Regional differences in the activation of synaptosomal mitochondrial Ca2+ 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.