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

In the gastrointestinal musculature, interstitial cells of Cajal (ICC) distribute and regulate the gastrointestinal motility. Another type of mesenchymal cell, known as the fibroblast-like cell (FLC), has also been reported to be juxtaposed to the ICC. In this study, we examined the immunohistochemical properties of FLC in the murine gastrointestinal musculature using antibodies to small conductance Ca2+-activated K+ channel 3 (SK3), platelet-derived growth factor receptor alpha (PDGFR alpha), and CD34. SK3-immunopositive (SK3-ip) cells were observed in the musculature throughout the gastrointestinal tract. These SK3-ip cells were distinct from the ICC that were identified by c-Kit immunoreactivity. In the muscular layers, SK3-ip cells were bipolar in shape and were associated with the intramuscular ICC and nerve fiber bundles. In the myenteric layer multipolar-shaped SK3-ip cells encompassed the myenteric ganglia. SK3-ip cells in the subserosal plane formed a cellular network with their ramified processes. The distribution pattern of the SK3-ip cells in the ICC-deficient W-v/W-v mutant mice was similar to that in normal mice. We also demonstrated that SK3-ip cells showed the intense PDGFR alpha immunoreactivity that was previously examined in FLC. However, CD34 immunoreactivity, one of the markers of human FLC, was not observed in SK3-ip cells with the exception of subserosal FLC. Thus, our observations indicate that SK3- and PDGFR alpha-double immunopositive cells are FLC in the murine gastrointestinal musculature and behave as a basic cellular element throughout the gastrointestinal musculature.