Enzymes of cardiac energy metabolism in Amazonian teleosts and the fresh-water stingray (Potamotrygon hystrix)

Abstract

The maximal in vitro activity of key enzymes of energy metabolism was determined in heart from three Amazonian teleosts, matrinchã (Brycon cephalus), acará açu (Astronotus ocellatus), and tambaqui (Collossoma macropomum), as well as an elasmobranch, the fresh-water stingray (Potamotrygon hystrix). All species are obligate water breathers. Hearts of Amazonian teleosts have activity levels of the glycolytic enzymes hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), and lactate dehydrogenase (LDH) similar to north temperate and Antarctic species when comparisons are made within the usual body temperature range. In contrast, activity level of enzymes required for aerobic oxidation of fatty acids, citrate synthase (CS), carnitine palmitoyl transferase (CPT), and 3-hydroxyacyl CoA dehydrogenase (HOAD) were all substantially lower in the Amazonian teleosts compared to other teleosts. The enzyme profile suggests that 1) activity levels of enzymes of carbohydrate metabolism are conserved over a wide range of body temperatures, and 2) Amazonian teleosts have a much greater reliance upon anaerobic metabolism from glucose than aerobic metabolism to sustain energy production. The heart of fresh-water stingray has high levels of CS, HK, PFK, and PK, implying an aerobic metabolism which is glucose based. In contrast to marine elasmobranchs, the fresh-water stingray has detectable levels of CPT and HOAD, suggestive of a capacity for low-level fatty acid catabolism. As such, the inability of muscle of marine elasmobranchs to utilize fatty acids as an energy source may not be a common feature of all elasmobranchs. © 1996 Wiley-Liss, Inc.