scholarly journals The effect of calcium and magnesium on the spontaneous release of transmitter at insect motor nerve terminals

1978 ◽  
Vol 75 (1) ◽  
pp. 101-112
Author(s):  
H. M. Washio ◽  
S. T. Inouye
Keyword(s):  
Calcium Concentration ◽  
Neuromuscular Junctions ◽  
Calcium Ionophore ◽  
Reciprocal Relationship ◽  
Magnesium Concentration ◽  
Extracellular Potassium ◽  
Muscle Fibres ◽  
Bathing Solution ◽  
Spontaneous Release ◽  
Calcium And Magnesium

1. The effect of the extracellular calcium and magnesium concentrations and calcium ionophore, X-537A, on the frequency of miniature excitatory post-synaptic potentials (MEPSPs) was studied in cockroach leg muscle fibres. 2. The frequency of MEPSPs increased as the calcium concentration was increased from 0.1 to 10 mM. In the presence of 10 mM magnesium, however, raising the calcium concentration from 0.1 to 1 mM slightly depressed the frequency. In saline containing elevated potassium (20.8 mM), increasing the calcium concentration produced a much higher frequency than that in the normal potassium saline (10.8 mM) in the absence of magnesium. Raising the extracellular potassium concentration was without effect unless the bathing solution contained calcium. 3. The frequency of the miniature potentials was reduced as the magnesium concentration was raised from 0 to 10 mM, depending on the presence of calcium ions. On the contrary, a slightly increased frequency was observed in the low calcium saline as the magnesium concentration was raised from 1 to 10 mM. The reciprocal relationship between calcium and magnesium and the time course of the effect suggest that both ions act at the same surface sites in the presynaptic membrane. 4. X-537A elicited a transient increase in frequency followed by a fall of the frequency to a very low rate. Further application of the ionophore was without effect. The effect of X-537A on the spontaneous release of transmitter at the insect neuromuscular junction was comparable with that on the spontaneous acetylcholine release in vertebrate neuromuscular junctions.

Reflex Control of Abdominal Flexor Muscles in the Crayfish

1965 ◽  
Vol 43 (2) ◽  
pp. 229-246
Author(s):  
DONALD KENNEDY ◽  
KIMIHISA TAKEDA
Keyword(s):  
Neuromuscular Junctions ◽  
Reciprocal Relationship ◽  
Muscle Fibres ◽  
Reflex Inhibition ◽  
Motor Axons ◽  
Efferent Nerve ◽  
Temporal Properties ◽  
Presynaptic Mechanisms ◽  
Flexor Muscles ◽  
Central Inhibition

1. Fibres from the tonic, superficial abdominal flexor muscles in the crayfish receive a complex, highly polyneuronal innervation from among five motor axons and one inhibitor. All efferent nerve fibres show some degree of ‘spontaneous’ activity. 2. The muscle fibres therefore exhibit a constant flux of membrane potential, and hence of tension, in intact preparations. Depolarization is the result of facilitation and/or summation of junctional potentials of various amplitudes, and in some fibres of superimposed electrogenic responses. Neighbouring fibres tend to show similar innervation patterns, more distant ones dissimilar ones. 3. No useful distinction may be made between ‘fast’ and ‘slow’ motor axons. A given axon may produce junctional potentials of very different amplitudes (and some what different rise-times) in neighbouring muscle fibres while another exhibits a precisely reciprocal relationship. The largest axon produces facilitating junctional potentials in all the muscle fibres it innervates, but others may exhibit facilitation in one muscle fibre and antifacilitation in another. 4. Most muscle fibres are innervated by two or three excitatory axons; fibres with single, quadruple or quintuple motor innervation are relatively rare. There is a pronounced tendency for fibres with a rich excitatory innervation to receive the inhibitor as well. The innervation is not shared equally among motor axons: one serves over 90% of the muscle fibres, and two others 20% or less. Statistical analysis of the combinations of motor axons serving muscle fibres reveals that these are apparently random, with all variations from randomness accountable on the grounds of broad regional differences in distribution. 5. The motor axons are selectively activated by specific reflex inputs. Since muscle fibres receive, on the average, only a restricted sample of the available motor supply, it follows that they participate differentially in different reflex actions. Evidence is presented that the firing pattern of motor nerves is appropriate for the temporal properties of their neuromuscular junctions. 6. Reflex inhibition is accomplished by central inhibition of all excitatory motor outflow, accompanied by reciprocal firing in the inhibitor axon. This and the fact that less than half the muscle fibres receive inhibitory innervation demonstrate that, in contrast to the one other crustacean system analysed, reflex inhibition is primarily a central event. Peripheral inhibition in the slow flexor system must serve mainly as a device to achieve repolarization and thus terminate contractions. Such action necessarily depends upon post-synaptic rather than presynaptic mechanisms.

A dual effect of cobalt ions on the spontaneous release of transmitter at insect motor nerve terminals

1982 ◽  
Vol 98 (1) ◽  
pp. 353-361
Author(s):  
H. Washio
Keyword(s):  
External Surface ◽  
Motor Nerve ◽  
Reciprocal Relationship ◽  
Muscle Fibres ◽  
Nerve Terminals ◽  
Spontaneous Release ◽  
Dual Effect ◽  
Competitive Antagonist ◽  
Cobalt Ions ◽  
Equilibrium Dissociation

1. The effect of extracellular cobalt on the frequency of miniature excitatory post-synaptic potentials (MEPSPs) was studied in cockroach leg muscle fibres that had been depolarized with 20.8 mM-K saline. 2. Cobalt ions had a dual effect on the spontaneous release of transmitter, an inhibitory action being followed by an acceleratory. A reciprocal relationship between Ca2+ and Co2+ was found for both the inhibitory and acceleratory effects. 3. The equilibrium dissociation constant for Co2+ as a competitive antagonist of spontaneous release ranged from 0.4 to 0.65 mM. It is concluded that Co2+ is much more potent than Mg2+ in suppressing spontaneous transmitter release at the insect neuromuscular junction. The antagonism by extracellular Co2+ appears to occur only at the external surface site on the terminal membrane.

scholarly journals A comparative study of serum calcium and magnesium levels in women with pre-eclampsia and normotensive women

2021 ◽  
Vol 10 (6) ◽  
pp. 2420
Author(s):  
Saloni Sethi ◽  
Ankita Chaudhary ◽  
Priya Sonkhya ◽  
Premlata Mital ◽  
Aditi Arora ◽  
...  
Keyword(s):  
Pregnant Women ◽  
Serum Calcium ◽  
Negative Correlation ◽  
Calcium Concentration ◽  
Serum Magnesium ◽  
Measured Data ◽  
Magnesium Concentration ◽  
Multisystem Disorder ◽  
Ionic Calcium ◽  
Calcium And Magnesium

Background: Pre-eclampsia is transient but potentially dangerous complication of pregnancy. Despite of pre-eclampsia's prevalence and severity, the pathophysiology of this multisystem disorder is still poorly understood and its aetiology has not yet been fully elucidated. Recently, nutritional deficiency especially micronutrients deficiency is gaining prominence in the pathogenesis of pre-eclampsia. Hypocalcaemia and hypomagnesaemia have been implicated in the pathogenesis of pre-eclampsia. This study has been done to compare serum calcium and magnesium levels in women with pre-eclampsia and normotensive women and their association with severity of pre-eclampsia.Methods: 50 women with pre-eclampsia and 50 normotensive women were included in the study and serum calcium and magnesium levels were measured. Data were analyzed.Results: The serum ionic calcium concentration was significantly lower in the pre-eclamptic cases compared to the normotensive controls (3.34±1.35 versus 4.37±0.74, p=0.0000) similarly serum magnesium concentration was significantly lower in the pre-eclamptic cases compared to the normotensive controls (1.68±0.41 versus 1.94±0.42, p-0.002). Mean serum ionic Ca levels in severe pre-eclampsia group was significantly lower than normotensive pregnant women (p=0.0000) as well as mild pre-eclampsia group (p=0.001). Mean serum Mg in severe pre-eclampsia was significantly lower than normotensive pregnant women (p=0.0008) as well as mild pre-eclampsia group (p=0.03). Serum ionic Ca and Mg had a negative correlation with systolic and diastolic blood pressure.Conclusions: Based on this study, measurements of serum ionic calcium and magnesium among women at risk of for pre-eclampsia may be used to predict the onset and severity of pre-eclampsia.

The Effect of Calcium and Magnesium on Rabbit Blood Platelet Aggregation in Vitro

1964 ◽  
Vol 12 (01) ◽  
pp. 179-200 ◽  
Author(s):  
Torstein Hovig
Keyword(s):  
Platelet Aggregation ◽  
Cation Exchange ◽  
Calcium Concentration ◽  
Blood Platelets ◽  
Blood Platelet ◽  
Rabbit Blood ◽  
Calcium And Magnesium ◽  
Induced Aggregation ◽  
Blood Platelet Aggregation

SummaryThe effect of calcium and magnesium on the aggregation of rabbit blood platelets in vitro was studied, with the following results:1. Platelet aggregation induced by ADP or collagen could be prevented by EGTA or EDTA. The aggregating effect was restored by recalcification. The effect was also restored by addition of magnesium in EDTA-PRP, but not in EGTA-PRP unless a surplus of calcium was present.2. Calcium remained in concentrations of the order of 0.15–0.25 mM after dialysis or cation exchange of plasma. Aggregation of washed platelets resuspended in such plasma could not be produced with ADP or collagen, unless the calcium concentration was increased or that magnesium was added.3. The adhesiveness of blood platelets to collagen was reduced in EGTA-PRP and EDTA-PRP. Release of ADP from platelets influenced by collagen could not be demonstrated either in EGTA-PRP (presence of magnesium) or in EDTA-PRP.4. It is concluded that calcium is a necessary factor both for the reaction leading to release of ADP and for the the aggregation produced by ADP.5. Thrombin induced aggregation of washed platelets suspended in tris-buffered saline in the presence of calcium. No effect of magnesium could be observed unless small quantities of calcium were present.

ABOLITION OF MAGNESIUM-INDUCED HYPOCALCAEMIA BY ACUTE THYRO-PARATHYROIDECTOMY IN THE CAT

1970 ◽  
Vol 64 (1) ◽  
pp. 150-158 ◽  
Author(s):  
S. Pors Nielsen
Keyword(s):  
Sodium Chloride ◽  
Flow Rate ◽  
Magnesium Chloride ◽  
Calcium Concentration ◽  
Plasma Calcium ◽  
Magnesium Concentration ◽  
Isotonic Sodium Chloride ◽  
Plasma Calcium Concentration ◽  
High Concentrations ◽  
Plasma Magnesium

ABSTRACT Intravenous infusion of isotonic magnesium chloride into young cats with a resultant mean plasma magnesium concentration of 7.7 meq./100 g protein was followed by a significant lowering of the plasma calcium concentration in 90 minutes. The rate of decrease of plasma calcium is consistent with the hypothesis that calcitonin is released by magnesium in high concentrations. There was no decrease in the plasma calcium concentration in cats of the same weight thyroparathyroidectomized 60 min before an identical magnesium chloride infusion or an infusion of isotonic sodium chloride at the same flow rate. The hypercalciuric effect of magnesium could not account for the hypocalcaemic effect of magnesium. Plasma magnesium concentration during magnesium infusion into cats with an intact thyroid-parathyroid gland complex was slightly, but not significantly higher than in acutely thyroparathyroidectomized cats.

The Regulation of Calcium and Magnesium in the Brackish Water Polychaete Nereis Diversicolor O.F.M

1970 ◽  
Vol 53 (2) ◽  
pp. 425-443
Author(s):  
C. R. FLETCHER
Keyword(s):  
Brackish Water ◽  
Calcium Concentration ◽  
Sea Water ◽  
Calcium Influx ◽  
Coelomic Fluid ◽  
Nereis Diversicolor ◽  
Active Uptake ◽  
Calcium And Magnesium ◽  
Electrochemical Potentials

1. Nereis diversicolor tolerates changes in the concentration of calcium and magnesium in its coelomic fluid proportional to the concentrations in the medium between chlorosities of 100-1000 mM/kg of water. 2. In lower salinities both ions are maintained relatively constant providing that the ratios of these ions to chloride in the medium are similar to the ratios in sea water. 3. The ratio of the concentration of calcium in the coelomic fluid to the concentration in the medium is a function of the salinity of the medium but not of the calcium concentration. 4. Both calcium and magnesium are at lower electrochemical potentials in the coelomic fluid than in the medium, indicating that it is not necessary to invoke active uptake. 5. The rate of calcium influx is substantial. 6. In salinities below to mM of chloride/kg of water the urine must contain less calcium than the coelomic fluid. 7. The significance of these results is discussed.

scholarly journals Changes in miniature endplate potential frequency during repetitive nerve stimulation in the presence of Ca2+, Ba2+, and Sr2+ at the frog neuromuscular junction.

1981 ◽  
Vol 77 (5) ◽  
pp. 503-529 ◽  
Author(s):  
J E Zengel ◽  
K L Magleby
Keyword(s):  
Nerve Stimulation ◽  
Transmitter Release ◽  
Neuromuscular Junctions ◽  
Fourth Power ◽  
Bathing Solution ◽  
Frog Neuromuscular Junction ◽  
Repetitive Nerve Stimulation ◽  
Time Constants ◽  
Endplate Potential ◽  
Induced Changes

Miniature endplate potentials (MEPPs) were recorded from frog sartorious neuromuscular junctions under conditions of reduced quantal contents to study the effect of repetitive nerve stimulation on asynchronous (tonic) quantal transmitter release. MEPP frequency increased during repetitive stimulation and then decayed back to the control level after the conditioning trains. The decay of the increased MEPP frequency after 100-to 200-impulse conditioning trains can be described by four components that decayed exponentially with time constants of about 50 ms, 500 ms, 7 s, and 80 s. These time constants are similar to those for the decay of stimulation-induced changes in synchronous (phasic) transmitter release, as measured by endplate potential (EPP) amplitudes, corresponding, respectively, to the first and second components of facilitation, augmentation, and potentiation. The addition of small amounts of Ca2+ or Ba2+ to the Ca2+-containing bathing solution, or the replacement of Ca2+ with Sr2+, led to a greater increase in the stimulation-induced increases in MEPP frequency. The Sr-induced increase in MEPP frequency was associated with an increase in the second component of facilitation of MEPP frequency; the Ba-induced increase with an increase in augmentation. These effects of Sr2+ and Ba2+ on stimulation-induced changes in MEPP frequency are similar to the effects of these ions on stimulation-induced changes in EPP amplitude. These ionic similarities and the similar kinetics of decay suggest that stimulation induced changes in MEPP frequency and EPP amplitude have some similar underlying mechanisms. Calculations are presented which show that a fourth power residual calcium model for stimulation-induced changes in transmitter release cannot readily account for the observation that stimulation-induced changes in MEPP frequency and EPP amplitude have similar time-courses.

scholarly journals Post-synaptic morphology of mouse neuromuscular junctions is linked to muscle fibre type

2020 ◽  
Author(s):  
Aleksandra M. Mech ◽  
Anna-Leigh Brown ◽  
Giampietro Schiavo ◽  
James N. Sleigh
Keyword(s):  
Motor Neuron ◽  
Muscle Fibre ◽  
Fibre Type ◽  
Neuromuscular Junctions ◽  
Fibre Diameter ◽  
Neuromuscular Diseases ◽  
Neuronal Morphology ◽  
Muscle Fibre Type ◽  
Muscle Membrane ◽  
Muscle Fibres

AbstractThe neuromuscular junction (NMJ) is the highly specialised peripheral synapse formed between lower motor neuron terminals and muscle fibres. Post-synaptic acetylcholine receptors (AChRs), which are found in high density in the muscle membrane, bind to acetylcholine released into the synaptic cleft of the NMJ, ultimately facilitating the conversion of motor action potentials to muscle contractions. NMJs have been studied for many years as a general model for synapse formation, development and function, and are known to be early sites of pathological changes in many neuromuscular diseases. However, information is limited on the diversity of NMJs in different muscles, whether muscle fibre type impacts NMJ morphology and growth, and the relevance of these parameters to neuropathology. Here, this crucial gap was addressed using a robust and standardised semi-automated workflow called NMJ-morph to quantify features of pre- and post-synaptic NMJ architecture in an unbiased manner. Five wholemount muscles from wild-type mice were dissected and compared at immature (post-natal day, P7) and early adult (P31-32) timepoints. Post-synaptic AChR morphology was found to be more variable between muscles than that of the motor neuron terminal and there were greater differences in the developing NMJ than at the mature synapse. Post-synaptic architecture, but not neuronal morphology or post-natal synapse growth, correlates with fibre type and is largely independent of muscle fibre diameter. Counter to previous observations, this study indicates that smaller NMJs tend to innervate muscles with higher proportions of fast twitch fibres and that NMJ growth rate is not conserved across all muscles. Furthermore, healthy pre- and post-synaptic NMJ morphological parameters were collected for five anatomically and functionally distinct mouse muscles, generating reference data that will be useful for the future assessment of neuromuscular disease models.Graphical Abstract

scholarly journals Myomirnas Role in Als Suggest a Crosstalk between Muscle and Motor Neuron

2018 ◽  
Author(s):  
Valentina Pegoraro ◽  
Antonio Merico ◽  
Corrado Angelini
Keyword(s):  
Skeletal Muscle ◽  
Motor Neuron ◽  
Aerobic Exercise ◽  
Muscle Atrophy ◽  
Motor Neurons ◽  
Neuromuscular Junctions ◽  
Neurodegenerative Disorder ◽  
Disease Process ◽  
Muscle Fibres ◽  
Wide Range

Amyotrophic lateral sclerosis (ALS) is a rare, progressive, neurodegenerative disorder caused by degeneration of upper and lower motor neurons. The disease process leads from lower motor neuron involvement to progressive muscle atrophy, weakness, fasciculations for the upper motor neuron involvement to spasticity. Muscle atrophy in ALS is caused by a dysregulation in the molecular network controlling fast and slow muscle fibres. Denervation and reinnervation processes in skeletal muscle occur in the course of ALS and are modulated by rehabilitation. MicroRNAs (miRNAs) are small non-coding RNAs that modulate a wide range of biological functions under various pathophysiological conditions. MiRNAs can be secreted by various cell types and they are markedly stable in body fluids. MiR-1, miR-133 a, miR-133b, and miR-206 are called “myomiRs” and are considered markers of myogenesis during muscle regeneration and neuromuscular junction stabilization or sprouting. We observed a positive effect of a standard aerobic exercise rehabilitative protocol conducted for six weeks in 18 ALS patients during hospitalization in our center. We correlated clinical scales with molecular data on myomiRs. After six weeks of moderate aerobic exercise, myomiRNAs were down-regulated, suggesting an active proliferation of satellite cells in muscle and increased neuromuscular junctions. Our data suggest that circulating miRNAs modulate during skeletal muscle recovery in response to physical rehabilitation in ALS.

Non-motile sensory cilia and neuromuscular junctions in a ctenophore independent effector organ

1965 ◽  
Vol 162 (988) ◽  
pp. 333-350 ◽  
Keyword(s):  
Neuromuscular Junctions ◽  
Ciliated Cell ◽  
Sensory Nerve ◽  
Spatial Summation ◽  
Muscle Cells ◽  
Sensory Cells ◽  
Muscle Fibres ◽  
Water Displacement ◽  
Single Finger ◽  
Effector Organ

Non-motile cilia of the (9 + 2) pattern, having a specialized onion-like root structure, act as sensitive receptors of water displacement and thereby detect vibrations of small objects in the water nearby. These receptors are situated on sensory nerve cells on finger-like processes up to 1 cm long, on the surface of the ctenophore Leucothea ( = Eucharis) multicornis . In response to vibration a single finger can shoot outwards as an independent effector by an extension of its mesogloeal hydrostatic skeleton, acted on by circular and transverse muscle fibres which run mainly through the mesogloea. A copepod which may be hit is immobilized, presumably by a poisonous secretion. Retraction is brought about by longitudinal ectodermal fibres. The neuromuscular junctions have presynaptic vesicles of 30 to 50 nm diameter, a cleft of 15 to 20 nm wide, and occur at discrete points far from each other on the muscle cells, suggesting that excitation is propagated along the muscle fibres. No direct connexion has been traced between a sensory ciliated cell and a muscle fibre, but sensory cells connect with nerve net neurons and these form synapses with each other and with muscle cells. There are numerous nerve fibres in the epithelium and synapses with vesicles on one side of a cleft 12 to 15 nm wide occur between them sufficiently closely for spatial summation to be possible. The separate co-ordination of movements of extension, retraction and bending requires that certain types of sensory cells be connected specifically, if in directly, with muscle fibres of a particular directionality. This provides a primitive example of specificity of connexions which must imply two overlapping nerve nets.

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