TEA-insensitive K-channels in the crab giant axon

TTX and TEA-insensitive permeabilities were studied in the crab giant axon under voltage-clamp. Membrane currents in the presence of internal TEA (40 mmol/l) and external TTX (300 nmol/l) may be analyzed as the sum of two components: a linear component, identified as the so-called leakage current, and a non-linear component, identified as a TEA-insensitive potassium channel. Ion permeability ratio of the TTX and TEA insensitive cation channel calculated from reversal potential shows the following sequence pK+:pNa+:pCs+:pRb+:pNH+4 = 1.00:0.16:0.16:0.09:0.06. TEA-insensitive outward currents, carried mainly by Cs+, may be recorded in the presence of different external solutions. Voltage-dependence and equilibrium potential of this channel in physiological conditions allows to postulate its contribution to maintain the cell depolarized during repetitive firing.