Inner hair cells (IHCs) of guinea-pigs were separately isolated from the apical and basal turn and the potassium currents were measured by the whole-cell voltage-clamp technique. The potassium current flows through two types of membrane conductance: a fast (I(k,f)), tetraethylammonium (TEA)-sensitive conductance and a slow (I(k,s)), TEA-resistant conductance. Membrane conductance demonstrated no significant differences between apical IHCs and basal IHCs. Reversal potentials were -65+/-2 mV and -68+/-5 mV in apical and basal IHCs, respectively. The rate of outward current activation was voltage dependent and faster in basal IHCs than in apical IHCs. TEA effect was stronger on basal IHCs than on apical IHCs, suggesting that I(k,f) is dominant in basal IHCs.