Abstract 486: Role of the Adenine Nucleotide Translocator Family in the Mitochondrial Permeability Transition Pore

Cardiomyocyte necrosis is dependent on the prolonged opening of the mitochondrial permeability transition pore (MPTP) which has escaped molecular identification for decades. Once thought to be comprised of the adenine nucleotide translocator (ANT) family, this hypothesis has fell by the way side when it was shown that liver mitochondria devoid of ANT 1 and 2 still display MPTP opening, even though these mitochondria were desensitized to MPTP opening and required a greater calcium bolus for it to engage. Thus, the ANT family has been labeled as a critical regulator of the MPTP and not the pore forming component. However, mice express three isoforms of ANT and only two of the three isoforms where deleted when ANTs were deemed to be non-essential. We hypothesize that the third ANT isoform may have compensated for the loss of the other two ANT family members during this analysis. Here, we have generated mice lacking all isoforms of ANT in a heart-, liver-, or cell-specific manner. Surprisingly, mice lacking all isoforms of ANT specifically in the liver are viable and are highly resistant to MPTP opening. Indeed, the amount of calcium required to engage the MPTP in mitochondria lacking all ANTs is 11 fold higher than wild type mitochondria and greater than 2 fold higher than wild type mitochondria treated with the MPTP inhibitor cyclosporine A (CsA). Furthermore, the treatment of CsA on ANT null liver mitochondria completely blocks MPTP opening suggesting that the ANT family is the primary pore in the liver. However, when subjected to extreme levels of calcium, a cyclophilin D (CypD) dependent pore engages. CypD is the MPTP trigger located in the matrix of the mitochondria which is inhibited by CsA and in wild type mitochondria high levels of calcium are enough to overcome the inhibition of CypD to open the pore. But, in ANT depleted liver mitochondria, extremely high levels of calcium do not override CypD inhibition which is suggestive of the presence of an additional pore. Further experimentation is underway to determine if MPTP-conductance is detectable by patch clamping mitoplasts lacking all isoforms of ANT.