Maintenance of extracellular fluid volume homeostasis is essential for hemodynamic stability, and abnormalities of renal sodium handling have been linked to cardiovascular disease and hypertension. Ultimate regulation of sodium excretion in the kidney occurs in the distal nephron via conductive transport through the amiloride sensitive epithelial Na+ channel (ENaC). ENaC expression and activity in the apical membrane of epithelial cells is the rate limiting step in Na+ reabsorption not only in kidney collecting duct, but in airway epithelia and colon as well. Abnormalities of ENaC function have been demonstrated in hereditary forms of hypertension, renal salt wasting, and cystic fibrosis. The long term goal of this research is to understand the factors that regulate ENaC expression in the apical membrane of epithelial cells and the mechanisms by which hormones, physiologic conditions and other channels (such as the cystic fibrosis transmembrane regulator, CFTR) control ENaC function. Experiments will define the synthesis, apical expression, endocytosis, recycling and degradation of ENaC subunits in well polarized kidney cells. We will then examine a novel paradigm to explain the non-coordinate regulation of ENaC subunits under basal and hormonally-stimulated conditions that we and other investigators have observed.
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