Figure 1222

Pathogenic model for nephrogenic diabetes insipidus (NDI). The principle cell of the inner medullary collecting duct is the site where fine tuning of the final urinary composition and volume occurs. As shown, the binding of arginine vasopressin (AVP) to the vasopressin V2 receptor (V2R) stimulates a series of cyclic adenosine monophosphate-(cAMP) mediated events that results in the fusion of cytoplasmic vesicles carrying water channel proteins (aquaporin-2 [AQP2]), with the apical membrane, thereby increasing the water permeability of this membrane. Water exits the cell through the basolateral water channels AQP3 and AQP4. In the absence of AVP, water channels are retrieved into cytoplasmic vesicles and the water permeability of the apical membrane returns to its baseline low rate [37].

Genetic studies have identified mutations in two proteins involved in this water transport process, the V2 receptor and AQP2 water channels. Most patients (>90%) inherit NDI as an X-linked recessive trait. In these patients, defects in the V2 receptor have been identified. In the remaining patients, the disease is transmitted as either an autosomal recessive or autosomal dominant trait involving mutations in the AQP2 gene [38,39]. ADH— antidiuretic hormone; ATP—adenosine triphosphate.

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