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A study was conducted to analyze a unique three-dimensional airway epithelial explant preparation and examine its application for ion transport experiments. Nasal polyps were obtained from normal subjects. The transepithelial potential difference was determined in epithelial spheroids transferred to a Ringer solution. Results indicated the usability of the preparation method for the airway surface epithelium.

The effects of didecanoyl-L-phosphatidylcholine (DDPC) on the epithelial transport mechanism were analyzed in rabbit nasal airway epithelium. DDPC induced the reversible closure of amiloride-sensitive sodium channels in the isolated nasal airway epithelium and impaired the anion selectivity of the paracellular pathway. Alterations in ion transport mechanism were caused by the interference of DDPC on lipid/integral protein interactions in the lipid bilayer of the cell membrane.

Electrophysiological and ion-flux measurements were conducted on rabbit nasal epithelium to determine mechanisms of cellular ion transport. The cellular ion transport of rabbit epithelium is similar to the ion transport mechanisms of human native airway epithelium. The serosa-positive potential differences of rabbit nasal epithelium under in vivo conditions induces active Na+ absorption though an anion-selective paracellular pathway.

Pedersen, Peter Steen, Niels-Henrik Holstein-Rathlou, Per Leganger Larsen, Klaus Qvortrup, and Ole Frederiksen. Fluid absorption related to ion transport in human airway epithelial spheroids. Am. J. Physiol. 277 (Lung Cell. Mol. Physiol. 21): L1096-L1103, 1999.--Airway epithelium explants from cystic fibrosis (CF) patients and non-CF subjects formed monolayered spheres, with the apical ciliated cell membrane facing the bath and the basolateral cell membrane pointing toward a fluid-filled lumen. With the use of two microelectrodes, transepithelial potential difference and changes in potential difference in response to passage of current pulses were recorded, and epithelial resistance and the equivalent short-circuit current were calculated. Non-CF control potential difference and short-circuit current values were significantly lower than the CF values, and amiloride inhibited both values. Fluid transport rates were calculated from repeated measurements of spheroid diameters. The results showed that 1) non-CF and CF spheroids absorbed fluid at identical rates (4.4 [micro]l [multiplied by] [cm.sup.-2] [multiplied by] [h.sup.-1]), 2) amiloride inhibited fluid absorption to a lower residual level in non-CF than in CF spheroids, 3) [Cl.sup.-]-channel inhibitors increased fluid absorption in amiloride-treated non-CF spheroids to a level equal to that of amiloride-treated CF spheroids, 4) hydrochlorothiazide reduced the amiloride-insensitive fluid absorption in both non,CF and CF spheroids, and 5) osmotic water permeabilities were equal in non-CF and CF spheroids (~27 x [10.sup.-7] cm [multiplied by] [s.sup.-1] [multiplied by] [atm.sup.-1]). amiloride; hydrochlorothiazide; osmotic permeability; current-voltage relationship; cystic fibrosis

In this study, we demonstrate a novel regulatory mechanism by which mucosal nucleotides via P2Y receptors decrease paracellular Cl− ion permeability in natural rabbit airway epithelium (in addition to a decrease in active Na+ absorption). In contrast to primary cultures, the natural airway epithelium is a low-resistance epithelium, and an equivalent circuit model predicts that changes of more than ∼12% in transepithelial conductance ( G t) must include an effect on paracellular conductance ( G s). Mucosal P2Y receptor stimulation with uridine triphosphate (UTP; 200 μM) decreased G t by up to 50% (average, 24%) and simultaneously decreased the paracellular Cl− permeability (mucosa-to-serosa Cl− flux) by 16%, but had no effect on mannitol permeability. The G t response to UTP was mimicked and attenuated by ionomycin (1 μM), suggesting a dependence on Ca2+ i. Amiloride (100 μM) and hyperosmolarity (+75 mM mannitol) also decreased G t, indicating a role of cell shrinkage. Elevation of cAMP with forskolin (8 μM) or isoproterenol (10 μM) increased G t by 55 and 32%, and forskolin increased paracellular Cl− permeability by 37% without affecting mannitol permeability. The opposite effects of Ca2+ i and cAMP on G t suggest an autocrine nucleotide signaling sequence where P2Y-dependent decrease in passive, paracellular Cl− transport is succeeded by a reversion of this effect due to P1-receptor-stimulated cAMP formation by adenosine originating from a time-dependent breakdown of mucosal ATP. [ABSTRACT FROM AUTHOR]