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

Abstract

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.