QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Mommsen, T. Articles by Walsh, P. Search for Related Content PubMed Articles by Mommsen, T. Articles by Walsh, P.

Journal of Experimental Biology, Vol 156, Issue 1 407-418, Copyright © 1991 by Company of Biologists

JOURNAL ARTICLES

Metabolic and enzymatic heterogeneity in the liver of the ureogenic teleost Opsanus beta

TP Mommsen and PJ Walsh
Department of Biochemistry and Microbiology, University of Victoria, BC, Canada.

Viable toadfish hepatocytes were separated into distinct subpopulations by gradient centrifugation. Although 3-5 density subpopulations were obtained for each fish, only two metabolically and enzymatically different subpopulations could be discerned. In all cases, hepatocytes with the lowest density (less than 1.040 g ml-1) were more oxidative in scope, as judged by the activities of mitochondrial enzymes (citrate synthase, aspartate aminotransferase, glutamate dehydrogenase); activities of these enzymes (normalised to cell protein) were on average two- to threefold higher than in subpopulations with higher densities. Lower-density hepatocytes also contained higher levels of the urea cycle enzymes arginase and ornithine carbamoyltransferase. The higher-density subpopulations showed no significant differences from each other in enzymatic activities. Compared with lower-density cells, these hepatocytes had higher activities of two cytosolic enzymes, malate dehydrogenase and glutathione-S-transferase. There was no distinct distribution pattern for alanine aminotransferase and glutamine synthetase. Despite generally lower oxidative enzyme content, higher-density hepatocytes were metabolically more active, with 2.5- to fourfold higher rates of urea synthesis, gluconeogenesis and oxidation of lactate. We conclude that, although the toadfish liver shows distinct enzymatic and metabolic heterogeneity, this heterogeneity is dissimilar to the zonation pattern in the livers of mammals, in that separated toadfish hepatocyte types did not appear to possess exclusive metabolic functions. Notably, all cells were capable of metabolic functions that are strictly localised in mammalian liver. In nitrogen metabolism, glutamine synthetase displays a distribution pattern commensurate with its unique metabolic function in the liver of the ureogenic toadfish. Further, all subpopulations possessed detoxification capabilities as indicated by high levels of glutathione-S-transferase, a 'phase II' conjugation enzyme.

This article has been cited by other articles:

				J. F. Barimo, S. L. Steele, P. A. Wright, and P. J. Walsh Dogmas and controversies in the handling of nitrogenous wastes: Ureotely and ammonia tolerance in early life stages of the gulf toadfish, Opsanus beta J. Exp. Biol., May 15, 2004; 207(12): 2011 - 2020. [Abstract] [Full Text] [PDF]