Localization of Ca2+-Activated K+ Channel, SK3, in Fibroblast-Like Cells Forming Gap Junctions With Smooth Muscle Cells in the Mouse Small Intestine

Abstract

In the present study, we examined the expression and the localization of apamin-sensitive small conductance Ca(2+)-activated K(+) channels (SK channels) in the mouse intestine. SK3-immunoreactivity (IR) was detected in both ileum and colon. Double staining experiments showed that SK3-IR was colocalized with prolyl 4-hydroxylase (PH(alpha))-IR, but not with c-Kit-IR which are markers of fibroblast cells and the interstitial cells of Cajal (ICC), respectively. Although SK3-IR was colocalized with vimentin-IR, which is another marker of ICC, the reactivity of SK3-immunopositive cells was weaker than that of ICC. The SK3-immunopositive cells were similarly present in the intestine of c-Kit mutant mice (W/W(V)), in which ICC were absent, and its wild-type mice. The immuno-electron microscopic analysis indicated that SK3 was localized in the cells that had some similar morphological features to ICC, but obviously different from ICC. The SK3-immunopositive cells had gap junctions with the smooth muscle cells. The gap junctions were smaller than those between ICC and smooth muscle cells. These results indicate expression of SK3 in fibroblast-like cells, but not in ICC, and suggest participation of the cells in the intestinal motility.

Immunohistochemical demonstration of c-Kit-negative fibroblast-like cells in murine gastrointestinal musculature

“…Our previous study showed PDGFR immunoreactivity in FLC and the co-localization of PDGFR and SK3 immunoreactivities in the murine GI tract (Iino et al, 2009a). Vanderwinden et al (2002) and Fujita et al (2003) showed that SK3 immunoreactivity was preferentially distributed in c-Kit-immunonegative FLC in human and murine GI tracts. From these findings, we postulated that FLC in murine GI musculature possessed SK3 immunoreactivity.…”

“…CD34 was first reported to be immunohistochemically expressed in the human FLC, but was barely detected in the murine FLC (Vanderwinden et al, 1999(Vanderwinden et al, , 2000(Vanderwinden et al, , 2002. SK3 immunoreactivity has been reported in human and murine FLC (Vanderwinden et al, 2002;Fujita et al, 2003) although some reports showed the expression of SK3 immunoreactivity in ICC of several species (Fujita et al, 2001;Klemm and Lang, 2002;Piotrowska et al, 2003) or in smooth muscle cells of the murine GI tract (Ro et al, 2001). We recently showed that PDGFR immunoreactivity was specifically distributed in FLC in the murine GI musculature and was co-localized with SK3 (Iino et al, 2009a).…”

Ascending contraction and descending relaxation in the distal colon of mice lacking interstitial cells of Cajal

“…Immunohistochemical study was carried out by the method described previously Fujita et al, 2003). Briefly, mice were deeply anesthetized with pentobarbital sodium (50 mg/kg, i.p.…”

P2Y receptor-mediated transient relaxation of rat longitudinal ileum preparations involves phospholipase C activation, intracellular Ca2+ release and SK channel activation

“…Moreover, the effect of ATP was significantly reduced in PDGFRα-expressing cells from P2Y 1 -knockout mice, indicating a major role of P2Y 1 in these cells [40] . It is therefore conceivable that these cells are also important mediators of purinergic relaxation in the rat ileum, which harbors SK3-expressing fibroblast-like cells that form gap junctions with smooth muscle cells [42] , as has recently been shown in the murine colon [43] . Another limitation of our study might be that purinergic receptors are also expressed in epithelial cells and hence are involved in secretory processes [44][45][46] .…”