Mitochondrial FF-ATPase and permeability transition pore response to sulfide in the midgut gland of Mytilus galloprovincialis.

The molecular mechanisms which rule the formation and opening of the mitochondrial permeability transition pore (mPTP), the lethal mechanism which permeabilizes mitochondria to water and solutes and drives the cell to death, are still unclear and particularly little investigated in invertebrates. Since Ca increase in mitochondria is accompanied by mPTP opening and the participation of the mitochondrial FF-ATPase in the mPTP is increasingly sustained, the substitution of the natural cofactor Mg by Ca in the FF-ATPase activation has been involved in the mPTP mechanism. In mussel midgut gland mitochondria the similar kinetic properties of the Mg- or Ca-dependent FF-ATPase activities, namely the same affinity for ATP and bi-site activation kinetics by the ATP substrate, in spite of the higher enzyme activity and coupling efficiency of the Mg-dependent FF-ATPase, suggest that both enzyme activities are involved in the bioenergetic machinery. Other than being a mitochondrial poison and environmental contaminant, sulfide at low concentrations acts as gaseous mediator and can induce post-translational modifications of proteins. The sulfide donor NaHS, at micromolar concentrations, does not alter the two FF-ATPase activities, but desensitizes the mPTP to Ca input. Unexpectedly, NaHS, under the conditions tested, points out a chemical refractoriness of both FF-ATPase activities and a failed relationship between the Ca-dependent FF-ATPase and the mPTP in mussels. The findings suggest that mPTP role and regulation may be different in different taxa and that the FF-ATPase insensitivity to NaHS may allow mussels to cope with environmental sulfide.