Primary Molecular Disorders and Secondary Biological Adaptations in Bartter Syndrome

Figure 1

Segmentation of sodium reabsorption. Sodium reabsorption in tubular epithelial cells proceeds along a general two-step mechanism that includes a/an active extrusion of intracellular sodium ions by the basolateral sodium pump that is common to all tubular segments, b/ a passive apical entry of sodium dissipating the electrochemical gradient generated by the sodium pump via an exchanger or a cotransporter or a sodium channel that is specific to each tubular segment. Briefly, 175 L/1.73 m² of plasma roughly containing 20 moles of sodium chloride are filtered every day by the glomeruli, and 99 to 100% of this amount is reabsorbed in the convoluted and straight tubules (60%), the thick ascending limb of the Henle loop (30%), the distal convoluted tubule (7%), the connecting and the collecting duct (0 to 3%, controlled by aldosterone and angiotensin-2). The thin descending and ascending limbs of the Henle loop do not display any capacities to reabsorb sodium. Proximal tubular failure leads to the Fanconi syndrome where sodium wasting is associated with numerous solute wasting (potassium, bicarbonates, calcium, phosphates, glucose, aminoacids). Failure of the large ascending limb of the Henle loop is responsible for the Bartter syndrome, of the distal convoluted tubule for the Gitelman syndrome, and of the collecting duct for type 1 Pseudohypoaldosteronism [3].