Meeting Abstract

98.5  Thursday, Jan. 7  Glucose Inhibition and Temperature Sensitivity of Glycogen Phosphorylase in Rainbow Trout BOLINGER, M.T.*; RODNICK, K.J.; Idaho State University; Idaho State University bolimark@gmail.com

Glycogen is an important endogenous fuel that is mobilized primarily by glycogen phosphorylase (GP). GP is highly regulated and can exist in activated (a) and inactivated (b) forms based on the presence or absence of adenosine monophosphate (AMP). Storage of glycogen and GP activity varies between tissues, and the latter may be influenced by carbohydrate inhibition and temperature. Trout are carnivorous ectotherms that are relatively intolerant of carbohydrate. Our objective was to determine the extent of GP inhibition by glucose and temperature sensitivity in ventricle, liver and white muscle tissue of sexually-immature male and female fish. GP activity was measured spectrophotometrically using glycogen as substrate at 14°C in the presence of glucose (1.25 to 50 mM). To assess thermal sensitivity (Q10), measurements were also carried out at 24°C. At 14°C, GP activity (-AMP) was 50-60% higher in ventricle and white muscle than liver while with AMP it was twice as high in striated muscle than liver. A physiological concentration of intracellular glucose (5 mM) inhibited GP activity (-AMP) by 39, 14, and 3% in white muscle, ventricle, and liver respectively. In contrast, GP activity (+AMP) was inhibited less and uniformly (8-11%) in all three tissues. Based on a Q10 of ~3, GP was quite sensitive to temperature and might limit glycogen use at cold temperatures. In summary, glucose can serve as a potent inhibitor of GP activity in multiple tissues of the rainbow trout and help define glycogen utilization rates. Higher levels of intracellular glucose in trout muscle compared with mammals may increase the importance of other glycogenolytic enzymes. A high temperature sensitivity of GP may also promote glycogen mobilization at higher body temperatures, and the potential loss of glycogen.