Effects of Hypoxia, Hyperbaria and Hyposmosis on Ecto- ATPase Activity in Scorpionfish (Scorpaena porcus L.) Erythrocytes

Resumo

Effects of hypoxic, hyperbaric and hyposmotic exposures on activity of erythrocyte membrane-bound ecto-ATPase were studied in the scorpionfish Scorpaena porcus L. One-hour autogenic hypoxia evoked a drop while longer hypoxia (12, 24 h)–a rise in the enzyme activity. Hyperbaric exposure, irrespective of its duration, evoked the same stimulation of ecto-ATPase activity in vivo. In vitro, instead, hydrostatic pressure caused a significant drop in the enzyme activity. Hyposmosis stimulated ecto-ATPase activity when the medium was diluted to 50% of its basal level, however, a stronger dilution (70%) led to its inhibition. Under hypoxia, changes in ecto-ATPase activity of scorpionfish erythrocytes are, most likely, due to a shift in the hormonal background and the plasma acid–base equilibrium. The reasons behind the activation of erythrocyte ecto-ATPase in response to hyperbaric pressure are obscure. Under in vitro conditions, the direct effect of hyperbaria and hyposmosis on scorpionfish erythrocytes may be due to alterations in characteristics of plasma membrane microviscosity and in the ecto-ATPase conformational state as manifested in fluctuations of enzyme activity during experiments.