bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interactions leading to horizontal cell responses in the turtle retina
Authors: Fuortes M. G. F. , Simon E. J. 
Published: December 2014

1. Small responses to large fields of dim monochromatic lights were recorded intracellularly from luminosity horizontal cells (L‐cells), chromaticity horizontal cells (C‐cells) and cones in the retinae of turtles, Pseudemys scripta elegans.2. Responses of cones to brief flashes applied over steady backgrounds were studied in order to interpret the corresponding responses of horizontal cells. Steady red or green backgrounds make the responses of red‐sensitive cones smaller, faster and often diphasic. Green backgrounds have similar effects on the responses of green‐sensitive cones to green flashes, but red backgrounds do not change them appreciably. Responses of double cones have properties intermediate between those of red and green cones.3. L‐cells of both type I and type II are hyperpolarized by all visible wave‐lengths, and their spectral sensitivity in the linear range resembles that of red cones. Their responses are not invariant with respect to colour, and their sensitivity to green relative to red stimuli increases during red backgrounds. These properties suggest that L‐cells are activated mainly by red cones but also receive impingement from the red members of double cones.4. Spectral properties of red/green C‐cells resemble those of green cones as modified by the recurrent action of L‐cells. They can be explained assuming that red/green C‐cells receive their principal impingement from green cones and subsidiary interactions from green/blue C‐cells and the green members of double comes.5. The spectral sensitivity of the hyperpolarizing responses of green/blue C‐cells is ascribed to impingement from blue cones. Their depolarizing responses have complex properties which suggest that they are brought about by the activity of both L‐cells (probably through the blue cones) and red/green C‐cells.6. It is concluded that the main properties of the responses of the horizontal cells can be explained by a simple circuit in which each horizontal cell is connected to a corresponding type of cone and the L‐cells have a recurrent impingement on all cones. The scheme is modified by additional interactions which operate on the responses of each horizontal cell type.
The dependence of evoked transmitter release on external calcium ions at very low mean quantal contents
Authors: Crawford A. C. 
Published: December 2014

1. The mean quantal content of the frog end‐plate potential was examined under conditions that reduced evoked transmitter release to very low values.2. When the calcium concentration of the Ringer is reduced below 10−4
M a deviation occurs from the fourth power dependence of the mean quantal content (m) on the calcium concentration such that more quanta are released than is expected from the behaviour of m at higher calcium concentrations.3. At 10−5
M this extra quantal release is more than two orders of magnitude greater than that predicted by the fourth power relationship.4. The calcium dependence of very low values of m was studied in low calcium Ringer in which the calcium was buffered by either citrate or EDTA. It was found that in the fourth power dependence of m on the external calcium concentration changes rather suddenly to an approximately linear dependence.5. The inclusion of small concentrations of cobalt in the Ringer was found to reduce m to very low values even in the presence of millimolar concentrations of calcium.6. The fourth power dependence of m on the external calcium concentration at high values of m was unaffected by the presence of cobalt. At low quantal contents the transition to a linear dependence on external calcium was again seen, but was shifted to calcium concentrations that did not require buffering.7. The fourth power to linear transition is discussed in terms of its relevance to the relationship between m and the m.e.p.p. frequency.
The short range stiffness of active mammalian muscle and its effect on mechanical properties
Authors: Rack Peter M. H. , Westbury D. R. 
Published: December 2014

1. The tension in tetanized cat soleus and lateral gastrocnemius muscles was measured during alternating lengthening and shortening movements. Sinusoidal movements were sometimes used; on other occasions the movement was at a constant velocity but with periodic reversal of direction.2. With constant velocity movements of small amplitude the tension rose steeply during lengthening and fell during shortening in a relatively simple way. With longer movements the tension at first changed steeply as it had done with the smaller movement, but later in the movement the resistance of the muscles decreased so that the tension change became more gradual. The muscles resisted a small movement or the first part of a larger movement with a ‘short range stiffness’ which did not persist as the movement continued.3. So long as the constant velocity movement was not too slow the short range stiffness was independent of velocity though it lasted for more of a fast movement than of a slow one.4. In small movements the muscle was never extended beyond its short range stiffness, and the over‐all peak‐to‐peak tension change was therefore large compared with the amplitude of movement. When, with larger movements, the muscle was stretched into a range in which it became more compliant, the peak‐to‐peak force fluctuation did not increase by an equivalent amount, and over the whole course of the movement the force change per unit extension was smaller.5. When the movement was confined to a short range, little work was expended in driving the muscle through a cycle of movement; its properties were essentially elastic. With larger amplitudes the muscle met the movement with a frictional resistance, the tension during lengthening then being greater than during shortening. A considerable amount of work had then to be done on the muscle to maintain the movement.6. The short range stiffness was also apparent in the response to sinusoidal movements.7. The short range stiffness was attributed to elastic properties of cross‐bridges between thick and thin filaments in the myofibrils.8. The effect of the short range stiffness on the mechanical properties of the limb is discussed.
Active transport of iodide and other anions across the choroid plexus
Authors: Wright Ernest M. 
Published: December 2014

1. An in vitro preparation of the frog choroid plexus was used to study mechanisms of anion transport.2. It was observed that, in the absence of electrochemical potential gradients, there were net fluxes of I−, SCN−, TcO4−, and Br− across the plexus, from the ventricular to the serosal surface. The net flux of I− reached a maximum at a concentration of 250 μ
M.3. On the basis of competition effects it was concluded that the affinity of the transport process for anions was: ClO4 > ReO4 ∼ BF4 > SCN ∼ SeCN > I > NO3 > Br > Cl.4. Ouabain, oligomycin, phloretin and 2,4‐DNP inhibited the net transport of anions, but phlorrhizin, furosemide, 2,4,6‐trinitro‐m‐cresolate, reducing agents, and antithyroid agents did not. Ouabain and phloretin were only effective on the ventricular side of the preparation.5. Anion transport required the presence of both Na and K. The requirement for Na was specific, but Rb, and to a lesser extent Cs, could substitute for K. Na in either the ventricular or the serosal fluids could partially stimulate anion transport, but K was only effective in the ventricular solution.6. TcO4−, SCN− and I− were accumulated within the choroidal epithelium from the ventricular fluid, but not from the serosal fluid. Accumulation was inhibited by ouabain and ClO4−.7. The unidirectional influx of I− across the apical cell membrane was about an order of magnitude greater than the flux across the epithelium. This flux was inhibited by ClO4−, ouabain, and Na‐free solutions.8. These experiments suggest the following mechanism for anion transport across the plexus: anions are actively transported into the epithelium, by a ouabain sensitive, Na/K dependent pump located in the brush border membrane. The anions are accumulated within the epithelium, and, finally, they pass into the serosal fluid down their electrochemical potential gradient. Relations between anion transport, Na/K transport, and Na/K ATPases are discussed.
Effect of calcium and vasopressin on the response of frog skin to prostaglandin E1
Authors: Hall W. J. , Martin J. D. G. 
Published: December 2014

1. Prostaglandin E1 increases sodium transport as measured by short circuit current (SCC) across isolated frog skin whereas calcium, added to the external Ringer fluid, decreases sodium transport. To help establish the site of action of prostaglandin the possible interaction of these two agents on sodium transport has been examined.2. The effect of a standard dose of prostaglandin (0·5 × 10−6
M) on the short circuit current was tested on paired skins with either zero or high calcium (22·4 m
M) in the external Ringer fluid. In ten experiments the responses to prostaglandin (expressed in μA/cm2) were not significantly affected by external calcium.3. In another series of experiments the chelating agent, EGTA, was included in calcium‐free external Ringer in order to promote greater depletion of skin calcium. The response of these skins to the standard dose of prostaglandin was of the same order of magnitude as that of control skins. The response was not sustained in contrast to that of normal skins and skins in high‐calcium fluids.4. In a further series of experiments the reverse procedure was adopted whereby the response of the skin to low and high doses of calcium in the external Ringer was recorded in control conditions and when the skin had responded fully to twice the standard dose of prostaglandin. In addition, the calcium‐sensitive current was calculated for each skin in both circumstances. The latter was unchanged on addition of prostaglandin, and graded doses of calcium caused the same degree of inhibition of the short circuit current.5. The results show no interaction between external calcium and prostaglandin and also no need for external calcium in prostaglandin stimulation of sodium transport.6. The findings do not support the concept of chelation by prostaglandin of calcium from critical sites on the skin as the primary mechanism of its action on sodium transport. The results closely parallel those of a similar type of study into the relationship between vasopressin and external calcium on frog skin also.7. When frog skin has responded fully to either prostaglandin E1 or vasopressin, it shows no response to the other, although removal of calcium from the external Ringer fluid causes a further increase in short circuit current.8. Vasopressin causes a further increase in short circuit current in skins treated with prostaglandin F1α. Prostaglandin F1α may be a weaker agonist on frog skin than either vasopressin or prostaglandin E1.
A study of pace‐maker activity in intestinal smooth muscle
Authors: Connor J. A. , Prosser C. L. , Weems W. A. 
Published: December 2014

1. Electrical activity of longitudinal muscle from cat intestine was recorded in the double sucrose gap.2. Approximately 20% of the preparations demonstrated slow, spontaneous fluctuations of membrane voltage, slow waves. This activity, although quite uniform in a given preparation, showed considerable inter‐preparation variation with respect to amplitude, frequency and wave form.3. Application of steady hyperpolarizing current decreased slow‐wave frequency and increased slow‐wave amplitude while depolarizing currents increased frequency and decreased amplitude.4. Some preparations with no spontaneous slow‐wave activity developed slow waves when the membrane was hyperpolarized into a given range which, depending on the preparation, varied in size from 10 to 40 mV. Step or ramp depolarization of the membrane from hyperpolarized levels triggered slow waves in some preparations.5. When the membrane potential of a slow‐wave generating preparation was clamped at the resting potential, spontaneous inward‐directed current transients were observed.6. No changes in membrane conductance were observed during the course of a slow wave.7. The slow‐wave pattern was simulated for individual preparations by applying the membrane current measured under voltage clamp to the passive membrane resistance and capacitance measured independently under current clamp.8. In addition to the defined slow‐wave activity, voltage‐dependent oscillations in membrane potential were sometimes observed.9. Application of 10−5
M ouabain irreversibly blocked slow waves and produced a membrane depolarization equal to or slightly greater than the slow wave crest. Repolarization of the membrane to the resting potential, or hyperpolarization, failed to restore slow‐wave activity.10. Removal of external potassium produced a reversible sequence of events almost identical to those following ouabain application.11. Replacement of 50% of the external sodium chloride with sucrose produced no changes in slow‐wave activity with respect to rates of rise or fall, maximum amplitude or frequency. Sucrose replacement of all external sodium chloride eliminated slow waves after 5 min; however, activity could be restored by a slight hyperpolarization. Longer exposures to the modified bath abolished activity.12. Following a conditioning exposure to potassium‐free Krebs solution, readmission of potassium at normal concentration produced a mean hyperpolarization of 20·5 mV and in spontaneous preparations an arrest of activity.13. Pump current in sodium‐loaded, non‐spontaneously active preparations was measured by voltage clamp and was observed to be voltage‐dependent.14. The results of this study indicate that an electrogenic pump is present in longitudinal muscle of cat duodenum, and that oscillations in the level of pump current produce slow waves.
Slow recovery from inactivation of inward currents in mammalian myocardial fibres
Authors: Gettes L. S. , Reuter H. 
Published: December 2014

1. Reactivation kinetics of the rapid and slow inward currents in ventricular fibres have been assessed by studying the maximum rate of rise ((dV/dt)max) of the action potential upstroke and the duration of the plateau in progressively earlier premature responses. Reactivation of the slow inward current was also studied by voltage clamp technique in sheep and pig ventricular trabeculae.2. The time constant of recovery of (dV/dt)max was voltage dependent and increased from less than 20 msec when the resting membrane potential was more negative than −80 mV to more than 100 msec when the resting membrane potential was between −65 and −60 mV. Similar results were obtained in Purkinje fibres. These results suggest that the time constant for reactivation is slower than the time constant for inactivation of the rapid inward current system by at least one order of magnitude.3. The time constant of recovery of plateau duration was also voltage dependent and increased from 30 to 70 msec as the membrane potential was changed from −85 to −60 mV.4. The reactivation time constant of the slow inward current determined by voltage clamp experiments were similar to the results obtained by analysis of plateau duration. At potentials less negative than −60 mV the time constant of reactivation became progressively longer. Unlike reactivation time constants of (dV/dt)max, the time constants of reactivation of the slow inward current were similar to the time constants of inactivation.5. Our results indicate that (a) in premature action potentials, time as well as voltage are important determinants of (dV/dt)max in myocardial and Purkinje fibres, (b) the kinetics of reactivation of the rapid inward current in cardiac fibres are different from those in nerve and (c) plateau duration of premature action potentials in ventricular myocardial fibres is largely determined by the kinetics of reactivation of the slow calcium inward current.
Differential reaction of fast and slow α‐motoneurones to axotomy
Authors: Kuno M. , Miyata Y. , Muñoz‐Martinez E. J. 
Published: December 2014

1. The properties of medial gastrocnemius (m.g., fast α) and soleus (sol., slow α) motoneurones of the cat were examined with intracellular electrodes 8–119 days after section of the muscle nerves.2. The axonal conduction velocity was significantly decreased in both m.g. and sol. motoneurones after chronic section of the muscle nerves.3. The amplitude of overshoot of action potentials was significantly increased in both m.g. and sol. motoneurones following section of the muscle nerves.4. No significant changes in the resting membrane potential or the input resistance were observed for sol. motoneurones, whereas m.g. motoneurones showed a slight decrease in the resting potential and a slight increase in the input resistance.5. The duration of after‐hyperpolarization was significantly decreased in sol. motoneurones, whereas that in m.g. motoneurones remained virtually unchanged or increased slightly following section of the muscle nerves.6. The changes described above were not seen in the preparations examined 29–46 days after section of the lumbosacral dorsal roots, suggesting that alterations in the motoneurone properties observed after section of the muscle nerves resulted from axotomy of the motoneurones rather than from sensory deprivation.7. The differences in electrophysiological properties between m.g. and sol. motoneurones were less prominent in axotomized animals than in control, unoperated cats.8. It is concluded that fast (m.g.) and slow (sol.) α‐motoneurones have qualitatively different properties. A possible ‘dedifferentiation’ of fast and slow α‐motoneurones by axotomy is discussed.
The permeability to tetraethylammonium ions of the surface membrane and the intercalated disks of sheep and calf myocardium
Authors: Weingart Robert 
Published: December 2014

1. Efflux experiments and longitudinal diffusion experiments were performed to determine the permeability of the surface membrane and of the nexal membrane of sheep and calf ventricular muscle to radioactive [1‐14C]tetraethylammonium cations ([14C]TEA) at 25° C.2. Efflux curves were analysed as the sum of three exponential processes with time constants for TEA loss of 2·7, 13·3, and 832 min.3. The first component was attributed to the exchange of extracellular free TEA, the second to extracellular, probably mucopolysaccharide bound TEA, and the third to intracellular free TEA.4. From the decay of the first phase the tortuosity factor for extracellular radial movement of TEA ions was calculated as 1·59.5. The permeability of the surface membrane to [14C]TEA was estimated as 6·06 × 10−8 cm/sec.6. A tenfold change of [K]o from 5·4 to 54 m
M resulted in a 2·75‐fold decrease of the permeability of the surface membrane; a fifteenfold change (5·4 to 81 m
M) resulted in a 4·24‐fold decrease.7. From longitudinal non‐steady state diffusion experiments the permeability of the nexal membrane to [14C]TEA turned out to be 1·27 × 10−3 cm/sec.8. The permeability of the nexal membrane to TEA is 21,000 times larger than that of the surface membrane. This finding is consistent with the concept of low resistance pathways between myocardial cells.9. From a comparison of the dimensions of radiopotassium, [14C]TEA and Procion Yellow, and the study of their diffusional properties, the pores within the nexal membrane of the intercalated disks are deduced to have a diameter of somewhat more than 10 Å.
Selective glycogen depletion pattern in human muscle fibres after exercise of varying intensity and at varying pedalling rates
Authors: Gollnick P. D. , Piehl Karin , Saltin B. 
Published: December 2014

1. Glycogen depletion pattern in human skeletal muscle fibres was studied after bicycle exercise of varying intensity performed at different pedalling rates. Work intensities studied were equivalent to 30–150% of V̇O2 max. with pedalling rates of 30–120 rev/min.2. Glycogen depletion increased dramatically with increasing exercise intensity; depletion was 2·7 and 7·4 times greater respectively at workloads demanding 64 and 84% V̇O2 max. than at workloads calling for 31% V̇O2 max. Even greater rates of glycogen utilization occurred at supramaximal loads.3. Slow twitch, high oxidative (ST) fibres were the first to lose glycogen (reduced PAS staining) at all workloads below V̇O2 max. Progressive glycogen depletion occurred in fast twitch (FT) fibres as work continued. Large quantities of glycogen remained in the muscle after 3 hr of exercise at low exercise intensity. This was almost exclusively found in FT fibres. At workloads exceeding maximal aerobic power, there was an initial depletion of glycogen in both fibre types. Varying the pedalling rate and, thus, the total force exerted in each pedal thrust had no effect on the pattern of glycogen depletion in the fibres.4. Results point to primary reliance upon ST fibres during submaximal endurance exercise, FT fibres being recruited after ST fibres are depleted of glycogen. During exertion requiring energy expenditure greater than the maximal aerobic power, both fibre types appeared to be continuously involved in carrying out the exercise.
Absence of action potentials in frog slow muscle fibres paralysed by botulinum toxin
Authors: Miledi R. , Spitzer N. C. 
Published: December 2014

1. As shown previously, slow muscle fibres of the frog develop the ability to produce action potentials in 2 weeks after denervation.2. Normal transmission at the slow fibre neuromuscular junction gives a junction potential of 11 mV average (range 6–20 mV), caused by summation of potentials from several motor axons.3. Botulinum toxin injected intramuscularly into the iliofibularis blocks the neuromuscular junction of slow fibres in 6 days at room temperature. Single nerve stimuli give junction potentials of 0·05 mV average (range 0–1·6 mV). Contraction of slow fibres in response to tetanic stimulation is eliminated.4. No action potentials could be elicited in botulinum treated fibres, even 6½ weeks after injection of toxin. This finding is discussed in relation to the possible involvement of a ‘trophic’ factor regulating the action potential mechanism in frog slow muscle fibres.
The absorption of a mixture of amino acids by rat small intestine
Authors: Bronk J. R. , Leese H. J. 
Published: December 2014

1. The absorption of a mixture of amino acids by the small intestine has been studied in vitro with mucosal slices from rat jejunum. The mixture contained eighteen amino acids and was used at a concentration of 9·5 m
M in the incubation medium. The uptake of fifteen of the amino acids was followed in each sample with the aid of an amino acid analyser.2. The endogenous amino acid content of the slices decreased during preparation and further substantial losses occurred when the slices were preincubated for 30 sec before the addition of the amino acid mixture to the incubation medium.3. When the slices were incubated with the amino acid mixture for 4·5 min all of the amino acid studied were accumulated to give concentration ratios of approximately 2·0.4. The amino acids were taken up rapidly by the tissue so that on average 82% of the amino acids absorbed in 4·5 min had already accumulated after one min of incubation.5. The data for individual amino acids revealed no obvious competition between the various amino acids, and the extent to which the various amino acids were accumulated by the tissue was proportional to their concentrations in the mixture.6. When the Na+ in the incubation medium was replaced by Li+, the slices accumulated all of the amino acids studied to concentrations significantly higher than those in the incubation medium. However, the concentration ratios obtained with the Li+ medium were all lower than those obtained with the Na+ medium and averaged slightly more than 1·5.7. When the Na+ in the incubation medium was replaced by K+ there was little amino acid accumulation, although concentration ratios significantly greater than one were achieved for aspartic acid, glycine, histidine and methionine.