Increased Ca2+ influx through Na+/Ca2+ exchanger during long-term facilitation at crayfish neuromuscular junctions

Intense motor neuron activity induces a long-term facilitation (LTF) of synaptic transmission at crayfish neuromuscular junctions (NMJs) that is accompanied by an increase in the accumulation of presynaptic Ca 2+ ions during a test train of action potentials. It is natural to assume that the increas...

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Bibliographic Details
Published in:The Journal of physiology 2007-12, Vol.585 (2), p.413-427
Main Authors: Minami, Akira, Xia, Yan‐fang, Zucker, Robert S.
Format: Article
Language:English
Subjects:
Action Potentials - physiology
Animals
Astacoidea
Calcium - metabolism
Cambaridae
Electric Stimulation
Freshwater
Motor Neurons - physiology
Muscle, Skeletal - innervation
Muscle, Skeletal - physiology
Neuromuscular Junction - physiology
Neuronal Plasticity - physiology
Neuroscience
Sodium - metabolism
Sodium-Calcium Exchanger - physiology
Sodium-Potassium-Exchanging ATPase - physiology
Synaptic Transmission - physiology
Up-Regulation - physiology
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Summary:Intense motor neuron activity induces a long-term facilitation (LTF) of synaptic transmission at crayfish neuromuscular junctions (NMJs) that is accompanied by an increase in the accumulation of presynaptic Ca 2+ ions during a test train of action potentials. It is natural to assume that the increased Ca 2+ influx during action potentials is directly responsible for the increased transmitter release in LTF, especially as the magnitudes of LTF and increased Ca 2+ influx are positively correlated. However, our results indicate that the elevated Ca 2+ entry occurs through the reverse mode operation of presynaptic Na + /Ca 2+ exchangers that are activated by an LTF-inducing tetanus. Inhibition of Na + /Ca 2+ exchange blocks this additional Ca 2+ influx without affecting LTF, showing that LTF is not a consequence of the regulation of these transporters and is not directly related to the increase in [Ca 2+ ] i reached during a train of action potentials. Their correlation is probably due to both being induced independently by the strong [Ca 2+ ] i elevation accompanying LTF-inducing stimuli. Our results reveal a new form of regulation of neuronal Na + /Ca 2+ exchange that does not directly alter the strength of synaptic transmission.
ISSN:0022-3751
1469-7793
DOI:10.1113/jphysiol.2007.143032