bluuebunny/crossref_metadata_2025 huggingface dataset:
[3H]gamma‐Aminobutyric acid uptake into neuroglial cells of rat superior cervical sympathetic ganglia.
Authors: Bowery N G , Brown D A , White R D , Yamini G
Published: December 2014

1. The influx of [3H]gamma‐aminobutyric acid ([3H]GABA) into isolated rat superior cervical ganglia has been measured by radioassay, supplemented by autoradiography. Ganglia were incubated in oxygenated Krebs solution at 25 degrees C, containing 10 microM‐amino‐oxyacetic acid. Under these conditions more than 95% of accumulated tritium was unmetabolized [3H]GABA. 2. Ganglionic radioactivity increased linearly with incubation time, to yield an intracellular fluid/extracellular fluid concentration ratio (Ci/Co) of about 200 after 6 hr in 0.5 microM‐external [3H]GABA. 3. Uptake showed saturation with an apparent transport constant (KT) of 6.8 microM and maximum influx velocity (Jmaxi) of 7 mumole 1. cell fluid‐1‐ min‐1. 4. The influx rate at Co = 0.5 microM was unaltered by raising intracellular GABA from 0.2 to 1 mM. 5. Influx velocity increased with temperature (5‐‐35 degrees C) in a monotonic manner with an apparent activation energy of 14 kcal mole‐1. 6. Concentrative uptake was depressed by reducing external [Na+] with ouabain, by raising [K+]o above 20 mM, or by removing external Cl‐. Uptake was not particularly sensitive to Ca2+ or Mg2+ ions. 7. Utake of [3H]GABA (0.5 microM) was inhibited by beta‐guanidinopropionic acid (apparent KI, 28 microM), beta‐alanine (KI, 55 microM), gamma‐amino‐beta‐hydroxybutyric acid (KI, 220 microM), beta‐amino‐n‐butyric acid (KI, 708 microM), 3‐aminopropanesulphonic acid (KI, 832 microM) and taurine (KI greater than 1 mM). Uptake was not depressed by 1 mM‐glycine, alpha‐alanine, leucine, serine, methionine or alpha‐amino‐iso‐butyric acid. 8. Radioactively labelled methionine, leucine, glycine, serine, beta‐alanine and taurine (concentrations less than or equal to 5 microM) were also taken up by ganglia. Of these, only uptake of beta‐alanine and taurine were significantly depressed by 1 mM‐GABA. 9. Autoradiographs confirmed that [3H]GABA and [3H] beta‐alanine were taken up predominantly into extraneuronal sites (presumed to be neuroglial cells). Methionine, leucine, glycine and serine showed preferential accumulation in neurones. Neuronal uptake of leucine was not prevented by inhibiting protein synthesis. 10. Calculations of net fluxes from unidirectional tracer fluxes suggest that the sympathetic glial cells are capable of promoting net uptake of GABA at external concentrations above 1 microM.
Spatial and temporal properties of X and Y cells in the cat lateral geniculate nucleus.
Authors: Derrington A M , Fuchs A F
Published: December 2014

1. Extracellular recordings were obtained from units in the dorsal lateral geniculate nucleus of anaesthetized cats. 2. Of sixty‐nine units, sixty‐three could be unambiguously identified as either X (n = 33) or Y (n = 30) by testing the presence of a null response to stationary sine wave gratings presented in different spatial phases. 3. In response to stationary gratings flashed on and off, Y cells exhibited bigger, more transient responses than X cells. 4. All Y cells but few X cells exhibited a shift effect (modulated periphery effect). 5. In response to drifting sine wave gratings of different spatial frequencies, X cells preferred higher spatial frequencies and showed smaller peak contrast sensitivities and somewhat narrower tuning curves than Y cells. 6. In response to a sine wave grafting of optimal spatial frequency drifting at different velocities, X and Y cells had similar temporal tuning curves. However, Y cells, largely because they preferred lower spatial frequencies, preferred higher drift velocities than X cells. 7. Our data suggest that X and Y cells can be differentiated objectively on the basis of a number of discharge parameters. These parameters are compared with similar data collected by others from neurones in the visual cortex.
Effect of visual experience on tubulin synthesis during a critical period of visual cortex development in the hooded rat.
Authors: Cronly‐Dillon J , Perry G W
Published: December 2014

1. In some species, restriction of visual experience in early life may affect normal functional development of visual cortical cells. The purpose of the present study was to determine if visual deprivation during post‐natal development in the hooded rat also affects the production in brain cells of certain molecular components such as tubulin, that are needed for growth and maintenance of synapses and neurites. 2. Norwegian black hooded rats were reared under a variety of conditions of visual deprivation. At various stages of development the animals were killed and the rate of synthesis of tubulin in visual and motor cortex determined. Tritiated colchicine was used to assay tubulin and L‐[14C]leucine injected into the brain ventricles 2 hr before death was used to measure rate of tubulin synthesis. 3. In rats reared in normal light there is a marked elevation in visual cortex tubulin synthesis that spans the period from eye‐opening (13 days) until approximately 35 days. This elevation in tubulin synthesis is absent in animals reared in darkness from birth or deprived of pattern vision by eyelid suture. Also the effect of visual deprivation on tubulin synthesis was specifically confined to visual cortex and was not found for the motor cortex. Similarly, the incorporation of L‐[14C]leucine into total protein in visual cortex was unaffected by dark rearing. Hence the stimulation of tubulin synthesis by visual experience in rat visual cortex is not attributable to a general non‐specific stimulation of protein synthesis. 4. Rats that were dark‐reared from birth and then exposed to a lighted environment for 24 hr during a certain critical period that extends from eye‐opening (13 days) until approximately 35 days, displayed a significant increase in visual cortex tubulin rats that were brought into the light later than 35 days showed no significant increase in tubulin synthesis when compared with their continuously dark‐rearer controls. 5. It is suggested that the number of synapses and cytoplasmic processes that a developing cell can maintain depends on the size of the tubulin pool available to that cell. Tubulin in brain only has a half‐life of about 4 days, so when the level of tubulin drops this could result in competition between different synapses for the limited supply of tubulin needed for their maintenance, a factor which may contribute to the structural plasticity of the visual cortex during the critical period.
The action of acetylcholine and catecholamines on an intracellular calcium store in the smooth muscle cells of the guinea‐pig taenia coli.
Authors: Casteels R , Raeymaekers L
Published: December 2014

1. The role of an intracellular Ca store in excitation‐contraction coupling was studied by recording isometric tension development of thin strips (100‐150 micron in diameter) of taenia coli incubated in Ca‐free solution containing 2 mM‐EGTA. 2. The smooth muscle cells of taenia coli do not contract during exposure to a K+‐rich and Ca‐free solution. However a contractile response can be elicited by acetylcholine or carbachol at concentrations exceeding 10(‐6) M. These contractions are probably induced by a release of intracellular Ca. Ca is also released from the same store, although less effectively, by histamine and caffeine. 3. The amount Ca in the intracellular store, as revealed by the magnitude of the carbachol contraction in Ca‐free solution, increases after contractions have been induced by high (K+)0 or by solutions containing low concentrations of carbachol. This contraction amplitude decreases after stimulation with a high concentration of carbachol. The amount of Ca in the filled store is sufficient for a near‐maximal contraction. 4. The activation of beta‐receptors during a K+‐depolarization reduces the height of the contracture and induces a carbachol response in Ca‐free solution which is higher than that obtained after a preceding K+ depolarization without isoprenaline. This observation indicates that an increased uptake of Ca into the carbachol‐sensitive store contributes to the relaxing effect of beta‐agonists. 5. In the tissues which have been loaded with 45Ca in a K+‐depolarizing solution, a release of Ca into Ca‐free solution is observed when the muscle is stimulated with carbachol, but not when it is stimulated with Ca‐free high K+. The release is larger when isoprenaline was present during the loading with 45Ca. 6. The removal of Na+ from the solution exerts a complex and unexplained action on the Ca store. Substitution of Na+ by Tris+ and by K+ have similar effects. 7. It is concluded that the smooth muscle cells of the guinea‐pig taenia coli have an intracellular store of Ca which participates in excitation‐contraction coupling. The store is sensitive to muscarinic agonists, beta‐agonists and monovalent ions, but is not affected by depolarization of the outer membrane.
Possible mechanism of the inhibitory effect of ouabain on renin secretion from rat renal cortical slices.
Authors: Churchill P C
Published: December 2014

1. The effects of ouabain on renin secretion by rat renal cortical slices were studied. 2. Renin secretion was inhibited by 10(‐3) M‐ouabain in the presence of free Ca (10(‐4) to 2.6 x 10(‐3) M). Inhibition was blocked at Ca less than 10(‐8) M. 3. The effect of free Ca on ouabain‐inhibition was shown to be independent of the presence of EGTA, completely reversible, and unrelated to passive leakage of renin from non‐viable cells, as assessed by simultaneous release of lactate dehydrogenase activity (LDH). 4. It is proposed that, as a result of inhibition of Na, K‐ATPase by ouabain, (a) intracellular Na increases in the renin‐secreting juxtaglomerular cells, (b) intracellular Ca increases, via an Na‐Ca exchange mechanism, and (c) that Ca accumulation, in some unknown manner, inhibits renin secretion.
The mechanism of coupled transport of sodium and chloride in isolated urinary bladder of the trout.
Authors: Fossat B , Lahlou B
Published: December 2014

1. Transepithelial fluxes of Na and Cl were measured in dissected trout bladders mounted in Ussing chambers. The mucosa‐to‐serosa fluxes appeared to comprise a linear and a saturating (Km = 8 mM) component as a function of the luminal concentration of the ion. The over‐all permeability for Cl was higher than for Na. Removal of either ion from the mucosal side induced the disappearance of the net flux of the co‐ion even when the substituting ions were not impermeant. This indicated a complete and specific mutual dependence between the Na and Cl transports. A large part (30‐50%) of Cl exchanges was ascribed to an exchange‐diffusion process. 2. In order to localize the site of ion copuling, the apical uptakes of Na and Cl were measured by short‐term exposure (2 min) to radioisotopes. The apical fluxes were similar to the transepithelial fluxes and therefore appeared to be the limiting factor for ion transfer. Ionic replacements on the mucosal side showed that the coupling between Na and Cl and Cl/Cl exchange occurs at this step.
Effect of thumb anaesthesia on weight perception, muscle activity and the stretch reflex in man.
Authors: Marsden C D , Rothwell J C , Traub M M
Published: December 2014

1. We have confirmed the results of Gandevia & McCloskey (1977) on the effect of thumb anaesthesia on perception of weights lifted by the thumb. Weights lifted by flexion feel heavier and weights lifted by extension feel lighter. 2. The change in size of the long‐latency stretch reflex in flexor pollicis longus or extensor pollicis longus after thumb anaesthesia cannot explain the effect on weight perception by removal or augmentation of the background servo assistance to muscular contraction. 3. During smooth thumb flexion, thumb anaesthesia increases e.m.g. activity in flexor pollicis longus and extensor pollicis longus for any given opposing torque. 4. During smooth thumb extension the opposite occurs: e.m.g. activity in both extensor and flexor pollicis longus decreases. 5. Clamping the thumb at the proximal phalanx to limit movement solely to the interphalangeal joint reduces or abolishes the effect of anaesthesia on both weight perception and e.m.g. activity during both flexion or extension tasks. 6. Gandevia & McCloskey's findings on the distorting effects of thumb anaesthesia on weight perception cannot be used to support the hypothesis of an efferent monitoring system of the sense of effort. Our results emphasize the close functional relationship between cutaneous and joint afferent information and motor control.
The role of the flocculus of the monkey in saccadic eye movements.
Authors: Noda H , Suzuki D A
Published: December 2014

1. Purkinje cell discharges were recorded from the flocculus of monkeys either spontaneously making saccadic eye movements (saccades) or trained to fixate a small visual target presented on a tangent screen. In the trained monkeys, saccades of known magnitude and direction were induced by changing the position of the fixation target. 2. Among 513 Purkinje cells, 343 units (66.9%) paused during saccades in all directions (286 units) or in particular directions (57 units). In most units, there were intimate temporal relationships between the beginnings of pauses and saccades, and between the ends of pasuses and saccades. 3. The pause in activity preceded saccades by an average of 9.6 msec, with a maximum lead time of 30 msec. In a fraction of the units (7.6%), the pause started after the onset of saccades. 4. There were 104 units (20.3%) which showed bursts during saccades in all directions (eighty‐two units) or in particular directions (twenty‐two units). 5. In sixty‐six units (12.8%) a burst was associated with saccades in one direction and a pause in the opposite direction. 6. The burst in the burst and burst‐pause units preceded saccades by an average of 3.8 msec. There was no significant difference in the lead times between these two groups of units. 7. There was a linear relationship between the duration of the pause in Purkinje cell activity and that of the accompanying saccade. A linear relationship was also seen between the pause duration and the magnitude of saccade.
Processing of eye movement signals in the flocculus of the monkey.
Authors: Noda H , Suzuki D A
Published: December 2014

1. Extracellular recordings were made from afferents to the Purkinje cells of the flocculus of monkeys either spontaneously making saccadic eye movements (saccades) or trained to fixate a small visual target projected on a tangent screen. In the trained monkeys, saccades of known magnitude and direction were induced by changing the position of the fixation target. 2. Among a population of 108 units, eight were climbing fibres, seventy‐one were mossy fibres, and twenty‐nine were non‐Purkinje cells. Based on their discharge patterns the latter two groups of units were categorized into one of four classes. 3. Long‐lead burst units (twenty‐two units) exhibited saccade‐related discharges substantially before saccade onset (average: 113 msec). Most of these (twenty units) discharged for saccades in a particular direction, while the remainder exhibited discharges for saccades in all directions. All units were essentially silent between saccades. 4. Burst units (twenty‐seven units) started discharging slightly before saccades (average: 6.9 msec). Discharges were associated with saccades in all directions (sixteen units) or in preferred directions (eleven units) and were not observed during periods of fixation. 5. Burst‐tonic units (twenty‐two units) were characterized by saccade‐related burst and position‐related intersaccadic tonic activity. 6. Tonic units (thirty‐seven units) exhibited position‐related tonic activity. The position‐related activity in both burst‐tonic and tonic units was observed only for fixation points within a specified region. The units were silent for fixation positions outside this region of preferred fixation.
Effects of endurance training on muscle fibre ATP‐ase activity, capillary supply and mitochondrial content in man.
Authors: Ingjer F
Published: December 2014

Seven young females were subjected to 24 weeks of intensive endurance training. Adaptive changes in myofibrillary ATP‐ase activity, capillary supply and mitochondrial content were investigated with light‐ and electron microscopy in needle biopsies from the quadriceps femoris. 1. The average value for the maximal oxygen uptake increased from 45.7 to 57.2 (ml . kg‐1 min‐1) (25.2%, P less than 0.005). 2. The average number of capillaries per muscle fibre increased from 1.39 to 1.79 (28.8%, P less than 0.005). Since no significant change in fibre area was found, this suggests that a considerable number of new capillaries have been formed during the training period. 3. An increased capillary supply of all fibre types was found, being greatest for type I and smallest for type IIB. 4. The relative amount of type I fibres before and after the training period was 57.9 and 56.5% respectively (n.s.), for type IIA fibres 26.4 and 31.5% (P less than 0.005), for type IIB fibres 9.2 and 3.4% (P less than 0.005) and for type IIC fibres 0.4 and 2.2% (P less than 0.005). Thus, in the type II group, significant changes in subtypes take place during the endurance training. The data suggest that type IIAB may represent a transitional state between type IIA and IIB. 5. Correlation of capillary supply, myofibrillar ATP‐ase activity and mitochondrial content (determined semiquantitatively of individual muscle fibres indicators that the capillary supply to a given fibre is more closely related to its mitochondrial content than to the fibre type as determined on the basis of myofibrillar ATP‐ase activity.
Reflex pathways in the abdominal prevertebral ganglia: evidence for a colo‐colonic inhibitory reflex.
Authors: Kreulen D L , Szurszewski J H
Published: December 2014

1. In vitro experiments were performed on preparations consisting of prevertebral ganglia attached to the entire colon of guinea‐pigs. The colon was divided into an orad and a caudad segment and intraluminal pressure was recorded from the terminal end of each segment. Intracellular recordings were simultaneously obtained from neurones in the coeliac plexus. 2. The source of mechanosensory input from the colon paralleled the responses to mesenteric nerve stimulation. That is, section of the mesenteric nerve that contributed the strongest synaptic input to a neurone eliminated most of the mechanosensory input to that neurone. 3. The origin of the mechanosensory input to some neurones could be localized as coming from either the orad or caudad segment of the colon. In the coeliac ganglia 68% of the neurones tested responded primarily to orad distension and 37% to caudad distension. In the superior mesenteric ganglion 57% responded to orad distension and 43% to caudad distension. 4. Repetitive stimulation of the mesenteric nerve trunks arising from the prevertebral ganglia inhibited contractions differentially in the orad and caudad segments. The inferior coeliac nerves inhibited primarily the orad segments of colon and the lumbar colonic nerves inhibited primarily the caudad segments of colon. Stimulation of the superior coeliac nerves did not alter the motility of either segment. 5. When one of the colonic segments was distended, contractions in the other colonic segment were inhibited in 71% of the distensions. This inhibition operated in both directions: either orad inhibiting caudad or vice versa. 6. Cutting the intermesenteric nerve which communicates between the orad and caudad prevertebral ganglia eliminated the inhibitory reflex. 7. These experiments provide evidence for a colo‐colonic inhibitory reflex mediated through pathways in the prevertebral ganglia.
The action of salicylate ions on the frog node of Ranvier.
Authors: Attwell D , Bergman C , Ojeda C
Published: December 2014

1. The effects of salicylate on the membrane currents in the frog node of Ranvier were investigated. 2. External salicylate slows the falling phase of the action potential, with little effect on the action potential amplitude. 3. External salicylate has no effect on the leak current. 4. Most of the actions of external salicylate can be attributed to a simple incorporation of negative charge into the membrane surface. The h infinity, tau h, tau m and m infinity curves for the sodium current are shifted to more negative potentials, as are the n infinity and k infinity curves for the potassium current. Potassium ion accumulation prevented analysis of the action of salicylate on the time constant of the potassium current kinetics. 5. In addition to the h infinity and tau h curves being shifted to more negative potentials, the shapes of the curves are also changed by salicylate. These shape changes cannot be explained by conventional homogeneous surface charge theory. Possible explanations for these changes are discussed. 6. Internal salicylate has similar effects to external salicylate: the gating variable curves for the sodium current are shifted in the negative direction on the voltage axis, rather than in the positive direction expected if negative charge were added to the inner surface of the nodal membrane. This may be due to salicylate crossing the membrane and binding preferentially to a receptor at the external surface, or might be due to a rise in intracellular calcium concentration following inhibition of oxidative phosphorylation.
Non‐passive chloride distribution in mammalian heart muscle: micro‐electrode measurement of the intracellular chloride activity.
Authors: Vaughan‐Jones R D
Published: December 2014

1. Liquid ion‐exchanger Cl‐ ‐sensitive micro‐electrodes were used to make continuous measurements of the intracellular Cl activity, aCli, of quiscent sheep cardiac Purkinje fibres in vitro. 2. aCli was higher than that expected from a passive distribution, (which would have been about 5 mM). It was 3‐‐4 times hiable; EC1 was about 35 mV positive to Em. It was over twice as high in the nominal absence of bicarbonate/CO2 (when the buffer‐system was HEPES/O2) but was not always so stable, and ECl was about 20 mV positive to Em. 3. Experiments designed to assess the maximum possible error likely to occur in the measurement of aCli showed that this could not be large and that the estimates of ECl were accurate to within 8 mV. 4. The ability of Cl to move down both concentration and potential gradients was established by demonstrating a loss of aCli in Cl‐free solutions and a gain when Em was depolarized positive to ECl in high‐K solutions. In both cases, the changes were complete within about 100‐‐160 min. 5. The decline of aCli in Cl‐free solutions (glucuronate‐substituted) was not significantly affected by changes of [Ca]o from 0 to 12 mM or by the depolarizations of Em of up to 60 mV that sometimes occurred in low or zero [Ca]o. 6. Only 2‐‐3 mM‐aClo was sufficient to impede substantially the ready loss of aCli in HEPES‐buffered solutions. 7. In high‐K solutions (45 mM), Cl appeared to be passively distributed since, at equilibrium, Em and ECl differed by less than 2 mV. 8. In HEPES‐buffered Tyrode, ECl of quiescent papillary muscle of the guinea‐pig was, on average, 39 mV positive to Em. 9. It is concluded that liquid ion‐exchanger Cl‐ ‐sensitive micro‐electrodes are suitable for studying the Cl regulation of sheep Prukinje fibres, and probably of other cardiac tissues. The measurements of resting aCli are quite accurate when using either HEPES or bicarbonate‐buffered Tyrode. The results are discussed in relation to estimates of the apparent membrane Cl permeability under various conditions and the possible existence of an inwardly directed ‘Cl pump'.
The responses of Golgi tendon organs to stimulation of different combinations of motor units.
Authors: Gregory J E , Proske U
Published: December 2014

1. Afferent discharges were recorded from stretch receptors identified as Golgi tendon organs, in the medial gastrocnemius and soleus muscles of the cat. 2. The response of a tendon organ was recorded during stimulation of one or more motor units selected for the intensity of discharge elicited from the receptor during twitch and tetanic contractions. 3. Repetitive stimulation of a single motor unit could evoke in a tendon organ a firing rate of up to 174 impulses/sec. The mean rate for a total of 90 motor units was 65 (+/‐ 32 S.D.) impulses/sec. No significant difference in effectiveness could be detected between motor units covering a wide range of contraction speeds, tetanic tensions and susceptibility to fatigue. 4. The response of a tendon organ to contraction of several motor units in combination was greater than from stimulating any one motor unit alone but less than predicted from the algebraic sum of individual responses. 5. The relation between firing rate and tension was plotted for combined stimulation of up to ten motor units. The relation was found to be a straight line provided the size of the response elicited by each motor unit in the stimulated bundle was similar or when responses were ranked according to their intensity. When one motor unit evoked a much more powerful response than others it tended to dominate the discharge and disturb the linearity. 6. Evidence is provided that the sites of stimulus transduction for motor units which exert their effect directly on the receptor can be relatively independent of one another. It is argued that on such occasions summation of responses may be attributed to mechanisms operating at the level of impulse generation.
Mechanisms involved in differential conduction of potentials at high frequency in a branching axon.
Authors: Grossman Y , Parnas I , Spira M E
Published: December 2014

1. The ionic mechanisms involved in block of conduction of action potentials following high frequency stimulation were studied in a branching axon of the lobster Panulirus penicillatus. 2. A 2‐3 mM increase in extracellular K concentration (normal concentration 12 mM) produced block of conduction into both daughter branches. 3. While conduction block induced by high frequency stimulation occurs first into the large daughter branch and only later into the smaller one, propagation into both branches is blocked simultaneously by increased extracellular K concentration. 4. Increasing extracellular K by 2‐3 mM resulted in membrane depolarization, reduction in membrane resistance and reduced excitability. The latter two effects were larger than expected from the small depolarization. It appears that increase of extracellular K has direct effects on membrane excitability. 5. It is suggested that block of conduction after high frequency stimulation results from accumulation of K in the extracellular space. However, in order to account for differential conduction block in the two branches one must assume differential buildup of extracellular K concentration around the two branches during high frequency stimulation. 6. Ultrastructural studies using La and horseradish peroxidase as extracellular markers show that the space around the two branches is similar and is open to the extracellular space. Therefore differences in periaxonal volume cannot account for differential buildup of K around the two branches. 7. It is demonstrated that the lobster axon has a Na+/K+ electrogenic pump. After blocking this pump with ouabain, stimulation at high frequency resulted in a conduction block in the two branches almost at the same time. 8. Injection of Ca2+ intracellularly into the thick branch prevents or delays the appearance of conduction block after high frequency stimulation. 9. A mechanism based on these findings is suggested to explain the differential conduction block seen after high frequency stimulation in a branching axon with almost ideal impedance matching.
Uptake of [3H]benzamil at different sodium concentrations. Inferences regarding the regulation of sodium permeability.
Authors: Aceves J , Cuthbert A W
Published: December 2014

1. The effect of benzamil on short‐circuit current in frog skin was measured at different external sodium concentrations. A linear relationship exists between the concentration of benzamil reducing short‐circuit current by 50% and the external sodium concentration, indicative of some form of competitive antagonism between sodium and benzamil. 2. Uptake of [3H]benzamil into isolated frog skin epithelium and whole skin (0.95 cm2 pieces) was measured at different external sodium concentrations. With a sodium concentration of 111 mM in the external medium the uptake of [3H]benzamil is linear with concentration. Uptake amounted to 8.8 f‐mole nM‐1, a value similar to the linear component of the uptake measured at low (1.1 mM) sodium concentration. 3. Using a variety of other conditions the maximal number of specific binding sites for [3H]benzamil was calculated from displaceable binding and the fractional occupancy, the latter being derived from the inhibition of short‐circuit current. This approach gave similar binding site densities to those reported previously at low sodium concentrations. 4. The reduction in specific [3H]benzamil uptake at high sodium may result from two mechanisms, competition of sodium with the ligand for an external binding site and a reduction in the site density as the intracellular sodium concentration increases. 5. It is concluded that the saturation of sodium transport which occurs at high sodium concentration is likely a consequence of the reduced availability of entry sites, rather than saturation of the uptake process.
The labelling of vesicles in frog endothelial cells with ferritin.
Authors: Loudon M F , Michel C C , White I F
Published: December 2014

1. The labelling of endothelial cell vesicles with ferritin has been investigated by electron microscopy. Single capillaries in the frog mesentery have been perfused with solutions of known concentrations of ferritin for known periods before fixing the tissue in situ by superfusion with osmium tetroxide. 2. At 17 degrees C, the percentage of lumenal vesicles labelled with ferritin increased as the period of perfusion was increased up to 16 sec prior to fixation. When perfusions were longer than 16 sec, the percentage of vesicles labelled with ferritin remained fairly constant at 70%. 3. At 3 degrees C, no more than 25% of the lumenal vesicles were labelled during the first 30 sec. 4. After correcting the data for losses of ferritin due to sectioning, the distribution of ferritin molecules in the lumenal vesicles was consistent with a Poisson distribution. 5. After perfusions of 16 sec or longer, the number of ferritin molecules per labelled vesicle was roughly three to four times less than would be predicted from the lumenal concentration. 6. At all times there was a gradient of vesicles labelled with ferritin across the endothelial cells, i.e. the percentage of lumenal vesicles labelled was greater than that for cytoplasmic vesicles which in turn was greater than that for vesicles at the ablumenal surface. 7. Whereas the labelling of lumenal vesicles from zero time up to 16‐20 sec, the main increase in labelling of cytoplasmic vesicles occurred between 10 and 20 sec. 8. It is concluded that there is a major diffusion barrier to ferritin molecules either close to the endothelial cell surface or across the necks of the lumenal vesicles. It also appears that ferritin molecules do not have access to vesicles during the latter part of their residence at the lumenal surface.
Acid secretion from the completely isolated blood perfused canine stomach.
Authors: Pilot M A
Published: December 2014

1. The canine gastric arterial supply was isolated and perfused by means of an extracorporeal circuit. The gastric venous blood was returned to the dog's venous system. Histamine acid phosphate (20 microgram min‐1) infused intra‐arterially gave a mean peak acid output of 2.3 m‐mole per 10 min. 2. When a plateau of acid secretion was observed, the gastric venous blood was diverted to the oxygenator, by‐passing the dog entirely (vascular isolation). This resulted in an immediate decrease in acid output which fell to or near zero by 90 min after isolation. 3. In three dogs, part of a lung was perfused in series with the stomach before total isolation of the gastric vasculature. With histamine stimulation, acid secretion was observed for about 1 hr with a peak acid output of 0.5 m‐mole per 10 min during the period of total isolation. 4. Indomethacin (10 mg kg‐1) was given to five dogs approximately 1 hr before vascular isolation. After acid secretion reached a plateau (mean peak acid output 2.3 m‐mole per 10 minutes), the gastric circulation was isolated by diverting the gastric venous blood to the oxygenator. Acid secretion was maintained for 50 min, after which it gradually declined to reach 30% of the peak value after 2 hr. 5. Indomethacin (10 mg kg‐1) and methysergide bimaleate (1 mg) were given I.V. to five dogs approximately 1 hr before vascular isolation. After acid secretion reached a plateau (peak output 3.0 m‐mole per 10 min), the gastric circulation was isolated by diverting the gastric venous blood to the oxygenator. The plateau of secretion was maintained for a further 2 hr with no inhibition. 6. Methysergide bimaleate given alone did not prevent the inhibition of secretion caused by the total vascular isolation of the stomach. 7. These results suggest that in the isolated canine stomach preparation naturally occurring inhibitors of gastric acid secretion, which are normally metabolized at least in part in the lungs, accumulate in the circulation and may account for the observed suppression of acid secretion.
Saturation of the response to light in Limulus ventral photoreceptor.
Authors: Brown J E , Coles J A
Published: December 2014

1. Limulus ventral photoreceptor cells were voltage‐clamped with two intracellular micro‐electrodes. The light‐induced membrane current was recorded for brief stimuli. From observation of discrete waves (quantum bumps) at low stimulus energies and the early receptor potential at high energies, the stimulus energy was related to the number of rhodopsin molecules photosiomerized. 2. In the dark‐adapted cell the log (peak light‐induced current) reached almost its maximum value when about 10(3) of the 10(9) rhodopsin molecules in the cell were photoisomerized. 3. The magnitude of the maximum light‐induced current was not significantly altered after iontophoresis of EGTA into the cell. This treatment is known to counteract the Ca2+‐mediated reduction in sensitivity to light. 4. Current pulses were injected into the unclamped cell during the receptor potential. The form of the voltage deflexion (a step followed by a curve) suggested that the effective electrical equivalent of the cell was a membrane capacitance in parallel with a light‐dependent membrane resistance, Rm, and in series with another, light‐invariant, resistance, Rs. Rs ranged from 7 to 24 k omega (five cells). 5. During a receptor potential the ratio Rm/Rs was never observed to fall below 1.7 no matter how intense the light flash. Hence, it is concluded that the light‐induced current saturated essentially because Rm fell to a minimum value. 6. Charging curves gave a value for the capacitance, and hence the area, of the surface membrane. From this it was estimated that there were 10(5)‐10(6) microvilli on each cell. 7. These results show that the light‐induced increase in membrane conductance in a dark‐adapted cell comes close to its maximum value when the number of photoisomerizations is about 1/1000 the total number of microvilli. We suggest that absorption of a photon by a rhodopsin molecule in a microvillus causes an increase in membrane conductance on parts of the surface membrane beyond that microvillus. 8. In the presence of moderate background illumination the sensitivity to non‐saturating superimposed flashes was greatly decreased (e.g. by 10(3) while the saturating light‐induced current was only slightly decreased (e.g. by 15%). At higher background intensities the saturating light‐induced current was further decreased (e.g., with a background that photoisomerized 10(6.25) molecules per second the saturating light‐induced current was reduced by 47%).
The resting membrane potential of frog sartorius muscle.
Authors: Hironaka T , Morimoto S
Published: December 2014

1. The absolute resting membrane potential of the frog sartorius muscle was determined in Ringer solution at 20 degrees C. 2. Membrane potentials were measured with 0.03, 0.1, 0.3, 1.0 and 3.0 M‐KCl electrodes; potentials, including the micro‐electrode‐tip potentials, were ‐62.4, ‐75.7, ‐83.0, ‐87.7 and ‐90.7 mV respectively. 3. Membrane potentials were corrected for the liquid junction potentials between the Ringer and KCl solutions, and the myoplasm and the KCl solutions of the micro‐electrodes, using the Henderson's liquid junction equation. 4. The cation (U) and anion (V) conductances of the myoplasm were adjusted to give a constant membrane potential after correction for liquid junction potentials. The final values for U and V were 5.6 and 1.3 mmho/cm respectively, resulting in a membrane potential of ‐93.0 mV. 5. The correction for the liquid junction potential was ‐2.6 mV when a 3 M‐KCl micro‐electrode was used.
Interaction of permeant ions with channels activated by acetylcholine in Aplysia neurones.
Authors: Marchais D , Marty A
Published: December 2014

1. Aplysia neurones with an excitatory response to acetylcholine (ACh) were voltage‐clamped, and the ACh‐induced currents were studied using noise and relaxation techniques. The mean channel open time, tau, and the amplitude of the elementary current, iel, were determined from these experiments, and the variation of these parameters with the ionic content of the extracellular solution was analysed. The goal of this work was to test whether permeant ions may bind in a voltage‐dependent manner to channel sites and thereby hinder channel closing, as has been proposed before (Ascher, Marty & Neild, 1978a). 2. The relation between tau and the membrane potential V has a similar shape in normal sea water and after total replacement of Na ions with Li or Cs. In contrast, the shape of the tau(V) relation is modified if Na is replaced by Mg, Sr, or Ba. 3. Replacing the divalent cations (Mg and Ca) present in normal sea water with Na results in a decrease of tau and an increase of iel. Both effects are enhanced by cell hyperpolarization. 4. Similarly partial replacement of Na by Sr causes a voltage‐dependent decrease of iel. 5. Experiments were performed in solutions containing Na and sucrose, or Mg and mannitol. In both cases tau was smaller than in an isotonic Na or Mg solution. 6. None of the above observations can be accounted for on the sole basis of outer surface potential changes. 7. A quantitative model of the interaction between permeant ions and ACh‐sensitive channels is proposed. The possible relevance of this model for the interpretation of tau(V) curves in other systems is discussed.
Action of salicylate ions on the electrical properties of sheep cardiac Purkinje fibres.
Authors: Cohen I , Noble D , Ohba M , Ojeda C
Published: December 2014

1. In sheep Purkinje fibre preparations, salicylate ions produce reversible changes in resting potential and in action potential duration. In most preparations these effects resemble those produced by ‐ow extracellular K concentration: the resting potential first increases and then decreases, the action potential is prolonged and eventually, low potential oscillations occur in the plateau range. In a few preparations, action potential shortening occurs. 2. The threshold current for initiating action potentials by an intracellular electrode is reversibly increased by salicylate. 3. The activation curve, soo(Em), for the pace‐maker K current, iK2, shifted in a hyperpolarizing direction. The magnitude of the shift is about ‐5 mV in 5 mM‐salicylate and ‐30 mV in 50 mM‐salicylate. 4. The apparent reversal potential for iK2 is shifted in a negative direction. The magnitude of this shift at a given salicylate concent;ation varies with the K concentration. In an extracellular K concentration of 2.7 mM an average shift of ‐18 mV occurs in 10 mM‐salicylate; in 8 mM, the average shift is only ‐1 mV. 5. It is proposed that most of these effects may be produced by an increase in surface negative potential produced by the binding of salicylate to the cell membrane. This would produce the hyperpolarizing shift of activation curves for ionic current and, by increasing surface K activity, may lead to stimulation of the Na‐K pump to produce an increase in the K gradient across the cell membrane.
Recurrent inhibition and afterhyperpolarization following motoneuronal discharge in the cat.
Authors: Hultborn H , Pierrot‐Deseilligny E , Wigström H
Published: December 2014

1. The relation between the size of a monosynaptic reflex (varying from the smallest values to the maximal motor response) and the output from Renshaw cells was investigated. This relation was extremely variable from one Renshaw cell to another. However, a linear relation between the reflex size and the early discharge emerged when the responses of all the Renshaw cells were averaged or when the summed activity of a pool of Renshaw cells was estimated by recording the recurrent inhibition in their target motoneurones. It was concluded that the lowest threshold motoneurones were efficient in producing recurrent inhibition. 2. In motoneurones, recorded intracellularly, the size of the depression caused by the afterhyperpolarization was compared to the maximum autogenetic recurrent inhibition. Under the particular experimental conditions used to mimic human experiments (Hultborn & Pierrot‐Deseilligny, 1979a), it was found that recurrent inhibition had the same order of magnitude as the depression caused by afterhyperpolarization. 3. The additional depression caused by the summation of afterhyperpolarizations of two consecutive spikes was measured. It was shown that a summation of importance equal to the maximum autogenic recurrent inhibition required a mean interspike interval of 25 msec.
Ionic mechanisms of repolarization in the guinea‐pig taenia coli as revealed by the actions of strontium.
Authors: Inomata H , Kao C Y
Published: December 2014

1. The actions of Sr2+ on the smooth muscle of the guinea‐pig taenia coli have been studied under constant‐current and voltage‐clamp conditions. 2. In replacing Ca2+, Sr2+ (2.5 mM) prolongs the duration of the action potential by slowing the rate of repolarization, but increases the steady‐state membrane conductance. These changes occur in preparations in Krebs solution as well as in preparations in a Na+‐free tetraethylammonium medium. 3. When [Sr2+]o is increased to 20 mM, the amplitude of the spike is increased, and the duration shortened. 4. Under voltage‐clamp conditions, Sr2+ carries the early inward current (Ia). Increasing [Sr2+]o increases the maximum Ia and shifts its reversal potential (Ea) towards more positive voltages, without affecting the conductance, ga. 5. Sr2+ does not affect the steady‐state inactivation of Ia, but markedly slows the rate of inactivation. 6. In all concentrations, Sr2+ enhances the late outward current (Ib, chiefly Ik), by increasing the conductance, gb. The degree of increase is greater in higher [Sr2+]o. 7. Ca2+ at concentrations of 1 or 2.5 mM added to Sr2+ solutions partially reverses the above effects, suggesting the presence of some competition for the same channel or binding sites or both. 8. The results indicate that in the taenia coli, there is a component of the K+‐conductance system which is sensitive to [Sr2+]o and to [Ca2+]o. 9. They also suggest that the inactivation of the early inward current is an important mechanism underlying the repolarization of the action potential, and that IK probably has a delayed and gradual onset.
Discharges of intracerebellar nuclear cells in monkeys.
Authors: Harvey R J , Porter R , Rawson J A
Published: December 2014

1. Conscious monkeys were trained with food rewards to perform movement tasks with the left forelimb and to accept manipulation of the joints and muscles and natural non‐noxious stimulation of the skin of all four limbs. 2. Recordings were made from 217 cells situated in the left interpositus and dentate nuclei of the cerebellum. The identity of seventy‐seven cells as cerebellar projection neurones was definitively established by activating them antidromically from the brachium conjunctivum near the contralateral red nucleus. 3. Modulation in the natural activity of 129 of these crebellar nuclear cells (sixty in interpositus; sixty‐nine in dentate) occurred in a reproducible manner in temporal association with a phase of the self‐paced movement tasks performed by the animal using the ipsilateral arm and hand. The discharges during motor performance of forty‐two dentate and forty‐five interpositus cells were shown to be associated with movement about a particular joint or region of the forelimb whenever that movement occurred. 4. Cells whose discharges were related to proximal joint movements (shoulder, elbow) and cells related to distal joint movements (wrist, fingers) were encountered in both the dentate and interposed nuclei. 5. The cells were tonically active at rest. Most commonly, accelerations in the discharge were related to movement of a joint or the limb in one direction and a reduction or cessation of activity accompanied movement in the opposite direction. 6. For some cells, variation of the amount of discharge demonstrated during movement performance could be related to the range of the movement or its duration, more activity being characteristic of more prolonged movement performance through larger angles of joint displacement. 7. The dentate and interpositus cells whose discharges were most strongly and consistently related to movements of the forelimb were concentrated in the mid region and caudal half of either nucleus. 8. None of seventy‐three dentate neurones examined showed appreciable responses to stimulation of the skin or manipulation of joints and muscles of the fore‐ or hind limbs and only two cells responded to unexpected perturbation of movement performance. 9. No influence resulting from peripheral afferent input from the ipsilateral forelimb was detected in any interpositus cell whose firing was unchanged during ipsilateral arm movements. 10. Of the sixty interpositus cells whose discharge rates changed during motor performance, twenty‐eight were demonstrated to be in receipt of input from receptors in the ipsilateral hand or arm, which could be activated by brisk tapping of the skin and sometimes by gentle squeezing of the forearm. 11. In the passive relaxed animal, manipulation of joints was ineffective in modifying the discharges of most interpositus neurones and, in all cases, prolonged pressure upon the skin elicited only transient responses...
The control of sets of motoneurones by local interneurones in the locust.
Authors: Burrows M
Published: December 2014

1. A motoneurone innervating a muscle in a hind leg of a locust is controlled in a graded manner by many non‐spiking, local interneurones. There is overlap and fractionation of control between these interneurones. Some interneurones depolarize the motoneurone over part of its range, others hyperpolarize it, whilst some do both. 2. The interneurones organize the small number of motoneurones that innervate one muscle into overlapping sets of various sizes. A motoneurone can therefore be activated individually or in particular combinations with its fellow motoneurones. 3. The motoneurones innervating two muscles of a joint are also organized into overlapping sets by many local interneurones. This permits the motoneurones to the two muscles to be activated reciprocally, together, or independently. 4. One interneurone can elicit a co‐ordinated movement of one, two or even three joints in a hind leg that are components of the normal behaviour of the locust. 5. A single interneurone acting alone does not usually elicit the maximum output from one motoneurone, nor a complete piece of behaviour. A stronger contraction of a muscle and a more complete movement results from the action of groups of interneurones. 6. It is suggested that local interneurones, exerting graded control over motoneurones are a major element in the organization of motor patterns in the locust.