Characterization of a novel splice variant of delta ENaC subunit in human lungs.
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Zhao RZ, Nie HG, Su XF, Han DY, Lee A, Huang Y, Chang Y, Matalon S, Ji HL
Characterization of a novel splice variant of delta ENaC subunit in human lungs.
Am J Physiol Lung Cell Mol Physiol. 2012 Jun 15;302(12):L1262-72. doi: 10.1152/ajplung.00331.2011. Epub 2012 Apr 13.
- PubMed ID
- 22505667 [ View in PubMed]
- Abstract
Salt absorption via apical epithelial sodium channels (ENaC) is a critical rate-limiting process in maintaining airway and lung lining fluid at the physiological level. delta ENaC (termed delta1 in this article) has been detected in human lung epithelial cells in addition to alpha, beta, and gamma subunits (Ji HL, Su XF, Kedar S, Li J, Barbry P, Smith PR, Matalon S, Benos DJ. J Biol Chem 281: 8233-8241, 2006; Nie HG, Chen L, Han DY, Li J, Song WF, Wei SP, Fang XH, Gu X, Matalon S, Ji HL, J Physiol 587: 2663-2676, 2009) and may contribute to the differences in the biophysical properties of amiloride-inhibitable cation channels in pulmonary epithelial cells. Here we cloned a splicing variant of the delta1 ENaC, namely, delta2 ENaC in human bronchoalveolar epithelial cells (16HBEo). delta2 ENaC possesses 66 extra amino acids attached to the distal amino terminal tail of the delta1 ENaC. delta2 ENaC was expressed in both alveolar type I and II cells of human lungs as revealed by in situ hybridization and real-time RT-PCR. To characterize the biophysical and pharmacological features of the splicing variant, we injected Xenopus oocytes with human ENaC cRNAs and measured whole cell and single channel currents of delta1betagamma, delta2betagamma, and alphabetagamma channels. Oocytes injected with delta2betagamma cRNAs exhibited whole cell currents significantly greater than those expressing delta1betagamma and alphabetagamma channels. Single channel activity, unitary conductance, and open probability of delta2betagamma channels were significantly greater compared with delta1betagamma and alphabetagamma channels. In addition, delta2betagamma and delta1betagamma channels displayed significant differences in apparent Na(+) affinity, dissociation constant for amiloride (K(i)(amil)), the EC(50) for capsazepine activation, and gating kinetics by protons. Channels comprising of this novel splice variant may contribute to the diversities of native epithelial Na(+) channels.