Ca 2+ Storage Capacity of Rat Brain Mitochondria Declines During the Postnatal Development Without Change in ROS Production Capacity

Ca²⁺ overload of mitochondria and oxidants are considered as crucial factors inducing the opening of the permeability transition pore (PTP) in mitochondria. The interdependence between permeability transition (PT), calcium retention capacity (CRC), and reactive oxygen species (ROS) generation was studied in mitochondria from immature and mature rat brain. Brain mitochondria isolated from 1-day- and 1-week-old rats are much more resistant to Ca²⁺-triggered PT in phosphate-containing incubation medium than mitochondria from adult brain, since the CRC decreases with development. CRC of mitochondria from 1-week-old rat brain was higher than for adult rat brain (450 ± 112 vs. 175 ± 35 nmol Ca²⁺ per mg of protein). In contrast, for ROS generation there was no age difference. In immature and mature mitochondria, basal, respiratory chain-inhibited or glutathione-depleted ROS generations were similar. In addition, the extent of the Ca²⁺ load was without effect on the basal ROS generation before mitochondria underwent PT. In summary, ROS generation does not crucially affect the ability of immature mitochondria to buffer high levels of extramitochondrial Ca²⁺ without undergoing PT. However, we hypothesize that the high resistance of immature mitochondria is related to the low content of some PTP complex constituents, such as creatine kinase.