Digitonin perfusion in the study of metabolic zonation of the rat liver: potassium as an intracellular concentration reference.

The mammalian liver microcirculation seems to be uniquely organized in order to create maximum difference of the biochemical milieu to which the upstream (periportal) and downstream (perivenous) parenchymal cells are exposed. Indeed the existence of a subdivision of hepatocytes in zones of different metabolic function, long predicted by enzyme zonation studies (for a review, see Jungermann & Katz, 1982), has now been documented in direct studies for gluconeogenesis, urea synthesis and glutamine synthesis (Haussinger. 1983: Quistorff. 1985; Poso et al. 1986; Quistorff rt al., 1986). However, an understanding of the physiological implications of this functional subdivision is still lacking. Since such zonation can be expected to be closely related to the perfusion pattern of the liver, a technique which utilizes the direction of liver perfusion as the discriminatory principle in the selective study of periportal and perivenous cells would appear to be optimal. The digitonin perfusion technique is based on this principle (Quistorff et af., 1985). The technique has developed in two directions: either for direct use of the eluate in the study of enzyme and metabolite contents of the periportal and the perivenous zone (Quistorff & Grunnet, 1987) or using the digitonin perfusion for selective destruction of part of the microcirculation, followed by isolation of hepatocytes from the non-affected part by standard collagenase perfusion techniques (Lindros & Penttila. 1985; Quistorff, 1985; Quistorff et af., 1986). This paper discusses the mode of action of the digitonin perfusion and also introduces K + as a reference substance, allowing estimation of enzyme activity distribution within the microcirculatory unit of the liver as well as intracellular concentrations of cytosolic metabolites.