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Published on: February 20, 2016
Action potentials must admit calcium to evoke transmitter release
1Department of Molecular and Cell Biology, University of California, Berkekey 94720.
Nature
|March 14, 1991
Summary
Neurotransmitter release relies on internal calcium, not just voltage. Elevating internal calcium without influx, even without action potentials, triggered release, supporting the calcium hypothesis for neuronal signaling.
Area of Science:
- Neuroscience
- Cellular Biology
- Neurotransmission
Background:
- Two hypotheses explain neurotransmitter release: the calcium hypothesis and the calcium-voltage hypothesis.
- The calcium hypothesis posits that calcium ions trigger release after depolarization opens channels.
- The calcium-voltage hypothesis suggests depolarization directly triggers release via voltage-induced protein conformational changes in the presence of calcium.
Purpose of the Study:
- To investigate the mechanisms underlying neurotransmitter release at the crayfish neuromuscular junction.
- To differentiate between the calcium hypothesis and the calcium-voltage hypothesis.
Main Methods:
- Calcium influx was blocked using cobalt or manganese ions in a calcium-free Ringer solution.
- Internal calcium concentration ([Ca2+]i) was elevated using a caged calcium compound.
- Transmitter release was measured at the crayfish neuromuscular junction.
- Fura-2 was used to measure intracellular calcium levels.
Main Results:
- When calcium influx was blocked, elevated internal calcium alone was sufficient to cause neurotransmitter release.
- Presynaptic action potentials did not affect transmitter release under these conditions.
- The results indicate that depolarization is not directly required for triggering release when internal calcium is high.
Conclusions:
- The findings strongly support the calcium hypothesis for neurotransmitter release.
- Neuronal signaling mechanisms are primarily driven by intracellular calcium dynamics.
- Voltage-gated calcium channels play a crucial role in initiating the calcium-dependent release process.
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