Modification of nasal membrane potential difference with inhaled amiloride and loperamide in the cystic fibrosis (CF) mouse

Background - In the airway of subjects with cystic fibrosis (CF) the combination of defective cAMP mediated chloride secretion and enhanced sodium absorption leads to dehydration of mucosal mucus and is reflected in an increased transepithelial potential difference (PD). The airway secretions may be less viscid and easier to expectorate if sodium (and water) reabsorption is inhibited. Methods - To evaluate the response to sodium blocking agents, changes in the nasal PD in 20 transgenic CF mice were compared with 14 control mice (MF1 strain) before and after administration of nebulised amiloride and loperamide (both in a concentration of 1 mmol/l). The duration of action for both drugs was also determined after a single inhaled dose of 1 mmol/l for two minutes. Results - The median basal PD was -24 mV in controls and -28 mV in CF mice (p < 0.01). This fell in CF mice after amiloride and loperamide administration by 15 mV and 14 mV, respectively, compared with a decrease of 7 mV and 5.5 mV in controls (p < 0.01). There was no further change in PD when loperamide was given after amiloride. This suggests that loperamide and amiloride may act on sodium absorption via similar mechanisms. Loperamide had a longer duration of action after a single administration than amiloride. Conclusion - The administration of amiloride and loperamide reduces the transepithelial potential and inhibits sodium reabsorption in the CF mouse airway. Further studies are required to determine if the more prolonged action of loperamide could be of therapeutic use.