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 language||English (US)|
|Number of pages||6|
|Journal||Journal of Neurochemistry|
|State||Published - Mar 1983|
All Science Journal Classification (ASJC) codes
- Cellular and Molecular Neuroscience