Colocalization of chromogranin A and inositol 1,4,5-trisphosphate receptor in ciliated cells of the bovine oviduct.

Previous investigations of the expression of chromogranin A (CgA) have been performed primarily in neuroendocrine tissues containing amine and peptide secretory vesicles. More recently it has been shown that CgA, as a high capacity Ca2+ storage protein, interacts with the inositol 1,4,5-trisphosphate receptor/Ca2+ channel (InsP3R) which has been found to be selectively localized in oviductal cells of the mouse. To examine a possible role of this coupling in the Ca2+-dependent ciliary movement, we investigated the topographical and cellular distribution of cells positive for CgA and inositol 1,4,5-trisphosphate receptor type 2 (InsP3R2) in the bovine oviduct at different stages of the oestrous cycle. Using immunohistochemical techniques on paraffin-embedded tissue we have successfully shown that CgA is selectively expressed in ciliated cells of the bovine oviduct. The labelled cells show intense positive staining in the apical surface area in close vicinity to the ciliary apparatus. CgA-positive ciliated cells are most frequently observed at dioestrous while a lower number appears at oestrous. Additionally, secretory and intraepithelial neuroendocrine cells consistently do not stain with the CgA-antiserum. We then investigated whether the reported expression of the InsP3R in oviductal cells of the mouse corresponds to the expression of the InsP3R in bovine oviductal cells. Using a polyclonal antibody to the type 2 InsP3R, we found that the receptor is also selectively expressed in a similar matter to CgA in the apical cytoplasm of ciliated cells. This is the first morphological demonstration of the colocalization of CgA and InsP3R in epithelial ciliated cells of the bovine oviduct. Our results suggest that CgA and InsP3R could be involved in controlling the ciliary activity of oviductal epithelial cells.