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 The in vivo effect of lipopolysaccharide on the spontaneous release of transmitter from motor nerve terminals

1995 ◽  
Vol 116 (2) ◽  
pp. 1757-1760 ◽  
Author(s):  
Shing H. Liu ◽  
Tzong J. Sheu ◽  
Ruey H. Lin ◽  
Shoei Y. Lin-Shiau
Keyword(s):  
Motor Nerve ◽  
Nerve Terminals ◽  
Spontaneous Release ◽  
Motor Nerve Terminals

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.

Propagation of electric activity in motor nerve terminals

1965 ◽  
Vol 161 (985) ◽  
pp. 453-482 ◽  
Keyword(s):  
Motor Nerve ◽  
Electric Activity ◽  
Muscle Fibres ◽  
Nerve Terminals ◽  
Terminal Branch ◽  
Direct Stimulation ◽  
Motor Nerve Terminals ◽  
End Plate ◽  
Synaptic Terminals ◽  
Set Up

External micro-electrodes were used to stimulate non-myelinated motor nerve terminals and to record pre- and post-synaptic responses at the neuromuscular junction of the frog. The synaptic terminals of the motor axon are electrically excitable. Antidromic nerve impulses can be set up by local stimulation of terminals along the greater part of their length. Presynaptic spikes can be recorded from the non-myelinated terminal parts of motor axons. As the impulse proceeds towards the tip of the terminal branch, the shape of the spike changes from a predominantly negative to a predominantly positive-going wave. Similar changes occur in muscle fibres near their tendon junctions, and can be attributed to the special local-circuit conditions at the ‘closed end’ of a fibre. The velocity of impulse propagation in motor nerve endings was determined by three different methods: ( a ) from the latency of antidromic nerve spikes elicited at different points along terminals, ( b ) from two-point recording of spikes along a terminal, ( c ) from the differential latency of focal end-plate potentials recorded at two spots of a myoneural junction. The average velocity obtained by these methods was approximately 0.3 m/s at 20 °C. Extracellular muscle fibre spikes recorded at junctional spots showed no significant differences from those recorded elsewhere, provided the spikes were initiated by direct stimulation and did not coincide with transmitter action. Direct current polarization produces a graded increase in frequency of miniature end-plate potentials when the endings are being depolarized, and sudden high-frequency bursts during excessive hyperpolarization. External two-point recording shows that these bursts arise independently at different spots of the synaptic terminals.

Visual identification of nerve terminals in living isolated skeletal muscle

1972 ◽  
Vol 181 (1065) ◽  
pp. 421-430 ◽  
Keyword(s):  
Electron Microscopy ◽  
Schwann Cells ◽  
Motor Nerve ◽  
Postsynaptic Membrane ◽  
Muscle Fibres ◽  
Nerve Terminals ◽  
Necturus Maculosus ◽  
Visual Identification ◽  
Collagenase Treatment ◽  
Nerve Muscle

1. The unmyelinated terminal branches of motor nerve fibres were clearly resolved in live, unstained skeletal muscles of the frog and of the mudpuppy (Necturus maculosus), using Nomarski optics. The observations were supplemented by several histological procedures, including electron microscopy, and by extracellular recordings from the nerve terminals. 2. In live motor nerve terminals of the mudpuppy one can see a series of varicosities, which in the electron microscope are shown to contain accumulations of synaptic vesicles. Junctional folds in the muscle fibres are confined to the areas opposite the varicosities. Terminal branches of the frog’s motor axon are also varicose, but the swellings are so closely spaced that they can be seen only after staining or by electron microscopy. 3. Nuclei of Schwann cells are recognized along living nerve terminals. Electrophoretic injection of a fluorescent dye, Procionyellow, into the cell bodies of Schwann cells enables one to see the distribution of their processes with the light microscope. 4. Visibility of terminal arborizations was improved by bathing nerve-muscle preparations in solutions of collagenase for 15 to 30 min, thereby removing much of the connective tissue. After longer collagenase treatment nerve terminals could be lifted off muscle fibres with a micropipette, thus exposing the postsynaptic membrane.

scholarly journals Spontaneous Miniature Potentials in Denervated Coxal Muscle Fibres of the American Cockroach

1986 ◽  
Vol 120 (1) ◽  
pp. 143-151
Author(s):  
HIROSHI WASHIO
Keyword(s):  
Nerve Stimulation ◽  
American Cockroach ◽  
Muscle Fibres ◽  
Nerve Terminals ◽  
Distal Stump ◽  
Spontaneous Release ◽  
Nerve Section ◽  
Functional Changes ◽  
Nerve Muscle ◽  
Regenerating Nerve

1. Functional changes following denervation have been studied by intracellular recording at the neuromuscular junction of the cockroach coxal muscle. 2. Spontaneous subthreshold activity disappeared together with nerve-muscle transmission in about 2 days after nerve section at 26°C. The onset of the failure was mainly dependent on the temperature and also on the length of the transected distal stump. After complete cessation of the miniature excitatory postsynaptic potentials (MEPSPs) for about 3 weeks at 26°C, the miniature potentials resumed at a slower rate. Regeneration occurred faster when axotomy was performed by crushing the nerve rather than by sectioning. 3. Resumption of the MEPSPs was accompanied by response to nerve stimulation. However, hypertonic and hypotonic saline, and excess potassium, failed to increase the frequency of the resumed MEPSPs recorded between 15 and 45 days following denervation. 4. It is suggested that the resumed spontaneous release of transmitter may be derived from regenerating nerve terminals.

Sign in / Sign up

Export Citation Format

Share Document