Effect of Shiga Toxin on NaCl Transport in Rat Distal Colon

Abstract

Background: Shiga toxin causes net fluid secretion in rabbit jejunum by selectively targeting, and inhibiting protein synthesis in, absorptive villous cells. The effect of Shiga toxin on the colon, where it is presumably produced, is not known. This study was undertaken to investigate the effect of Shiga toxin on the rat distal colon. Methods: Net absorption of water and Na was determined by in vivo perfusion of closed loops of rat colon pre-exposed to Shiga toxin or saline. Unidirectional and net fluxes of 22Na and 36Cl were measured in vitro under voltage-clamp conditions across rat distal colon mucosa pre-exposed to Shiga toxin. Shiga toxin binding to sections of rat distal colon was localized by immunohistochemistry. Protein synthesis was measured in surface and crypt colonocytes with 3H-leucine incorporation. Results: In the in vivo perfusion studies net absorption of Na and water was increased in Shiga toxin-treated colon compared with controls (P < 0.01). In the studies carried out in vitro, JnetNa and JnetCl across Shiga toxin-treated mucosa were found to be significantly higher than in control tissue (P < 0.001 and P < 0.01, respectively). Net absorption of Na or Cl did not increase further in the presence of 25 mM butyrate, indicating the absence of short-chain fatty acids (SCFA)-linked NaCl absorption in Shiga toxin-treated colon. Moreover, Shiga toxin-treated colon failed to respond to theophylline, which induced secretion in the normal colon. Immunohistochemistry showed Shiga toxin binding to crypt cells but not to surface cells in the distal colon. Shiga toxin inhibited protein synthesis (by 27.3%) in crypt cells but not in surface cells (P < 0.05). Conclusions: An unexpected increase in water and NaCl absorption was noted in Shiga toxin-treated rat distal colon, which appears to result from selective effects of the toxin on secretory crypt cells.