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 C-14-lactate and C-14-alanine and the production of CO2 from C-14-glucose. Carbon dioxide production from lactate was low in C (0.11-mu-mol.g-1.h-1) and H( 0.05-mu-mol.g-1.h-1) conditions but increased dramatically in E (0.41-mu-mol.g-1.h-1) and R (0.45-mu-mol.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-mu-mol.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.