Mitochondrial cAMP exerts positive feedback on mitochondrial Ca2+ uptake via the recruitment of Epac1

Abstract

We have previously demonstrated in H295R adrenocortical cells that the Ca2+-dependent production of mitochondrial cAMP (mt-cAMP) by the matrix soluble adenylyl cyclase (sAC; encoded by ADCY10) is associated with enhanced aldosterone production. Here, we examined whether mitochondrial sAC and mt-cAMP fine tune mitochondrial Ca2+ metabolism to support steroidogenesis. Reduction of mt-cAMP formation resulted in decelerated mitochondrial Ca2+ accumulation in intact cells during K+-induced Ca2+ signalling and also in permeabilized cells exposed to elevated perimitochondrial [Ca2+]. By contrast, treatment with the membrane-permeable cAMP analogue 8-Br-cAMP, inhibition of phosphodiesterase 2 and overexpression of sAC in the mitochondrial matrix all intensified Ca2+ uptake into the organelle. Identical mt-cAMP dependence of mitochondrial Ca2+ uptake was also observed in HeLa cells. Importantly, the enhancing effect of mt-cAMP on Ca2+ uptake was independent from both the mitochondrial membrane potential and Ca2+ efflux, but was reduced by Epac1 (also known as RAPGEF3) blockade both in intact and in permeabilized cells. Finally, overexpression of sAC in the mitochondrial matrix potentiated aldosterone production implying that the observed positive feedback mechanism of mt-cAMP on mitochondrial Ca2+ accumulation may have a role in the rapid initiation of steroidogenesis.