Identification of a voltage- and calcium-dependent non-selective cation channel in cultured adult and fetal human nasal epithelial cells.

The apical membranes of cultured human nasal epithelial cells from adults and fetuses were investigated with the patch-clamp technique. Amiloride-insensitive, calcium- and voltage-dependent, non-selective cation channels were found in 4% of the cell-attached, and 18% of the inside-out and outside-out patches (n = 412). Multiple functional channels were present in more than 90% of these patches, with a mean of 3.9 channels per patch (n = 55). The current-voltage relationship can be described by the Goldman equations and the single channel conductance was 20.1 +/- 0.3 pS (n = 29) in adult and 20.7 +/- 0.4 pS (n = 44) in fetal cells in symmetrical 150 mM NaCl solutions. The channels were highly selective for cations: P Na/P Cl was 30 in adult and 45 in fetal experiments. They were equally permeable for K+ and Na+, somewhat less for Cs+, and impermeable for choline+ and tetraethylammonium+. The open probability was voltage dependent: it increased approximately 2-fold with 30 mV depolarization in the potential range from -60 mV to +60 mV. The channels were activated by Ca2+ concentrations of about 10(-4) M at the cytoplasmic side, but were insensitive to extracellular Ca2+ and amiloride (10(-4) M). The non-selective cation channels found in apical membranes of cultured fetal nasal epithelial cells were not different from the adult ones.