The Neuromuscular Junction Revisited: Ca2+ Channels and Transmitter Release in Cholinergic Neurones in Xenopus Nerve and Muscle Cell Culture

Although the entry of calcium ions into the presynaptic nerve terminals through voltage-gated Ca2+ channels is now universally recognized as playing an essential role in evoked transmitter release at the neuromuscular junction (NMJ), and indeed in chemical synapses generally, we have as yet very little direct knowledge of the Ca2+ channels of the presynaptic terminals. In this work, making use of cocultured nerve and muscle cells from Xenopus embryos, we studied the NMJ formed between the soma of identified cholinergic neurones and myoball, which allowed the use of patch-clamps on both the pre- and postsynaptic components. Both whole-cell and single-channel recordings of Ca2+ channels in the presynaptic cell were made. We found only one type of voltage-gated Ca2+ channel with highvoltage activation and slow inactivation characteristics, allowing its classification either as the L or the N type. The channels were susceptible to block by metenkephalin but not to block by nifedipine or to enhancement by Bay K 8644. This combination of pharmacological properties favours their classification as the N type. Preliminary observations on the correlation between calcium currents and transmitter release disclosed a strikingly rapid run-down of the evoked release with unchanged calcium currents and spontaneous release during whole-cell recording, indicating a specific wash-out effect on some link between calcium entry and evoked transmitter release.

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Dopamine Modulation of Calcium Currents in Pyloric Neurons of the Lobster Stomatogastric Ganglion

Journal of Neurophysiology ◽

10.1152/jn.00037.2003 ◽

2003 ◽

Vol 90 (2) ◽

pp. 631-643 ◽

Cited By ~ 40

Author(s):

Bruce R. Johnson ◽

Peter Kloppenburg ◽

Ronald M. Harris-Warrick

Keyword(s):

Calcium Channel ◽

Transmitter Release ◽

Stomatogastric Ganglion ◽

Calcium Currents ◽

Voltage Gated ◽

Pyloric Network ◽

Pyloric Dilator ◽

Voltage Dependent ◽

Inward Currents ◽

Dopamine Modulation

We examined the dopamine (DA) modulation of calcium currents (ICa) that could contribute to the plasticity of the pyloric network in the lobster stomatogastric ganglion. Pyloric somata were voltage-clamped under conditions designed to block voltage-gated Na+, K+, and H currents. Depolarizing steps from –60 mV generated voltage-dependent, inward currents that appeared to originate in electrotonically distal, imperfectly clamped regions of the cell. These currents were blocked by Cd2+ and enhanced by Ba2+ but unaffected by Ni2+. Dopamine enhanced the peak ICa in the pyloric constrictor (PY), lateral pyloric (LP), and inferior cardiac (IC) neurons and reduced peak ICa in the ventricular dilator (VD), pyloric dilator (PD), and anterior burster (AB) neurons. All of these effects, except for the AB, are consistent with DA's excitation or inhibition of firing in the pyloric neurons. Enhancement of ICa in PY and LP neurons and reduction of ICa in VD and PD neurons are also consistent with DA-induced synaptic strength changes via modulation of presynaptic ICa. However, the reduction of ICa in AB suggests that DA's enhancement of AB transmitter release is not directly mediated through presynaptic ICa. ICa in PY and PD neurons was more sensitive to nifedipine block than in AB neurons. In addition, nifedipine blocked DA's effects on ICa in the PY and PD neurons but not in the AB neuron. Thus the contribution of specific calcium channel subtypes carrying the total ICa may vary between pyloric neuron classes, and DA may act on different calcium channel subtypes in the different pyloric neurons.

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Clumping and oscillations in evoked transmitter release at the frog neuromuscular junction.

The Journal of Physiology ◽

10.1113/jphysiol.1978.sp012321 ◽

1978 ◽

Vol 278 (1) ◽

pp. 513-523 ◽

Cited By ~ 26

Author(s):

H Meiri ◽

R Rahamimoff

Keyword(s):

Neuromuscular Junction ◽

Transmitter Release ◽

Frog Neuromuscular Junction ◽

Evoked Transmitter Release

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Calcium From Internal Stores Triggers GABA Release From Retinal Amacrine Cells

Journal of Neurophysiology ◽

10.1152/jn.00604.2005 ◽

2005 ◽

Vol 94 (6) ◽

pp. 4196-4208 ◽

Cited By ~ 24

Author(s):

Ajithkumar Warrier ◽

Salvador Borges ◽

David Dalcino ◽

Cameron Walters ◽

Martin Wilson

Keyword(s):

Transmitter Release ◽

Metabotropic Glutamate Receptor ◽

Amacrine Cell ◽

Ryanodine Receptors ◽

Amacrine Cells ◽

Gaba Release ◽

Voltage Gated ◽

Metabotropic Glutamate ◽

Inositol 1,4,5 Trisphosphate ◽

Evoked Transmitter Release

The Ca2+ that promotes transmitter release is generally thought to enter presynaptic terminals through voltage-gated Ca2+channels. Using electrophysiology and Ca2+ imaging, we show that, in amacrine cell dendrites, at least some of the Ca2+ that triggers transmitter release comes from endoplasmic reticulum Ca2+ stores. We show that both inositol 1,4,5-trisphosphate receptors (IP3Rs) and ryanodine receptors (RyRs) are present in these dendrites and both participate in the elevation of cytoplasmic [Ca2+] during the brief depolarization of a dendrite. Only the Ca2+ released through IP3Rs, however, seems to promote the release of transmitter. Antagonists for the IP3R reduced transmitter release, whereas RyR blockers had no effect. Application of an agonist for metabotropic glutamate receptor, known to liberate Ca2+ from internal stores, enhanced both spontaneous and evoked transmitter release.

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Voltage-gated currents of rabbit A- and B-type horizontal cells in retinal monolayer cultures

Visual Neuroscience ◽

10.1017/s0952523800001711 ◽

1994 ◽

Vol 11 (2) ◽

pp. 369-378 ◽

Cited By ~ 26

Author(s):

Stefan Löhrke ◽

Hans-Dieter Hofmann

Keyword(s):

Single Channel ◽

Ionic Currents ◽

Calcium Currents ◽

Horizontal Cells ◽

Delayed Rectifier ◽

Patch Clamp Recording ◽

Voltage Gated ◽

Monolayer Cultures ◽

Inward Currents

AbstractIn monolayer cultures prepared from immature early postnatal rabbit retina, small populations of neurons can be demonstrated to differentiate into apparently mature A- and B-type horizontal cells. Using wholecell, single-channel, patch-clamp recording techniques, we have analyzed the pattern of voltage-gated conductances expressed by mammalian horizontal cells under these conditions. A total of six different voltage-dependent ionic currents were recorded. Tetrodotoxin-sensitive fast sodium inward currents (INa) were found in 81% of the A-type and 90% of the B-type cells. Inward calcium currents could be demonstrated in all cells tested after blockade of other conductances. Two types of outward potassium currents with properties of the 4–aminopyridine-sensitive transient IA and the tetraethylammonium sensitive delayed rectifier IK, respectively, could be characterized in whole-cell recordings. An inward rectifying potassium current (Ianom) typical for horizontal cells was activated in response to hyperpolarizing voltage steps. These types of currents have also been described in dissociated adult horizontal cells from lower vertebrates and cat. With single-channel recordings on inside-out patches excised from B-type cells, an additional Ca2+-dependent current (IK(Ca)) was observed which, so far, has not been described in horizontal cells developing in situ. Our results demonstrate that cultured rabbit horizontal cells express a set of voltage-gated currents which largely, but not completely, corresponds to that described in situ for horizontal cells of other species. The culture system will allow further investigation of developmental and functional aspects of mammalian horizontal cells.

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Involvement of both L- and N-type voltage-dependent Ca2+ channels in KCl- and veratridine-evoked transmitter release from non-adrenergic, non-cholinergic nerves in the rabbit iris sphincter muscle

Naunyn-Schmiedeberg s Archives of Pharmacology ◽

10.1007/pl00004995 ◽

1997 ◽

Vol 355 (5) ◽

pp. 638-644 ◽

Cited By ~ 9

Author(s):

M. Kageyama ◽

Hiromi Fujita ◽

Katsuhiko Nakata ◽

Eiichi Shirasawa

Keyword(s):

Transmitter Release ◽

Sphincter Muscle ◽

Cholinergic Nerves ◽

Voltage Dependent ◽

Rabbit Iris Sphincter Muscle ◽

Rabbit Iris Sphincter ◽

Ca2 Channels ◽

Evoked Transmitter Release ◽

Rabbit Iris ◽

Iris Sphincter

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Leucomyosuppressin, a novel insect neuropeptide, inhibits evoked transmitter release at the mealworm neuromuscular junction

Neuroscience Letters ◽

10.1016/0304-3940(88)90646-5 ◽

1988 ◽

Vol 95 (1-3) ◽

pp. 137-142 ◽

Cited By ~ 16

Author(s):

Daisuke Yamamoto ◽

Sachiyo Ishikawa ◽

G.Mark Holman ◽

Ronald J. Nachman

Keyword(s):

Neuromuscular Junction ◽

Transmitter Release ◽

Insect Neuropeptide ◽

Evoked Transmitter Release

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Actions of adenosine on spontaneous or evoked transmitter release at the frog neuromuscular junction

Neuroscience Research Supplements ◽

10.1016/0921-8696(90)90818-n ◽

1990 ◽

Vol 11 ◽

pp. S122

Author(s):

Yoriko Takikawa ◽

Noriko Takeuchi

Keyword(s):

Neuromuscular Junction ◽

Transmitter Release ◽

Frog Neuromuscular Junction ◽

Evoked Transmitter Release

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Voltage-gated calcium currents in whole-cell patch-clamped bullfrog dorsal root ganglion cells: effects of cell size and intracellular solutions

Brain Research ◽

10.1016/0006-8993(95)01414-4 ◽

1996 ◽

Vol 711 (1-2) ◽

pp. 138-145 ◽

Cited By ~ 2

Author(s):

A.M. Holohean ◽

C.A. Rodriguez ◽

J.C. Hackman ◽

R.A. Davidoff

Keyword(s):

Dorsal Root Ganglion ◽

Cell Size ◽

Dorsal Root ◽

Ganglion Cells ◽

Calcium Currents ◽

Whole Cell ◽

Voltage Gated ◽

Dorsal Root Ganglion Cells

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

Journal of Neurophysiology ◽

10.1152/jn.1998.80.6.3233 ◽

1998 ◽

Vol 80 (6) ◽

pp. 3233-3246 ◽

Cited By ~ 42

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.

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