Effects of hydroxyl radicals on outwardly rectifying chloride channels in a cultured human bronchial cell line (16HBE14o-).

Respiratory pathologies can result from the exposure of airway epithelial cells to oxidative stress. We studied the effects of the hydroxyl radical *OH, for which there is no natural intra- or extracellular scavenger, on an outwardly rectifying chloride channel (ORCC). In the human bronchial cell line 16HBE14o-, the cytoplasmic side of ORCC in inside-out excised membrane patches was exposed to *OH created by simultaneously superfusing Fe2+ and H2O2 in front of the patch-pipette. ORCC was activated by depolarizing voltage steps. Its open probability (Po) increased with bath [Ca2+] above 1 microM. Upon brief exposure to *OH, ORCC first closed and then alternated between periods of closure and normal activity. The duration of closure increased with the duration of *OH exposure but voltage steps could reopen the channel. After 10 min exposure to *OH, however, the channel closed irreversibly, regardless of the number of subsequent voltage steps or the duration of washing. Low [Ca2+] in the bath accelerated the irreversible closure of the channel in the presence of *OH. Intracellular application of *OH progressively inhibited ORCC activity by inducing long closure periods that increased with time. This might have important pathophysiological implications in the process of inflammation.