Regulation of citrate transport and pyruvate dehydrogenase in rat kidney cortex mitochondria by bicarbonate.

1. Bicarbonate increased citrate and 2-oxoglutarate accumulation when rat kidney cortex mitochondria were incubated with pyruvate or L(-)-palmitoyl carnitine in the presence of L-malate. 2. Bicarbonate stimulated the exit of citrate from mitochondria. The Km for bicarbonate was 13.5 mM and the Vmax was 0.59 nmol/min/mg of protein at 10 degrees. 3. The bicarbonate-stimulated exit of citrate from the mitochondria was prevented by inhibitors of the tricarboxylate, dicarboxylate, and phosphate transport systems. 4. The activity of pyruvate dehydrogenase was significantly increased by preincubation of rat kidney mitochondria with bicarbonate. This bicarbonate-induced activation was not observed in presence of inhibitors of citrate transport. Bicarbonate did not activate pyruvate dehydrogenase in rat heart mitochondria. Bicarbonate had no effect on pyruvate dehydrogenase activity in either broken mitochondria or whole tissue preparations. 5. The mechanism of this activation is discussed in the light of the known regulatory properties of pyruvate dehydrogenase, pyruvate carboxylase, and citrate synthase.