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 Ca2+ ions during a test train of action potentials. It is natural to assume that the increased Ca2+ influx during action potentials is directly responsible for the increased transmitter release in LTF, especially as the magnitudes of LTF and increased Ca2+ influx are positively correlated. However, our results indicate that the elevated Ca2+ entry occurs through the reverse mode operation of presynaptic Na+/Ca2+ exchangers that are activated by an LTF-inducing tetanus. Inhibition of Na+/Ca2+ exchange blocks this additional Ca2+ 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 [Ca2+]i reached during a train of action potentials. Their correlation is probably due to both being induced independently by the strong [Ca2+]i elevation accompanying LTF-inducing stimuli. Our results reveal a new form of regulation of neuronal Na+/Ca2+ exchange that does not directly alter the strength of synaptic transmission.
Minami
Akira
A
University of California, Molecular and Cell Biology Department, 111 Life Sciences Addition, Berkeley, CA 94720-3200, USA.
Xia
Yan-Fang
YF
Zucker
Robert S
RS
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D003400:Astacoidea; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009469:Neuromuscular Junction / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*; D015854:Up-Regulation / Q000502:physiology
D019831:Sodium-Calcium Exchanger; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium