Comparison of Voltage-Dependent45Ca2+Uptake Rates by Synaptosomes Isolated from Rat Brain Regions

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Abstract
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.