Mitochondrial cAMP exerts positive feedback on mitochondrial Ca(2+) uptake via the recruitment of Epac

Abstract

We have previously demonstrated in H295R adrenocortical cells that the Ca(2+)-dependent production of intramitochondrial cAMP (mt-cAMP) by the matrix soluble adenylyl cyclase (sAC) is associated with enhanced aldosterone production. Now we examined whether mitochondrial sAC and mt-cAMP fine-tune mitochondrial Ca(2+) metabolism to support steroidogenesis. Reduction of mt-cAMP formation resulted in decelerated mitochondrial Ca(2+) accumulation in intact cells during K(+)-induced Ca(2+) signalling and also in permeabilised cells exposed to elevated perimitochondrial [Ca(2+)]. Conversely, the membrane-permeable 8-Br-cAMP, inhibition of phosphodiesterase 2 and overexpression of sAC in the mitochondrial matrix all intensified Ca(2+) uptake into the organelle. Identical mt-cAMP dependence of mitochondrial Ca(2+) uptake was observed in HeLa cells as well. Importantly, the enhancing effect of mt-cAMP on Ca(2+) uptake was independent from both the mitochondrial membrane potential and Ca(2+) efflux but was reduced by Epac1 blockade both in intact and in permeabilised cells. Finally, overexpression of sAC in the mitochondrial matrix potentiated aldosterone production implying that the observed positive feedback mechanism of mt-cAMP on mitochondrial Ca(2+) accumulation may have a role in the rapid initiation of steroidogenesis.