Physiological and pharmacological studies have demonstrated that extracellular ATP, acting through P2Y2 purinoceptor, modulates water permeability of renal medullary collecting duct cells and the secretion of ions, mucin, and surfactant phospholipids by respiratory epithelia. Here we provide direct molecular evidence for the expression of P2Y2 purinoceptor in these cells. RT-PCR confirmed P2Y2 purinoceptor mRNA expression in rat lung and kidney and demonstrated expression in renal collecting ducts. Northern analysis showed that both lung and kidney express one 3.6-kb P2Y2 purinoceptor mRNA transcript. Immunoblots using peptide-derived polyclonal antibody to P2Y2 purinoceptor showed that inner medullary collecting ducts (IMCD) express two distinct and specific products (47 and 105 kDa) and account for the majority of the receptor expression in inner medulla, whereas the 105-kDa form is predominant in lung. Immunoperoxidase labeling on cryosections showed localization of receptor protein in the apical and basolateral domains of IMCD principal cells and in the secretory cells (Clara cells and goblet cells) of the terminal respiratory bronchioles.