Localization of epithelial sodium channel and aquaporin-2 in rabbit kidneycortex

The amiloride-sensitive epithelial sodium channel (ENaC) and the vasopressi n-dependent water channel aquaporin-2 (AQP2) mediate mineralocorticoid-regu lated sodium- and vasopressin-regulated water reabsorption, respectively. D istributions of ENaC and AQP2 have been shown by immunohistochemistry in ra ts. Functional data from rabbits suggest a different distribution pattern o f these channels than in rats. We studied, by immunohistochemistry in the r abbit kidney cortex, the distributions of ENaC and AQP2, in conjunction wit h marker proteins for distal segments. In rabbit cortex ENaC is restricted to the connecting tubule (CNT) cells and cortical collecting duct (CCD) cel ls. The intracellular distribution of ENaC shifts from the apical membrane in the most upstream CNT cells to a cytoplasmic location further downstream in the CNT and in the CCD cells. AQP2 is detected in the CCD cells exclusi vely. The anatomic subdivisions in the rabbit distal nephron coincide exact ly with distributions of apical transport systems. The differences between rabbits and rats in the distribution patterns of ENaC and AQP2 may explain functional differences in renal salt and water handling between these speci es.