Abstract
Topical intranasal application of the antifungal Amphotericin B (AmphoB) has been shown as an effective medical treatment of chronic rhinosinusitis. Because this antibiotic forms channels in lipid membranes, we considered the possibility that it affects the properties and/or cell surface expression of ion channels/pumps, and consequently transepithelial ion transport. Human nasal epithelial cells were exposed apically to AmphoB (50 μM) for 4 h, 5 days (4 h daily), and 4 weeks (4 h daily, 5 days weekly) and allowed to recover for 18–48 h. AmphoB significantly reduced transepithelial potential difference, short‐circuit current, and the amiloride‐sensitive current. This was not due to generalized cellular toxicity as judged from normal transepithelial resistance and mitochondrial activity, but was related to inhibitory effects of AmphoB on ion transport proteins. Thus, cells exposed to AmphoB for 4 h showed decreased apical epithelial sodium channels (ENaC) activity with no change in basolateral Na^+^K^+^‐ATPase activity and K^+^ conductance, and reduced amount of αENaC, α1‐Na^+^K^+^‐ATPase, and NKCC1 proteins at the cell membrane, but no change in mRNA levels. After a 5‐day treatment, there was a significant decrease in Na^+^K^+^‐ATPase activity. After a 4‐week treatment, a decrease in basolateral K^+^ conductance and in αENaC and α1‐Na^+^K^+^‐ATPase mRNA levels was also observed. These findings may reflect a feedback mechanism aimed to limit cellular Na^+^ overload and K^+^ depletion subsequently to formation of AmphoB pores in the cell membrane. Thus, the decreased Na^+^ absorption induced by AmphoB resulted from reduced cell surface expression of the ENaC, Na^+^K^+^‐ATPase pump and NKCC1 and not from direct inhibition of their activities. © 2005 Wiley‐Liss, Inc.