Metabolism of Isolated Hepatopancreas Cells from the Blue Crab (Callinectes sapidus) under Simulated Postexercise and Hypoxic Conditions

The metabolic fate of lactate (and incidentally alanine) and the occurrence and importance of gluconeogenic processes in the hepatopancreas in Crustacea are still controversial. The use of isolated cells seemed appropriate to address this problem more directly. Cells isolated from the hepatopancreas of blue crabs, Callinectes sapidus, were suspended in solutions reproducing as closely as possible actual in vivo acid-base and respiratory conditions during four different situations: control (C, pH = 7.6, CO₂ = 0.25%, O₂ = 21%, [L-lac] = 0.5 mM, [Ala] = 0.5 mM), hypoxia (H, pH = 7.9, CO₂ = 0.1%, O₂= 2%, [L-lac] = 0.5 mM, [Ala] = 0.5 mM), postexercise (E, pH = 7.2, CO₂ = 1%, O₂= 21%, [L-lac] = 15 mM, [Ala] = 5 mM), and recovery (R, pH = 7.6, CO₂ = 0.25%, O₂= 21%, [L-lac] = 5 mM, [Ala] = 5 mM). We measured the production of CO₂ and glucose from 14C-lactate and 14C-alanine and the production of CO₂ from 14C-glucose. Carbon dioxide production from lactate was low in C (0.11 μmol · g⁻¹ · h⁻¹) and H (0.05 μmol · g⁻¹ · h⁻¹) conditions but increased dramatically in E (0.41 μmol · g⁻¹ · h⁻¹) and R (0.45 μmol · g⁻¹ · h⁻¹) conditions. Similar trends, but with lower rates, were found for CO₂ production from alanine. Glucose synthesis from lactate was detected in E conditions (0.061 μmol · g⁻¹ · h⁻¹), but no glucose was synthesized from alanine. We discuss these results with our previous findings on enzymatic activities in the hepatopancreas, and we conclude that hepatopancreas must have a definite but moderate role in the removal of lactate after exercise in the blue crab.