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Omega-conotoxin does not block the verapamil-sensitive calcium channels at mouse motor nerve terminals
1Department of Physiology and Pharmacology, University of Strathclyde, Glasgow, U.K.
Abstract:
Release of acetylcholine at the neuromuscular junctions of skeletal muscle is not sensitive to organic Ca2+ channel blockers. However, in mouse motor nerve endings, extracellular recording reveals that a verapamil-sensitive Ca2+ current can be induced after block of K+ channels. Recordings of extracellular action potentials from inside the perineural sheaths of nerves innervating mouse triangularis sterni muscles reveal that this verapamil-sensitive current is not blocked by omega-conotoxin, and hence, it does not involve channels similar to the L-channels of neuronal cell bodies.
Insights
Skeletal muscle acetylcholine release is insensitive to calcium channel blockers. However, mouse motor nerve endings show a verapamil-sensitive calcium current, distinct from neuronal L-channels, after potassium channel blockade.
Area of Science:
- Neuroscience
- Pharmacology
- Muscle Physiology
Background:
- Acetylcholine release at neuromuscular junctions is crucial for muscle contraction.
- Organic calcium channel blockers typically do not affect this process.
- Understanding calcium currents in motor nerve endings is key to neuromuscular function.
Purpose of the Study:
- To investigate the presence and characteristics of calcium currents in mouse motor nerve endings.
- To determine the sensitivity of these currents to specific blockers like verapamil and omega-conotoxin.
- To differentiate these currents from known neuronal calcium channels.
Main Methods:
- Extracellular recordings from mouse motor nerve endings.
- Induction of calcium currents after potassium channel blockade.
- Application of verapamil and omega-conotoxin to assess channel sensitivity.
- Extracellular action potential recordings within nerve sheaths.
Main Results:
- A verapamil-sensitive calcium current was successfully induced in mouse motor nerve endings after potassium channel block.
- This verapamil-sensitive current was not inhibited by omega-conotoxin.
- The findings suggest the current does not involve channels homologous to neuronal L-type calcium channels.
Conclusions:
- Mouse motor nerve endings possess a unique verapamil-sensitive calcium current.
- This current is pharmacologically distinct from neuronal L-channels.
- The identified calcium current may play a role in regulating neurotransmitter release at the neuromuscular junction.