Spontaneous miniature potentials from insect muscle fibres

Usherwood, P.N.R.

doi:10.1113/jphysiol.1963.sp007246

Cited by 90 publications

(5 citation statements)

References 18 publications

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“…increase the frequency of m iniature potentials a t various peripheral synapses (Liley 1956 ;Blackman et al 1963;Usherwood 1963). Similar effects were observed in ra t spinal motoneurons (figure 3a, b).…”

Section: R Esultssupporting

confidence: 79%

Inhibitory miniature synaptic potentials in rat motoneurons

Takahashi

1984

Proc. R. Soc. Lond. B.

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In the newborn rat spinal cord, spontaneous potentials were recorded, with KC1 electrodes, from motoneurons in the presence of tetrodotoxin (10 -6 g ml -1 ) to abolish nerve impulses. These potentials occurred at low frequencies (< 2 Hz), and their mean amplitude was a fraction of 1 mV. An increase of osmolarity with sucrose or an increase of extracellular K + , increased the frequency of miniature synaptic potentials. The amplitude of the spontaneous potentials was increased by intracellular injection of C1 - . Strychnine (2-25 µM) completely abolished the spontaneous potentials. It is suggested that these potentials are produced by the spontaneous release of packages of inhibitory transmitter at synapses on motoneurons.

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Section: R Esultssupporting

confidence: 79%

Inhibitory miniature synaptic potentials in rat motoneurons

Takahashi

1984

Proc. R. Soc. Lond. B.

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“…While no information on chemical identity of a transmitter can yet be made by inspection of the shape of a synaptic vesicle, there is good evidence that transmitter diversity may be paralleled by vesicle morphology, as in the correlation between terminals containing non-spherical vesicles and inhibitory function, discussed by Uchizono (1965Uchizono ( , 1967, Atwood &Jones (1967), andNakajima (1970). The uniform disposition of spherical and non-spherical vesicles in lamprey axons is here interpreted as according with the evidence that a common release mechanism is 28-2 involved in the secretion of chemically diverse transmitters-as suggested by the similarity of spontaneous miniature end-plate potentials in insect non-cholinergic junctions (Usherwood 1963) to these resulting from low-frequency release of quantal amounts of acetylcholine from motor nerve terminals on vertebrate skeletal muscle (Fatt & Katz 1952;del Castillo & Katz 1954;Katz 1962).…”

Section: Discussionmentioning

confidence: 66%

On the significance of cross-bridges between microtubules and synaptic vesicles

Smith

1971

Phil. Trans. R. Soc. Lond. B

120

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Observations on the fine structure of synaptic and non-synaptic axoplasm in the spinal cord of the lamprey ammocoete ( Petromyzon marinus ) are described. Previous studies on this material revealed a close association between spherical vesicles and axoplasmic microtubules near central synapses, and observations were consistent with the suggestion that synaptic vesicles become detached from oriented microtubules in the focal clusters adjoining the presynaptic membrane across which transmitter release takes place. These observations have been extended to include axons containing non-spherical or ellipsoidal vesicles— possibly containing a transmitter chemically and functionally distinct from that in spherical synaptic vesicles. Structural cross-bridges between both microtubules and vesicle populations are now described; these are found not only in the vesicle concentrations bordering synaptic foci, but also in non-synaptic axoplasmic regions where sparsely distributed vesicles are found in association with microtubules. It is suggested that the bridging between vesicles and microtubules may reflect a mechanism for transport of the former—a possibility in accord with cumulative evidence of involvement of microtubules in rapid intracellular translocation in a variety of cells. It is proposed that arrival of excitation at a synaptic site is not only coupled with transmitter release across the axon plasma membrane, but that events at the cell membrane may in turn be coupled with a means of supplying vesicles to the synaptic locus. This hypothesis suggests that the synapse may rely on distant parts of the neuron, perhaps including the cell body, for materials involved in synaptic transmission.

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“…Thus it is conceivable that attenuation of the MEPSPs in the insect muscle fibre is larger than 32 % at its maximum. On the other hand, Usherwood (1963) found that extracellular calcium and magnesium ions at concentrations below 10 mM had little effect on the amplitude of the miniature potentials in this insect muscle fibre. Since the amplitude of the miniature potentials should be proportional to the input resistance of the fibre (Katz & Thesleff, 1957), it seems likely that the effect of these ions at concentrations below 10 mM on the cable properties of the muscle fibre is small.…”

Section: Electrical Properties Of the Muscle Membrane And Spontaneous Miniature Potentialsmentioning

confidence: 62%

“…The spontaneous miniature potentials in insect muscle fibres, which were first recorded intracellularly by Usherwood (1961), have been extensively studied. Usherwood (1963) observed the influence of potassium, calcium and magnesium ions in the external solution on the miniature frequency of the muscle fibres. However, the effect of altering the ionic composition of the external medium of insect muscle fibres has not been comprehensively studied.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Calcium and Magnesium on the Spontaneous Release of Transmitter At Insect Motor Nerve Terminals

Washio¹,

Inouye²

1978

Journal of Experimental Biology

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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.

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Spontaneous miniature potentials from insect muscle fibres

Cited by 90 publications

References 18 publications

Inhibitory miniature synaptic potentials in rat motoneurons

Inhibitory miniature synaptic potentials in rat motoneurons

On the significance of cross-bridges between microtubules and synaptic vesicles

The Effect of Calcium and Magnesium on the Spontaneous Release of Transmitter At Insect Motor Nerve Terminals

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