Transport of l-proline and α-aminoisobutyric acid in the isolated rat kidney glomerulus

Abstract

Isolated rat kidney glomeruli were used to study amino acid transport in vitro. Uptake of l-proline and α-aminoisobutyric acid is slower in the glomerulus than in other parts of kidney. Amino acid uptake in glomeruli is dependent on tissue integrity, Na + and energy metabolism. The glomerulus can achieve concentrative uptake which can be supported by glycolysis. Uptake is saturable and two systems were identified for l-proline, the transport K m values of which were 0.1 and 5.3 mM. These values were similar to those of systems serving l-proline transport in the rat kidney cortex slice. α-Aminoisobutyric acid uptake does not reach a steady state, behaving as if efflux were deficient. The K m value for the α-aminoisobutyric acid mediation was 33 mM; a low- K m component for α-aminoisobutyric acid transport identified in other tissues was apparently absent in the glomerulus. Glomeruli thus accumulate amino acids by mediations which resemble those of the tubule but which also have characteristics particular to the glomerulus.