α-Latrotoxin Actions in the Absence of Extracellular Ca<sup>2+</sup> Require Release of Stored Ca<sup>2+</sup>
α-Latrotoxin (αLTX) causes exhaustive release of neurotransmitters from nerve terminals in the absence of extracellular Ca<sup>2+</sup> (Ca<sup>2+</sup><sub>e</sub>). To investigate the mechanisms underlying this effect, we loaded mouse neuromuscular junctions wit...
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| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-02-01
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| Series: | Toxins |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2072-6651/17/2/73 |
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| Summary: | α-Latrotoxin (αLTX) causes exhaustive release of neurotransmitters from nerve terminals in the absence of extracellular Ca<sup>2+</sup> (Ca<sup>2+</sup><sub>e</sub>). To investigate the mechanisms underlying this effect, we loaded mouse neuromuscular junctions with BAPTA-AM. This membrane-permeable Ca<sup>2+</sup>-chelator demonstrates that Ca<sup>2+</sup><sub>e</sub>-independent effects of αLTX require an increase in cytosolic Ca<sup>2+</sup> (Ca<sup>2+</sup><sub>cyt</sub>). We also show that thapsigargin, which depletes Ca<sup>2+</sup> stores, induces neurotransmitter release, but inhibits the effect of αLTX. We then studied αLTX’s effects on Ca<sup>2+</sup><sub>cyt</sub> using neuroblastoma cells expressing signaling-capable or signaling-incapable variants of latrophilin-1, a G protein-coupled receptor of αLTX. Our results demonstrate that αLTX acts as a cation ionophore and a latrophilin agonist. In model cells at 0 Ca<sup>2+</sup><sub>e</sub>, αLTX forms membrane pores and allows the influx of Na<sup>+</sup>; this reverses the Na<sup>+</sup>-Ca<sup>2+</sup> exchanger, leading to the release of stored Ca<sup>2+</sup> and inhibition of its extrusion. Concurrently, αLTX stimulates latrophilin signaling, which depletes a Ca<sup>2+</sup> store and induces transient opening of Ca<sup>2+</sup> channels in the plasmalemma that are sensitive to inhibitors of store-operated Ca<sup>2+</sup> entry. These results indicate that Ca<sup>2+</sup> release from intracellular stores and that Ca<sup>2+</sup> influx through latrophilin-activated store-operated Ca<sup>2+</sup> channels contributes to αLTX actions and may be involved in physiological control of neurotransmitter release at nerve terminals. |
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| ISSN: | 2072-6651 |