Ubiquitous presence of gluconeogenic regulatory enzyme, fructose-1,6-bisphosphatase, within layers of rat retina

To shed some light on gluconeogenesis in mammalian retina, we have focused on fructose-1,6-bisphosphatase (FBPase), a regulatory enzyme of the process. The abundance of the enzyme within the layers of the rat retina suggests that, in mammals in contrast to amphibia, gluconeogenesis is not restricted to one specific cell of the retina. We propose that FBPase, in addition to its gluconeogenic role, participates in the protection of the retina against reactive oxygen species. Additionally, the nuclear localization of FBPase and of its binding partner, aldolase, in the retinal cells expressing the proliferation marker Ki-67 indicates that these two gluconeogenic enzymes are involved in non-enzymatic nuclear processes

Cardiac Glycosides Ouabain and Digoxin Interfere with the Regulation of Glutamate Transporter GLAST in Astrocytes Cultured from Neonatal Rat Brain

Glutamate transport (GluT) in brain is mediated chiefly by two transporters GLT and GLAST, both driven by ionic gradients generated by (Na+, K+)-dependent ATPase (Na+/K+-ATPase). GLAST is located in astrocytes and its function is regulated by translocations from cytoplasm to plasma membrane in the presence of GluT substrates. The phenomenon is blocked by a naturally occurring toxin rottlerin. We have recently suggested that rottlerin acts by inhibiting Na+/K+-ATPase. We now report that Na+/K+-ATPase inhibitors digoxin and ouabain also blocked the redistribution of GLAST in cultured astrocytes, however, neither of the compounds caused detectable inhibition of ATPase activity in cell-free astrocyte homogenates (rottlerin inhibited app. 80% of Pi production from ATP in the astrocyte homogenates, IC50 = 25 μM). Therefore, while we may not have established a direct link between GLAST regulation and Na+/K+-ATPase activity we have shown that both ouabain and digoxin can interfere with GluT transport and therefore should be considered potentially neurotoxic

Technical and Comparative Aspects of Brain Glycogen Metabolism.

It has been known for over 50 years that brain has significant glycogen stores, but the physiological function of this energy reserve remains uncertain. This uncertainty stems in part from several technical challenges inherent in the study of brain glycogen metabolism, and may also stem from some conceptual limitations. Factors presenting technical challenges include low glycogen content in brain, non-homogenous labeling of glycogen by radiotracers, rapid glycogenolysis during postmortem tissue handling, and effects of the stress response on brain glycogen turnover. Here, we briefly review aspects of glycogen structure and metabolism that bear on these technical challenges, and discuss ways these can be overcome. We also highlight physiological aspects of glycogen metabolism that limit the conditions under which glycogen metabolism can be useful or advantageous over glucose metabolism. Comparisons with glycogen metabolism in skeletal muscle provide an additional perspective on potential functions of glycogen in brain

Detection of glutamate released by neurons with an enzyme-based microelectrode: applications and limitations

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Angiogenesis of liver metastases: role of sinusoidal endothelial cells.

PURPOSE: Tumor-induced angiogenesis requires migration and remodeling of endothelial cells derived from pre-existing blood vessels. Vascular endothelial growth factor is the growth factor most closely implicated in the development of neovessels in colon cancer. However, vascular endothelial growth factor-specific receptors flt-1 and KDR mRNA expression are absent in normal sinusoid vessels surrounding vascular endothelial growth factor-producing secondary hepatic tumors. Thus, the potential role of sinusoidal endothelial cells in the mechanism of neovessel formation within liver metastatic carcinomas remains unclear. The purpose of this study was to determine whether sinusoidal endothelial cells are involved in tumor angiogenesis in a syngeneic model of liver metastases from colorectal cancer. METHODS: Sinusoidal endothelial cells were identified by fluorescence microscopy after uptake of acetylated low density lipoprotein labeled with a fluorescent probe (dioctadecylindocarbocyanine). One hundred microliters of dioctadecylindocarbocyanine acetylated low density lipoprotein were injected intraportally at the start of experiment in BD IX rats. Two days later, intraportal injection of 10(7) DHD K12, a chemically induced colon carcinoma cell line, was performed in syngeneic BD IX rats. Animals were killed one week later and the livers were processed for routine histologic examination and immunohistochemistry using the rat endothelial cell antigen-1 monoclonal antibody. RESULTS: In normal parenchyma fluorescence was associated with sinusoidal cells but not with endothelium of large blood vessels. Thus, specific acetylated low density lipoprotein uptake allowed histological differentiation of sinusoidal endothelial cells from other large-vessel endothelial cells present in the hepatic parenchyma. In tumor-bearing liver a spatial gradient of fluorescence was generated. Labeled cells accumulated at the periphery of the metastases. When tumors grow beyond 200 microm, neovessel formation was observed; there was an invasion of fluorescent-labeled cells from the periphery, which were arranged in a tubular formation within neoplasia. CONCLUSION: In liver metastases tumor vessels are lined with sinusoidal endothelial cells. Identification of a specific cell type involved in the formation of the stromal compartment of tumors has important implications. Sinusoidal endothelial cells express well-characterized surface receptors and differ morphologically and metabolically from large-vessel endothelia. They should be considered as attractive targets for future and existing antiangiogenic strategies directed against the stromal compartment of liver metastases