bluuebunny/crossref_metadata_2025 huggingface dataset:
The detection of gas bubbles in guinea‐pigs after decompression from air saturation dives using ultrasonic imaging.
Authors: Daniels S , Davies J M , Paton W D , Smith E B
Published: December 2014

1. Bubble formation in the hind limb of anaesthetized guinea‐pigs, after decompression from two different saturation exposures to air, 0.69 and 0.83 MPa gauge, has been studied using an ultrasonic pulse‐‐echo imaging technique. 2. A qualitative analysis of the bubble formation, observed over a 30 min period after decompression, showed that profuse, largely stationary bubble formation occurred within 3 min of the decompression from 0.83 MPa gauge but that extensive stationary bubble formation was not observed until 17 min after decompression from 0.69 MPa gauge. Electrocardiogram changes appeared coincidently with the appearance of major bubble formation after the 0.83 MPa decompression but after the 0.69 MPa decompression changes were not observed until the end of the 30 min surveillance period, considerably later than the occurrence of a large number of bubbles. 3. A quantitative analysis of the echo patterns recorded during the 60 sec decompression and for 60 sec after the decompression demonstrated that the increase in severity of the decompression corresponded to an increase of 152% in the number of bubbles observed. The echoes observed during this period have been identified as either transient or persistent and their distribution of size, location and times of appearance and duration have been described. 4. From the quantitative analysis approximate estimates of the contribution by mobile, intravascular gas bubbles to the elimination of the excess gas have been made. These estimates range from 0.01 to 0.9% after the 0.69 MPa decompression and from 0.06 to 6% after the 0.83 MPa decompression. 5. It is concluded that the pulse‐‐echo ultrasonic imaging technique provides a powerful means of analysing the distributions of bubble formation, both qualitatively and quantitatively, after decompression; it has the important attribute of being able to monitor both moving and stationary bubbles simultaneously in a variety of tissue types.
The linear dynamic properties of phototransduction in the fly compound eye.
Authors: French A S
Published: December 2014

1. Photoreceptor cells in the compound eye of the fly Phormia regina were stimulated with a green light emitting diode whose output was modulated by a pseudo‐random noise generator while the resulting fluctuations in membrane potential were measured with intracellular microelectrodes. 2. The responses to repeated sequences of identical pseudorandom patterns were averaged together to give frequency response functions having a significantly improved signal to noise ratio at frequencies where the response has not previously been characterized accurately. 3. Measured frequency response functions could not be fitted by a set of simple exponential time constants but could be well fitted by a model including two under‐damped second order time constants. 4. The phase data had no detectable asymptote and could only be accounted for by a model which includes a pure time delay. 5. Residual fluctuations in the phase data with frequency suggest that a small portion of the recorded signal arises from a delayed interaction with lateral or proximal cells.
A smooth muscle inhibitory material from the bovine retractor penis and rat anococcygeus muscles.
Authors: Gillespie J S , Martin W
Published: December 2014

1. A material that powerfully inhibits the bovine retractor penis and rat anococcygeus muscles has been extracted from these muscles. The inhibitory activity is unaffected by atropine 10(‐6) M, phentolamine 5 x 10(‐6) M or propranolol 5 x 10(‐6) M. 2. This inhibitory material exists in two forms, a stable but inactive form and an unstable inhibitory form. As isolated the material is in the stable, inactive form and is converted into the active form by a brief exposure to acid. The optimum for conversion is pH 2.0 and the active form, after neutralization, reverts with time to the inactive but can be reactivated by a further exposure to acid. The reversion to the inactive form is temperature sensitive, and is rapid at 37 degrees C. 3. The inhibitory material, both active and inactive, is irreversibly destroyed by 2 min in a boiling water bath or by exposure to U.V. irradiation. 4. The inhibitory material is not confined to tissues known to possess a non‐adrenergic non‐cholinergic innervation. Similar activity has been detected in extracts os skeletal and cardiac muscle and of the liver. The poorly innervated rat uterus and the non‐innervated human umbilical artery, however, gave only small and variable amounts. The possible relationship of this material to non‐adrenergic non‐cholinergic nerves is discussed.
The reflexion coefficient as a measure of transepithelial permeability in the isolated rabbit pancreas.
Authors: Bonting S L , De Pont J J , Fleuren‐Jakobs A M , Jansen J W
Published: December 2014

1. The reflexion coefficients of a number of non‐electrolytes and electrolytes have been determined in the isolated rabbit pancreas. 2. The reflexion coefficients of the following non‐electrolytes were: urea, ‐0.02; glycerol, 0.06; erythritol, 0.11; sorbitol, 0.41; mannitol, 0.42; arabinose, 0.72; xylose, 0.74, assuming a value of 1.00 for sucrose. 3. These values are equal within the experimental error to values previously obtained with a tracer technique for the same preparation, but they are significantly lower than those reported by other investigators for the isolated perfused cat pancreas. 4. Addition of 100 mM‐sucrose to the bathing medium resulted in proportionally increased Na+ and K+ concentrations in the secreted fluid. The secreted fluid remained isotonic with the bathing medium under all circumstances. 5. Addition of 10(‐5) M‐carbachol to the bathing medium led to a reduction in the reflexion coefficient of sucrose from 1 to 0.85, but only when 25 mM‐sucrose was used. 6. The reflexion coefficients of electrolytes were: NaCl, 0.50; KCl, 0.51; NaHCO3, 0.52 and choline chloride, 1.02. 7. It is concluded that the isolated rabbit pancreas is highly permeable, both to electrolytes and to small non‐electrolytes, probably being more leaky than any other epithelium studied so far.
selective elimination of motor nerve terminals in the rat soleus muscle during development.
Authors: Miyata Y , Yoshioka K
Published: December 2014

1. The pattern of innervation and either frequency of miniature end‐plate potentials (m.e.p.p.s) or acetylcholine (ACh) sensitivity was examined in individual fibres of the soleus muscle in new‐born rats to elucidate the mechanism of elimination of motor nerve terminals. 2. the number of motor nerve terminals innervating a muscle fibre was judged by the difference in latencies of end‐plate potentials evoked by stimulation of the ventral roots L4 and L5. 3. At early developmental stages, about 50% of soleus muscle fibres were usually singly innervated by the L5 ventral root and this nerve to fibre relation did not change throughout the developmental days. In contrast to the L5 root, the L4 root innervated all the muscle fibres polyneuronally at day 6. In day 16 or older animals, the remaining half of the fibres were singly innervated by the L4 ventral nerves. Therefore, it is concluded that the elimination of motor nerve terminals in the soleus muscle occurs selectively only for the L4 ventral nerves. 4. The number of polyneuronally innervated fibres was increased, to some extent, within 2 days after transection of the spinal cord at day 12. It is suggested that the increased polyneuronal innervation following the inactivity produced by cordotomy may reflect the recovery of terminals which had lost function only a short time previously during elimination. 5. Though frequency of m.e.p.p.s increased from day 6 to adult age as previously reported, there was no significant difference in the frequencies between singly and polyneuronally innervated fibres at any age. Cord transection at day 12 caused no change in the frequency. 6. ACh sensitivity observed in singly innervated fibres was similar to that in polyneuronally innervated fibres. Furthermore, cordotomy on day 12 did not induce an increase in ACh sensitivity around the end‐plate. It is concluded that the elimination of terminals is not causally related to changes in ACh sensitivity. 7. The possible mechanisms of selective elimination of terminals and the process of elimination are discussed.
Nerve growth factor and an anticomplimentary protease in mouse saliva elicited by nerve stimulation.
Authors: Partlow L M , Wallace L J , Wardell L J
Published: December 2014

1. Three substances previously identified in mouse saliva ((1) biologically active nerve growth factor (NGF), (2) a material immunologically identical to the alpha‐subunit of 7S‐NGF and (3) an anticomplementary protease) were quantified in both mandibular gland saliva and mixed salivary secretions elicited by stimulation of either the sympathetic or parasympathetic nerves to the salivary glands. 2. The concentrations and specific activities of all three substances in pure mandibular saliva equalled or exceeded those found in mixed secretions from all salivary glands. 3. All three substances were found to be primarily secreted as a result of sympathetic rather than parasympathetic nerve stimulation as their concentrations and specific activities were much greater in sympathetic than in parasympathetic mixed salivary secretions. 4. Bioactive NGF, alpha‐subunit‐like material, and an anticomplementary protease were demonstrated to be released selectively through activation of alpha‐adrenergic receptors as the concentrations and specific activities of all three substances were markedly reduced by pre‐treatment with an alpha‐adrenergic blocker (phenoxybenzamine) but not by pre‐treatment with either a muscarinic or a beta‐adrenergic blocker (atropine or propranolol, respectively). 5. Measurement of total protein in saliva elicited by sympathetic nerve stimulation following pre‐treatment with an alpha‐adrenergic, beta‐adrenergic, or muscarinic blocking agent demonstrated that proteins other than those examined in the present study must be released by activation of beta‐adrenergic receptors.
Common interneurones in reflex pathways from group 1a and 1b afferents of knee flexors and extensors in the cat.
Authors: Czarkowska J , Jankowska E , Sybirska E
Published: December 2014

1. Input from group I afferents of knee flexors and extensors to interneurones in Rexed's laminae V‐VI in the cat spinal cord was analysed by use of intracellular recording and electrical stimulation of the nerves to differentiate between group Ia and Ib synaptic actions. The aim was to find out if these interneurones may mediate synaptic actions of both group Ia and Ib afferents. 2. 28% of the forty‐nine neurones analysed were excited by both group Ia and group Ib afferents; 32% were inhibited by both and 35% were excited by the one and inhibited by the other. Taking into account all of these actions, input from both subgroups of group I afferents was found in nearly 60% of neurones. Most were also excited and/or inhibited by group I afferents of ankle and toe extensors. 3. Selective (excitatory and/or inhibitory) input from Ia afferents was found in 18% and from Ib afferents in 22% of the neurones. 4. Excitation was evoked from Ia afferents of either knee flexors or extensors but not from both. In several of the neurones Ia i.p.s.p.s were, however, evoked from both posterior biceps‐semitendinosus and quadriceps. 5. Intracellular staining with horseradish peroxidase revealed axonal projections of laminae V‐VI interneurones to motor nuclei as well as to the intermediate zone, ipsilateral as well as contralateral. No correlation was found between patterns of input from group I afferents and axonal projections, and interneurones co‐excited by Ia and Ib afferents were among these with different axonal projections.
Common interneurones in reflex pathways from group 1a and 1b afferents of ankle extensors in the cat.
Authors: Jankowska E , Johannisson T , Lipski J
Published: December 2014

1. Input from group I afferents of ankle and toe extensors, other muscles, skin nerves and descending tracts to interneurones of Rexed's laminae V‐VI in the cat spinal cord was analysed using intracellular recording from these interneurones. Adequate stimuli (muscle stretches) were used to activate selectively group Ia muscle spindle afferents of triceps surae and plantaris while other fibre systems were excited electrically. 2. Ia and Ib afferents of ankle and toe extensors were found to co‐excite, co‐inhibit or exert opposite synaptic actions in 41, 33, and 50% of the analysed interneurones, respectively. Taking into account both excitatory and inhibitory input from these two groups of afferents, 64% of the interneurones appeared to be used in common in reflex pathways from muscle spindles and tendon organs of ankle and toe extensors. 3. Selective input from Ib afferents of triceps surae and plantaris (excitation and/or inhibition) was found in 36% of the interneurones; there was evidence for a similarly selective input from Ia afferents. 4. A great majority (over 90%) of the interneurones excited by group I afferents were also inhibited by group I afferents, from either the same or other muscles. 5. Both monosynaptic and disynaptic e.p.s.p.s from Ia and/or Ib afferents from other muscles and from fibres in the ipsilateral funiculi were found in a great proportion of the same interneurones, together with disynaptic e.p.s.p.s from low threshold cutaneous afferents. 6. Intracellular staining with horseradish peroxidase revealed four different patterns of axonal projections of the analysed interneurones: (i) projections to motor nuclei and the intermediate region, (ii and III) projections only to the intermediate region, locally or combined with projections to different rostro‐caudal levels, and (iv) projections to the opposite side of the spinal cord. 7. A large proportion of interneurones projecting to motor nuclei displayed input from both Ia and Ib afferents although such an input was a feature of interneurones with other projections as well. No systematic differences in the input from group I afferents were found for interneurones with different axonal projections. In contrast disynaptic e.p.s.p.s of cutaneous origin and monosynaptic e.p.s.p.s upon stimulation of ipsilateral spinal tracts appeared predominantly in interneurones projecting to motor nuclei.
Input‐output relationships of central neural circuits involved in respiration in cats
Authors: Eldridge Frederic L. , Gill‐Kumar Pritam , Millhorn David E.
Published: December 2014

1. Inspiratory output responses, measured as integrated phrenic activity, to hypercapnia, to unilateral and bilateral carotid sinus nerve stimulation and to combinations of these stimuli were determined in paralysed, vagotomized and glomectomized cats whose end‐tidal PCO2 was kept constant by means of a servo‐controlled ventilator. In addition, the effect on these responses of the mechanism that causes the respiratory after‐discharge was determined.

2. Above the threshold for rhythmic activity, the inspiratory response to hypercapnic stimulation of the central chemoreceptor was curvilinear, showing progressively smaller increments of output for equal increments of PCO2 as the latter became higher.

3. The combining of stimuli from right and left carotid sinus nerves failed to show an algebraically additive effect; the response was approximately 70% of that predicted from a summing of the separate stimuli given alone.

4. The response to a constant carotid sinus nerve test stimulus was progressively decreased in magnitude as the pre‐stimulus level of respiratory activity was increased by conditioning stimulation of the central chemoreceptors by hypercapnia, by stimulation of the opposite carotid sinus nerve or by the mechanism that generates an after‐discharge.

5. From a descriptive standpoint, our findings show that there is a negative or hypoadditive interaction between the peripheral and central inputs at the level of the central respiratory controller. However, we present evidence that, rather than being a specific interaction between peripheral and central inputs, the response is due to the properties of a neural component of the central pathway. This component is common to both inputs and develops progressive saturation of its neural elements as its activity increases.

6. In addition, the neural mechanism which generates a respiratory after‐discharge appears to saturate completely at a lower level of inspiratory activity than that at which the common pathway develops complete saturation. This finding supports the idea that this mechanism represents an independent input to the respiratory controller.

7. Because the described a‐linear response characteristics of the central respiratory controller are due to its inherent neuronal properties rather than to specific interactions between inputs, we suggest that studies of such ‘interactions’ must be interpreted with this consideration in mind.
Mechanical properties and myosin light chain composition of skinned muscle fibres from adult and new‐born rabbits.
Authors: Julian F J , Moss R L , Waller G S
Published: December 2014

1. The maximum velocity of shortening, Vmax, and stiffness were measured in skinned single fibre segments from psoas and soleus muscles of adult rabbits and psoas muscles of new‐born rabbits, and the myosin light chain composition was also determined in the same segments used in the mechanical studies. 2. Vmax was obtained at 15 degrees C during maximal activation at pCa 5.49 using a method involving measurement of the time required to take up various amounts of slack imposed on the segments. Stiffness was measured during activation at 10 degrees C by application of length steps complete in 0.6 msec. The myosin light chain composition of the segments was then determined by SDS‐polyacrylamide gel electrophoresis. 3. Only fast type light chains were found to be present in the psoas fibre segments, though the relative amounts of myosin LC1f, LC2f and LC3f in these segments was somewhat variable. In most instances, the sum of the amounts of LC1f and LC3f present was equivalent to the amount of LC2f. Only slow type light chains were found in the soleus segments and the sum of the amounts of LC1as and LC1bs was about equal to the amount of LC2s. 4. The results indicate that there are no consistent relationships between Vmax, tension development or stiffness and LC1f/LC2f in the segments from adult and new‐born psoas muscles, or between these mechanical parameters and LC1as/LC2s or LC1bs/LC2s in the adult soleus segments. However, the psoas segments, which had light chains of the fast type, had Vmax values that were consistently higher than those of the soleus segments, which had light chains of the slow type. 5. The stiffness values obtained in each of the three kinds of muscle were similar, suggesting that cross‐bridge stiffness is similar in rabbit skeletal muscles of different type and age. Moreover, the results indicate that the amount of end compliance introduced by the connections to the fibre segments has a marked influence on the stiffness that is measured.
Functional properties of monkey motor cortex neurones receiving afferent input from the hand and fingers
Authors: Lemon R. N.
Published: December 2014

1. Records have been made from area 4 of the cerebral cortex in five conscious monkeys. The properties of 216 neurones responsive to natural stimulation of the hand and fingers have been investigated.

2. 46% of these neurones responded only to cutaneous stimulation (especially light brushing across the glabrous skin) and a further 38% responded only to movement of the digits. 4% responded to brief prods of the hand. 12% of the sample responded to more than one stimulus modality.

3. Many hand‐input neurones, including pyramidal tract neurones, responded at short‐latency (8‐15 msec) to light mechanical stimulation of the hand and to weak electrical stimulation of the median nerve.

4. Responsive neurones were found at all depths of the cortical grey matter. Responses of shortest latency were encountered in neurones probably located in layers IV and V.

5. The behaviour of eighty hand‐input neurones was analysed during a simple, stereotyped task which involved pulling a lever and collecting a food reward from a small well. For comparison, the activity of 117 neurones with inputs from the wrist, elbow or shoulder was also analysed.

6. Nearly all hand‐input neurones modulated their activity either before (48/80) or during (29/80) the retrieval of the reward which required precision grip between index finger and thumb. Many were silent during proximal arm movements and some displayed activity patterns independent of these movements.

7. By contrast, the activity of many neurones with proximal arm (elbow, shoulder) inputs was unrelated to food retrieval and manipulation, but well related to arm movements.

8. Forty‐three of the eighty neurones had cutaneous input from the hand. Twenty‐seven were active before hand contact. Thirty‐five modulated their discharge when contact was made (twenty‐one excitation, fourteen inhibition).

9. Most hand‐input neurones were more active during fractionated movements of the hand or fingers than during power or ball grips requiring simultaneous flexion of all digits. Neurones with glabrous inputs often showed intense activity during small, precise finger movements and during active tactile exploration without the aid of vision.

10. Analysis of the discharge frequency of twenty‐five hand‐input neurones revealed that some (mainly non‐pyramidal tract neurones) had a similar mean frequency and range of modulation during both active movement and passive stimulation. Others (mainly pyramidal tract neurones) had a greater frequency range and higher mean frequency during active than during passive movements.
Calcium depletion in frog muscle tubules: the decline of calcium current under maintained depolarization.
Authors: Almers W , Fink R , Palade P T
Published: December 2014

1. Ca2+ currents in frog skeletal muscle fibres were studied with a voltage‐clamp technique. Under membrane depolarization maintained for several seconds, Ca2+ current was found to decline with time constants of 0.2‐2 sec when [Ca2+]o = 10 mM. 2. Ca2+ currents are diminished by nifedipine, D‐600, tetracaine and Ni2+. 3. When peak current is diminished by making the membrane potential positive, by block with drugs or by substituting the relatively less permeant Mn2+ for Ca2+ then the rate of decline is diminished also. When peak current is increased by recording at relatively negative membrane potentials or by substituting for Ca2+ the more permeant ions Ba2+ or Sr2+, then the rate of decline is increased in proportion. Evidently, the size of the current determines the rate of decline. 4. Decline of current is greatly slowed in isotonic Ca2+ saline or when the [Ca2+]o is buffered by the organic anion malate. These findings indicate that the decline of current arises from Ca2+ depletion in an extracellular compartment, most probably the transverse tubules. On this basis, an analysis of Ca2+ current decline and recovery leads to the following conclusions. 5. Ca2+ current flows almost entirely across the membranes of the transverse tubules. 6. After allowing for the tortuosity of the tubular network, the apparent diffusion coefficient for Ca2+ in the transverse tubules is about 2.6 X 10(‐6) cm2/sec, three times less than the diffusion coefficient for K+ in the transverse tubules and about three times less than the diffusion coefficient for Ca2+ in free solution. 7. The transverse tubule lumen does not appear to have a large Ca2+‐buffering capacity in the millimolar range. At [Ca2+]o = 10 mM, the tubule lumen binds less than 0.6 dissociable Ca2+ ions for every free ion.
Developmental changes in metabolism and transport properties of capillaries isolated from rat brain.
Authors: Betz A L , Goldstein G W
Published: December 2014

1. Capillaries were isolated from the brains of 1‐ to 45‐day‐old rats in order to study the development of metabolic and transport aspects of the blood‐brain barrier. 2. The hydroxyproline content of capillary hydrolysates increased nearly threefold between 5 and 45 days of age. This finding is consistent with histological studies showing thickening of capillary basement membrane during development. 3. The activities of L‐DOPA decarboxylase and monoamine oxidase were greatest in capillaries from 10‐day‐old rat brain. Thus, the metabolic blood‐brain barrier for amine precursors is present during early development. 4. Capillaries from all ages were able to metabolize glucose, beta‐hydroxybutyrate and palmitate. The rate of glucose oxidation more than doubled between 21 and 30 days of age but subsequently decreased. In contrast, beta‐hydroxybutyrate and palmitate oxidation increased throughout development. These data suggest a sparing effect by alternate fuels on glucose metabolism. 5. Capillary glucose uptake was similar at 10 and 30 days of age and activity of the ouabain‐sensitive K+ pump (measured using 86Rb+) was relatively constant at all ages. In contrast, Na+‐dependent neutral amino acid transport was not present until after 21 days of age. Since this transport system may be responsible for the active efflux of neutral amino acids from brain to blood, it is likely that this process does not occur at the immature blood‐brain barrier. 6. We conclude that various aspects of brain capillary functions show distinct developmental patterns which may be related to changes in blood‐brain barrier permeability during development.
Analysis of subthreshold pace‐maker currents in chick embryonic heart cells.
Authors: Clay J R , Shrier A
Published: December 2014

1. Small re‐aggregates of cells dissociated from the ventricles of 7‐day‐old chick embryonic hearts beat spontaneously in low external potassium concentration (Ko = 1.3 mM) tissue culture medium. This activity was blocked by the addition of tetrodotoxin (TTX) or potassium ions to the external medium. 2. A two‐micro‐electrode voltage‐clamp technique was used to analyse the subthreshold currents responsible for the pace‐maker depolarization. 3. Voltage‐clamp steps 6‐10 sec in duration revealed a time‐dependent current having first order kinetics. Its membrane potential range of steady‐state activation was ‐90 to ‐60 mV. 4. The current kinetics were qualitatively similar to those of Hodgkin & Huxley (1952b) with a peak time constant of approximately 1 sec at V = ‐75 mV. The kinetics were independent of Ko. 5. The time‐dependent current was attributed to gated membrane channels. The fully activated current‐voltage (I‐V) relation of the channels was determined from the ratio of the amplitudes of the time‐dependent currents during and after voltage‐clamp steps following the procedure of Noble & Tsien (1968). 6. The fully activated I‐V relation displayed inward rectification with negative slope conductance at potentials more than 15 mV positive to its reversal potential. Changes of Ko shifted the I‐V curve along the voltage axis like a potassium electrode. 7. The time‐independent (background) current was obtained by subtracting the gated channel current from the steady‐state I‐V curve. This current also rectified in the inward direction. 8. The inwardly rectifying I‐V relations were theoretically described by a channel having a row of ion‐selective sites along which ions move in a single file (Hodgkin & Keynes, 1955), and a membrane‐bound particle which blocked the channel in a voltage‐dependent manner. 9. The relationship of the voltage‐clamp results to spontaneous activity is discussed and comparisons are made with measurements from whole embryonic heart and other cardiac tissues.
Development of sodium permeability inactivation in nodal membranes.
Authors: Kniffki K D , Siemen D , Vogel W
Published: December 2014

1. The time course of inactivation of the sodium permeability was studied in myelinated nerve fibres of Xenopus laevis using the voltage‐clamp technique of Nonner (1969). The potassium currents were blocked by 10 mM‐tetraethylammonium chloride (TEA). The remaining currents were corrected for leakage and capacity currents. 2. The decay of the sodium current was double‐exponential confirming Chiu's (1977) findings The slower time constant was observed in TEA‐free solutions by clamping to VK in high potassium concentrations. 3. The fast time constant was similar to tau h of Frankenhaeuser (1960), whereas the slower time constant was about four times larger and also decreased with increasing depolarization. 4. Arrhenius plots of both time constants can be well approximated by straight lines for temperatures between 0 and 25 degrees C. 5. The entire sodium current induced by single voltage‐clamp pulses was fitted by a non‐linear least‐square routine to the Frankenhaeuser‐Huxley equations extended by Chiu's three‐state kinetics. With rare exceptions for potentials between 37 and 70 mV the fit was better without a delay in the onset of the inactivation of the sodium current. 6. The time course of inactivation was also studied in two‐pulse experiments where a prepulse of varying duration was directly followed by a test pulse. The peak sodium currents were normalized by the associated peak currents without a prepulse. 7. The relative peak sodium current as a function of the prepulse duration had a sigmoid time course. The early deviation from an exponential decay is due to the activation arising during the prepulse and is implicit in the classical equations quoted above. It is therefore not necessarily a sign of a delay in the inactivation process. 8. To eliminate errors due to activation in two‐pulse experiments, the decaying part of the test sodium currents was extrapolated back to the onset of the test pulse. These current values at t = 0 plotted as a function of the prepulse duration revealed no delay at the beginning of inactivation. Within the accuracy of our measurements a possible delay of more than 100 microseconds (at 5‐10 degrees C) could be excluded.
Spontaneous recovery from depolarizing drugs in rat diaphragm.
Authors: Creese R , Mitchell L D
Published: December 2014

1. The end‐plate region in surface fibres of rat diaphragm was located by the use of polarizing filters. 2. Carbachol (100 microM) produced depolarization at the end‐plate to ‐55 mV, as shown by continuous recording, with some indication of spontaneous recovery in the presence of the drug. The miniature end‐plate potentials disappeared and remained absent. 3. By repeated sampling it was found that the resting potential at the end‐plate had largely recovered after 45 min in the presence of carbachol. Individual fibres showed much variation in the rate of recovery, and in some fibres the repolarization was rapid. 4. In the absence of K, carbachol produced depolarization at the end‐plate without significant recovery, as shown by repeated sampling. 5. When muscles were exposed to ouabain (100 microM) in addition to carbachol the end‐plate remained depolarized without recovery for 60 min. The effect of ouabain was reversible: withdrawal of ouabain (in the presence of carbachol) led to substantial recovery. 6. Suberyldicholine (100 microM) gave results which were similar to those produced by carbachol. 7. It was inferred that the spontaneous recovery of membrane potential in the presence of carbachol and of suberyldicholine is a process which is sensitive to K and to ouabain.
Membrane capacitance in hyperpolarized muscle fibres.
Authors: Huang C L
Published: December 2014

1. Voltage clamp experiments on muscle fibres compared transients to 10 mV steps at hyperpolarized voltages between VT = ‐100 to ‐185 mV with controls obtained at VC = ‐85 mV. 2. Membrane capacitance fell by 15%, 13% and 4.5% per 100 mV hyperpolarization fro ‐85 mV in hypertonic low chloride, hypertonic high chloride and isotonic high chloride‐containing solutions respectively. 3. The charge moved by the ‘on’ and ‘off’ parts of the applied step was equal over the voltages studied. This suggests that the changes were capacitative rather than ionic in origin. The changes could not be explained in terms of the cable properties of the transverse tubular system. They may therefore reflect non‐linear capacitance in the muscle membrane itself. 4. Subtracting control transients at ‐85 mV from transients obtained at different voltages gave monotonically decaying charge movements. In the frequency domain, these charge movements possessed real and imaginary permittivities resembling those of a ‘Debye’ particle. 5. It is concluded that muscle membranes have non‐linear capacitances even at voltages far hyperpolarized to those in which familiar voltage‐dependent processes occur.
Motor unit contractions initiating impulses in a tendon organ in the cat.
Authors: Gregory J E , Proske U
Published: December 2014

1. Responses, identified as coming from Golgi tendon organs, were recorded in afferent nerve fibres supplying the cat soleus muscle. 2. Receptor discharge was recorded during stimulation of single, selected motor units. The degree of summation of responses to combined stimulation of pairs of motor units was compared with the effect of stimulating each motor unit separately. Whenever individual response frequencies differed by a large amount there was little summation on combined stimulation. 3. The response of tendon organ to the second of a pair of closely spaced tetanic contractions of a motor unit showed adaptation of the discharge. Adaptation could also be induced by a conditioning contraction from another motor unit. The amount of ‘cross‐adaptation’ could be correlated with the difference in individual response frequencies of the two motor units and with the degree of summation on combined stimulation. 4. A mechanical model is proposed to account for these observations. The muscle fibre from each motor unit is envisaged to pull on a collagen strand which supports one of the receptor terminals. The non‐linear summation of responses on combined stimulation and the phenomenon of cross‐adaptation are accounted for by mechanical cross‐links between collagen strands such that one muscle fibre pulls on more than one receptor terminal.
The gastric emptying of small volumes given in quick succession.
Authors: Erskine L , Hunt J N
Published: December 2014

1. Ten subjects were given solutions of 33 mM‐trisodium citrate or 505 mM‐glucose, by tube into the stomach; either 25, 50, 100 or 200 ml. were instilled. The gastric contents were recovered, after 3 min with the trisodium citrate solution and after 10 min with the solution of glucose, then the stomach was washed out with 250 ml. water. Each volume was instilled six times in quick succession on one day with the trisodium citrate solution, and four times on another day with the solution of glucose. The recovered volume of the original meal, which contained Phenol Red, was assessed from the amount of dye in the combined recovery and wash. Each day's procedure was replicated on three days. 2. About half of the trisodium citrate solution was recovered after 3 min and about half the solution of glucose after 10 min, independent of the volume instilled. 3. Glucose slowed gastric emptying. The effect was seen when amounts as low as 1.5 g passed into the duodenum in 10 min. 4. Within‐subject, the volumes of trisodium citrate (a distending gastric stimulus) recovered at 3 min allowed predictions of the volumes of glucose solution (a gastric distending and a duodenal osmotic stimulus) recovered at 10 min. 5. The volumes recovered on one day fell progressively with successive instillations of 25, 50 and 100 ml. 6. The results showed that the control system governing gastric emptying responded to volume and osmotic stimuli even when the intragastric volumes were as small as those in the stomach during the interdigestive periods.
The development of electrical properties of identified neurones in grasshopper embryos.
Authors: Goodman C S , Spitzer N C
Published: December 2014

1. We have examined the development of the electrical properties of five identified neurones in grasshopper embryos between days 10 and 13 of embryogenesis (hatching occurs on day 20). DUM 3,4,5; DUM 4,5; DUM 5; the H cell; and the H cell sibling are the progeny of two different precursor cells. Electrical coupling and electrical excitability were assayed by intracellular recordings. 2. Midway through embryogenesis, on day 10, the five cells are highly electrically coupled to each other and are electrically inexcitable. The temporal sequence of the development of electrical excitability and electrical coupling is described for DUM 3,4,5; 4,5; and 5. The H cell and H cell sib undergo the same sequence one day later. 3. The first non‐linear membrane property to appear is delayed rectification which appears on day 11 and can be blocked by tetraethylammonium (TEA). In some cells at about day 11, the addition of TEA to normal saline unmasks a Na+‐dependent action potential in the axon. 4. The first action potential in normal saline is a Na+‐dependent response that appears in the axon at day 11‐11.5. 5. The next stage of excitability in normal saline is the appearance about day 11.5 of a Na+‐dependent action potential in the median neurite between the soma and the two axons. In some cells at about day 11.5, the addition of TEA unmasks an excitable response in the soma. 6. Overshooting action potentials appear in the soma about day 12; the inward current is carried by both Na+ and Ca2+; TEA causes a prolonged shoulder on the falling phase of the action potential. A short time later, TEA causes a long‐duration CA2+ plateau. 7. A progressive decrease in the degree of electrical coupling among the cells occurs between days 10 and 12.5. Complete uncoupling is never observed before day 11, but has always occurred by day 12.5. 8. Two methods were used to demonstrate that electrical coupling does not mask the presence of excitable inward current channels and thus make the cells appear inexcitable. First, we exposed the cells to veratridine. The cells which normally generate excitable Na+ response are depolarized by it; the younger inexcitable cells are not. Secondly, we electrically isolated the cells by killing the somata of their neighbours. The input resistance increased, yet the extent of excitability remained unchanged. 9. There is variability in the precise temporal relationship of excitability and uncoupling. Pairs of cells from different embryos of the same ate can generate the same type of action potentials and yet be coupled in one embryo and uncoupled in another. Electrical excitability and uncoupling appear to be causally unrelated and independent events, occurring at about the same developmental stage.
Localization of sodium pump sites in cat pancreas.
Authors: Bundgaard M , Møller M , Poulsen J H
Published: December 2014

1. Cat pancreases were exposed to [3H]ouabain either by perfusion, or by incubation of slices, with Krebs‐‐Henseleit bicarbonate solution containing [3H]ouabain, and [3H]ouabain binding sites were localized by light microscopical autoradiography. 2. Acinar cells were found to possess only a few [3H]ouabain binding sites located on the basolateral plasma membranes. 3. The epithelial cells lining the intercalated and interlobular ducts were heavily labelled. The [3H]ouabain binding sites were located on the basolateral membranes. 4. Since secretion of pancreatic juice can be abolished by ouabain, it is concluded that the duct cells, especially those of the numerous small (intercalated) and intermediate‐sized (interlobular) ducts are responsible for pancreatic secretion of electrolytes and water. 5. The localization of the (Na+ + K+)‐activated ATPase to the basolateral membranes of the cells excludes a direct role of the transport enzyme in the secretion of Na+. However, a model is proposed where the Na+ + K+)‐activated ATPase plays a crucial, though indirect role in pancreatic secretion of electrolytes and water.
The role of the parasympathetic system in the control of insulin release in the conscious calf.
Authors: Bloom S R , Edwards A V
Published: December 2014

1. The effect of atropine (0.2 mg/kg) on the release of insulin from the pancreas, in response to both exogenous and endogenous hyperglycaemia, has been investigated in conscious 2‐ to 5‐week‐old calves. 2 The rise in mean plasma insulin concentration in response to infusions of glucose, which raised the concentration of glucose in the plasma by about 4.0 mmol/l, was significantly depressed in calves with cut splanchnic nerves by prior administration of atropine. 3. The rise in plasma insulin concentration, which normally follows stimulation of the splanchnic nerves in the conscious calf (Bloom & Edwards, 1980), was almost completely suppressed by prior administration of atropine. 4. These findings are discussed in relation to those of other workers with other species. The results indicate that the parasympathetic innervation to the pancreas plays an important part in the control of insulin release in response to hyperglycaemia.
Are acetylcholine‐induced increases in 42K efflux mediated by intracellular cyclic GMP in turtle cardiac pace‐maker tissue?
Authors: Fleming B P , Giles W , Lederer J
Published: December 2014

1. 42K efflux has been measured from small strips of turtle sinus venosus tissue in order: (a) to characterize further the pharmacology of the acetylcholine response and (b) to test whether cyclic guanosine 3':5'‐monophosphoric acid (cyclic GMP) is the intracellular mediator of this response. 2. The 42K wash‐out curves show that the fractional escape rate (FER) of 42K efflux is nearly constant after 60‐80 min, indicating that after this time period 42K FER is controlled by barrier‐limited diffusion from a single intracellular compartment. 3. The threshold of the dose‐response relationship for the acetylcholine‐induced increase in 42K FER is about 10(‐8) M and the Km is 2.75 x 10(‐7) in non‐eserinized preparations. 4. This acetylcholine response is completely blocked by atropine; but nicotinic blockers produce no detectable reduction of it. 5. Exogenous application of lipid‐soluble analogues of cyclic GMP (dibutyryl or 8‐bromo‐cyclic GMP applied at 2‐3 mM for 30 min) failed to mimic the acetylcholine‐induced augmentation of 42K FER. 6. Experiments in which sodium nitroprusside (5 x 10(‐4) M for 30 min) was applied in order to stimulate the guanylate cyclase and hence produce a large, maintained increase in intracellular cyclic GMP failed to show a significant increase in 42K FER. 7. When acetylcholine (10(‐6)M) was applied in the presence of O[Ca2+]0 (in an attempt to inhibit the guanylate cyclase) there was no significant reduction in the acetylcholine‐induced increases in 42K FER. 8. Hence, these three indirect tests indicate that the muscarinic acetylcholine‐induced increase in 42K FER in cardiac pace‐maker tissue is unlikely to be mediated entirely by changes in the levels of intracellular cyclic GMP.
Changes in 42K efflux produced by alterations in transmembrane calcium movements in turtle cardiac pace‐maker tissue.
Authors: Fleming B P , Giles W
Published: December 2014

1. 42K efflux has been measured from small strips of turtle sinus venosus which were electrically paced. Three different procedures for altering transmembrane calcium influx have been utilized to test whether changes in 42K efflux may be modulated by changes in intracellular calcium levels. 2. No significant changes in the 42K fractional escape rate (FER) were observed when external calcium was reduced to O mM or increased to 4 x normal (10 mM). In these experiments extracellular divalent cation concentration was held constant by adding or removing magnesium ions. 3. Application of 10 mM‐Ba2+ also failed to alter 42K FER consistently. In red blood cells and snail neurones addition of barium ions has been shown to reduce significantly the calcium‐mediated potassium current. 4. A tenfold increase in pacing rate (0.5‐5 Hz) resulted in an augmented 42K FER, but repetition of this rate change in O mM‐Ca2+ indicated that this increase in 42K FER was not strongly dependent on the amount of calcium entry. 5. Attempts to load the pace‐maker cells with calcium by using the ionophore A23187 (10 micrograms ml . ‐1 of 2.0 x 10(‐5) M) consistently resulted in very large increases in 42K FER. However, this effect (i) was blocked by atropine and (ii) was markedly reduced by pretreating the tissues with hemicholinium, indicating that A23187‐induced release of acetylcholine from the endogenous nerve terminals was responsible for the observed increase in 42K FER. 6. In summary, three different experimental tests indicate that the majority of the 42K efflux is not tightly linked to transmembrane calcium movement in sinus venosus pace‐maker tissue.
Analysis of synaptic potentials in mitral cells in the isolated turtle olfactory bulb.
Authors: Mori K , Nowycky M C , Shepherd G M
Published: December 2014

1. The synaptic responses of mitral cells have been analysed in intracellular recordings from the isolated olfactory bulb of the turtle. 2. The response of a mitral cell to a single volley in the lateral olfactory tract consisted of and antidromic impulse and a complex hyperpolarizing potential that had the properties of an inhibitory post‐synaptic potential. The inhibitory response consisted of two successive components I1 and I2, followed by a prolonged hyperpolarization. 3. High‐gain recordings revealed miniature hyperpolarizing potentials during the I1 and I2 responses. Both the miniature potentials and the I1 and I2 responses were increased in amplitude by depolarizing injected currents, and decreased and reversed in polarity by hyperpolarizing currents. The input conductance was increased during the I2 component. In some cells the I1 and I2 components, recorded with micropipettes filled with potassium acetate or potassium citrate, were depolarizing. 4 A single orthodromic volley in the olfactory nerves elicited a complex depolarizing‐hyperpolarizing potential in mitral cells. The depolarization consisted of two successive components, E1 and E2. The hyperpolarization consisted of two successive components, I1 and I2, followed by a prolonged hyperpolarization. 5. The depolarizing components had the properties of excitatory post‐synaptic potentials. They decreased in amplitude with depolarizing current injection and increased with hyperpolarizing injection. The hyperpolarizing components resembled the I1 and I2 components of the tract‐evoked responses in their timing and properties. 6. It is postulated that the E1 component reflects the initial excitation by olfactory nerve terminals of the mitral cell dendritic tufts in the olfactory glomeruli. The I1 component is postulated to arise from dendrodendritic synaptic input mediated by interneurones, mainly granule cells. The E2 and I2 components are likely to arise mainly from intrinsic synaptic circuits within the olfactory bulb.