Regional differences in the activation of synaptosomal mitochondrial Ca uptake by spermine in rat brain

Several properties of Ca²⁺ uptake by isolated synaptosomal mitochondria were characterized by using a repetitive Ca²⁺ loading technique. Synaptosomal mitochondria maintained extramitochondrial Ca²⁺ concentration at submicromolar levels when challenged with successive additions of small amounts of Ca²⁺. Ca²⁺ uptake under these conditions was markedly stimulated by the presence of spermine, a polyamine found in high concentrations in brain. Moreover, mitochondria isolated from telencephalic areas of rat brain were activated to a greater extent by spermine than were mitochondria from non-telencephalic brain regions. The present results support the idea that brain mitochondria could play a significant role in limiting the intraneuronal rise in Ca²⁺ that follows stimulation or injury. In addition, telencephalic mitochondria exhibit more flexibility in the regulation of Ca²⁺ uptake than do mitochondria from phylogenetically older non-telencephalic brain regions and this could be related to differences in Ca²⁺ influx mechanisms in these brain regions.