Biophysical features of a new cloned delta ENaC subunit

Abstract

The epithelial sodium channels (ENaC) is the critical rate‐limiting determinant in maintaining airway and lung lining fluid. δ ENaC (δ1) has been detected in human lung epithelial cells in addition to α, β, and γ subunits. Here we cloned a splicing variance of δ1 counterpart, termed as δ2 ENaC, in human bronchial epithelial cell line 16HBE140. Compared with δ1 subunit, δ2 ENaC possesses 66 extra amino acid residues in its cytosolic amino terminal tail. To characterize the biophysical and pharmacological features of the δ2 ENaC, we comparably examined the whole‐cell and single channel properties associated with δ1βγ and δ2βγ hENaC expressed in Xenopus oocytes. The relative cation selectivity ratio of Na+/Li+/K+ (1/0.69/0.09) for δ2βγ ENaC was similar with that of δ1βγ ENaC (1/0.64/0.07). And there was no significant difference in external Na+ affinity between δ1βγ and δ2βγ hENaC. The apparent dissociation constant for amiloride (Kiamil), EC50 value of capsazepine, proton gating kinetics for δ2βγ ENaC, however, significantly differed from those of δ1βγ ENaC. Single‐channel patch clamp results revealed that unitary conductance, single channel activity (NPo), and gating kinetics varied between δ1βγ and δ2βγ ENaC. Our data demonstrate that heterologously expressed δ1 and δ2 ENaC channels are segregated by their biophysical and pharmacological properties, at least partially accounting for the diverse native epithelial Na+ channels in lung epithelial cells. Supported by HL087017 and HL095435.