Subsynaptosomal distribution of calcium during aging and 3,4-diaminopyridine treatment.

Since previous studies showed that calcium uptake by synaptosomes from rodents declines with aging, the subsynaptosomal distribution of calcium was determined with the disruption method of Scott et al. Calcium uptake by the mitochondrial (digitonin-resistant) and non-mitochondrial (digitonin-labile) compartments, as well as total uptake, were determined at 2, 5 and 10 min. After a 10 min incubation under resting conditions (5 mM-KCl), total calcium uptake decreased at 10 months (-14.6%) and 30 months (-33.0%) of age; mitochondrial calcium uptake increased by 10 months (+ 11.2%) but declined by 30 months (-17.5%); the non-mitochondrial calcium compartment declined at 10 (-34.7%) and 30 (-43.4%) months when compared to the 3 month old control. With potassium depolarization (31 mM-KCl), total calcium uptake declined from 100% (3 months) to 73.8% (10 months) or 53.0% (30 months); mitochondrial calcium uptake declined from 100% (3 months) to 85.6% (10 months) or 68.4% (30 months); non-mitochondrial calcium uptake decreased at 10 (-34.3%) and 30 (-57.7%) months of age when compared to 3 months (100%). The deficits in calcium homeostasis are not due to changes in synaptosomal volumes or to diminished membrane potentials, as assessed by tetraphenylphosphonium ion accumulation. 3,4-Diaminopyridine partially reversed the alterations in total, mitochondrial and non-mitochondrial calcium uptake by synaptosomes from aged mice.