1. Role of the kidneys in the intermediary metabolism
Role of the kidneys in the intermediary metabolism
Process of urine formation requires a lot of energy (eg for active transport of ions). It is therefore not surprising that kidney cells need very intense energy metabolism. This applies especially to tubular epithelial cells in the renal cortex, which have better blood supply and more mitochondria, place for aerobic processes (produce more energy). These cells can utilize almost all nutrients – glucose, fatty acids / ketone bodies and amino acids (significance of glutamine). Metabolism of cells in renal medulla is limited by an insufficient oxygen supply, most ATP molecules is thus obtained in the anaerobic glycolysis.
Kidneys represent a significant organ of gluconeogenesis.
Metabolism of glutamine
Glutamine (Gln) is produced mainly in skeletal muscle from branched-chain amino acids (Leu, Ile, Val). In its molecule body stores toxic ammonia:
Glu + ATP + NH4+ → Gln + H2O + ADP + P
Cells with rapid turnover rate (tubular cells in kidneys, enterocytes, immune cells) are the main consumers of glutamine from blood. It serves as an energy substrate and as a nitrogen donor in some synthetic pathways.
Glutaminase reaction has a high activity in kidneys. Unused nitrogen from glutamine can be secreted into the urine or incorporated into alanine, which transports it to the liver (nitrogen is used for synthesis of urea). Carbon skeleton of glutamine forms α-ketoglutarate that can be oxidized, converted to glucose or is released as serine or alanine.
Subchapter Authors: Josef Fontana and Petra Lavríková