Nicotine-induced endocytosis of amiloride-sensitive sodium channels in human nasal epithelium

In previous studies we developed and introduced a method to examine the transport mechanisms of ions in primary cell cultures of human nasal epithelium. In the current study, substances, especially nicotine, that influence these mechanisms are investigated. Specimens of nasal and paranasal epithelium of patients treated by endonasal surgery because of chronic sinusitis (n = 217) were used as primary cell cultures. Cell cultures of smokers (n = 83) and non-smokers (n = 134) were differentiated. Transepithelial Ussing chamber measurements were performed to examine sodium channel functions and to evaluate the influence of nicotine. These examinations were accompanied by simultaneous continuous capacitance measurements. Whereas transepithelial parameters, such as short-circuit current, (Isc), potential (Vt) and resistance (Rt), in tissues derived from smokers and non-smokers showed no difference, the transepithelial conductance was reduced immediately in cell cultures with apical application of nicotine (2 mM). This decrease was accompanied by a marked reduction of epithelial surface area. In the presence of nicotine, amiloride (100 microM) completely lost its inhibitory capacity. Amiloride-insensitive sodium channels were unaffected by nicotine, as proved by Na+ substitution. Furthermore, the Na+ channel blocker was accompanied by an increase in intracellular Ca2+. We conclude that the nicotine-induced increase in intracellular calcium (Ca2+) has stimulated Ca2+-dependent protein kinase (PKC). PKC promotes endocytosis removing amiloride-sensitive Na+ channels from the cell membrane into the cell by means of vesicular transport.