ACTIVATION OF POTASSIUM CHANNELS BY HYPOXIA AND REOXYGENATION IN THE HUMAN LUNG ADENOCARCINOMA CELL-LINE A549

Active oxygen species are generated in cells during pathophysiologic c onditions such as inflammation and postischemic reperfusion. If oxygen radical scavengers are added before reperfusion, then the magnitude o f injury is reduced. We investigated whether free radicals generated f ollowing exposure to hypoxia and reoxygenation activate voltage-depend ent K+ ion channels in tumor cells in vitro. Using the technique of wh ole cell voltage clamping, we recorded currents from two families of p otassium (K+) channels that were activated following reoxygenation. On e of these groups possessed the electrophysical characteristics of a t etraethylammonium (TEA)-sensitive delayed rectifier channel and the ot her possessed characteristics of a Tea-insensitive slow inactivating c hannel. We present evidence which suggests that K+ channels are activa ted following reoxygenation but not during the hypoxia phase. The K+ c urrents decayed with time following reoxygenation. The decay character istics of the K+ currents depended on the duration and level of hypoxi a to which the cells were exposed. To determine whether activation of K+ channels by reoxygenation was initiated by free radicals, we pretre ated cells with N-Acetyl L-Cysteine (NAC), a free radical scavenger, a nd found that this pretreatment abolished the currents induced by reox ygenation. We also present evidence that free radicals do not directly act on the channel itself, but activate a protein kinase which, in tu rn, activates the K+ channels. Taken together, these results indicate that one of the early responses to oxidative stress is the activation of K+ currents. (C) 1993 Wiley-Liss, Inc.