Lipopolysaccharides modify amiloride‐sensitive Na+ transport processes across H441 lung epithelial cells

Abstract

Bacterial infections modify the ion transport processes that control lung fluid homeostasis. We investigated the effects of bacterial lipopolysaccharides (LPS) on amiloride‐sensitive Na+ transport across H441 cells. Monolayers were cultured at air interface on permeable supports for 7 days, mounted in Ussing chambers and bathed in physiological saline. Mean resistance (Rt) was 296 ± 69 Ωcm2, n = 5. Incubation with 15μgml−1 LPS for 8 hours caused a reduction in amiloride‐sensitive Isc (10 μM amiloride) from 29 ± 4 to 20 ± 3 μ Acm−2, p<0.05 n = 5. There was no change in amiloride‐insensitive Isc or resistance. Pre‐treatment of cells with 20μM PD98059 (MAPK inhibitor) prevented the effect of LPS (29 ± 3.0 μAcm−2, p<0.05 n = 6). LPS also shifted the amiloride concentration effect curve from an EC50 for amiloride of 6.8 × 10−7 M in control cells to 6.4 × 10−6 M in LPS treated cells p<0.05, n = 4. Using cell‐attached patch recordings we identified two constitutively active amiloride‐sensitive cation channels in the apical membrane of H441 cells. A 5pS highly Na+ selective ENaC–like channel and an 18pS non‐selective cation channel (NSC). Treatment with LPS increased the frequency of patches containing the less amiloride‐sensitive NSC by over 50%. We suggest that LPS alters the expression of ENaC/NSC channels in H441 cells resulting in a reduced amiloride‐sensitivity and Na+ conductance. Supported by The Wellcome Trust & BBSRC.