INHIBITORY EFFECTS OF OXIDANTS ON N-TYPE K-LYMPHOCYTES AND XENOPUS OOCYTES( CHANNELS IN T)

Reactive oxygen species (ROS) appear to be involved in Fas-induced pro grammed cell death, We have previously demonstrated a tyrosine-kinase- dependent inhibition of the n-type K+ channels (K-n) by Fas stimulatio n. Thus, the effect of hydrogen peroxide (H2O2) on the function of K-n was examined using the patch-clamp technique. Incubation of Jurkat hu man T lymphocytes with 100 mu M H2O2 resulted in a 46 +/- 5% inhibitio n of the macroscopic whole-cell current, Experiments performed at the single-channel level using the cell-attached configuration revealed th at the probability of the channel being open diminished upon incubatio n in H2O2. The effect was not dependent on src-like kinases, since H2O 2 did not trigger tyrosine phosphorylation of the K-n channel protein and herbimycin A did not prevent channel inhibition. K(v)1.3 channels underly the K-n of T lymphocytes and were expressed Xenopus oocytes an d subjected to electrophysiological analysis by the two-electrode volt age-clamp technique. Application of 1 mM H2O2 and 500 mu M t-BOOH (ter t, butylhydroperoxide) resulted in a marked inhibition of the K+ curre nt within 20 min. Both the membrane-permeable thiol-group oxidizing ag ent DTNP [2,2'-dithiobis-(5-nitropyridine)] and the membrane-impermeab le DTNB [5,5'-Dithiobis-(2-nitrobenzoic acid)] (50 mu M) inhibited K(v )1.3 channels, suggesting that extracellular domains of K(v)1.3 are af fected. These results point to a direct modulation of K-n by various o xidative agents.