Ecto-ATPase Activity in Goldfish Hepatocytes

Abstract

The present work deals with the identification of Ecto-ATPase (E-ATPase) activity in intact and viable hepatocytes of goldfish and its putative role in cellular energetics under energy-limiting conditions. The hepatocytes of goldfish are an adequate cellular system for this purpose since, on the one hand, they have shown great tolerance to intracellular ATP depletion¹ and also because the well known cytotoxic effect of extracellular ATP on mammalian hepatocytes² is not observed, allowing the incubation of these cells with the nucleotide for extended periods. Additionally, given the fact that goldfish is a known eurythermic species we will use temperature as an experimental variable by: 1) acclimating fish chronically at different temperatures and; 2) exposing isolated hepatocytes to different assay temperatures during the measurement of E-ATPase activity. Exposure of fish or cells to low temperatures produces a depression in the rate of virtually all biological processes, including the various transport mechanisms across the plasma membrane. Nevertheless in the long term several processes are triggered that often compensate for the temperature effect. Thus, given the dynamic responses of membranes to temperature and the fact that liver E-ATPase is an integral membrane protein³, this approach will enable us to learn to what extent E-ATPase activity is involved in the adaptive response of hepatocytes to temperature changes and also to define the temperature dependence of the enzyme.