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

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 (R t ) was 296 ± 69 Ωcm 2 , n = 5. Incubation with 15μgml −1 LPS for 8 hours caused a reduction in amiloride‐sensitive I sc (10 μM amiloride) from 29 ± 4 to 20 ± 3 μ Acm −2 , p<0.05 n = 5. There was no change in amiloride‐insensitive I sc 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 EC 50 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.