Electrophysiological studies of H441 human distal airway epithelial cells showed that thapsigargin caused a Ca²⁺ -dependent increase in membrane conductance (G_Tot) and hyperpolarization of membrane potential (V_m). These effects reflected a rapid rise in cellular K⁺ conductance (G_K) and a slow fall in amiloride-sensitive Na⁺ conductance (G_Na). This increase in G_Tot was antagonized by Ba²⁺, a non-selective K⁺ channel blocker and abolished by clotrimazole, a KCNN4 inhibitor, but unaffected by other selective K⁺ channel blockers. Moreover, 1-ethyl-2-benzimidazoline (EBIO), which is known to activate KCNN4, increased G_K with no effect upon G_Na. RT-PCR based analyses confirmed expression of mRNA encoding Kcnn4 and suggested that two related K⁺ channels (KCNN1 and KCNMA1) were absent. Subsequent studies showed that EBIO stimulates Na⁺ transport in polarized monolayers without affecting [Ca²⁺]_i suggesting that the activity of KCNN4 might influence the rate of Na⁺ absorption by contributing to G_K. Transient expression of KCNN4 cloned from H441 cells conferred a Ca²⁺- and EBIO-sensitive K⁺ conductance upon CHO cells, but this channel was inactive if [Ca²⁺]_i was < 0.2 µM. Subsequent studies of amiloride-treated H441 cells showed that clotrimazole had no effect upon V_m despite clear depolarizations in response to increased [K⁺]_o. These findings thus indicate that KCNN4 does not contribute to V_m in unstimulated cells. The present data thus establish that H441 cells express Kcnn4, highlight the importance of G_K to the control of Na⁺ absorption but, since KCNN4 is quiescent in resting cells. this channel cannot contribute to resting G_K or influence basal Na⁺ absorption.