Anion and cation permeability of a large conductance anion channel in the T84 human colonic cell line.

A large conductance multi-state channel was identified and characterized in single channel recordings from cell-attached and excised patches of the human colonic tumor cell line, T84. The channel activity was dependent on the presence of both permeable cations and anions. In Na(+)-free symmetrical Cl- solutions or Cl(-)-free symmetrical Na+ solutions the channel was inactive. Addition of 5 mM NaCl (NaI or KCl) induced channel activity. The selectivity sequence obtained from the shift in reversal potential was I- (1.9) > Cl- (1) > Na+ (0.5) > K+ (0.3). SO2-(4), SCN- (thiocyanate) and NMDG+ were impermeant. Multiple subconductance states were identified at all voltages explored (+/- 90 mV). The minimum conductance encountered in symmetrical 100 mM NaCl was a 15 pS substrate, the maximum, 210 pS. The channel appeared to be composed of multiples of the 15 pS subunits which were reversibly blocked by the loop diuretic bumetanide (5 microM).