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M Israël

Publications and source records attributed to M Israël.

At least 91 records · Page 5Linked to original sources
PubMed1980

[Changes in the number and distribution of intramembranous particles of electric organ synaptosomes of Torpedo during synaptic activity].

Cholinergic synaptosomes were depolarized with KCl or treated with a venom extracted from the annelid Glycera convoluta. This venom was shown to increase considerably the frequency of the miniature endplate potentials at neuromuscular junctions. The synaptosomes were frozen and fractured in the absence of any fixative or cryoprotectant. Synaptic activity decreased the number of small (6 to 8 nm) particles in the P faces of the presynatic membrane, while the large particles (above 8 nm) increased on both P and E faces. It is suggested that these modifications are related to ionic flux or more directly to the release of transmitter.

Animals↗
PubMed1980

ATP-dependent calcium uptake by cholinergic synaptic vesicles isolated from Torpedo electric organ.

Cholinergic synaptic vesicles were purified from Torpedo electric organ to near morphological homogeneity. They were isolated in a K+ environment. A method is described for the preparation of concentrated synaptic vesicles that allows uptake studies by conventional techniques. An ATP-Mg-dependent calcium uptake associated with synaptic vesicles is characterized. The uptake system transports calcium against a high concentration gradient. The maximum accumulation rate is obtained for the calcium, Mg++ and ATP concentrations likely to be found in the nerve terminal cytoplasm. It is suggested that synaptic vesicles are implicated in the removal of the calcium entering the nerve terminal during synaptic activity.

Acetylcholine↗
PubMed1980

Calcium uptake by cholinergic synaptic vesicles.

Pure synaptic vesicles have been isolated in sucrose-KCl media. They are able to take up calcium in the presence of ATP and Mg. This is based on the following evidence. First, the synaptic vesicle fraction is the gradient peak for calcium uptake. Second, it was not possible to separate ACh and ATP from the uptake peak after refractionation of synaptic vesicles. Third, the fraction appears very pure on morphological and biochemical grounds. The physiological significance of the calcium uptake by synaptic vesicles is discussed.

Acetylcholine↗
PubMed1979

Rapid acetylcholine and adenosine triphosphate oscillations triggered by stimulation of the Torpedo electric organ.

1. When the electric organ of Torpedo is stimulated a large number of synchronized cholinergic synapses are activated. This permits the measurement of changes in the tissue level of ACh associated with the release process, usually recorded as an electric discharge. 2. At 5 Hz stimulation the output per impulse and the amount of cytoplasmic (free ACh) declines for about 30 s. The output then remains constant while ACh is synthesized for about 90 s. Finally, the output and cytoplasmic ACh are exhausted after 120 s. These 'slow wave' changes in ACh represent about 50% of the total. 3. Superimposed on the 'slow wave' are rapid oscillations of 5 s period, which represent about 30% of the total ACh. 4. The amount of ATP oscillates in phase with ACh. These oscillations might result from regulation of enzymes involved in the synthesis of transmitter. 5. The amplitude of electrical discharge does not normally oscillate. Transmitter output is therefore not directly related to ACh concentration changes. The mechanism releasing ACh is a saturable process.

Acetylcholine↗
PubMed1978

The release of ATP triggered by transmitter action and its possible physiological significance: retrograde transmission.

1. When a slice of electric organ of Torpedo is stimulated and superfused with a solution containing a firefly lantern extract, it is possible to measure the release of ATP after each nerve impulse as a light emission. 2. The postsynaptic action of released ACh induces the release of ATP by the postsynaptic cell. Most of the released ATP is of postsynaptic origin. 3. Ion fluxes associated with depolarization, or depolarization itself, trigger the release of ATP from postsynaptic and presynaptic membranes (synaptosomes). 4. ATP is able to block ACh release; a postsynaptic "retrograde transmission" able to control presynaptic transmitter release is possible.

Acetylcholine↗
PubMed1977

[Liberation of adenosine triphosphate after depolarization of the Torpedo electroplaque by potassium chloride].

The release of ATP after potassium depolarization was measured on fragments of electric tissue incubated in a solution containing the firefly extract. Light emission was proportional to the extracellular KCL concentration. In contrast to the release of ATP after single nerve impulses, the release after direct KCL depolarization was insensitive to curare of eserin.

Adenosine Triphosphate↗
PubMed1977

Oscillation of acetylcholine during nerve activity in the Torpedo electric organ.

The amount of transmitter in the electric organ of Torpedo was measured with a time resolution of 1 sec in the course of stimulation. In parallel, the modifications of the electrophysiological response were analysed by determining the conductance increase (deltaG) and the electromotive force of electroplaques. Large changes in the level of total acetylcholine (ACh) were seen during stimulation. These changes were two-fold: a slow wave and, superimposed on it, a rapid oscillation. The slow wave raised total ACh to the initial level, or even higher. It was probably related to modifications in the amount of ACh released since it corresponded to characteristic inflections in the evolution of the deltaG curve. The slow wave and this physiological parameter were similarly affected when the experiments were performed at a reduced temperature. The rapid oscillation had an amplitude of about 20-40% of the total ACh. It was undamped and its period was 4-5 sec. In contrast to the slow wave, no clear physiological change associated with the rapid oscillation has been observed. The slow wave and rapid oscillation occurred in the 'free pool' of ACh, whereas bound ACh, the fraction associated with synaptic vesicles, was not affected by these changes. A dynamic description of synaptic activity is proposed. The content of 'free' ACh is used and renewed completely after a few tens of impulses, so that transmission seems to imply the continual recycling of the same pool of transmitter rather than utilization of a large preloaded store. The release process must then be integrated in rapid metabolic loops.

Acetylcholine↗
PubMed1975

[Periodical variations of the level of acetylcholine during stimulation of torpedo electric organ].

When tissue samples of the electric organ of the Torpedo fish, are taken every second during a period of stimulation at 5/s, it is noticed that their acetylcholine level oscillates in a quasi-sinusoidal shape. The amplitude of the oscillation is of about 350 nmoles/g and its period of 4 to 6 seconds. The speed of acetylcholine formation during such a process is extremely high.

Acetylcholine↗