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

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 F_OF₁-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 (ANT_M), cytosolic (ANT_C), and pore (ANT_P) 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.