Immunolocalization of Tandem Pore Domain K⁺ Channels in the Rat Carotid Body

Abstract

Tandem pore domain K⁺ channels can be divided into six subfamilies; TWIK, TASK, TREK, TALK, THIK and TRESK (Patel and Lazdunski, 2004). Its subfamily consists of several subunits. These channel subunits. have 4 transmembrane segments and 2 pore domains. These channels are ubiquitously expressed in the body including central and peripheral nervous systems. Of these channels, TASK (TWIK-related acid-sensitive K⁺ channels) family including TASK-1, TASK-2 and TASK-3 are inhibited by extracellular low pH (Lesage, 2003). In addition, it has been shown that TASK-1 and TASK-3 are closed by hypoxia (Hartness et al., 2001; Lewis et al., 2001). Thus, these channels are one of the candidates for oxygen and/or CO₂/H⁺ sensor in chemosensory cells. In the isolated glomus cells of the carotid body, Buckler et al. (2000) found TASK-like current with electrophysiological method and expression of TASK-1 mRNA. On the other hand, TREK (TWIK-related K⁺ channels), comprises three subunits, TREK-1, TREK-2 and TRAAK (Kim, 2003). These channels are regulated by polyunsaturated fatty acid, cellular volume, intracellular pH and general anesthetics. It has been suggested that they play an important role in potent neuroprotection (Lesage, 2003). Furthermore, Miller et al. (2003) reported that acute hypoxia occluded human TREK-1 expressed in the HEK293 cells under ischemic and/or acidic conditions. On the contrary, other reports demonstrated that TREK-1 was not oxygen sensitive (Buckler and Honore, 2005; Caley et al., 2005). To discuss the function of the tandem pore domain K⁺ channels in the chemosensory organ, we reported that the immunoreactivities for TASK and TREK subfamilies in the carotid body (Yamamoto et al., 2002; Yamamoto and Taniguchi, 2004). Furthermore, no immunoreactivity for TRAAK was found in the paraganglion cells in the sympathetic ganglia (Yamamoto and Taniguchi, 2003). In the present study, therefore, we summarize the immunohistochemical localization of tandem pore domain K⁺ channels in the rat paraganglion cells.