Comparative Biochemistry and Physiology Part A 119 (1998) 999 – 1007 Glucose, pyruvate and lactate efflux by the perfused liver of a teleost, Clarias batrachus during aniso-osmotic exposure Carina Goswami, Nirmalendu Saha * Department of Zoology, Biochemical Adaptation Laboratory, North -Eastern Hill Uniersity, Shillong -793022, India Received 28 January 1997; received in revised form 17 December 1997; accepted 22 December 1997 Abstract Glucose, lactate and pyruvate efflux by the perfused liver of the walking catfish, Clarias batrachus was studied during aniso-osmotic exposure. During hypo-osmotic exposure ( -80 mOsmol l -1 , maintained with NaCl), glucose, lactate and pyruvate efflux by the perfused liver significantly decreased by 55, 19 and 16%, respectively. During hyper-osmotic exposure ( +80 mOsmol l -1 , maintained with NaCl), efflux increased by 57, 12 and 18%, respectively. Similar effects of glucose, lactate and pyruvate efflux by the perfused liver was also seen when the anisotonicity of the medium was adjusted with mannitol instead of NaCl. The decrease of glucose, lactate and pyruvate efflux during hypo-osmotic exposure was correlated with the stimulation of glycogen synthesis and the reverse was true during hyper-osmotic exposure. These observations were supported by changes in glycogen phosphorylase a (GPase a ) and glycogen synthase a (GSase a ) activities. During hypo-osmotic exposure ( -80 mOsmol l -1 ), the GPase a activity decreased by 1.93 fold and GSase a activity increased by 1.63 fold, while during hyper-osmotic exposure ( +80 mOsmol l -1 ), the GPase a activity increased by 1.58 fold and GSase a activity decreased by 1.95 fold. The total activity of both the enzymes were not effected by a short term exposure to aniso-osmotic conditions, suggesting that the alterations in GPase a and GSase a activity were mainly due to changes of their phosphorylation status during aniso-osmotic exposure. A direct correlation exists between glucose efflux and the hydration status of the perfused liver. These alterations of glucose metabolism are probably necessary by this walking catfish to meet the different energy demand, and also for maintenance of glucose homeostasis under osmotic stress. © 1998 Elsevier Science Inc. All rights reserved. Keywords: Glucose; Pyruvate; Lactate; Glycogen; Carbohydrate metabolism; Glycogen phosphorylase; Glycogen synthase; Perfused liver; Aniso-osmotic conditions; Osmotic stress; Clarias batrachus ; Hydration status 1. Introduction Development of diverse metabolic strategies under various environmental conditions is the key to the evolution of organisms. The success of a group in a particular niche is due to its possessing appropriate adaptational flexibility in the metabolic strategies. Os- molarity change is a major problem faced regularly by various groups of organisms. Maintenance of cell vol- ume is a prerequisite for any living organism to sustain the osmolarity changes faced regularly by the organism either in the environment or within the body. It is a phenomenon which not only occurs in vitro, but also in animal tissue cells in vivo when the organism is an osmoconformer and is subjected to changes in the environment (for review, [13]). Cell volume is frequently being challenged either due to intestinal absorption of water, to various amino acids and metabolites, or to exposure to different osmotic environments especially in case of aquatic animals. When living cells are suddenly exposed to hypo-os- motic media, they initially swell more or less like a perfect osmometers because of water entry, but within minutes retain almost their original volume. This be- haviour is considered regulatory volume decrease * Corresponding author. Fax: +91 364 250076; e-mail: nsaha@ nehus.ren.nic.in 1095-6433/98/$19.00 © 1998 Elsevier Science Inc. All rights reserved. PII S1095-6433(98)00017-8