Luminal oxidants selectively modulate electrogenic ion transport in rat colon

Figure 1 Luminal H₂O₂ transiently stimulates Cl secretion. After the addition of 10 mmol/L H₂O₂ to the apical surface of unstripped rat distal colon segments at time 0 (in white circles, n = 4), basal Isc increased significantly compared to control (black circles, n = 4), with maximal secretion occurring 5 min after the addition of the oxidant (P < 0.001).

Figure 2 Oxidant-stimulated secretion is sensitive to basolateral atropine. Both phenylarsine oxide (PAO, 0.2 mmol/L) and chloramine T (ClT, 5 mmol/L) showed a similar prosecretory effect when they were added luminally to rat distal colon. A: Preincubation of colon segments with basolateral atropine (1 g/L) for ten minutes (added at time -10; in white circles, n = 3) suppressed the increase in Isc induced by luminal cysteine oxidizing agent PAO added at time 0 (control in black circles; n = 3; P < 0.01 between groups); B: A similar result was observed with the methionine oxidizing compound chloramine T. Basolateral incubation with 1 g/L of atropine (added at time -10; in white circles, n = 8) suppressed the secretory response caused by ClT added at time 0 (in black circles, n = 8; P < 0.001 between groups).

Figure 3 cAMP-activated secretion is blocked by luminal H₂O₂. Incubation of rat distal colon with 10 mmol/L H₂O₂ for 30 min (white circles; n = 6) inhibited the rise in Isc caused by 10 μmol/L forskolin added at time 0 (control in black circles; n = 6; P < 0.01) in white circles, n = 8) and suppressed the secretory response caused by ClT added at time 0 (in black circles, n = 8; P < 0.001 between groups).

Figure 4 Ca²⁺-stimulated Cl^- secretion is not affected by luminal by luminal H₂O₂. Incubation of rat distal colon with 10 mmol/L H₂O₂ for 30 min (white circles; n = 6) slightly enhanced the response induced by 100 μmol/L carbachol (control in black circles; n = 6; NS).