Inhibition of amiloride-sensitive Na+ absorption by activation of MR in mouse endometrial epithelium

Previous studies have demonstrated amiloride-sensitive Na+ absorption under basal conditions and cystic fibrosis transmembrane conductance regulator ( CFTR)-mediated Cl- secretion following neurohormonal stimulation in the mou se endometrial epithelium. The present study investigated the inhibition of amiloride-sensitive Na+ absorption accompanying activation of CFTR in the mouse endometrium using the short-circuit current (I-sc) technique. RT-PCR demonstrated the coexpression of CFTR and epithelial Na+ channels (ENaC) in primary cultured mouse endometrial epithelia and cultured endometrial mono layers exhibited a basal amiloride-sensitive I-sc of 5.4 +/- 0.6 muA/cm(2). The amiloride-sensitive current fell to 3.1 +/- 0.5 muA/cm(2) after stimul ation with forskolin. When the possible contribution of Na+ absorption to t he I-sc was eliminated by amiloride (1 muM) or Na+ replacement, the forskol in-induced I-sc was not reduced, but rather increased significantly compare d with that in the absence of amiloride or in Na+-containing solutions (P < 0.02), indicating that the forskolin-induced I-sc was mediated by Cl- secr etion, portion of which may be masked by concurrent inhibition of basal Na absorption if the contribution of Na+ is not eliminated. When the contribu tion of Cl- to the I-sc was eliminated by diphenylamine 2,2'-dicarboxylic a cid (DPC, 2 mM) or Cl- replacement, forskolin now decreased, rather than in creased the I-sc, demonstrating the inhibition of Na+ absorption upon stimu lation. Our data suggest an interaction between CFTR and ENaC, which may be the underlying mechanism for balancing Na+ absorption and Cl- secretion ac ross the mouse endometrial epithelium.