Adenine nucleotides regulate Ca2+ transport in brain mitochondria.

Adenine nucleotides (ADP greater than ATP) greatly enhance Ca2+ uptake and retention in rat brain mitochondria. In the presence of both spermine and ADP, brain mitochondria sequester Ca2+ down to cellular free Ca2+ levels, suggesting a role for mitochondria in modulating Ca2+ cycles in brain cells. Analysis of the effects of various inhibitors on Ca2+ uptake and efflux suggest that locking the ADP/ATP translocator in its M-state stimulates electrogenic Ca2+ uptake and, to a lesser extent, inhibits Ca2+ efflux. It is suggested that this effect is due to a modulation of the surface charge on the M-side which enhances Ca2+ dissociation from the carriers.