Expression of functional P2Y6 receptors was demonstrated in primary cultures of human bronchial cells (NHBE cells). P2Y6 receptors were located only on the apical membranes of NHBE cells. Their stimulation by UDP induced a chloride secretion (short-circuit current) reflected by the development of two Isc components (Ifast and Ilate). A pharmacological characterization of those two Isc components showed the involvement of CaCC and CFTR channel activity in Ifast and Ilate respectively. Ifast was also found to be under control of basolateral SK4 channels. Indeed, inhibition of SK4 channels opening by clotrimazole dramatically reduced Ifast amplitude. The epithelial ion transporting phenotype depends on the cellular state of differentiation. As previously reported, we observed that Ultroser G increased the epithelial tightness and Na+-transport capacity while IL-13 switch the epithelial ion transport phenotype from a Na+-absorbing to a Cl--secreting one. In our study, we report for the first time a change in the K+ cell permeability associated to IL-13-induced cell differentiation. IL-13 treatment increased the-resting K+ permeability as well as the Ca2+-dependent K+ permeability stimulated by UDP or ionomycin. SK4 channels activity, underlying the Ca2+-dependent K+ permeability was in particular increased by IL-13. The on/off effect of IL-13 on P2Y6-induced Cl-secretion may help to identify the molecular determinants responsible for the CaCC channel activity.

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