CONTROL OF KEY CARBOHYDRATE-METABOLIZING ENZYMES BY INSULIN AND GLUCAGON IN FRESHLY ISOLATED HEPATOCYTES OF THE MARINE TELEOST HEMITRIPTERUS-AMERICANUS

The effects of scombroid insulin (10−7 M) and bovine glucagon (10−7 M) on key regulatory enzymes of glycolysis and gluconeogenesis are examined in freshly isolated hepatocytes of the sea raven, Hemitripterus americanus, following a 45 and 180 min incubation. Glucagon increased the Vopt of PEPCK, PK, GPT, and LDH, but decreased the substrate activity ratios of both PK and PFK‐1 (the latter only at inhibitory ATP concentrations) at 180 min. Glucagon also decreased Fru‐2,6‐P2 levels at both 45 and 180 min. Insulin decreased the Vopt for LDH at 180 min and decreased the F6P activity ratio for PFK‐1 at both 0.5 mM and 1.5 mM ATP at 45 and 180 min, with larger decreases occurring at the later time period (to 13% of the control value). Insulin also decreased Fru‐2,6‐P2 concentrations at 180 min and increased alanine uptake. PEPCK and PK were not affected by insulin. These data indicate that glucagon alters the characteristics of a variety of enzymes in the glycolytic/gluconeogenic sequence, while the major impact of insulin is at the level of PFK‐1 and alanine uptake. Copyright © 1990 Wiley‐Liss, Inc., A Wiley Company