Temporal Characteristics of Potassium‐Stimulated Acetylcholine Release and Inactivation of Calcium Influx in Rat Brain Synaptosomes

J. B. Suszkiw, Michael O'Leary

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Abstract

Abstract: The time course of Ca2+‐dependent [3H]acetylcholine ([3H]ACh) release and inactivation of 45Ca2+ entry were examined in rat brain synaptosomes depolarized by 45 mM [K+]o. Under conditions where the intrasynaptosomal stores of releasable [3H]ACh were neither exhausted nor replenished in the course of stimulation, the K+‐evoked release consisted of a major (40% of the releasable [3H]ACh pool), rapidly terminating phase (t1/2= 17.8 s), and a subsequent, slow efflux that could be detected only during a prolonged, maintained depolarization. The time course of inactivation of K+‐stimulated Ca2+ entry suggests the presence of fast‐inactivating, slow‐inactivating, and noninactivating, or very slowly inactivating, components. The fast‐inactivating component of the K+‐stimulated Ca2+ entry into synaptosomes appears to be responsible for the rapidly terminating phase of transmitter release during the first 60 s of K+ stimulus. The noninactivating Ca2+ entry may account for the slow phase of transmitter release. These results indicate that under conditions of maintained depolarization of synaptosomes by high [K+]o the time course and the amount of transmitter released may be a function of the kinetics of inactivation of the voltage‐dependent Ca channels.

Original languageEnglish (US)
Pages (from-to)868-873
Number of pages6
JournalJournal of Neurochemistry
Volume41
Issue number3
DOIs
StatePublished - Jan 1 1983

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Synaptosomes
Acetylcholine
Rats
Transmitters
Brain
Depolarization
Calcium
Kinetics

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Cellular and Molecular Neuroscience

Cite this

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abstract = "Abstract: The time course of Ca2+‐dependent [3H]acetylcholine ([3H]ACh) release and inactivation of 45Ca2+ entry were examined in rat brain synaptosomes depolarized by 45 mM [K+]o. Under conditions where the intrasynaptosomal stores of releasable [3H]ACh were neither exhausted nor replenished in the course of stimulation, the K+‐evoked release consisted of a major (40{\%} of the releasable [3H]ACh pool), rapidly terminating phase (t1/2= 17.8 s), and a subsequent, slow efflux that could be detected only during a prolonged, maintained depolarization. The time course of inactivation of K+‐stimulated Ca2+ entry suggests the presence of fast‐inactivating, slow‐inactivating, and noninactivating, or very slowly inactivating, components. The fast‐inactivating component of the K+‐stimulated Ca2+ entry into synaptosomes appears to be responsible for the rapidly terminating phase of transmitter release during the first 60 s of K+ stimulus. The noninactivating Ca2+ entry may account for the slow phase of transmitter release. These results indicate that under conditions of maintained depolarization of synaptosomes by high [K+]o the time course and the amount of transmitter released may be a function of the kinetics of inactivation of the voltage‐dependent Ca channels.",
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N2 - Abstract: The time course of Ca2+‐dependent [3H]acetylcholine ([3H]ACh) release and inactivation of 45Ca2+ entry were examined in rat brain synaptosomes depolarized by 45 mM [K+]o. Under conditions where the intrasynaptosomal stores of releasable [3H]ACh were neither exhausted nor replenished in the course of stimulation, the K+‐evoked release consisted of a major (40% of the releasable [3H]ACh pool), rapidly terminating phase (t1/2= 17.8 s), and a subsequent, slow efflux that could be detected only during a prolonged, maintained depolarization. The time course of inactivation of K+‐stimulated Ca2+ entry suggests the presence of fast‐inactivating, slow‐inactivating, and noninactivating, or very slowly inactivating, components. The fast‐inactivating component of the K+‐stimulated Ca2+ entry into synaptosomes appears to be responsible for the rapidly terminating phase of transmitter release during the first 60 s of K+ stimulus. The noninactivating Ca2+ entry may account for the slow phase of transmitter release. These results indicate that under conditions of maintained depolarization of synaptosomes by high [K+]o the time course and the amount of transmitter released may be a function of the kinetics of inactivation of the voltage‐dependent Ca channels.

AB - Abstract: The time course of Ca2+‐dependent [3H]acetylcholine ([3H]ACh) release and inactivation of 45Ca2+ entry were examined in rat brain synaptosomes depolarized by 45 mM [K+]o. Under conditions where the intrasynaptosomal stores of releasable [3H]ACh were neither exhausted nor replenished in the course of stimulation, the K+‐evoked release consisted of a major (40% of the releasable [3H]ACh pool), rapidly terminating phase (t1/2= 17.8 s), and a subsequent, slow efflux that could be detected only during a prolonged, maintained depolarization. The time course of inactivation of K+‐stimulated Ca2+ entry suggests the presence of fast‐inactivating, slow‐inactivating, and noninactivating, or very slowly inactivating, components. The fast‐inactivating component of the K+‐stimulated Ca2+ entry into synaptosomes appears to be responsible for the rapidly terminating phase of transmitter release during the first 60 s of K+ stimulus. The noninactivating Ca2+ entry may account for the slow phase of transmitter release. These results indicate that under conditions of maintained depolarization of synaptosomes by high [K+]o the time course and the amount of transmitter released may be a function of the kinetics of inactivation of the voltage‐dependent Ca channels.

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