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)-O-.. 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)-O-. created by simultaneously superfusing Fe2+ and H2O2 in front of the patch-pipette, ORCC was activated by depolarizing voltage steps. Its open probability (P-o) increased with bath [Ca2+] above 1 mu M. Upon brief exposure to (OH)-O-., ORCC first closed and then alternated between periods of closure and normal activity. The duration of closure increased with the duration of (OH)-O-. exposure but voltage steps could reopen the channel. After 10 min exposure to (OH)-O-., 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)-O-., Intracellular application of (OH)-O-. progressively inhibited ORCC activity by inducing long closure periods that increased with time. This might have important pathophysiological implications in the process of inflammation.