Carbohydrate metabolism and hepatic zonation in the Atlantic hagfish, Myxine glutinosa liver: effects of hormones

Abstract

Viable Atlantic hagfish (Myxine glutinosa) hepatocytes were isolated from combined or separated large and small lobes and carbohydrate metabolism was studied. Cells had low levels of glycogen (16-30 μmol·g(-1)), and low rates of total glucose production (TGP; 0-480 nmol·h(-1)·g(-1) cells). Lactate flux to glucose (5.5 nmol·h(-1)·g(-1)) and CO2 (76 nmol·h(-1)·g(-1)) was lower than reported values for teleosts, with a low percentage (30%) of the lactate carbon reaching glucose. Insulin significantly increased total glucose production and gluconeogenesis and decreased 6-phosphofructo 1-kinase (PFK-1) activities and glucose oxidation, while glucagon was without effect on any parameter studied. Forskolin significantly increased TGP. Epinephrine (Epi), norepinephrine (NEpi), isoproterenol (Iso), and phenylephrine (Phe) all decreased CO2 production from lactate; propanolol blocked the effects of Epi, NEpi, and Iso. The large lobe, accounting for 65% of total liver mass, had a higher glycogen content and higher CO2 production from lactate compared to the small lobe. Furthermore, enzyme activities in the large lobe were greater than in the small lobe, with the exception of glycogen phosphorylase (GPase) which exhibited smaller %a values in the large lobe. These data indicate the presence of a hormonally-responsive carbohydrate metabolism in hagfish hepatocytes, which is qualitatively and quantitatively different between the two liver lobes.