on the surface membrane, but an effect within the T‐system is not ruled out.
Mechanical studies on the retractor bulbi muscle and its motor units in the cat
Authors: Lennerstrand Gunnar
Published: December 2014

1. For a description of some of the mechanical properties of the retractor bulbi muscle in the cat, the isometric tension development was studied in one of the four slips of the muscle and in single retractor bulbi motor units.

2. The motor units and the muscle were activated by stimulating their motoneurones of origin in the abducens nucleus.

3. All twenty‐eight motor units studied were of the same fast, twitch type, which fatigued quickly. Similarities between the motor units and the muscle with regard to isometric tension development strongly suggest that the retractor bulbi is composed exclusively of this type of motor unit.

4. On an average the motor unit had a twitch rise time of 9·2 msec and a half‐decay time of 11·4 msec. The twitch tension was 36·7 mg. At stimulation with 175 pulses/sec or above the tetanus fused. The maximal tetanic tension developed was 440 mg and the maximal rate of tension rise was 24·5 g/sec. To prolonged tetanic stimulation most of the units fatigued completely within 10–15 sec.

5. In a slip of the muslce similar values were obtained for contraction time, half‐decay time, fusion frequency and fatigability. Tetanic tension reached 11·7 g and the maximal speed of tetanic contraction was 255 g/sec.

6. As in other extrinsic eye muscles a linear relation was found between length and tension in the activated retractor bulbi. An increase in activation induced a parallel shift in the curves to higher tension values but the slopes of the curves remained unchanged. The average slope value was 1·7 g/mm.
The spontaneous release of transmitter from insect nerve terminals as predicted by the negative binomial theorem
Authors: Rees D.
Published: December 2014

1. In the retractor unguis muscles of Periplaneta americana and Blaberus giganteus, the rate of spontaneously occurring miniature potentials from nerve‐muscle synapses associated with the ‘white’ muscle fibres was greater than that observed in the ‘red’ muscle fibres.

2. In 5% of the intracellular recordings, particularly from the ‘white’ fibres, short ‘bursts’ of relatively high (20‐100 sec−1) rates of m.e.p.p.s occurred infrequently in an unpredictable manner. This bursting phenomenon was not observed in extracellular recordings of the miniature potential discharge.

3. Rigorous statistical analyses indicated that the spontaneous mode of transmitter release at cockroach retractor unguis muscle fibres was predictable by the negative binomial theorem with a 90% reliability.

4. Perfusion of nerve‐muscle preparations with high Mg2+ salines resulted in low spontaneous discharge rates which were characterized by a negative binomial distribution.

5. The fit of the data to the negative binomial theorem implied some mutual interaction between those processes responsible for the spontaneous release of transmitter from cockroach nerve terminals.
Effects of thymol on the electrical and mechanical properties of the guinea‐pig taenia coli
Authors: Ito Y. , Kuriyama H.
Published: December 2014

Effects of thymol (0·02‐2 m
M) on the electrical and mechanical activities of the smooth muscle cells of the guinea‐pig taenia coli were investigated with either micro‐electrode or double sucrose gap methods.

1. Thymol, in a concentration of more than 0·03 m
M, reduced the amplitude and maximum rate of rise of the spikes without any change of the membrane potential. When the concentration was increased to 0·3 m
M, thymol completely blocked the spontaneous and evoked spike activities. In a concentration of more than 0·1 m
M, thymol reduced the membrane resistance in proportion to the concentration without any change of the membrane potential.

2. Ionic mechanisms involved in the effects of thymol on the membrane resistance were investigated in various ionic environments. The results showed that in concentrations below 0·5 m
M thymol might selectively increase the Cl‐conductance of the membrane. Participations of Na and K ion in the effects of thymol on the membrane resistance could be eliminated. However, at more than 1 m
M, thymol increased the membrane conductance non‐selectively. Excess Ca in the external solution partly suppressed the action of thymol on the taenia coli.

3. Potentiation of the twitch tension was not observed on treatment with any concentration of thymol.

4. After pre‐treatment with thymol (0·5 m
M), isotonic K Krebs solution depolarized the membrane and reduced the membrane resistance as observed in the absence of thymol. However, thymol completely suppressed the K‐induced contracture.

5. Application of excess Ca and acetylcholine during the maintained contracture evoked by isotonic K Krebs solution induced further development of the contracture. However, on pre‐treatment with thymol, neither excess Ca nor acetylcholine could evoke a mechanical response in isotonic K Krebs solution.

6. The results obtained from the present experiments are discussed in relation to the roles of Ca on the smooth muscle cells.
Responses of bipolar cells in the retina of the turtle
Authors: Schwartz E. A.
Published: December 2014

The responses of bipolar cells in the retina of the turtle have been studied by intracellular recording. Two types of bipolar cell have been identified: one gave graded depolarizing and the other graded hyperpolarizing responses to small circles of light (100 μm diameter). The responses of both types of cell were similar in the following respects.

1. Both were extremely sensitive to dim light; the amplitude of response to a small circle of light increased with light intensity more steeply than the cone response.

2. Enlarging the diameter of a spot added an antagonistic effect which decreased response amplitude. This decrease in response amplitude was more apparent at dim than at bright light. Stimulating only distant areas of retina with an annulus produced a response of polarity opposite to that normally produced by a central spot. However, the responses of bipolar cells did not appear to be due to a simple summation of opposite polarity signals contributed from central and peripheral parts of their receptive fields.

3. When small spots or annuli of light were turned off there frequently occurred an overshooting OFF transient. The occurrence of OFF transients depended on the duration of the stimulus. Cones recorded under similar conditions produced an OFF depolarization. The size of cone OFF depolarizations increased with increasing duration of the preceding light; following approximately 3 sec of illumination their maximum amplitude was roughly 1/10 the amplitude of the preceding hyperpolarization. The size of OFF responses in both cone and bipolar cells was increased when horizontal cells were hyperpolarized by light.

It is concluded that bipolar cells produce large responses for very small cone responses, and, as a consequence, a small depolarization in cones following illumination produces large OFF transients in bipolar cells. Furthermore, the responses of bipolar cells do not appear to represent a simple summation of opposite polarity input from receptor and horizontal cells.