Meeting Abstract

P2.20  Friday, Jan. 4  A Comparison of Proglycogen and Macroglycogen in Cardiac, Hepatic, and White Skeletal Muscle Tissue in Male and Female Rainbow Trout (Oncorhynchus mykiss). BOLINGER, MT*; BATTIPROLU, PK; RODNICK, KJ; Idaho State University; Idaho State University; Idaho State University bolimark@isu.edu

While glycogen appears to be an important source of energy in teleost tissues, mammalian studies suggest that glycogen exists in two different pools (proglycogen (PG) and macroglycogen (MG)) that can be distinguished on the basis of their solubility in acid. PG molecules are smaller, protein-associated, and acid-precipitable whereas MG molecules are larger and acid-soluble. Comparative determinations of total tissue glycogen (TG), PG, and MG have not been conducted in teleosts. Our objective was to measure different glycogen pools using acid hydrolysis and enzymatic hydrolysis in cardiac, hepatic, and skeletal muscle tissue from immature rainbow trout of both sexes. Ventricles and livers were sampled from animals anesthetized by a blow to the head followed by freeze clamping the tissue. Due to the rapid activation of glycogenolysis by contraction, white muscle samples were taken from chemically-anesthetized fish. TG was higher in liver (42.3 � 5.0 mg/g) than in ventricle (7.3� 1.1 mg/g) and white muscle (7.2 � 0.9 mg/g). Sex differences were present in cardiac tissue where males had 32% more TG than females. In the three tissues, enzymatic hydrolysis underestimated TG values by 20-55% compared with acid hydrolysis. Using enzymatic hydrolysis, MG was much more abundant than PG in liver (12.3 � 1.2 vs. 3.0 � 0.2 mg/g), but was similar in heart and white muscle, and comparable between sexes. Sex differences in total cardiac glycogen suggest inequalities in glycogen synthesis, degradation, or regulation. Differences in MG vs. PG pools may also facilitate tissue-specific glycogen metabolism and responsiveness to hormones and or contractile activity. Supported by NSF grant IOB-517669.