scholarly journals Correlation between nerve terminal size and transmitter release at the neuromuscular junction of the frog

1971 ◽  
Vol 213 (3) ◽  
pp. 545-556 ◽  
Author(s):  
M. Kuno ◽  
S. A. Turkanis ◽  
J. N. Weakly
Keyword(s):  
Neuromuscular Junction ◽  
Nerve Terminal ◽  
Transmitter Release

Effects of adenosine on Ca2+ entry in the nerve terminal of the frog neuromuscular junction

1999 ◽  
Vol 77 (9) ◽  
pp. 707-714 ◽  
Author(s):  
Richard Robitaille ◽  
Sébastien Thomas ◽  
Milton P Charlton
Keyword(s):  
Neuromuscular Junction ◽  
Nerve Terminal ◽  
Nerve Stimulation ◽  
High Frequency ◽  
Transmitter Release ◽  
Synaptic Depression ◽  
Presynaptic Terminal ◽  
Nerve Terminals ◽  
Frog Neuromuscular Junction ◽  
Induced Changes

This study aimed to test whether nerve-evoked and adenosine-induced synaptic depression are due to reduction in Ca2+ entry in nerve terminals of the frog neuromuscular junction. Nerve terminals were loaded with the fluorescent Ca2+ indicator fluo 3 (fluo 3-AM) or loaded with dextran-coupled Ca2+ green-1 transported from the cut end of the nerve. Adenosine (10-50 µM) did not change the resting level of Ca2+ in the presynaptic terminal, whereas it induced large Ca2+ responses in perisynaptic Schwann cells, indicating that adenosine was active and might have induced changes in the level of Ca2+ in the nerve terminal. Ca2+ responses in nerve terminals could be induced by nerve stimulation (0.5 or 100 Hz for 100 ms) over several hours. In the presence of adenosine (10 µM), the size and duration of the nerve-evoked Ca2+ responses were unchanged. When extracellular Ca2+ concentration was lowered to produce the same reduction in transmitter release as the application of adenosine, Ca2+ responses induced by nerve stimulations were reduced by 40%. This indicates that changes in Ca2+ responsible for the decrease in release should have been detected if the mechanism of adenosine depression involved partial block of Ca2+ influx. Ca2+ responses evoked by prolonged high frequency trains of stimuli (50 Hz for 10 or 30 s), which caused profound depression of transmitter release, were sustained during the whole duration of the stimulation, and adenosine had no effect on these responses. These data indicate that neither adenosine induced synaptic depression nor stimulation-induced synaptic depression are caused by reductions in Ca2+ entry into the presynaptic terminal in the frog neuromuscular junction.Key words: adenosine, Ca2+, nerve terminal, transmitter release, synaptic depression.

scholarly journals A Cyclic Adenosine Monophosphate Link in the Catecholamine Enhancement of Transmitter Release at the Neuromuscular Junction

1974 ◽  
Vol 63 (5) ◽  
pp. 609-624 ◽  
Author(s):  
Michael D. Miyamoto ◽  
Bruce McL. Breckenridge
Keyword(s):  
Neuromuscular Junction ◽  
Nerve Terminal ◽  
Transmitter Release ◽  
Time Course ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Dibutyryl Camp ◽  
Miniature Endplate Potentials ◽  
Endplate Potentials

The frequency of miniature endplate potentials (mepps) in rat diaphragms was markedly increased by epinephrine and norepinephrine in preparations exposed to 15 mM K+. The effect was rapid in onset but gradually declined during continued exposure to the catecholamines. N6, O2'-dibutyryl adenosine 3',5'-monophosphate (dibutyryl-cAMP) also caused transient frequency increases resembling in time-course those observed with catecholamines. Contrary to previous reports, catecholamines and dibutyryl-cAMP had little effect on mepp frequency in preparations not treated with K+. Sustained increases with theophylline and decreases with adenosine were found in both K+-treated and untreated preparations. Analysis of the data obtained with catecholamines showed the intensity of the response to be a function of nerve terminal polarization. The inability of catecholamines and dibutyryl-cAMP to affect mepp frequency of untreated preparations argues against an obligatory role for cAMP in the neurosecretory mechanism. The findings are consistent with an action of catecholamines and cAMP in the regulation of transmitter release at fatigued preparations.

Influence of lanthanum on transmitter release at the neuromuscular junction

1971 ◽  
Vol 2 (3) ◽  
pp. 263-278 ◽  
Author(s):  
William A. DeBassio ◽  
Ronald M. Schnitzler ◽  
Rodney L. Parsons
Keyword(s):  
Neuromuscular Junction ◽  
Transmitter Release
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