Relation between mitochondrial swelling induced by inorganic phosphate and accumulation of P³² in mitochondrial Pi fraction

1. Rat liver mitochondria are swollen by inorganic phosphate in the medium of slightly hypotonic sucrose solution containing respiratory substrate and the mitochondrial swelling is inhibited or turned to shrink by ADP, respiratory inhibitor, anaerobiosis and uncoupler of oxidative phosphorylation. This mitochondrial swelling is not inhibited by the inhibitor of phosphorylating respiration such as oligomycin and tributyltin chloride. 2. Rat liver mitochondria are swollen by ATP in the presence of antimycin A, inorganic phosphate and 0.1 mM of CaCl2 and such a swelling is inhibited by oligomycin. 3. Accumulation of a small amont of P³² in acid soluble Pi fraction of rat liver mitochondria proceeds even in the medium containing neither ATP nor Ca++ but is inhibited by respiratory inhibitor, ATP, ADP and uncoupler of oxidative phosphorylation. The accumulation of P³² in mitochondria, however, is not inhibited by oligomycin. 4. The accumulation of P³² is induced by ATP in the presence of antimycin A and Ca++(O.l mM) and such an accumulation of P³² is inhibited by oligomycin. 5. It is suggested that the Pi-induced swelling of mitochondria is correlated to the accumulation of inorganic phosphate and both of them are tightly coupled to the initial step in the process of oxidative phosphoryaltion.