Hepatic zonation of carbon and nitrogen fluxes derived from glutamine and ammonia transformations

Abstract

BackgroundGlutaminase predominates in periportal hepatocytes and it has been proposed that it determines the glutamine-derived nitrogen flow through the urea cycle. Glutamine-derived urea production should, thus, be considerably faster in periportal hepatocytes. This postulate, based on indirect observations, has not yet been unequivocally demonstrated, making a direct investigation of ureogenesis from glutamine highly desirable.MethodsZonation of glutamine metabolism was investigated in the bivascularly perfused rat liver with [U-14C]glutamine infusion (0.6 mM) into the portal vein (antegrade perfusion) or into the hepatic vein (retrograde perfusion).ResultsAmmonia infusion into the hepatic artery in retrograde and antegrade perfusion allowed to promote glutamine metabolism in the periportal region and in the whole liver parenchyma, respectively. The results revealed that the space-normalized glutamine uptake, indicated by 14CO2 production, gluconeogenesis, lactate production and the associated oxygen uptake, predominates in the periportal region. Periportal predominance was especially pronounced for gluconeogenesis. Ureogenesis, however, tended to be uniformly distributed over the whole liver parenchyma at low ammonia concentrations (up to 1.0 mM); periportal predominance was found only at ammonia concentrations above 1 mM. The proportions between the carbon and nitrogen fluxes in periportal cells are not the same along the liver acinus.ConclusionsIn conclusion, the results of the present work indicate that the glutaminase activity in periportal hepatocytes is not the rate-controlling step of the glutamine-derived nitrogen flow through the urea cycle. The findings corroborate recent work indicating that ureogenesis is also an important ammonia-detoxifying mechanism in cells situated downstream to the periportal region.

A Cell Line Resource Derived from Honey Bee (Apis mellifera) Embryonic Tissues

“…We also observed that trypsinization for < 10 min at 32°C allowed for a homogenous suspension to be obtained for re-seeding and that the cells to be transferred were insensitive to the proteolytic activity of trypsin exposure. However, incubation periods with trypsin > 10 min led to cells that were slow to re-attach and/or injured, likely through irreversible damage of protein function [30]. …”

Inhibition of As(III) and Hg(II) caused aortic hypercontraction by eugenol, linalool and carvone

“…The excitation-relaxation mechanism of smooth muscle is regulated by changes in the intracellular calcium concentration (25), vasodilation by endothelium released nitric oxide (26), and excessive production of ROS (27). In this study, each of these pathways were inhibited to gain insight into the hypercontraction mechanisms of As(III) and Hg(II).…”

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

“…This method also revealed other functions, such as intercellular glutamine cycling (Häussinger 1983) and bile salt transport (Groothuis et al 1982). This technique was improved by including separate perfusion of both afferent vessels instead of only the portal vein (Comar et al 2010) and provided new insight into to the influence of arterial blood in the regulation of ammonia elimination. A distinct and more versatile approach was the isolation of hepatocytes from different locations of the liver lobules.…”