Abstract
The epithelial Na+ channel (ENaC), composed of three homologous subunits (α, β, and γ), is shown to be molecularly expressed in the apical membrane of surface cells of the distal colon. We have recently demonstrated that electrophysiological properties of an amiloride-sensitive macroscopic Na+ current in surface cells, which are freshly isolated from rectal colon of rats fed a normal Na+ diet resemble those reported for heterologously expressed αβγ-ENaC and that the currents are most likely responsible for electrogenic Na+ transport in rat rectum (Inagaki et al., Am.J.Physiol. Cell Physiol. 286 (2): C380-C390, 2004). Using the standard whole-cell patch-clamp technique, we have found that the surface cells also exhibit an inwardly rectifying anion current, which is activated by membrane hyperpolarization, has an anion selectivity sequence of Cl− > I−, and is blocked by external Zn2+. RT-PCR analysis showed the presence of transcripts of rClC-2 in rat rectal mucosa. Electrophysiological properties of the native currents were similar to those of whole-cell currents recorded from HEK-293 cells heterologously expressing rClC-2 cloned from rat rectal mucosa. We also demonstrated that both ENaC and ClC-2-like currents were recorded in the same surface cells. Collectively, these results provide the electrophysiological evidence for functional coexpression of ENaC and ClC-2-like channel in rat rectal surface cells. Possible role of ClC-2-like channel in electrogenic Na+ transport in the distal colon is also discussed. [Jpn J Physiol 54 Suppl:S58 (2004)]
