Expression of Ca2+-activated K+ channels, SK3, in the interstitial cells of Cajal in the gastrointestinal tract

A role for small-conductance Ca2+-activated K+ (SK) channels on spontaneous motility of the gastrointestinal tract has been suggested. Although four s ubtypes of SK channels were identified in mammalian tissues, the subtypes o f SK channel expressed in the gastrointestinal tract are still unknown. In this study, we investigated the expression and localization of SK channels in the gastrointestinal tract. RT-PCR analysis shows expression of SK3 and SK4 mRNA, but not SK1 or SK2 mRNA, in the rat intestine. SK3 immunoreactivi ty was detected in the myenteric plexus and muscular layers of the stomach, ileum, and colon. SK3-immunoreactive cells were stained with antibody for c-kit, a marker for the interstitial cells of Cajal (ICC), but not with tha t for glial fibrillary acidic protein in the ileum and stomach. Immunoelect ron microscopic analysis indicates that SK3 channels are localized on proce sses of ICC that are located close to the myenteric plexus between the long itudinal and circular muscle layers and within the muscular layers. Because ICC have been identified as pacemaker cells and are known to play a major role in generating the regular motility of the gastrointestinal tract, thes e results suggest that SK3 channels, which are expressed specifically in IC C, play an important role in generating a rhythmic pacemaker current in the gastrointestinal tract.