Correlation of rates of calcium entry and endogenous dopamine release in mouse striatal synaptosomes

The time course of simultaneous Ca2+ entry and endogenous dopamine release was examined in mouse striatal synaptosomes depolarized by 30 mM KCl. Ca2+ entry and endogenous dopamine release exhibited fast and slow phase processes. The fastest rates occurred between 0 and 1 s. Ca2+ uptake and dopamine release dropped off quickly with 5-15 s rates at 13 and 10%, respectively, of the 0-1 s rate. Both processes were maintained at relatively high rates at the 1-3 and 3-5 s intervals suggesting mixed fast and slow phase processes. Uptake of Ca2+ and release of dopamine occurred in parallel over the entire 30 s measurement period; however, approximately 70% of the Ca2+ uptake and dopamine release occurred within the first 5 s following depolarization. A calculated ratio of Ca2+ entry versus dopamine release showed that approximately 1-2 Ca2+ ions were required to cause the release of one dopamine molecule. This ratio remained constant from 1 to 15 s following depolarization. Our results suggest that Ca2+ entry is coupled to endogenous dopamine release for both the fast and slow phase process.