Ion transport defects underlying cystic fibrosis (CF) lung disease are characterized by impaired cyclic adenosine monophosphate (cAMP)-dependent Cl(-) conductance. Activation of Cl(-) secretion in airways depends on simultaneous activation of luminal Cl(-) channels and basolateral K(+) channels. We determined the role of basolateral K(+) conductance in cAMP- dependent Cl(-) secretion in native human airway epithelium obtained from non-CF and CF patients. CF tissues showed typical alterations of short-circuit currents with enhanced amiloride-sensitive Na(+) conductance and defective cAMP-mediated Cl(-) conductance. In non-CF tissues, Cl(-) secretion was significantly inhibited by the chromanol 293B (10 micromol/liter), a specific inhibitor of K(V)LQT1 K(+) channels. Inhibition was increased after cAMP-dependent stimulation. Similar effects were obtained with Ba(2+) (5 mmol/liter). In patch-clamp experiments with a human bronchial epithelial cell line, stimulation with forskolin (10 micromol/liter) simultaneously activated Cl(-) and K(+) conductance. The K(+) conductance was reversibly inhibited by Ba(2+) and 293B. Analysis of reverse-transcribed messenger RNA from non-CF and CF airways showed expression of human K(V)LQT1. We conclude that the K(+) channel K(V)LQT1 is important in maintaining cAMP-dependent Cl(-) secretion in human airways. Activation of K(V)LQT1 in CF airways in parallel with stimulation of residual CF transmembrane conductance regulator Cl(-) channel activity or alternative Cl(-) channels could help to circumvent the secretory defect.