Differences in presynaptic action of 4-aminopyridine and tetraethylammonium at frog neuromuscular junction

1987 ◽  
Vol 65 (5) ◽  
pp. 747-752 ◽  
Author(s):  
M. I. Glavinović
Keyword(s):  
Neuromuscular Junction ◽  
Transmitter Release ◽  
Action Potentials ◽  
Time Course ◽  
Potassium Conductance ◽  
Frog Neuromuscular Junction ◽  
Quantal Content ◽  
Low Concentrations ◽  
Voltage Dependent ◽  
Intracellular Ca

4-Aminopyridine markedly potentiates transmitter release at the frog cutaneous pectoris neuromuscular junction by increasing the quantal content even when applied at low concentrations (5–20 μM). This enhancement of transmitter release is associated with greater minimum synaptic latency, but the dispersion of the synaptic latencies does not appear much affected. This is in contrast with the action of tetraethylammonium (0.2–0.5 mM) in which case similar enhancement of transmitter release results not only in larger minimum synaptic latency but also in greater dispersion of the synaptic latencies. The time course of transmitter release associated with enhanced transmitter output is hence much more prolonged in the presence of tetraethylammonium than 4-aminopyridine, at least for low concentrations of 4-aminopyridine (5–20 μM). This indicates that their presynaptic actions differ significantly. This conclusion is further strengthened by the finding that unlike tetraethylammonium, 4-aminopyridine induces bursts of release, presumably by producing multiple action potentials in the nerve terminal. Tetraethylammonium probably acts by blocking the delayed potassium conductance, but the blockade of Ca2+-activated K+ conductance cannot be excluded. 4-Aminopyridine, however, probably blocks the fast inactivating (IA) K+ current, but it also may be acting directly on the voltage-dependent Ca2+ conductance or on the intracellular Ca2+ buffering.

scholarly journals Role of intracellular Ca2+ in stimulation-induced increases in transmitter release at the frog neuromuscular junction.

1994 ◽  
Vol 104 (2) ◽  
pp. 337-355 ◽  
Author(s):  
J E Zengel ◽  
M A Sosa ◽  
R E Poage ◽  
D R Mosier
Keyword(s):  
Neuromuscular Junction ◽  
Transmitter Release ◽  
Cyclopiazonic Acid ◽  
Progressive Increase ◽  
Repetitive Stimulation ◽  
Frog Neuromuscular Junction ◽  
Quantal Content ◽  
Carbonyl Cyanide ◽  
Stimulation Of

Under conditions of reduced quantal content, repetitive stimulation of a presynaptic nerve can result in a progressive increase in the amount of transmitter released by that nerve in response to stimulation. At the frog neuromuscular junction, this increase in release has been attributed to four different processes: first and second components of facilitation, augmentation, and potentiation (e.g., Zengel, J. E., and K. L. Magleby. 1982. Journal of General Physiology. 80:583-611). It has been suggested that an increased entry of Ca2+ or an accumulation of intraterminal Ca2+ may be responsible for one or more of these processes. To test this hypothesis, we have examined the role of intracellular Ca2+ in mediating changes in end-plate potential (EPP) amplitude during and after repetitive stimulation at the frog neuromuscular junction. We found that increasing the extracellular Ca2+ concentration or exposing the preparation to carbonyl cyanide m-chlorophenylhydrazone, ionomycin, or cyclopiazonic acid all led to a greater increase in EPP amplitude during conditioning trains of 10-200 impulses applied at a frequency of 20 impulses/s. These experimental manipulations, all of which have been shown to increase intracellular levels of Ca2+, appeared to act by increasing primarily the augmentation component of increased release. The results of this study are consistent with previous suggestions that the different components of increased release represent different mechanisms, and that Ca2+ may be acting at more than one site in the nerve terminal.

scholarly journals Presynaptic facilitation at the crayfish neuromuscular junction. Role of calcium-activated potassium conductance.

1991 ◽  
Vol 98 (6) ◽  
pp. 1181-1196 ◽  
Author(s):  
S Sivaramakrishnan ◽  
M S Brodwick ◽  
G D Bittner
Keyword(s):  
Neuromuscular Junction ◽  
Transmitter Release ◽  
Time Course ◽  
Potassium Conductance ◽  
Early Time ◽  
Release Mechanism ◽  
Free Calcium ◽  
Test Pulse ◽  
Current Pulses ◽  
Calcium Activated Potassium Conductance

Membrane potential was recorded intracellularly near presynaptic terminals of the excitor axon of the crayfish opener neuromuscular junction (NMJ), while transmitter release was recorded postsynaptically. This study focused on the effects of a presynaptic calcium-activated potassium conductance, gK(Ca), on the transmitter release evoked by single and paired depolarizing current pulses. Blocking gK(Ca) by adding tetraethylammonium ion (TEA; 5-20 mM) to a solution containing tetrodotoxin and aminopyridines caused the relation between presynaptic potential and transmitter release to steepen and shift to less depolarized potentials. When two depolarizing current pulses were applied at 20-ms intervals with gK(Ca) not blocked, the presynaptic voltage change to the second (test) pulse was inversely related to the amplitude of the first (conditioning) pulse. This effect of the conditioning prepulse on the response to the test pulse was eliminated by 20 mM TEA and by solutions containing 0 mM Ca2+/1 mM EGTA, suggesting that the reduction in the amplitude of the test pulse was due to activation of gK(Ca) by calcium remaining from the conditioning pulse. In the absence of TEA, facilitation of transmitter release evoked by a test pulse increased as the conditioning pulse grew from -40 to -20 mV, but then decreased with further increase in the conditioning depolarization. A similar nonmonotonic relationship between facilitation and the amplitude of the conditioning depolarization was reported in previous studies using extracellular recording, and interpreted as supporting an additional voltage-dependent step in the activation of transmitter release. We suggest that this result was due instead to activation of a gK(Ca) by the conditioning depolarization, since facilitation of transmitter release increased monotonically with the amplitude of the conditioning depolarization, and the early time course of the decay of facilitation was prolonged when gK(Ca) was blocked. The different time courses for decay of the presynaptic potential (20 ms) and facilitation (greater than 50 ms) suggest either that residual free calcium does not account for facilitation at the crayfish NMJ or that the transmitter release mechanism has a markedly higher affinity or stoichiometry for internal free calcium than does gK(Ca). Finally, our data suggest that the calcium channels responsible for transmitter release at the crayfish NMJ are not of the L, N, or T type.

Cation dependence of posttetanic potentiation of neuromuscular transmission

1987 ◽  
Vol 252 (1) ◽  
pp. C55-C62 ◽  
Author(s):  
S. Misler ◽  
L. Falke ◽  
S. Martin
Keyword(s):  
Neuromuscular Junction ◽  
Neuromuscular Transmission ◽  
Frog Neuromuscular Junction ◽  
Posttetanic Potentiation ◽  
Quantal Content ◽  
Quantal Release ◽  
New Findings ◽  
Pump Activity ◽  
Voltage Dependent ◽  
Quantal Release Of Neurotransmitter

We have investigated the possibility that much of posttetanic potentiation (PTP) of quantal release of neurotransmitter at the frog neuromuscular junction may be due to posttetanic accumulation of [Ca2+]i, via a plasmalemmal Cao2+-Nai+ exchanger that is powered by an increase in Nai+ during the tetanus. Our new findings on the cationic dependence of PTP are consistent with this hypothesis. 1) Several manuevers that decrease Na+-K+ pump activity, (decreasing [K+]o, replacing K+o with Rb+o or Li+o, or adding acetylstrophanthidin to Ringers), all increase the intratetanic rise and prolong the posttetanic decay of epp quantal content (m) and miniature epp frequency (fmepp). 2) Increasing [Ca2+]i or [Sr2+]o, but not [Mg2+]o, increases posttetanic fmepp in a graded fashion. 3) PTP of fmepp is still present after addition of Mn2+o, which blocks voltage dependent Ca2+ entry.

Different VAMP/Synaptobrevin Complexes for Spontaneous and Evoked Transmitter Release at the Crayfish Neuromuscular Junction

1998 ◽  
Vol 80 (6) ◽  
pp. 3233-3246 ◽  
Author(s):  
Shao-Ying Hua ◽  
Dorota A. Raciborska ◽  
William S. Trimble ◽  
Milton P. Charlton
Keyword(s):  
Neuromuscular Junction ◽  
Transmitter Release ◽  
Neurotransmitter Release ◽  
Action Potentials ◽  
Neuromuscular Junctions ◽  
Spontaneous Release ◽  
Intracellular Ca ◽  
Crayfish Neuromuscular Junction ◽  
Evoked Transmitter Release

Hua, Shao-Ying, Dorota A. Raciborska, William S. Trimble, and Milton P. Charlton. Different VAMP/synaptobrevin complexes for spontaneous and evoked transmitter release at the crayfish neuromuscular junction. J. Neurophysiol. 80: 3233–3246, 1998. Although vesicle-associated membrane protein (VAMP/synaptobrevin) is essential for evoked neurotransmitter release, its role in spontaneous transmitter release remains uncertain. For instance, many studies show that tetanus toxin (TeNT), which cleaves VAMP, blocks evoked transmitter release but leaves some spontaneous transmitter release. We used recombinant tetanus and botulinum neurotoxin catalytic light chains (TeNT-LC, BoNT/B-LC, and BoNT/D-LC) to examine the role of VAMP in spontaneous transmitter release at neuromuscular junctions (nmj) of crayfish. Injection of TeNT-LC into presynaptic axons removed most of the VAMP immunoreactivity and blocked evoked transmitter release without affecting nerve action potentials or Ca2+ influx. The frequency of spontaneous transmitter release was little affected by the TeNT-LC when the evoked transmitter release had been blocked by >95%. The spontaneous transmitter release left after TeNT-LC treatment was insensitive to increases in intracellular Ca2+. BoNT/B-LC, which cleaves VAMP at the same site as TeNT-LC but uses a different binding site, also blocked evoked release but had minimal effect on spontaneous release. However, BoNT/D-LC, which cleaves VAMP at a different site from the other two toxins but binds to the same position on VAMP as TeNT, blocked both evoked and spontaneous transmitter release at similar rates. The data indicate that different VAMP complexes are employed for evoked and spontaneous transmitter release; the VAMP used in spontaneous release is not readily cleaved by TeNT or BoNT/B. Because the exocytosis that occurs after the action of TeNT cannot be increased by increased intracellular Ca2+, the final steps in neurotransmitter release are Ca2+ independent.

Role of NSF in Neurotransmitter Release: A Peptide Microinjection Study at the Crayfish Neuromuscular Junction

2006 ◽  
Vol 96 (3) ◽  
pp. 1053-1060 ◽  
Author(s):  
I. Parnas ◽  
G. Rashkovan ◽  
V. O'Connor ◽  
O. El-Far ◽  
H. Betz ◽  
...  
Keyword(s):  
Amino Acid ◽  
Neuromuscular Junction ◽  
Neurotransmitter Release ◽  
Action Potentials ◽  
Time Course ◽  
Synaptic Delay ◽  
Quantal Content ◽  
Presynaptic Mechanisms ◽  
Crayfish Neuromuscular Junction

Peptides that inhibit the SNAP-stimulated ATPase activity of N-ethylmaleimide-sensitive fusion protein (NSF-2, NSF-3) were injected intra-axonally to study the role of this protein in the release of glutamate at the crayfish neuromuscular junction. Macropatch recording was used to establish the quantal content and to construct synaptic delay histograms. NSF-2 or NSF-3 injection reduced the quantal content, evoked by either direct depolarization of a single release bouton or by axonal action potentials, on average by 66 ± 12% (mean ± SD; n = 32), but had no effect on the time course of release. NSF-2 had no effect on the amplitude or shape of the presynaptic action potential nor on the excitatory nerve terminal current. Neither NSF-2 nor NSF-3 affected the shape or amplitude of single quantal currents. Injection of a peptide with the same composition as NSF-2, but with a scrambled amino acid sequence, failed to alter the quantal content. We conclude that, at the crayfish neuromuscular junction, NSF-dependent reactions regulate quantal content without contributing to the presynaptic mechanisms that control the time course of release.

Presynaptic effects of a trinitrobenzene analogue at the frog neuromuscular junction

1996 ◽  
Vol 76 (3) ◽  
pp. 1735-1743 ◽  
Author(s):  
M. Osanai ◽  
A. Tsuji ◽  
N. Suzuki ◽  
H. Kijima
Keyword(s):  
Neuromuscular Junction ◽  
Transmitter Release ◽  
Time Course ◽  
Control Level ◽  
Protein S ◽  
Specific Protein ◽  
Frog Neuromuscular Junction ◽  
Short Term ◽  
Similar Time ◽  
Presynaptic Nerve Terminal

1. Application of 0.15 mM 1-(hydroxyethylamino)-2,4,6-trinitrobenzene (HEATNB) to the frog neuromuscular junction induced a marked increase (4.0-fold) in the amplitude of nerve-evoked end-plate potentials (EPPs) obtained from intracellular and extracellular records, but only a slight increase (1.9-fold) in the frequency of miniature EPPs (MEPPs) obtained from intracellular records. The effects of HEATNB on EPP amplitude and MEPP frequency showed a similar time course, reaching a plateau level approximately 40 min after the start of application and returning to the control level after wash. The difference in the effects of HEATNB on EPP and MEPP frequency suggests that it specifically enhances synchronous transmitter release. 2. Comparing the effects and structure of HEATNB with those of 2,4,6-trinitrobenzene-1-sulfonic acid, we conclude that the observed increase in transmitter release is due to the effects of the trinitrobenzene moiety of those reagents. 3. The distribution of MEPP amplitude was unchanged by HEATNB treatment, indicating that its effects are presynaptic. 4. Among four components of short-term synaptic plasticity, HEATNB greatly decreased (approximately 70%) augmentation and increased (approximately 50%) potentiation, but had little effect on fast and slow facilitations. These results suggest that each of the short-term plasticities has a different mechanism and that HEATNB affects the same mechanisms as those of augmentation. 5. Even when a calcium chelator, bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid, was loaded into the presynaptic nerve terminal, the effects of HEATNB were not changed in nature, suggesting that effects of HEATNB persist independently of intracellular Ca2+ concentration. 6. These observations suggest that HEATNB may affect specific protein(s) involved primarily in synchronous transmitter release and not asynchronous release.

scholarly journals Desensitization onset and recovery at the potassium-depolarized frog neuromuscular junction are voltage sensitive.

1978 ◽  
Vol 71 (3) ◽  
pp. 285-299 ◽  
Author(s):  
B Scubon-Mulieri ◽  
R L Parsons
Keyword(s):  
Membrane Potential ◽  
Neuromuscular Junction ◽  
Time Constant ◽  
Time Course ◽  
Voltage Dependence ◽  
Onset Time ◽  
Control Voltage ◽  
Frog Neuromuscular Junction ◽  
End Plate ◽  
Voltage Dependent

The influence of voltage on the time-course of desensitization onset and recovery has been studied at the frog neuromuscular junction. The activation-desensitization sequence was determined from carbachol-induced end-plate currents in potassium-depolarized fibers voltage-clamped either to -40 mV or +40 mV. The time-course of both desensitization onset and recovery developed exponentially, with onset occurring more rapidly than recovery. Desensitization onset was voltage dependent, the onset time constant being 8.3 +/- 1.3 s (11 fibers) at -40 mV and 19.3 +/- 3.4 s (15 fibers) at +40 mV. Recovery from desensitization was also influenced by voltage. The extent of recovery after 2 min was 80.4 +/- 6.3% in those fibers voltage-clamped to -40 mV and 57.4 +/- 3.6% in those fibers voltage-clamped to +40 mV. The voltage dependence of desenistization onset and recovery did not result from a difference in ability to control voltage at these two levels of membrane potential. These results demonstrate that in the potassium-depolarized preparation the processes controlling both desensitization onset and recovery of sensitivity from the desensitivity from the desensitized state are influenced by membrane voltage.

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