Comparison of voltage-dependent 45Ca2+ uptake rates by synaptosomes isolated from rat brain regions.

45Ca2+ uptake by synaptosomes isolated from cerebral cortex, cerebellum, midbrain, and brain stem of male Sprague-Dawley rats was measured at 1-, 3-, 5-, 15-, 30-, and 60-s time periods. The fastest rate of depolarization-dependent calcium uptake occurred in each brain region between 0 and 1 s. Uptake rates dropped off quickly with 3-5-s rates at approximately 15-20% of those observed at 0-1 s in cerebral cortex, cerebellum, and midbrain. Uptake rates at the 1-3-s interval were maintained at a relatively high rate in these three brain regions suggesting mixed fast- and slow-phase processes. The magnitude and rate of 45Ca2+ uptake were similar in synaptosomes from cerebral cortex, cerebellum, and midbrain but were significantly less in brain stem synaptosomes. These results suggest a fast and a slow component to voltage-dependent 45Ca2+ uptake by presynaptic nerve terminals from various brain regions.