Unchanged Glycolytic Capacity in Rat Kidney under Conditions of Stimulated Gluconeogenesis. Determination of Phosphofructokinase and Pyruvate Kinase in Microdissected Nephron Segments of Fasted and Acidotic Animals

Abstract

The glycolytic capacity in rat kidney was studied under conditions of stimulated gluconeogenesis like 48 h starvation and 48 h acidosis induced by force-feeding with a NH4Cl/glucose solution. Rats fed ad libitum and force-fed with a glucose solution served as controls. The specific activities of the key enzymes phosphofructokinase and pyruvate kinase were determined in single segments of the nephron. The determinations were performed by microdissection of lyophilized tissue sections followed by enzymatic analysis, including oil well technique, enzymatic amplification, and fluorometric measurement.In the distal portion of the nephron of both fed and force-fed animals a 10-fold higher specific activity of phosphofructokinase and pyruvate kinase was found compared with the proximal portion, known as the site of renal gluconeogenesis. Starvation and acidosis altered neither the distribution pattern nor the specific activities of these enzymes.From these results it is concluded that renal glycolysis does not undergo alterations at the level of enzymatic activities in favour of renal gluconeogenesis, probably because of the separate localization of both pathways within the nephron.

Renal Expression of the Brain and Muscle Isoforms of Glycogen Phosphorylase in Different Cell Types

“…The transporting epithelia along the nephron [31] meet their high energy demand by mitochondrial oxidative metabolism [32]. However, the CD cells [33] which contain less mitochondria than cells of proximal and distal tubules [24] are more restricted to anaerobic glycolysis [30,34]. Glucose is transported from the peritubular capillaries into the cells, but glucosyl residues are also derived from cellular glycogen [30,35].…”

Immunohistochemical localization of acyl-CoA hydrolase/thioesterase multigene family members to rat epithelia

“…Moreover, in this region, fatty acid oxidation probably plays a major role due to very low activity of glycolysis, in contrast to the collecting duct where the glycolytic enzymes reach maximal activity and fatty acids represent a minor fuel (Schmid et al 1980;Le Hir and Dubach 1982). Interestingly, the capacity for peroxisomal beta-oxidation of fatty acids is very low in the distal tubules, but significantly high in both the proximal convoluted and straight tubules (Le Hir and Dubach 1982).…”

Functional localization of glucose transporter 2 in rat liver.

“…and glucose-6-phosphatase (Burch et al, 1978) are limited to the proximal tubule cells, and glycolytic enzymes, such as hexokinase (Lawrence et al, 1986;Schmidt et al, 1975). phosphofructokinase (Schmid et al, 1980). and pyruvate kinase (Schmid et al, 1980).…”