Mediation of the Effect of Nicotine on Kir6.1 Channels by Superoxide Anion Production

Abstract

KATP 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 KATP current. This inward current was significantly inhibited by PNU-37883A and by a specific anti-Kir6.1 antibody. Nicotine at 30 and 100 microM 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 microM increased the production of superoxide anion (O2) by 20.3 +/- 5.7%, whereas at 1 mM it significantly decreased the production of O2 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 of HX/XO on Kir6.1 current was abolished by tempol, a scavenger of O2. Tempol also abolished the stimulatory effect of 30 muM nicotine on Kir6.1 currents. In conclusion, nicotine stimulates Kir6.1 channel at least in part through the production of O2.

Tempol Prevents Altered K + Channel Regulation of Afferent Arteriolar Tone in Diabetic Rat Kidney

“…Recent studies of stably expressed Kir6.1 in HEK-293 cells (in the absence of any SUR subunit) revealed that co-application of hypoxanthine and xanthine oxidase produced a significant increase in Kir6.1 currents that could be abolished by tempol. 27 Thus, superoxide or other ROS might act directly on Kir6.1 to increase the contribution of K ATP channels to afferent arteriolar tone during T1D. Such a scenario might also contribute to the exaggerated impact of Ba 2+ -sensitive Kir2.1 channels on afferent arteriolar tone during diabetes.…”

Chemistry and Antihypertensive Effects of Tempol and Other Nitroxides

“…Other studies have implicated tempol in the regulation of the K ATP channel (Kir6.1) (Hanna et al, 2005). Superoxide enhanced K ATP channel activity in guinea pig cardiac myocytes yet decreased the K ATP channel opening probability in cerebral vessels (Liu and Gutterman, 2002; Gebremedhin et al, 2008).…”

“…Tempol may have activated K ATP channels on sympathetic neurons in this preparation because the blunting of the hypotensive action of intravenous tempol by glibenclamide was diminished in SHR pretreated with the ganglion blocking drug, hexamethonium (Chen et al, 2007a). Activation of K ATP channels also can generate ROS that were blocked by tempol (Hanna et al, 2005). …”

Mechanisms of nicotine-induced cutaneous vasodilation and sweating in young adults: roles for KCa, KATP, and KVchannels, nitric oxide, and prostanoids

“…Hence this response may be due to the activation of nicotinic receptors expressed on the endothelial cells of cutaneous blood vessels (Hagforsen et al 2002) Finally, nicotine may activate K ATP channels through increasing superoxide production as demonstrated under in vitro conditions (Hanna et al 2005). …”