Mediation of the effect of nicotine on Kir6.1 channels by superoxide anion production.

K A T P channels are a complex of regulatory sulfonylurea receptor subunits and the pore-forming inward rectifiers such as Kir6.1. Using the whole-cell patch-clamp technique, we investigated the interaction of nicotine with the Kir6.1 subunit as well as the underlying mechanism. Stable expression of Kir6.1 in HEK-293 cells yielded a detectable inward rectifier K A T P current. This inward current was significantly inhibited by PNU-37883A and by a specific anti-Kir6.1 antibody. Nicotine at 30 and 100 μM increased Kir6.1 currents by 42 ′ 11.8% and 26.2 ′ 14.6%, respectively (n = 4-6, P < 0.05). In contrast, nicotine at 1-3 mM inhibited Kir6.1 currents (P < 0.05). Nicotine at 100 μM increased the production of superoxide anion (O 2 . - ) by 20.3 ′ 5.7%, whereas at 1 mM it significantly decreased the production of O 2 . - by 37.7 ′ 4.3%. Coapplication of hypoxanthine (HX) and xanthine oxidase (XO) to the transfected HEK-293 cells resulted in a significant and reproducible increase in Kir6.1 currents (P < 0.05). The stimulatory effect ofHX/XO on Kir6.1 current was abolished by tempol, a scavenger of O 2 . - . Tempol also abolished the stimulatory effect of 30 μM nicotine on Kir6.1 currents. In conclusion, nicotine stimulates Kir6.1 channel at least in part through the production of O 2 . - .