Localisation of P2X5 and P2X7 receptors by immunohistochemistry in rat stratified squamous epithelia

In order to investigate whether purinoceptors are involved in the physiological renewal and regeneration of epithelia, we used immunohistochemical techniques on fresh frozen sections of various stratified squamous epithelial tissues (cornea, tongue, soft palate, oesophagus, vagina and footpad) of the rat and specific polyclonal antibodies to unique peptide sequences of P2X(1-7) receptors. Only two of the antibodies, anti-P2X(5) and anti-P2X(7), reacted with epithelial structures. P2X(5) immunoreactivity was mainly associated with the membranes of the proliferating and differentiating cell layers (spinous and granular layer) in both keratinised and non-keratinised epithelia and growing hair follicles. In contrast, P2X(7) immunoreactivity was clearly associated with the keratinisation process, the staining being most intense in the upper keratinised and the exfoliated layers. These findings suggest, for the first time, that P2X(5) and P2X(7) receptors play an important role in the physiological turnover of continuously regenerating cells, and further, raise the possibility that they represent novel targets for the development of pharmacological tools of potential benefit for diseases of epithelial dysfunction.