Calcium-Insensitive miniature endplate potentials at the neuromuscular junction

Synapse ◽  
1987 ◽  
Vol 1 (4) ◽  
pp. 281-292 ◽  
Author(s):  
Mark T. Lupa
Keyword(s):  
Neuromuscular Junction ◽  
Miniature Endplate Potentials ◽  
Endplate Potentials

Effect of Cooling on Neuromuscular Transmission in the Frog

1958 ◽  
Vol 192 (3) ◽  
pp. 464-470 ◽  
Author(s):  
Choh-Luh Li ◽  
Peter Gouras
Keyword(s):  
Critical Temperature ◽  
Neuromuscular Junction ◽  
Nerve Stimulation ◽  
Neuromuscular Transmission ◽  
The Other ◽  
Sartorius Muscle ◽  
Single Muscle ◽  
Miniature Endplate Potentials ◽  
Endplate Potentials ◽  
Muscle Responses

Recording with intracellular electrodes from endplate regions of frogs sartorius muscle showed that at –1°C miniature endplate potentials still occurred and that the resting membrane potentials differed very little from those recorded at room temperatures. The miniature potentials, however, were decreased in frequency and increased in amplitude by cooling; and at about 5°C, the amplitude began to fall while the frequency continued to be low. It was also at about 5°C that the muscle responses to nerve stimulation frequently consisted of endplate potentials only. Upon rewarming spike potentials again appeared. These observations suggest that there is a critical temperature for neuromuscular transmission, below which impediment of impulse transmission began; and in the frog it is 5°C. The experiments also demonstrated that during the process of cooling a blockage of impulses at one neuromuscular junction and transmission across the other in a single muscle fiber could occur.

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.

Effect of Hypertonicity on Augmentation and Potentiation and on Corresponding Quantal Parameters of Transmitter Release

1999 ◽  
Vol 81 (3) ◽  
pp. 1428-1431 ◽  
Author(s):  
Hong Cheng ◽  
Michael D. Miyamoto
Keyword(s):  
Nerve Stimulation ◽  
Transmitter Release ◽  
Ringer Solution ◽  
Hypertonic Solution ◽  
Repetitive Nerve Stimulation ◽  
Quantal Transmitter Release ◽  
Before And After ◽  
Miniature Endplate Potentials ◽  
Endplate Potentials ◽  
Made In

Effect of hypertonicity on augmentation and potentiation and on corresponding quantal parameters of transmitter release. Augmentation and (posttetanic) potentiation are two of the four components comprising the enhanced release of transmitter following repetitive nerve stimulation. To examine the quantal basis of these components under isotonic and hypertonic conditions, we recorded miniature endplate potentials (MEPPs) from isolated frog ( Rana pipiens) cutaneous pectoris muscles, before and after repetitive nerve stimulation (40 s at 80 Hz). Continuous recordings were made in low Ca2+ high Mg2+ isotonic Ringer solution, in Ringer that was made hypertonic with 100 mM sucrose, and in wash solution. Estimates were obtained of m (no. of quanta released), n (no. of functional release sites), p (mean probability of release), and vars p (spatial variance in p), using a method that employed MEPP counts. Hypertonicity abolished augmentation without affecting potentiation. There were prolonged poststimulation increases in m, n,and p and a marked but transient increase in vars p in the hypertonic solution. All effects were completely reversed with wash. The time constants of decay for potentiation and for vars p were virtually identical. The results are consistent with the notion that augmentation is caused by Ca2+ influx through voltage-gated calcium channels and that potentiation is due to Na+-induced Ca2+ release from mitochondria. The results also demonstrate the utility of this approach for analyzing the dynamics of quantal transmitter release.

The giant miniature endplate potentials frequency is increased in aged rats

2015 ◽  
Vol 584 ◽  
pp. 224-229 ◽  
Author(s):  
Paula A. Pousinha ◽  
Alexandra M. Correia ◽  
Ana M. Sebastião ◽  
Joaquim A. Ribeiro
Keyword(s):  
Aged Rats ◽  
Miniature Endplate Potentials ◽  
Endplate Potentials
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