bluuebunny/crossref_metadata_2025 huggingface dataset:
Fibre types, calcium‐sequestering proteins and metabolic enzymes in denervated and chronically stimulated muscles of the rat.
Authors: Gundersen K , Leberer E , Lømo T , Pette D , Staron R S
Published: December 2014

1. Fibre types, Ca2+‐sequestering proteins (parvalbumin, sarcoplasmic reticulum Ca2+‐ATPase), enzyme activities of energy metabolism, and lactate dehydrogenase isozymes were studied in extensor digitorum longus (EDL) and soleus muscles of adult rats after denervation and direct stimulation for 45‐61 days. The stimulation resembled the firing patterns of normal motor units (Hennig & Lømo, 1985) in either soleus (20 Hz, high amount) or EDL (150 Hz, low and high amount). 2. Low‐ and high‐amount 150 Hz stimulation maintained essentially normal properties in the denervated EDL and induced many EDL‐like properties in the denervated soleus, e.g. pronounced increases in Ca2+‐ATPase and parvalbumin contents, a rise in the glycolytic enzyme activities, as well as a reversal of the lactate dehydrogenase H/M subunit ratio. The 150 Hz high‐amount stimulation was not as efficient as the 150 Hz low amount in maintaining the fast properties of denervated EDL with the exception of the enzymes of aerobic oxidative metabolism. High‐amount 20 Hz stimulation maintained essentially normal properties in the soleus but induced only moderate slow muscle characteristics in the EDL. 3. The maintenance of essentially normal properties by 'native' and the changes induced by 'foreign' stimulus patterns in the absence of the nerve indicate that evoked muscle activity plays a major role in controlling the phenotypic expression of muscle properties. However, the different responses of the denervated fast‐ and slow‐twitch muscles to identical stimulus patterns further suggest that rat EDL and soleus muscles contain intrinsically different muscle fibres.
Sodium‐hydrogen ion exchange in rabbit renal cortical slices incubated in acetate media.
Authors: Macknight A D , McLaughlin C W , Scott R J
Published: December 2014

1. Thin slices (0.2‐0.3 mm) of rabbit renal cortex have been incubated in isosmotic oxygenated acetate media at 25 degrees C with or without ouabain (10(‐3) M), amiloride (2 x 10(‐3) M) or iodoacetamide (10(‐3) M). 2. Slices in normal isosmotic 146 mM‐sodium‐132 mM‐acetate media swelled as reported previously (Cooke & Macknight, 1984). This swelling was not prevented by amiloride or by metabolic inhibition. 3. Slices in isosmotic 132 mM‐choline‐132 mM‐acetate media gained much less water and were little affected by ouabain, amiloride or metabolic inhibition. Choline was able to substitute neither for sodium nor for potassium in activating preparations of renal cortical Na+‐K+‐ATPase in chloride or in acetate media. 4. Slices in isosmotic 20 mM‐sodium‐132 mM‐acetate medium swelled nearly as much as did slices in normal sodium acetate medium. However, this swelling was impaired markedly by amiloride, by ouabain and by metabolic inhibition. 5. There was a direct correlation between medium sodium concentration and slice water content as sodium was increased from 1.25 to 30 mM in 132 mM‐acetate media. However, up to a sodium concentration of 10 mM, amiloride (2 x 10(‐3) M) completely prevented this increase in water content. 6. Increasing medium amiloride concentration from 10(‐5) to 10(‐3) M progressively inhibited cellular swelling in 10 mM‐sodium‐132 mM‐acetate medium. It is concluded that, under these experimental conditions, the dominant pathway for hydrogen ion extrusion from the cells was via amiloride‐sensitive sodium‐hydrogen exchange. 7. The results are discussed in terms of a model which explains cellular swelling in acetate media in terms of (a) non‐ionic diffusion of acetic acid across plasma membranes impermeable to the acetate anion, (b) removal from the cells of the hydrogen ion gained with the acetate by amiloride‐sensitive sodium‐hydrogen counter‐transport and (c) subsequent extrusion of sodium from the cell accompanied by potassium uptake via the ouabain‐sensitive Na+‐K+‐ATPase. 8. The results provide evidence for ion movements across the luminal plasma membrane of proximal tubular cells in rabbit renal cortical slices.
Calcium conductance and firing properties of spinal motoneurones in the turtle.
Authors: Hounsgaard J , Mintz I
Published: December 2014

1. The contribution of Ca2+ conductance to the firing properties of motoneurones was investigated in transverse slices of the turtle spinal cord. 2. In the presence of tetrodotoxin (TTX), tetraethylamonium (TEA) in low extracellular concentration (less than 5 mM) promoted Ca2+ spikes. In higher concentrations of TEA, a suprathreshold depolarizing current pulse was followed by an after‐discharge of Ca2+ spikes riding on a Ca2+ plateau potential. 3. The Ca2+‐dependent plateau was also promoted by Cs+, 4‐aminopyridine (4‐AP) and apamin. However, Ca2+ spikes during plateaux were an order of magnitude faster when promoted by Cs+ or 4‐AP rather than TEA, and apamin did not promote Ca2+ spikes at all. 4. Ca2+ plateaux but not Ca2+ spikes were blocked by nifedipine. 5. In normal medium all effects of the transient Ca2+ influx during action potentials were attributable to its influence on the slow after‐hyperpolarization. The nifedipine‐sensitive, sustained Ca2+ influx was expressed exclusively as plateau potentials and only under conditions of reduced K+ current. 6. It is concluded that the transient and the sustained Ca2+ fluxes in spinal motoneurones are curtailed by different K+ conductances. The two Ca2+ responses are suggested as being mediated by two different types of Ca2+ channels.
Proportion of fatigue‐resistant motor units in hindlimb muscles of cat and their relation to axonal conduction velocity.
Authors: Emonet-Dénand F , Hunt C C , Petit J , Pollin B
Published: December 2014

1. A study of motor units to hindlimb muscles of cat has been made, with as complete a sample as possible of the motor axons to an individual muscle. In single experiments as much as 95% of the motor supply to a muscle has been examined. 2. The following muscles have been studied: peroneus brevis, peroneus tertius, peroneus longus, plantaris, gastrocnemius medialis, soleus, tenuissimus and lumbricalis superficialis. 3. Units were identified as slow resistant (S), fast resistant (FR), fast fatigable (FF) and fast intermediate (FI). The proportion of various motor unit types differs from one muscle to another. There is also some variation in the proportions to a given muscle from one animal to another. With the exceptions of soleus, which is entirely slow resistant, and gastrocnemius, which has relatively fewer resistant units, most muscles contain 60% or more of resistant (S and FR) units. 4. The conduction velocity ranges of FF, FR and FI units overlapped. There was little overlap between the conduction velocity ranges of these F units and of S units. 5. In individual experiments there was a strong and significant positive correlation between the logarithm of maximal tetanic tension and axonal conduction velocity in S and in S+FR units. In terms of contractile response the total fatigue‐resistant population appeared to be a continuum. The correlation coefficient between maximal tetanic tension and conduction velocity was also high in the totality of units of all types, although within the FF group there appeared to be little or no correlation. In pooled data there was much more scatter and these relations were less clear. This resulted largely from differences in the ranges of axonal conduction velocity for a given motor unit type from one animal to another. 6. There was a highly significant negative correlation between isometric twitch contraction time and axonal conduction velocity in individual experiments. This relationship could also be seen, but less clearly, in pooled data. 7. The possible bases for these relationships are discussed.
Activation of protein kinase C promotes glutamate‐mediated transmission at the neuromuscular junction of the mealworm.
Authors: Yamamoto D
Published: December 2014

1. Actions of protein kinase C activators, 1,2‐oleoylacetylglycerol (OAG) and 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA), on the glutamate‐mediated neuromuscular transmission in the mealworm, Tenebrio molitor, were studied by the microelectrode current‐clamp and voltage‐clamp techniques. 2. The activators OAG and TPA stimulate the evoked and spontaneous transmitter releases from the presynaptic terminal, as evidenced by an increase in the quantum content estimated by the number of failures of extracellular excitatory postsynaptic potentials (EPSPs), and in the frequency of miniature EPSPs. 3. Both OAG and TPA act on the postsynaptic membrane to enhance responses to the transmitter L‐glutamate. Protein kinase C activators increased the apparent maximum of the ionophoretic dose‐response curve for glutamate‐induced depolarization, without affecting the reversal potential and the voltage‐dependent decay rate for the excitatory postsynaptic current (EPSC) under voltage‐clamp conditions. 4. The postsynaptic effect of OAG and TPA is distinctly different from that of activators of cyclic nucleotide‐dependent protein kinases, such as octopamine, forskolin, CPT‐cyclic AMP (8‐(4‐chlorophenylthio)adenosine 3',5'‐cyclic monophosphate), and 8‐bromo‐cyclic GMP (8‐bromoguanosine 3',5'‐cyclic monophosphate) which decreased the postsynaptic sensitivity to L‐glutamate. 5. I suggest that the responsiveness of the receptor to L‐glutamate is under the control of these counteracting enzyme systems in the insect neuromuscular junction.
Kinetic states and modes of single large‐conductance calcium‐activated potassium channels in cultured rat skeletal muscle.
Authors: McManus O B , Magleby K L
Published: December 2014

1. Kinetic states and modes of a large‐conductance Ca2+‐activated K+ channel in excised patches of membrane from cultured rat skeletal muscle were studied with the patch clamp technique. Up to 10(6) open and shut intervals were analysed from each of seven different excised membrane patches containing a single channel. 2. Plots of the mean durations of consecutive groups of ten to fifty open and shut intervals were made to assess kinetic stability of the channel. Occasional abrupt decreases in the mean open interval duration from normal to different distinct levels, which were maintained for hundreds to thousands of consecutive intervals, indicated entry of the channel into different modes. 3. Four different kinetic modes were identified: normal mode, which included 96% of the intervals; intermediate open mode with 3.2% of the intervals; brief open mode with 0.5% of the intervals; and buzz mode with 0.1% of the intervals. The mean open interval durations were 61% of normal during the intermediate open mode, 12% of normal during the brief open mode, and 2.6% of normal during the buzz mode. 4. Most mode transitions were observed from the normal mode to one of the other modes and then back to normal. Sojourns in the normal mode lasted 5‐1000 s. Sojourns in the intermediate open, brief open, and buzz modes lasted 1.5‐150, 1‐7, and 0.01‐1 s, respectively. 5. During normal activity the distributions of interval durations were typically described by the sum of three to four exponential components for the open intervals and six to eight exponential components for the shut intervals, and this was the case for data obtained over a wide range of open channel probability resulting from different Ca2+i. These observations suggest that the channel can enter at least three to four open and six to eight shut states during normal activity. 6. The numbers of detected states for data sets of different sample sizes drawn from normal activity agreed with theoretical predictions, and were essentially independent of the segment of normal activity from which the data sets were drawn. These observations are consistent with relative stability of channel kinetics during normal activity. Detection of each additional open or shut state after the first was found to require a 3‐ to 10‐fold increase in the number of analysed events. 7. The intermediate open mode differed from the normal mode in that the longest open component of the four normal open components was absent.
Changes in binomial parameters of quantal release at crustacean motor axon terminals during presynaptic inhibition.
Authors: Atwood H L , Tse F W
Published: December 2014

1. The effects of presynaptic inhibition on quantal release of transmitter were investigated at neuromuscular junctions of the motor axon supplying one of the limb muscles of a crab (Pachygrapsus crassipes). 2. Binomial analysis of transmitter release recorded at selected neuromuscular junctions with an extracellular ‘macro‐patch’ electrode indicated high probability of release (p) from a limited number of available sites (n). During presynaptic inhibition, both n and p were reduced. 3. The binomial model provided a good description of results from non‐inhibited junctions. During presynaptic inhibition, results from some junctions could be described by the binomial model, while those from other junctions could not. An interpretation of this finding is that presynaptic inhibition differentially affects the probability of release at various release sites of the neuromuscular junctional complex. 4. A morphological study of the region of transmitter release under the macropatch electrode was made. Release‐dependent uptake of horseradish peroxidase (HRP) into presynaptic terminals was restricted to the region under the recording electrode, by perfusing the preparation with calcium‐free solution containing HRP. Transmitter release, and HRP uptake, occurred only at the site of the electrode, which was filled with a calcium‐containing solution. Subsequently, serial sections were prepared for electron microscopy and the region of transmitter release was reconstructed. 5. Numerous axo‐axonal synapses were found in the HRP‐labelled region. Thus, the morphological prerequisite for presynaptic inhibition exists at the site of transmitter release, and not exclusively at a more remote region. 6. The number of morphologically identified excitatory neuromuscular synapses exceeded the ‘release sites’ estimated from the binomial model (n) by a wide margin. Morphological differences among synapses were observed. It is proposed that not all morphologically identified synapses participated in transmitter release under the experimental conditions employed. Thus, morphologically defined synapses are likely to be non‐uniform in their response properties, including probability of transmitter release (p).
The potassium conductance of the resting squid axon and its blockage by clinical concentrations of general anaesthetics.
Authors: Haydon D A , Requena J , Simon A J
Published: December 2014

1. The effects of some neutral clinical and experimental general anaesthetics on the resting potential of normal squid axons and squid axons exposed to tetrodotoxin and 3,4‐diaminopyridine have been studied. 2. Depolarizations of 1‐4 mV were produced by all the anaesthetics at ‘clinical’ concentrations in the normal axon. Larger depolarizations (5‐11 mV) were produced by the same anaesthetic concentrations in axons exposed to tetrodotoxin and 3,4‐diaminopyridine. 3. The conductance of axons exposed to tetrodotoxin and either tetraethyl‐ammonium or 3,4‐diaminopyridine in zero Na+, 430 mM‐K+ artificial sea water was examined by voltage clamp and AC bridge techniques. 4. The evidence that this conductance is due predominantly to K+ is discussed. 5. Pre‐pulse protocols under voltage clamp have been used to show that part of this conductance arises from the incompletely blocked delayed rectifier. 6. Substantial reductions in this conductance are produced by anaesthetics at ‘clinical’ concentrations. 7. It is concluded that there is a component of the K+ conductance of the resting squid axon other than the Hodgkin‐Huxley delayed rectifier which is extremely sensitive to anaesthetics and which to an appreciable extent determines the resting potential.
Tubular mechanisms determining the urinary excretion of tritiated prostaglandin E2 in the anaesthetized rat.
Authors: Haylor J , Lote C J , Towers J D
Published: December 2014

1. The renal excretion of arterially injected tritiated prostaglandin E2 ([3H]PGE2) and its metabolites has been examined in the anaesthetized rat before and after the administration of probenecid (an inhibitor of proximal organic acid secretion). [14C]Inulin was employed as a freely filtered, non‐reabsorbable marker, while [3H]p‐aminohippurate was used to assess the inhibitory effect of probenecid. The experiments allowed us to quantify the tubular delivery, proximal secretion, intratubular metabolism, and tubular reabsorption of [3H]PGE2 by the whole kidney in vivo. 2. Following a single pass through the left kidney 25% of an injected dose of [3H]PGE2 was excreted, although only 1.7% of the injected 3H co‐chromatogrammed with cold PGE2. The chemical content of PGE2 in the isotope employed, produced a slight but significant (P less than 0.05) fall (12%) in the single‐pass excretion of [14C]inulin. 3. Intravenous probenecid (100 mg kg‐1 + 100 mg kg‐1 h‐1) completely inhibited the proximal tubular secretion of [3H]p‐aminohippurate, while the single‐pass excretion of [14C]inulin remained unchanged. Probenecid also reduced the blood pressure and urine flow, and decreased the binding of [3H]PGE2 to plasma protein from 59 to 41%. 4. Probenecid administration reduced the single‐pass excretion of 3H following an injection of [3H]PGE2 by 65% down to 8.5% of the injected dose. Due to the change in protein binding however, probenecid also increased the filtered load of [3H]PGE2 from 12 to 16% of the injected dose. 5. The following calculations were made concerning the tubular handling of [3H]PGE2 by the whole kidney in vivo. (i) Thirty‐five per cent of the injected dose of [3H]PGE2 was secreted by the proximal tubules on a single pass through the kidney, in addition 12% was filtered while 59% was protein bound. (ii) The tubular reabsorption of [3H]PGE2 was 47% of the filtered load. (iii) [3H]PGE2 was subject to a high degree of intratubular metabolism which at a minimum value represented about 50% of the filtered load. The metabolism of [3H]PGE2 also occurred during proximal tubular secretion.
The effect of cholecystokinin‐related peptides on periodic pancreatic secretion in fasting dogs.
Authors: Magee D F , Naruse S
Published: December 2014

1. The effect of cholecystokinin octapeptide (CCK‐8) and pentagastrin on periodic pancreatic secretion was studied in fasting conscious dogs. 2. Both CCK‐8 and pentagastrin, in small doses, prolonged the interval of periodic pancreatic secretion. Periodicity was disrupted by large doses of CCK‐8 and pentagastrin. 3. CCK‐8, at the dose which did not disrupt the cycle, raised the peak and the valley‐to‐valley means, but not the valley mean, of protein secretion in one cycle. Except at large doses, pentagastrin failed to increase the peak and valley mean, but increased mean, valley‐to‐valley protein secretion. Large doses of both pentagastrin and CCK‐8 increased protein secretion at the valley. 4. The peak of periodic pancreatic protein secretion was about half the observed maximum protein response to CCK‐8. 5. Atropine reduced pancreatic fluid and protein responses to small doses of CCK‐8 to the levels of valleys. At large doses, however, both responses were augmented by atropine. Hexamethonium reduced the responses to any dose of CCK‐8 to valley levels or less. Volume and protein responses to pentagastrin following atropine or hexamethonium were of similar magnitude to those at valleys. 6. It is concluded that CCK‐8 and pentagastrin stimulate pancreatic enzyme secretion directly by acting on acinar cells and indirectly by modifying cholinergic ganglionic activities which control periodic secretion in conscious dogs.
Function of identified motoneurones and co‐ordination of primary and secondary motor systems during zebra fish swimming.
Authors: Liu D W , Westerfield M
Published: December 2014

1. The activity of the two classes of motoneurones, primary and secondary, which innervate myotomal muscle fibres in the zebra fish, was monitored with electromyographic and intracellular techniques. 2. Simultaneous EMG and intracellular recordings from muscle fibres showed that the activity of the two motor systems and of individual primary motoneurones can be distinguished by recording EMG spikes during swimming. 3. Measurements of EMG spikes demonstrated that primary and secondary motoneurones are co‐ordinately activated over a wide range of conditions during normal swimming. 4. During swimming the primary motoneurones within a given segment are usually co‐activated although they sometimes fire independently. 5. When different primary motoneurones within a given segment are co‐activated, they fire nearly synchronously. 6. We conclude that the primary motoneurones are used principally, although not exclusively, during fast swimming, struggling and the startle response, whereas secondary motoneurones function primarily during slower swimming.
The effects of atropine and chronic sympathectomy on maximal parasympathetic stimulation of parotid saliva in rats.
Authors: Ekström J , Garrett J R , Månsson B , Tobin G
Published: December 2014

1. The effects of stimulating the postganglionic parasympathetic nerve to the parotid gland, the auriculo‐temporal nerve, continuously at 40 Hz for 80 min have been assessed on the flow of saliva and its amylase content during each 10 min period and on the glandular morphology at the end of the stimulation, in female Sprague‐Dawley rats under chloralose anaesthesia. Adrenergic responses were blocked by prior administration of dihydroergotamine (1 mg/kg I.P.) and propranolol (1 mg/kg I.P.). The contralateral unstimulated parotid gland from each animal was used for morphological control purposes. 2. In normal animals there was a copious flow of saliva reaching 3 ml or more in 80 min. It was well maintained after a gradual small decline and the flow in the last 10 min period was still 60% of that in the initial period. Amylase output was relatively high in the initial period but then declined more rapidly than the flow. The acini were densely packed with granules on the control side and showed a moderate amount of degranulation on the parasympathetically stimulated side. 3. After atropine (2 mg/kg I.V.), normal animals initially showed a moderate flow of saliva, being 41% of the non‐atropinized animals, but there was a rapid decline and the total flow over 80 min was only 15% of that in the non‐atropinized animals. The amylase secreted was also high initially and showed a rapid decline; the total amount secreted was similar to that in non‐atropinized animals. The morphology was similar to that in non‐atropinized animals and showed a similar loss of acinar granules on the stimulated side. 4. Chronic bilateral postganglionic sympathectomy (4‐6 weeks duration) caused a drastic reduction in the capacity of the gland to secrete saliva in response to parasympathetic stimulation, reaching only one‐third of that from normal animals. The initial output of amylase was greater than in normal animals but the total output was similar. The control unstimulated sympathectomized glands appeared similar morphologically to normal resting glands. However, on the parasympathetically stimulated side, besides the usual amount of acinar degranulation, there was also a conspicuous development of acinar vacuolation, not seen in the other groups of animals.(ABSTRACT TRUNCATED AT 400 WORDS)
Fura‐2 calcium transients in frog skeletal muscle fibres.
Authors: Baylor S M , Hollingworth S
Published: December 2014

1. Intact single twitch fibres from frog muscle were mounted at long sarcomere spacing (3.5‐4.2 microns) on an optical bench apparatus for the measurement of absorbance and fluorescence signals following the myoplasmic injection of either or both of the Ca2+ indicator dyes Fura‐2 and Antipyrylazo III. Dye‐related signals were measured at 16‐17 degrees C in fibres at rest and stimulated electrically to give a single action potential or brief train of action potentials. 2. The apparent diffusion constant of Fura‐2 in myoplasm, Dapp, was estimated from Fura‐2 fluorescence measured as a function of time and distance from the site of dye injection. On average (N = 7), Dapp was 0.36 x 10(‐6) cm2 s‐1, a value nearly 3‐fold smaller than expected if all the Fura‐2 was freely dissolved in the myoplasmic solution. The small value of Dapp is explained if approximately 60‐65% of the Fura‐2 molecules were bound to relatively immobile sites in myoplasm. 3. In resting fibres the fraction of Fura‐2 in the Ca2+‐bound form was estimated to be small, on average (N = 11) 0.06 of total dye. However, because of the large fraction of Fura‐2 not freely dissolved in myoplasm, and the indirect method employed for estimating Ca2+‐bound dye, calibration of the resting level of myoplasmic free Ca2+ ([Ca2+]) from the fraction of Ca2+‐bound dye was not considered reliable. 4. In response to a single action potential, large changes in Fura‐2 fluorescence (delta F) and absorbance (delta A) were detected, which had identical time courses. As expected, the directions of these transients corresponded to an increase in Ca2+‐dye complex. For wavelengths, lambda, between 380 and 460 nm, peak delta A(lambda) was closely similar to the Ca2+‐dye difference spectrum for Fura‐2 determined in in vitro calibrations. Beer's law was used to calibrate the concentration of Ca2+‐dye complex formed during activity (delta[CaFura‐2]) from the delta A(lambda) signal. Peak delta[CaFura‐2] was found to vary between 0.01 and 0.4 mM, depending on the total concentration of injected Fura‐2 ([Fura‐2T]), which ranged as high as 0.9 mM. 5. In fibres in which peak delta[CaFura‐2] was less than 0.06 mM, delta[CaFura‐2] had a limiting minimal half‐width of 50‐60 ms. However, as peak delta[CaFura‐2] increased (up to 0.3‐0.4 mM), delta[CaFura‐2] half‐width became markedly prolonged (up to 150‐200 ms), indicative of a strong buffering action of large concentrations of Fura‐2 on the underlying [Ca2+] transient (delta[Ca2+]).(ABSTRACT TRUNCATED AT 400 WORDS)
The nature of the presynaptic effects of (+)‐tubocurarine at the mouse neuromuscular junction.
Authors: Ferry C B , Kelly S S
Published: December 2014

1. The effects of (+)‐tubocurarine (TC) on tetanic run‐down and quantum content of end‐plate potentials (EPPs) were investigated in cut‐fibre preparations of mouse diaphragm. 2. (+)‐Tubocurarine, 0.15 microM, halved the amplitude of spontaneous miniature EPPs (MEPPs) and steepened the tetanic run‐down of EPPs evoked at 10 Hz by increasing the quantum content of the first EPP of the train while having no effect on quantum content of plateau EPPs. With stimulation at 1 Hz, there was little run‐down and the quantum content of all EPPs was increased by TC. 3. The use of binomial statistics to analyse release indicated that after TC the increase in the quantum content of the first EPP in the train at 10 Hz was due to an increase in n and that during the run‐down there was a decrease in p so that plateau EPP quantum content at 10 Hz was not different from control. 4. To elucidate a possible role of cholinoreceptors in the presynaptic effects of TC, studies were made on the effects of pancuronium or of alpha‐bungarotoxin (BTX), with concentrations and exposure times where they had postsynaptic effects equal to 0.15 microM‐TC. The run‐down of EPPs was unaffected by BTX, while pancuronium steepened it to a lesser extent than TC. 5. The anticholinesterase, ecothiopate, decreased the quantum content of plateau EPPs only at high frequencies of stimulation (50 Hz) and did not affect the presynaptic effects of TC at 10 Hz. 6. At concentrations which reduced MEPP amplitude, atropine (10 microM) or hexamethonium (50 microM) had no effect on EPP run‐down. 7. These results indicate that TC could have presynaptic effects via a presynaptic acetylcholine receptor, but that such a receptor may not have the same binding specificities as the postsynaptic receptor.
Synaptic control of hindlimb motoneurones during three forms of the fictive scratch reflex in the turtle.
Authors: Robertson G A , Stein P S
Published: December 2014

1. The turtle spinal cord produces three forms of the fictive scratch reflex in response to tactile stimulation of sites on the body surface. Common to all three forms is the rhythmic alternation of activity between hip protractor and hip retractor motoneurones. Hip protractor motoneurone activity is monitored via nerves innervating the hip protractor muscle puboischiofemoralis internus pars anteroventralis (VP‐HP). Hip retractor activity is monitored via nerves innervating several monoarticular hip retractor muscles, one hip adductor muscle, and several biarticular hip retractor‐knee flexor muscles (HR‐KF). Each form is characterized by the timing of activity of motoneurones innervating femorotibialis (FT‐KE), a monoarticular knee extensor muscle, within this alternating cycle (Robertson, Mortin, Keifer & Stein, 1985). In the present study, intracellular recordings revealed a corresponding regulation of synaptic drive to knee extensor motoneurones with respect to the synaptic drive to the motoneurones innervating antagonist muscles of the hip. These patterns of synaptic activation give rise to the distinct motor pattern underlying each form of the scratch reflex. 2. VP‐HP, HR‐KF and FT‐KE motoneurones all exhibited phasic depolarizing and hyperpolarizing changes in membrane voltage during the production of the rhythmic motor patterns underlying each stratch form. Membrane depolarization is caused by synaptic excitation (EPSPs) and gives rise to motoneurone discharge. Hyperpolarization is primarily the result of postsynaptic inhibition (IPSPs) mediated by an increased conductance of chloride ions (Cl‐) and ensures motor pool quiescence during antagonist activation. 3. VP‐HP motoneurones depolarized during activation of the VP‐HP motor pool and hyperpolarized during activation of the HR‐KF motor pool. HR‐KF motoneurones depolarized during activation of the HR‐KF motor pool and hyperpolarized during activation of the VP‐HP motor pool. In many cases, the amplitude of hyperpolarization was directly related to the intensity of the antagonist motor pool burst. During the rostral scratch, HR‐KF motor pool activity was sometimes deleted, along with the depolarizing wave in HR‐KF motoneurones and the hyperpolarizing wave in VP‐HP motoneurones. The interneurones providing the synaptic drive to these antagonist motoneurones appear, therefore, to have reciprocal activation patterns. 4. FT‐KE motoneurones depolarized during FT‐KE motor pool activation and hyperpolarized during FT‐KE motor pool quiescence. This alternation of opposing synaptic drive underlies the rhythmic activation of the FT‐KE motor pool during all scratch forms.(ABSTRACT TRUNCATED AT 400 WORDS)
Dopamine actions in vitro on enzyme and electrolyte secretion from normal and sympathectomized rat parotid glands.
Authors: Danielsson A , Henriksson R , Sundström S , Wester P
Published: December 2014

1. Adult rats were denervated unilaterally by removal of the left superior cervical ganglion or chemically denervated with 6‐hydroxydopamine or reserpine. Two weeks later the parotid glands were used for in vitro secretory studies and their catecholamines and major metabolites were measured. 2. Noradrenaline concentrations were reduced 2 weeks after surgical sympathectomy and reserpine pre‐treatment 18 h previously, whereas 6‐hydroxydopamine pre‐treatment for 3 days reduced both noradrenaline and dopamine concentrations. 3. Dopamine caused a prominent amylase release from incubated control glands. However, a subsensitivity for dopamine‐induced amylase release was recorded on the denervated side. 4. Dopamine caused a prominent potassium efflux measured as 86Rb+ efflux from control glands, but was without effect in denervated glands. This is in contrast to noradrenaline‐induced 86Rb+ efflux which was equally effective in both denervated and control glands. 5. Dopamine caused [3H]noradrenaline efflux in control glands, but was without effect in surgically denervated glands and in glands pre‐treated with reserpine or 6‐hydroxydopamine. 6. It is concluded that dopamine‐induced potassium release is caused by a presynaptic action on noradrenergic nerves, whereas dopamine‐induced amylase release has a presynaptic and a postsynaptic component. The results suggest a specific action of dopamine in salivary glands, with different effects on enzyme release and ionic fluxes.
Binocular co‐ordination of human horizontal saccadic eye movements.
Authors: Collewijn H , Erkelens C J , Steinman R M
Published: December 2014

1. The binocular co‐ordination of human horizontal saccades was analysed for the first time systematically over the full oculomotor range with a precise and accurate scleral sensor coil technique. Effects of amplitude (1.25‐80 deg), direction (adduction vs. abduction and centrifugal vs. centripetal) and eccentricity (symmetrical about primary or between primary and secondary positions) were systematically investigated in three subjects). 2. To minimize extraneous effects of stimulus presentation on the programming of saccades, subjects were instructed to voluntarily change their gaze between two continuously visible targets. These were positioned on an iso‐vergence locus, and thus contained no stimulus for disjunctive eye movements. 3. Under these conditions the amplitudes of the primary saccades of the two eyes were remarkably accurate; undershooting of the target by about 0.5 deg (independent of amplitude in the range 10‐70 deg) was typical. This finding contrasts with the undershooting by about 10% described in the literature as characteristic for other stimulus conditions. 4. Saccadic peak velocities saturated at a mean asymptotic level of 502 +/‐ 32 (S.D.) deg/s for saccades of 40 deg and larger. The duration was linearly related to amplitude for saccades up to 50 deg; for saccades of larger sizes the duration increased progressively more steeply. Skewness values (acceleration time as a fraction of total saccadic duration) decreased from about 0.45 for saccades up to 10 deg to about 0.20 for saccades of 50 deg and larger. 5. Binocular saccades showed an abduction‐adduction asymmetry and were not well yoked dynamically. The saccades of the abducting eye consistently had a larger size, a higher peak velocity, a shorter duration and were more skewed than the concomitant adducting saccades of the fellow eye. As a result, the eyes diverged transiently by as much as 3 deg during horizontal saccades. 6. Saccades also showed a marked centrifugal‐centripetal asymmetry. Peak velocities of saccades towards the primary position were about 10% higher than peak velocities of corresponding centrifugal saccades. 7. These directional asymmetries were the main source of variability in the pool of saccades. In comparison, intra‐ and intersubject variability was minor in our sample. 8. Post‐saccadic drift consisted of a vergence and a version component. The vergence component of this drift was a continuation of the vergence movement occurring during saccades. The version component, generally smaller than the vergence component, was directed towards the target position.(ABSTRACT TRUNCATED AT 400 WORDS)
An electrophysiological study of the in vitro, perfused brain stem‐cerebellum of adult guinea‐pig.
Authors: Llinás R , Mühlethaler M
Published: December 2014

1. We describe here a technique which allows the long‐term in vitro survival of the perfused isolated brain stem‐cerebellum of adult guinea‐pig. The viability of this preparation was assessed by comparing the electrophysiological properties of individual neurones and of neuronal pools to those obtained in vivo or in brain slices. The areas investigated included the cerebellar cortex, the inferior olive and the pontine nuclei. 2. Cerebellar field potential and intra‐ and extracellular single‐cell recordings could be obtained for as long as 15 h after the preparation was initially isolated. The waveforms of field potentials recorded at various depths in the cerebellar cortex following surface folial stimulation were similar to those recorded in vivo. Extracellular recordings from single Purkinje cells following white matter stimulation demonstrated antidromic as well as mossy‐ and climbing fibre‐mediated excitation. Stimulation of the cerebellar surface elicited orthodromic parallel fibre excitation of Purkinje cells and basket‐stellate and Golgi cell inhibition. 3. Intrasomatic and intradendritic recordings from Purkinje cells reproduced all the phenomenology described earlier under in vivo conditions and in vitro slice preparations. In addition, spontaneous excitatory synaptic potentials generating simple spikes (mossy fibre‐parallel fibre‐mediated activity) and complex spikes (climbing fibre‐mediated activity) were consistently observed. 4. Extracellular field potentials and extra‐ and intracellular recordings from inferior olive neurones were similar to those previously shown for the mammalian inferior olive. 5. Intracellular recordings were also obtained from pontine nuclei neurones, a major source of mossy fibre afferents to the cerebellum. Stimulation of the contralateral superior cerebellar peduncle produced antidromic invasion of these neurones whereas stimulation of the ipsilateral inferior cerebral peduncle resulted in their orthodromic activation. 6. The preparation responded to pharmacological challenge in a manner which demonstrated a sequential activation of sets of synaptic links in a given pathway. Thus, harmaline generated oscillations of inferior olivary neurones which were similar to those observed in vivo and which produced climbing fibre EPSPs in Purkinje cells at the same frequency as the inferior olivary oscillations. Climbing fibre activation of the Purkinje cells generated powerful inhibitory potentials in the cerebellar nuclear neurones at the same frequency.(ABSTRACT TRUNCATED AT 400 WORDS)
Electrophysiology of guinea‐pig cerebellar nuclear cells in the in vitro brain stem‐cerebellar preparation.
Authors: Llinás R , Mühlethaler M
Published: December 2014

1. Intracellular recordings were obtained from cerebellar nuclear neurones in the isolated brain stem‐cerebellar preparation of guinea‐pigs in vitro. The electrical properties of the cells were quite similar to those reported in in vitro slice studies. They had an average resting potential of ‐56.7 +/‐ 1.8 mV, an input resistance of 23.8 +/‐ 4.9 M omega, and a time constant of 12.5 +/‐ 2.7 ms. The action potentials had an average amplitude of 57.3 +/‐ 5.28 mV (n = 20). 2. In addition to the ionic mechanisms required for the generation of the fast action potential, cerebellar nuclear neurones displayed a low‐threshold Ca2+‐dependent spike which produced a powerful rebound excitation following anodal break. This type of electroresponsiveness was absent in the slice preparation. 3. The anodal break response was further enhanced by the presence of a non‐inactivating Na+ conductance similar to that described in Purkinje cells. 4. Following electrical stimulation of the cerebellar cortex or the underlying white matter, excitatory and inhibitory synaptic potentials (EPSP‐IPSP sequences) could be recorded in cerebellar nuclear neurones. The EPSPs were elicited by direct activation of collaterals of mossy or climbing fibre afferents. The IPSPs followed direct or orthodromic Purkinje cell activation. 5. The integrity of the olivo‐cerebellar system was tested by the administration of harmaline which produced powerful EPSP‐IPSP sequences or pure IPSPs in cerebellar nuclear neurones. These IPSPs were often followed by a rebound firing of the cells. 6. These results indicate that the olivo‐cerebellar pathway, in addition to its activation of the cerebellar cortex, exerts a powerful and complex set of synaptic events on cerebellar nuclear cells. As such it is a true afferent system, having a distinct role in cerebellar physiology.
The negative inotropic effect of acetylcholine on ferret ventricular myocardium.
Authors: Boyett M R , Kirby M S , Orchard C H , Roberts A
Published: December 2014

1. The effects of acetylcholine (ACh) on developed tension and intracellular Ca2+ concentration (as measured with aequorin) were studied in ferret papillary muscles, and on twitch shortening, the action potential and membrane currents in ferret ventricular myocytes. 2. Addition of ACh to ferret papillary muscles resulted in decreases in developed tension and the intracellular Ca2+ transient, both of which then partially recovered in the continued presence of ACh ('fade' of the response). On wash‐off of ACh both developed tension and the intracellular Ca2+ transient increased above control ('rebound') before returning to control values. 3. Addition of ACh to ferret ventricular myocytes resulted in a membrane hyperpolarization of 2 +/‐ 0.5 mV (mean +/‐ S.E.M.; n = 9), a decrease in action potential duration to 23 +/‐ 6% of control and a decrease in twitch shortening to 31 +/‐ 5% of control. In the continued presence of ACh these responses to ACh faded. Thirty seconds after the maximal effect of ACh, action potential duration had partially recovered to 34 +/‐ 6% of control and twitch shortening to 46 +/‐ 7% of control. 4. The effects of ACh on twitch shortening could be mimicked under voltage clamp by varying voltage clamp pulse duration to simulate the ACh‐induced changes in action potential duration. 5. When ACh was applied during a train of voltage clamp pulses of constant duration, 81% of the cells showed less than a 20% decrease in Ca2+ current and twitch shortening. However in 19% of the cells twitch shortening and the apparent Ca2+ current decreased by more than 30%. 6. In the 81% of cells, the normal decrease in twitch shortening was wholly the result of the shortening of the action potential. This in turn was the result of an increase in an outward background current which increased the rate of repolarization during the action potential. The ACh‐induced background current reversed at ‐89 +/‐ 2 mV and showed inward‐going rectification; these properties suggest that it was carried by K+. 7. In the 19% of cells, the normal decrease in twitch shortening was only partly the result of the shortening of the action potential (due to both the increase in outward background current as well as the apparent decrease in Ca2+ current). In these cells the decrease in twitch shortening may also have been partly the direct result of the apparent decrease of Ca2+ current.
Noradrenaline modulation of calcium channels in single smooth muscle cells from rabbit ear artery.
Authors: Benham C D , Tsien R W
Published: December 2014

1. Whole‐cell recordings of voltage‐gated Ca2+ current in single smooth muscle cells from rabbit ear artery were obtained with 110 mM‐Ba2+ as charge carrier. 2. Noradrenaline (NA, 1‐20 microM) produced a sustained increase in the dihydropyridine‐sensitive L‐type Ca2+ current, ranging up to 3‐fold in some cells. The dihydropyridine‐resistant T‐type Ca2+ current was not affected. 3. The time and voltage dependence of activation and inactivation of the L‐type current were not significantly changed during NA modulation. 4. The NA‐induced increase in L‐current was enhanced in magnitude and consistency by the inclusion of 200 microM‐GTP in the pipette (internal) solution. 5. The effect of NA on L‐current was not abolished by pre‐treatment with prazosin, phentolamine or propranolol, suggesting that it is not mediated by alpha‐ or beta‐adrenoceptors. 6. Phenylephrine (5 microM) was ineffective as an agonist, while adrenaline was approximately equipotent to NA. In these respects, the pharmacology of L‐current modulation resembles that of ‘gamma’‐adrenergic receptors (Hirst & Nield, 1980). 7. NA modulation of L‐type Ca2+ channels may be particularly important in promoting sympathetic vasoconstriction in resistance vessels where Ca2+ stores are relatively poorly developed and where NA‐evoked contractions are very sensitive to organic Ca2+ channel antagonists.
Active transport of lead by the calcium pump in human red cell ghosts.
Authors: Simons T J
Published: December 2014

1. Resealed human red cell ghosts containing lead buffers bring about a net transfer of lead from the cell interior to the outside. This transfer is ATP dependent. 2. The active transport of lead is characterized by a Vmax (maximum velocity) of 11 mmol/(l cells.h) and a KM (Michaelis constant) of 5 x 10(‐8) M for internal Pb2+, at pH 6.8 and 37 degrees C. 3. Lead efflux is antagonized by internal calcium, and is inhibited by vanadate with the same IC50 (inhibition constant) with which vanadate inhibits calcium pumping. 4. It is concluded that lead is transported by the calcium pump.
Adenosine 5'‐triphosphate activates acetylcholine receptor channels in cultured Xenopus myotomal muscle cells.
Authors: Igusa Y
Published: December 2014

1. Single‐channel currents activated by extracellular adenosine 5'‐triphosphate (ATP‐induced currents) were recorded in cultured muscle cells of Xenopus laevis using the cell‐attached patch clamp technique. 2. The amplitude histogram of the ATP‐induced currents had two distinct peaks, corresponding to 60 pS (high‐conductance (gamma) channels currents) and 41 pS (low‐gamma channel currents). The peak values of the currents were unaltered during 1‐6 days in culture. 3. The mean open time of the two types of ATP‐induced currents was 0.93 ms for high‐gamma and 0.86 ms for low‐gamma channel currents at 50 mV hyperpolarization. The reversal potential of the ATP‐induced current, estimated from the I‐V relationship, ranged between ‐5 and ‐15 mV. 4. The open‐state probability of currents induced by 10 microM‐ATP decreased in the presence of 20 microM‐d‐tubocurarine. 5. The frequency of ATP‐induced current events depended upon the ATP concentration. The current events were first detected at 0.1 microM‐ATP and occurred with increasing frequency up to 10 microM‐ATP. At concentrations higher than 10 microM, the frequency of current events decreased. 6. When acetylcholine (ACh, 0.1 nM) was applied together with various concentrations of ATP, the frequency of current events increased 2‐ to 3‐fold at the ATP concentration range between 0.1 and 10 microM. At higher concentrations of ATP the frequency decreased again. When ACh (0.1 nM) was applied without ATP, current events were rarely observed. 7. Two types of ATP‐induced currents were also observed with adenylylimido 5'‐diphosphate (AMP‐PNP) at one‐hundred micromolar concentrations. Neither AMP (adenosine 5'‐monophosphate) nor ADP (adenosine 5'‐diphosphate) (1‐500 microM) induced channel events. 8. It is concluded that the nicotinic ACh receptor channels in cultured Xenopus skeletal muscle cells are opened by micromolar concentrations of exogenous ATP. The possible physiological significance is discussed.