Apical and Basolateral ATP-Induced Anion Secretion in Polarized Human Airway Epithelia

Abstract

The present study investigated mechanisms underlying apical and basolateral P2Y(1)-mediated Cl(-) secretion in human airway epithelial cells. Apical and basolateral ATP induced short-circuit currents (I(sc)) with different properties via P2Y(1) receptors. The former comprised an immediate rise followed by a slow attenuation, whereas the latter was a transient rise with a higher peak and shorter duration (< 2 min). The actions of ATP were simulated by those of ADP, ADPbetaS, and ATPgammaS. Antagonists of phosphatidylinositol-phospholipase C (U73122, ET-18-OCH(3)) were without any effect on the bilateral ATP-induced I(sc), which were, in contrast, attenuated by a phosphatidylcholine-phospholipase C inhibitor (D609) and an adenylate cyclase inhibitor (SQ22536). The responses to ATP from either aspect were also sensitive to an intracellular Ca(2+) chelator, 1,2-bis (o-amino-phenoxy)-ethane-N,N,N',N'-tetraacetic acid tetra-(acetoxymethyl)-ester, or a Ca(2+)-activated K(+) channel inhibitor, charybdotoxin, although differential Ca(2+) signals were concomitant with each reaction. Nystatin permeabilization studies revealed a good correlation between the I(sc) and the basolateral K(+) current rather than the apical Cl(-) current under ATP-stimulated conditions. In conclusion, apical and basolateral P2Y(1) receptors couple with both phosphatidylcholine-phospholipase C and adenylate cyclase, leading to Cl(-) secretion, whose rate is essentially regulated by the Ca(2+)-activated K(+) channel-mediated K(+) conductance. This suggests the importance of this channel in airway mucociliary clearance.

Modelling Dysregulated Na+ Absorption in Airway Epithelial Cells with Mucosal Nystatin Treatment

“…Diverse responses to acute Nys challenge in Ussing chambers have been described in the literature. Although a pattern similar to the one we observed has been described in toad bladder A6 cells and rat colonic epithelium (13,25), other model systems (e.g., Calu-3 cells) responded to acute Nys exposure with a slower rise in I sc (10-20 min) and a plateau phase that was sustained for over 30 minutes (26,27). Since Nys binding to the plasma membrane is strictly dependent on sterol content (28), these differences might be attributed to differences in the apical membrane sterol composition in the different cell types studied.…”

Purinergic Signaling in the Airways

“…Diadenosine pentaphosphate (Ap 4 A) increased [Ca 2ϩ ] i in HBE1 cells derived from human bronchial epithelial cells, probably acting via P2Y 2 receptors (Laubinger et al, 2001). Multiple P2Y receptor subtypes seem to be present on both apical and basolateral membranes of human airway-derived Calu-3 cells (Chambers et al, 2002), including P2Y 1 receptors (Son et al, 2004). UTP stimulates alveolar fluid clearance in the distal airspaces of rat lungs (Sakuma et al, 2004).…”

Effects of Extracellular ATP on Bovine Lung Endothelial and Epithelial Cell Monolayer Morphologies, Apoptoses, and Permeabilities

“…Kolosova et al demonstrated that a long-lasting, nonhydrolyzed form of ATP (ATP␥S) given to mice after transtracheal administration of LPS prevented increases in bronchoalveolar lavage protein and white blood cell counts, Evans blue leakage into the lung, and decreased transendothelial cell electrical resistance (11). ATP has also been shown to induce anion secretion in airway epithelial cells and surfactant secretion in alveolar epithelial cells, both of which help to remove noxious particles from the lung (10,22,25). In addition, extracellular ATP appears to downregulate the human monocyte response to LPS through Tolllike receptor 4 (8).…”