Effect of chloride ions on giant miniature end‐plate potentials at the frog neuromuscular junction.

1. Intracellular recordings were made from muscle fibre No. 6 of the dorsal longitudinal flight muscle (DLM) of Drosophila melanogaster in both wild‐type flies and the temperature‐sensitive paralytic mutant, shibirets‐1 (shi). 2. Continuous recordings of the miniature excitatory junction potentials (MEJPs) in this fibre were made as the temperature was changed from 19 to 29 degrees C, and back to 19 degrees C. In shi flies, synapses become depleted of vesicles at 29 degrees C due to a temperature‐dependent blockage in the recycling process, while transmitter release proceeds normally. When the temperature is lowered to 19 degrees C, recycling is allowed to proceed and recovery of the full complement of synaptic vesicles gradually occurs in about 20 min. 3. It was observed that the MEJP amplitude distribution in shi flies was unimodal at 19 degrees C prior to heating (as was wild‐type), but during recovery from 8 min exposure to 29 degrees C became multimodal, with peaks at roughly integral multiples of the original peak prior to heating. This effect was never seen in wild‐type flies. 4. Also, during recovery, the MEJP did not occur randomly, but rather occurred in a clustered fashion. 5. It is concluded that during recovery from depletion in shi neuromuscular junctions, a condition exists which causes the synchronization of spontaneous release, causing multiquantal MEJPs or clustering of MEJPs, depending on the degree of synchronization. 6. The possible role of Ca2+ in this phenomenon is discussed.

Section: Discussionmentioning

confidence: 99%

Spontaneous release of multiquantal miniature excitatory junction potentials induced by a Drosophila mutant.

Ikeda

Koenig

1988

“…The induced gMEPPs persisted after returning the muscle to normal K+ solution. However, the finding that the increase in gMEPPs did not take place in the absence of Cl-led to the suggestion that the production of gMEPPs may be related, in some way, to a Cl--dependent process (Molenaar et al 1987).…”

Section: Variation Of Resting Cl-permeabilitymentioning

confidence: 97%

“…Recently Molenaar et al (1987) reported that gMEPPs can be induced by preincubation of the muscle in very high K' concentration media. They also reported that removal of Cl-is somehow involved in the generation of gMEPPs.…”

mentioning

confidence: 99%

Giant miniature end‐plate potentials at the untreated and emetine‐treated frog neuromuscular junction.

Alkadhi

1989

SUMMARY1. Intracellular recordings from the cutaneous pectoris muscle fibres of the frog showed that giant miniature end-plate potentials (gMEPPs) occurred in untreated preparations. Emetine (10 flM), after a 15-20 min delay, increased the frequency of gMEPPs. In both cases gMEPPs disappeared in the presence of (+ )-tubocurarine.2. There was no correlation between the frequency of gMEPPs and the frequeney of normal MEPPs (nMEPPs) in untreated or emetine-treated fibres.3. Tetraphenylborate (TPB, 50 /tM) applied to mutscles pre-treated with einetine caused the frequency and amplitude of both niME[Ps and gAIEPPs to (lecrease gradually. All MEPPs disappeared in about 10 min.4. Chloride permeability was modified by changing the pH of the Riinger solution.

“…Bevan, 1976) appear to exist, and although they rarely occur spontaneously, their frequency can be increased considerably under various conditions. In frog muscle an increase of the frequency of small MEPPs (Ceccarelli & Hurlbut, 1975;Ceccarelli, Grohovaz & Hurlbut, 1979;Kriebel & Florey, 1983) and of giant MEPPs (Pecot-Dechavassine & Couteaux, 1972;Heuser, 1974;Molenaar, Oen & Polak, 1985, 1987 has been observed after prolonged stimulation of ACh release. Giant MEPPs are probably not derived from pre-formed vesicles (Molenaar et al 1987).…”

Section: Introductionmentioning

confidence: 99%

“…In frog muscle an increase of the frequency of small MEPPs (Ceccarelli & Hurlbut, 1975;Ceccarelli, Grohovaz & Hurlbut, 1979;Kriebel & Florey, 1983) and of giant MEPPs (Pecot-Dechavassine & Couteaux, 1972;Heuser, 1974;Molenaar, Oen & Polak, 1985, 1987 has been observed after prolonged stimulation of ACh release. Giant MEPPs are probably not derived from pre-formed vesicles (Molenaar et al 1987). In fact, they might be derived from large vesicular structures which are formed during stimulation-induced recycling of vesicles (Ceccarelli, Hurlbut & Mauro, 1973;Heuser & Reese, 1973;Heuser, 1974).…”

Section: Introductionmentioning

confidence: 99%

Analysis of quantal acetylcholine noise at end‐plates of frog muscle during rapid transmitter secretion.

Molenaar

Oen

1988

Self Cite

SUMMARY1. Using the theory of noise analysis an attempt was made to measure frequency and amplitude of miniature end-plate potentials (MEPPs) under conditions of vigorous transmitter release. Frog sartorius muscles were incubated in a depolarizing (32 mM-K+) medium which lacked Ca2+ to prevent transmitter release. Subsequently, when the membrane potential had become stable at about -40 mV, end-plates were superfused with 4 mM-Ca2+-containing medium for 1 min periods with 5 min intervals between the superfusions.2. Most junctions ('fast' type) responded to Ca2+ with a relatively large, noisy depolarization (5-8-14-5 mV) which subsided rapidly during subsequent challenges with Ca2 . Other junctions ('slow' type) responded with only 1-1 6 mV depolarizations which were rather well sustained during the consecutive Ca2+ applications.3. From the variance, E2, and the depolarization, V, caused by Ca2+ the frequency n and amplitude factor q of the MEPPs were calculated. Values of n were 3-4 x 104 and 0_1-1 x 104 S-1 in the fast-and slow-type junctions, respectively. The mean value of q was 0-16 mV; it remained more or less constant in the fast-type junctions, but tended to decline in the slow-type junctions.4. As expected, cholinesterase inhibitors potentiated V and E2 as well as individual MEPPs. However, no advantage could be taken from this finding, since these drugs caused burst-like peaks superimposed on the voltage signal, precluding application of noise analysis.5. The results strongly suggest that, at least in the fast-type junctions, K+ caused an extremely rapid depletion of the store of transmitter quanta, whose mean size did not change appreciably in the course of the experiment. However, in the slow-type junctions during prolonged incubation, it cannot be excluded that the gradual decline of q was due to the release of newly formed, unripe quanta.