TISSUE DISTRIBUTION OF THE P2X(7) RECEPTOR

The P2X(7) receptor is a bifunctional molecule. The binding of ATP ind uces within milliseconds the opening of a channel selective for small cations, and within seconds a larger pore opens which allows permeatio n by molecules as large as propidium dyes (629 Da). In situ hybridizat ion using a digoxigenin-labelled riboprobe, and immunohistochemistry u sing an antibody raised against a C-terminal peptide sequence, were us ed to determine the distribution of the P2X(7) receptor mRNA and prote in in rat and mouse tissues and cell lines. The brain of newborn rats showed a 6 kb RNA by Northern blotting, but this was not detectable in adult brain. By in situ hybridization and immunohistochemistry, there was heavy labelling of ependymal cells in both newborn and adult brai n, but the brain parenchyma showed no labelling. However, P2X(7) recep tor-immunoreactive cells appeared in the penumbral region around an ar ea of necrosis evoked by prior occlusion of the middle cerebral artery , suggesting expression of the receptor by activated microglia. NTW8 c ells, a mouse microglial cell Line, strongly expressed the P2X(7) rece ptor mRNA and protein. The P2X(7) receptor mRNA and protein were also observed in the majority of bone marrow cells, including those separat ely identified by their expression of other antigens as granulocytes, monocyte/macrophages and B lymphocytes. The expression of P2X(7) recep tor by brain macrophages rather than neurons would be consistent with a role in brain repair following inflammation, infarction or immune in sult. (C) 1997 Elsevier Science Ltd.