MENZE, M.A.*; HUTCHINSON, K.; HAND, S.C.; Louisiana State Univ., Baton Rouge; Louisiana State Univ., Baton Rouge; Louisiana State Univ., Baton Rouge: Lack of a calcium-induced mitochondrial permeability transition in Artemia franciscana during early development.

When mammalian mitochondria are exposed to high calcium in the presence of phosphate, a massive swelling, uncoupling of respiration and release of cytochrome c occur. These changes are mediated by opening of the mitochondrial permeability transition pore (MPTP). Activation of the MPTP in vivo in response to hypoxic and oxidative stress leads to necrotic and apoptotic cell death. Considering that embryos of A. franciscana tolerate anoxia for years, we investigated the MPTP in this crustacean to reveal whether or not pore opening occurs. Minimum molecular constituents of the regulated MPTP in mammals are believed to be the voltage-dependent anion channel (VDAC), the adenine nucleotide translocator (ANT) and cyclophilin D. Western blot analysis revealed that mitochondria from A. franciscana possess all three required components. As expected, when measured with a Ca ²⁺-depended fluorescent probe, rat liver mitochondria release matrix calcium upon addition of 100 &microM extra-mitochondrial Ca²⁺, (indicating MPTP opening), whereas brine shrimp mitochondria continue to take up extra-mitochondrial Ca²⁺ and do not release internal stores even up to 1.0 mM exogenously-added Ca²⁺ (no MPTP opening). Furthermore, swelling of A. franciscana mitochondria in response to added Ca²⁺ was not observed in contrast to the rapid swelling of rat mitochondria after addition of 100 &microM Ca²⁺ as monitored by optical absorbance at 520 nm. While the absence of a functional MPTP in A. franciscana mitochondria could contribute to the extreme hypoxia tolerance in this species, we predict the absence of the MPTP may be a general feature of invertebrates. [NIH grant 1-RO1-GM071345-01 and DARPA grant N00173-01-1-G011].