Mitochondrial permeability transition pore in sea urchin female gametes

Mitochondrial permeability transition pore (MPTP) has been associated to calcium homeostasis and reactive oxygen species (ROS) generation in several cell types. While extensively investigated in somatic cells, there are few data regarding MPTP phenomenon in gametes. The aim of the present work was to investigate MPTP occurrence in sea urchin female gametes. The protonophores CCCP and FCCP, and the Ca²⁺ ionophore ionomycin, were used as pore inductors. Pore opening was monitored by mitochondrial potential sensitive probes and cobalt-quenched calcein assay. The pore desensitizer cyclosporin A (CsA) prevented the loss of mitochondrial inner membrane potential (ΔΨ_m) and pore opening induced by MPTP activators. The disruption of ΔΨ_m led to an increase in ROS generation, which was completely prevented by CsA. Our data also demonstrated that the increase in ROS production induced by MPTP opening requires extracellular Ca²⁺. In summary, the current study provides evidence about the occurrence of MPTP in sea urchin eggs in a similar manner as described in vertebrate somatic cells - CsA-sensitive, voltage- and Ca²⁺-triggered - and shows MPTP as a highly conserved physiological event through the evolution.