ZUR ENERGIEBEDÜRFTIGEN Ca2+-AKKUMULATION IN MITOCHONDRIEN AUS RATTENHIRN

—(1) The properties of a preparation of functional intact rat brain mitochondria are described and the resulting fraction is enzymatically characterized. (2) These mitochondria are able to accumulate Ca²⁺ in a respiration-dependent reaction without additions of P_i and/or adenine nucleotides. (3) As criteria the increased acidity of the incubation medium accompanying the energy-dependent Ca²⁺ accumulation, its inhibition by rotenon and Antimycin A, the acceleration of respiration and the redox change of the pyridine nucleotides were recorded and Ca²⁺ accumulation by the mitochondria was determined by complexemetric methods. (4) The maximum Ca²⁺ accumulation by rat brain mitochondria amounts to only 25 per cent of that by rat liver mitochondria under similar conditions (on the base per mg protein); after addition of 1 mm -ADP (without P_i) the comparable value was about 50 per cent.