AJP - Cell Physiology, Vol 265, Issue 4 C1050-C1060, Copyright © 1993 by American Physiological Society

ARTICLES

Sodium-permeable channels in the apical membrane of human nasal epithelial cells

T. C. Chinet, J. M. Fullton, J. R. Yankaskas, R. C. Boucher and M. J. Stutts
School of Medicine, University of North Carolina, Chapel Hill 27599-7020.

We used patch-clamp techniques to study the channels that underlie the Na+ conductance of the apical membrane of human normal nasal epithelial cells. Cells were cultured on permeable supports and studied after confluence. In 172 of 334 (52%) excised membrane patches, we observed 20-pS Na(+)-permeable channels that do not discriminate between Na+ and K+ (pNa/pK = 1.33). These nonselective cation channels contained subpopulations that differed by dependence of open probability on voltage and bath Ca2+ activity, suggesting two or more channel types with similar electrical properties. In the presence of 10(-4) M amiloride in the pipette, the proportion of excised patches with nonselective cation channels decreased to 52 of 139 patches (37%), but the decrease was spread across all subpopulations of nonselective cation channels in excised patches. Thus no distinctive Na(+)-selective amiloride-sensitive channels were identified in excised patches. In cell-attached patches, Na(+)-permeable channels were recorded in 56 of 262 patches (21%). Their conductance was 21.4 +/- 1.5 pS (n = 25), and most were selective for Na+ over K+ (pNa/pK > 6). In the presence of amiloride (10(-4) M) in the pipette, the frequency of lambda Na(+)-permeable channels in cell-attached patches decreased to 8 of 134 patches (6%), revealing a population of Na(+)-selective channels recorded in cell-attached patches that was inhibited by amiloride. We conclude that, in excised patches, Na(+)-permeable channels are nonselective for Na+ over K+ and < 30% appear to be amiloride sensitive. In contrast, in cell-attached patches, most channels that conduct sodium are 1) selective for Na+ over K+ and 2) amiloride sensitive. Although we have not discovered the explanation for the discrepancy between cell-attached and excised patch data, we speculate that the channels recognized on cell account for the amiloride-sensitive Na+ conductance of the apical membrane, whereas the excision process alters the properties of the Na(+)-permeable channels and/or activate new channels.

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