scholarly journals Interaction between Calcium Chelators and the Activity of P2X7 Receptors in Mouse Motor Synapses

2020 ◽  
Vol 21 (6) ◽  
pp. 2034 ◽  
Author(s):  
Anna Miteva ◽  
Alexander Gaydukov ◽  
Olga Balezina
Keyword(s):  
Neuromuscular Junctions ◽  
Motor Nerve ◽  
Control Level ◽  
Nerve Terminals ◽  
Quantal Content ◽  
Ach Release ◽  
P2x7 Receptors ◽  
Motor Nerve Terminals ◽  
Pannexin 1 ◽  
End Plate

The ability of P2X7 receptors to potentiate rhythmically evoked acetylcholine (ACh) release through Ca2+ entry via P2X7 receptors and via L-type voltage-dependent Ca2+ channels (VDCCs) was compared by loading Ca2+ chelators into motor nerve terminals. Neuromuscular preparations of the diaphragms of wild-type (WT) mice and pannexin-1 knockout (Panx1−/−) mice, in which ACh release is potentiated by the disinhibition of the L-type VDCCs upon the activation of P2X7 receptors, were used. Miniature end-plate potentials (MEPPs) and evoked end-plate potentials (EPPs) were recorded when the motor terminals were loaded with slow or fast Ca2+ chelators (EGTA-AM or BAPTA-AM, respectively, 50 μM). In WT and Panx1−/− mice, EGTA-AM did not change either spontaneous or evoked ACh release, while BAPTA-AM inhibited synaptic transmission by suppressing the quantal content of EPPs throughout the course of the short rhythmic train (50 Hz, 1 s). In the motor synapses of either WT or Panx1−/− mice in the presence of BAPTA-AM, the activation of P2X7 receptors by BzATP (30 μM) returned the EPP quantal content to the control level. In the neuromuscular junctions (NMJs) of Panx1−/− mice, EGTA-AM completely prevented the BzATP-induced increase in EPP quantal content. After Panx1−/− NMJs were treated with BAPTA-AM, BzATP lost its ability to enhance the EPP quantal content to above the control level. Nitrendipine (1 μM), an inhibitor of L-type VDCCs, was unable to prevent this BzATP-induced enhancement of EPP quantal content to the control level. We propose that the activation of P2X7 receptors may provide additional Ca2+ entry into motor nerve terminals, which, independent of the modulation of L-type VDCC activity, can partially reduce the buffering capacity of Ca2+ chelators, thereby providing sufficient Ca2+ signals for ACh secretion at the control level. However, the activity of both Ca2+ chelators was sufficient to eliminate Ca2+ entry via L-type VDCCs activated by P2X7 receptors and increase the EPP quantal content in the NMJs of Panx1−/− mice to above the control level.

Propagation of electric activity in motor nerve terminals

1965 ◽  
Vol 161 (985) ◽  
pp. 453-482 ◽  
Keyword(s):  
Motor Nerve ◽  
Electric Activity ◽  
Muscle Fibres ◽  
Nerve Terminals ◽  
Terminal Branch ◽  
Direct Stimulation ◽  
Motor Nerve Terminals ◽  
End Plate ◽  
Synaptic Terminals ◽  
Set Up

External micro-electrodes were used to stimulate non-myelinated motor nerve terminals and to record pre- and post-synaptic responses at the neuromuscular junction of the frog. The synaptic terminals of the motor axon are electrically excitable. Antidromic nerve impulses can be set up by local stimulation of terminals along the greater part of their length. Presynaptic spikes can be recorded from the non-myelinated terminal parts of motor axons. As the impulse proceeds towards the tip of the terminal branch, the shape of the spike changes from a predominantly negative to a predominantly positive-going wave. Similar changes occur in muscle fibres near their tendon junctions, and can be attributed to the special local-circuit conditions at the ‘closed end’ of a fibre. The velocity of impulse propagation in motor nerve endings was determined by three different methods: ( a ) from the latency of antidromic nerve spikes elicited at different points along terminals, ( b ) from two-point recording of spikes along a terminal, ( c ) from the differential latency of focal end-plate potentials recorded at two spots of a myoneural junction. The average velocity obtained by these methods was approximately 0.3 m/s at 20 °C. Extracellular muscle fibre spikes recorded at junctional spots showed no significant differences from those recorded elsewhere, provided the spikes were initiated by direct stimulation and did not coincide with transmitter action. Direct current polarization produces a graded increase in frequency of miniature end-plate potentials when the endings are being depolarized, and sudden high-frequency bursts during excessive hyperpolarization. External two-point recording shows that these bursts arise independently at different spots of the synaptic terminals.

scholarly journals Confocal Endomicroscopy of Neuromuscular Junctions Stained with Physiologically Inert Protein Fragments of Tetanus Toxin

Biomolecules ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1499
Author(s):  
Cornelia Roesl ◽  
Elizabeth R. Evans ◽  
Kosala N. Dissanayake ◽  
Veronika Boczonadi ◽  
Ross A. Jones ◽  
...  
Keyword(s):  
Tetanus Toxin ◽  
Neuromuscular Junctions ◽  
Motor Nerve ◽  
Full Length ◽  
Nerve Terminals ◽  
Motor Nerve Terminals ◽  
Mouse Muscle ◽  
Confocal Endomicroscopy ◽  
Derivatives Of

Live imaging of neuromuscular junctions (NMJs) in situ has been constrained by the suitability of ligands for inert vital staining of motor nerve terminals. Here, we constructed several truncated derivatives of the tetanus toxin C-fragment (TetC) fused with Emerald Fluorescent Protein (emGFP). Four constructs, namely full length emGFP-TetC (emGFP-865:TetC) or truncations comprising amino acids 1066–1315 (emGFP-1066:TetC), 1093–1315 (emGFP-1093:TetC) and 1109–1315 (emGFP-1109:TetC), produced selective, high-contrast staining of motor nerve terminals in rodent or human muscle explants. Isometric tension and intracellular recordings of endplate potentials from mouse muscles indicated that neither full-length nor truncated emGFP-TetC constructs significantly impaired NMJ function or transmission. Motor nerve terminals stained with emGFP-TetC constructs were readily visualised in situ or in isolated preparations using fibre-optic confocal endomicroscopy (CEM). emGFP-TetC derivatives and CEM also visualised regenerated NMJs. Dual-waveband CEM imaging of preparations co-stained with fluorescent emGFP-TetC constructs and Alexa647-α-bungarotoxin resolved innervated from denervated NMJs in axotomized WldS mouse muscle and degenerating NMJs in transgenic SOD1G93A mouse muscle. Our findings highlight the region of the TetC fragment required for selective binding and visualisation of motor nerve terminals and show that fluorescent derivatives of TetC are suitable for in situ morphological and physiological characterisation of healthy, injured and diseased NMJs.

Sign in / Sign up

Export Citation Format

Share Document