Adaptation to salinity by fish: Alterations in energy transducing status of muscle mitochondria

The adaptation to salinity: protein synthesis and some aspects of energy transduction in fish gill mitochondria

Exposure of freshwater fish to saline conditions brings about somewhat drastic changes in the mitochondrial energy metabolism. These include abolition of oxidative phosphorylation, ATP-induced contraction of swollen mitochondria and transhydrogenase activity. On the other hand the endogenous calcium levels and protein synthetic capacity are elevated. In vitro protein synthesis by mitochondria from freshwater and stressed fish shows qualitative and quantitative variations. Effluxing the excess calcium by treatment with NaCl or inhibiting the protein synthesis by chloramphenicol in stressed mitochondria restores almost all the functions. It is proposed that the energy potential formed by the mitochondrial membrane is channelized to perform different functions and that the ratio of channelization can be altered to suit the needs of the cell.

Salinity adaptation in fish: effect of thyroxine on mitochondrial status

Upon transfer of the fresh-water fish, Sarotherodon mossambicus, to 50% sea water, extensive changes take place in the functions of the gill mitochondria. The changes are (i) loss of ADP/O and RCI; (ii) loss of the ability to contract upon addition of ATP-Mg2+; (iii) lowered energy-dependent 45Ca uptake; (iv) increased amino acid incorporation capacity; (v) increased adenine nucleotide content; and (vi) a higher endogenous Ca2+ content. Administration of thyroxine to the fish reversed these changes, and the effect of thyroxine was also not transient. It is suggested that thyroxine promotes mitochondriogenesis, thereby effecting a restoration of the stress-affected mitochondrial functions.