Fig. 5.

Role of oxidants in hyperosmotic-induced hyperpolarization. A: effect of the antioxidant N-acetyl cysteine (NAC, 200 µM) on the hyperosmotic-induced hyperpolarization of goblet cells. Voltages were measured during a 10- to 30-min exposure to NAC-containing 360 (n = 6) or 300 mosM (n = 4) perfusates (details in materials and methods). To facilitate comparison, the goblet cell voltage in the NAC-free 360 mosM solution is shown (n = 28, data in Fig. 2). B: effect of 30 µM H₂O₂ on goblet cell voltage under normosmotic conditions. A 0.5- to 2-h exposure to H₂O₂ resulted in significant hyperpolarization, which was eliminated by glibenclamide (Glib). Noteworthy is that goblet cells in the 300 mosM/H₂O₂/glibenclamide group were more depolarized (P = 0.0197) than in 300 mosM/glibenclamide (data in Fig. 4B); thus, H₂O₂ appears to concomitantly activate a depolarizing current, as well as the glibenclamide-sensitive ATP-sensitive K⁺ (K_ATP) channel conductance. Sample sizes: 300 mosM, 12; 300 mosM/H₂O₂, 6; 300 mosM/H₂O₂/glibenclamide, 5. C: current-voltage (I–V) plots generated in the 300 mosM solution supplemented with 30 µM H₂O₂ in the absence (n = 6) or the presence of 0.5 µM glibenclamide (n = 6). This K_ATP blocker decreased (P = 0.0003) the conductance by inhibiting a current whose reversal potential was near equilibrium potential for K⁺ (E_K).