Systèmes de transport membranaires, génétique et nutrition ; l'exemple des anomalies congénitales du transport intestinal chez l'enfant

Abstract

As the plasma membrane of the cell, the intestinal epithelium ensures the selective functions of the entry and exit of nutriments or metabolites. These functions are controlled genetically by structural genes and eventually by regulatory genes which direct the expression of the former. The influence of some essential nutriments also plays a role. These aspects are illustrated for microorganisms. Selective, congenital intestinal malabsorptions, which are hereditary, occur in humans; their study leads to a better understanding of the genetic and nutritional control of transport mechanisms. Known anomalies of the intestinal transport of basic amino acids have been studied by showing the probable relationships with selective reabsorption deficiencies in the renale tubule and possible disorders of the urea cycle. Amino acid transport through the intestinal epithelium may be under a dual genetic control i.e. at the brush border (co-transport with sodium) as well as at the basal-lateral membrane (diffusion). It is emphasized that small peptides must be present in dietary solutions of enteral origin for amino acid absorption to be optimal. Selective malabsorption of glucose and galactose due to loss of the co-transport systems of glucose-sodium and galactose-sodium at the brush border is discussed. A comparison is made with anomalies of glucose reabsorption in the renal tubule. The digestive consequences (watery diarrhea) of the absence of sodium co-transports has been underlined. A generalization is proposed.