Crosstalk between adenine nucleotide transporter and mitochondrial swelling: experimental and computational approaches.

Mitochondrial metabolism and function are modulated by changes in matrix Ca2+. Small increases in the matrix Ca2+ stimulate mitochondrial bioenergetics, whereas excessive Ca2+ leads to cell death by causing massive matrix swelling and impairing the structural and functional integrity of mitochondria. Sustained opening of the non-selective mitochondrial permeability transition pores (PTP) is the main mechanism responsible for mitochondrial Ca2+ overload that leads to mitochondrial dysfunction and cell death. Recent studies suggest the existence of two or more types of PTP, and adenine nucleotide translocator (ANT) and FOF1-ATP synthase were proposed to form the PTP independent of each other. Here, we elucidated the role of ANT in PTP opening by applying both experimental and computational approaches. We first developed and corroborated a detailed model of the ANT transport mechanism including the matrix (ANTM), cytosolic (ANTC), and pore (ANTP) states of the transporter. Then, the ANT model was incorporated into a simple, yet effective, empirical model of mitochondrial bioenergetics to ascertain the point when Ca2+ overload initiates PTP opening via an ANT switch-like mechanism activated by matrix Ca2+ and is inhibited by extra-mitochondrial ADP. We found that encoding a heterogeneous Ca2+ response of at least three types of PTPs, weakly, moderately, and strongly sensitive to Ca2+, enabled the model to simulate Ca2+ release dynamics observed after large boluses were administered to a population of energized cardiac mitochondria. Thus, this study demonstrates the potential role of ANT in PTP gating and proposes a novel mechanism governing the cryptic nature of the PTP phenomenon.