INOSITOL PENTAPHOSPHATE IN THE ERYTHROCYTES OF AN AMAZONIAN FISH, THE PIRARUCU (ARAPAIMA GIGAS)

During the Alpha Helix expeditions to the rivers of the Amazon basin, inositol pentaphosphate (IPP) was detected in the erythrocytes of Arapaima gigas. We analyzed the intraerythrocytic phosphate levels of A. gigas specimens during the first year of life in captivity. IPP increased slowly during the first year, stabilizing at around 7 mM when the animals reached 1 - 1.5 m in length. ATP and GTP concentrations decreased in parallel. Wild animals within the same size range showed similar intraerythrocytic IPP levels. These changes represent qualitative and quantitative adjustments of the principal modulators of hemoglobin-oxygen affinity in the erythrocytes of A. gigas. These temporal changes seem to play an important physiological role, since this species changes its respiratory habit from aquatic respiration to obligatory air breathing, when it uses a modified swim bladder.