Membrane-specific expression of functional purinergic receptors in normal human nasal epithelial cells

Extracellular purines and pyrimidines regulate various physiological responses via the cell surface receptors known as purinoreceptors and may exert autocrine or paracrine effects on ion transport, fluid transport, ciliary beat frequency, and mucin secretion. Therefore, this study aims to investigate the expression patterns of the purinoreceptors in normal human nasal epithelial (NHNE) cells. In RT-PCR, the mRNAs for several P2X (P2X3, P2X4, P2X7) and P2Y (P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12) receptors were identified in NHNE cells. Functional localizations of P2 receptors were investigated by measuring intracellular calcium concentration ([Ca2+]i) increases in membrane-specific manner using a double-perfusion chamber. Absence of the responses of alphabeta-methylene ATP and 2-methylthio-ATP excluded functionally active P2X3, P2X4, and P2Y1 receptors as far as [Ca2+]i increase is concerned. Applications with ATP and UTP revealed that luminal membranes of NHNE cells express P2Y2 and P2Y6 receptors and basolateral membranes express P2Y2 receptor. Expressions of P2Y2 and P2Y6 receptors in NHNE cells were further verified by immunoblotting using specific antibodies. In addition, the results with 2,3-O-(4-benzoyl)-benzoyl-ATP indicate that the P2Y11 receptor may be present on the luminal side. In conclusion, the NHNE cells express functionally active P2Y2, P2Y6, and P2Y11 receptors in a membrane-specific pattern, which may play an important role in the control of mucin and fluid secretion in NHNE cells.