The effects of the ERK pathway on electrogenic transepithelial Na+ absorption by renal collecting duct cells were determined. Approximately 90% of the unstimulated short-circuit current (15 ± 1 μA/cm2, n = 10) across conditionally immortalized murine collecting duct epithelial cells (mCT1) is amiloride sensitive and is likely mediated by apical epithelial Na+ channels. Chronic exposure (24 h) of the epithelial monolayers to either EGF (50 ng/ml) or transforming growth factor-α (TGF-α; 20 ng/ml) reduced amiloride-sensitive short-circuit current by >60%. The inhibitory effect of EGF on Na+ absorption was not due to inhibition of basolateral Na+-K+-ATPase, because the pump current elicited by permeabilization of apical membrane with nystatin was not reduced by EGF. Chronic exposure of the mCT1 cells to EGF (20 ng/ml, 24 h) elicited a 70–85% decrease in epithelial Na+ channel subunit mRNA levels. Exposure of mCT1 cells to either EGF (20 ng/ml) or PMA (150 nM) induced rapid phosphorylation of p42/p44 (ERK1/2) and pretreatment of the monolayers with PD-98059 (an ERK kinase inhibitor; 30 μM) prevented phosphorylation of p42/p44. Similarly, pretreatment of mCT1 monolayers with PD-98059 prevented the EGF- and PMA-induced inhibition of amiloride-sensitive Na+ absorption. The results of these studies demonstrate that amiloride-sensitive Na+ absorption by renal collecting duct cells is regulated by the ERK pathway. This pathway may play a role in alterations in ion transport that occur in polycystic kidney disease.
Transforming growth factor- 1 decreases epithelial sodium channel functionality in renal collecting duct cells via a Smad4-dependent pathway
