Expression of ASIC2 in ciliated cells and stereociliated cells.

Acid-sensing ion channel 2 (ASIC2) plays a role as a mechanorecptor and acid receptor in the peripheral and central nervous systems. However, several recent studies have suggested that ASIC2 is expressed in several organs, in addition to the nervous system. We have examined the expression and distribution of ASIC2 in rat ciliated cells (trachea and oviduct) and stereociliated cells (epididymis, Corti organ, and ampullary crest) by immunohistochemistry and transmission electron microscopy (TEM). Immunohistochemistry revealed that ASIC2 was expressed in both ciliated cells and stereociliated cells, but the localization differed between these cell types. In ciliated cells, ASIC2 was coexpressed with a cilial marker (acetylated tubulin). In stereociliated cells stained with a stereocilial marker (phalloidin), ASIC2 was observed in the cell body. Observation by TEM suggested that ASIC2 expression was present at the apical side of the cilial membrane in ciliated cells and at the apical side of the cell body in stereociliated cells. This study thus indicates that the proton receptor ASIC2 is expressed in both ciliated and stereociliated cells.