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Prolonged Time Course of Glutamate Release from Nerve Terminals: Relationship Between Stimulus Duration and the Secretory Event
Author(s) -
Turner Timothy J.,
Dunlap Kathleen
Publication year - 1995
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1995.64052022.x
Subject(s) - depolarization , tetrodotoxin , chemistry , biophysics , neuroscience , membrane potential , glutamate receptor , stimulus (psychology) , electrophysiology , current clamp , batrachotoxin , voltage clamp , sodium channel , biology , sodium , biochemistry , receptor , psychology , organic chemistry , psychotherapist
The kinetics of synaptosomal [ 3 H]glutamate release were measured on a subsecond time scale to study the relationship between the length of depolarization and the duration of the secretory event. The time course of release evoked by elevated K + was complex, proceeding for several seconds after a 200‐ms depolarization. We developed a protocol for depolarizing excitable membranes on a millisecond time scale to deliver brief depolarizations, termed the synthetic action potential, by using batrachotoxin to activate Na + channels. Depolarization is achieved by superfusing with solutions containing elevated concentrations of Na + , and the duration of the depolarization is limited by including tetrodotoxin (TTX) in the superfusion solution to block Na + entry. Direct measurements of the time courses of Na + current and membrane depolarizations were made in batrachotoxin‐treated sensory neurons using patch clamp recording methods. Rapid increases in Na + and TTX concentrations produced transient increases in inward Na + current that decayed with a time course proportional to TTX concentration. Current clamp measurements indicated that, with 10 µ M TTX, depolarizations last ∼30 ms. Nonetheless, synaptosomal release of [ 3 H]glutamate triggered by the synthetic action potential remained prolonged. Brief neuronal action potentials at some synapses may trigger transmitter release that persists for several seconds.