Calcium and protein kinase C play a significant role in response to Shigella toxin in rabbit ileum both in vivo and in vitro.

The role of second messengers in Shigella toxin (STx) induced fluid secretion in rabbit ileum was evaluated. In vivo and in vitro studies were carried out in presence or absence of following modulators: Ca2+ ionophore A23187 (15 microM), l-verapamil (200 microM), phorbol-12-myristate-13-acetate (PMA, 200 ng), 1-(5-isoquinolinyl-sulphonyl)-2-methyl-piperazine (H-7, 15 microg) and indomethacin (20 microM). In in vivo studies, the fluid accumulation into rabbit ileal loops in response to STx was measured in presence or absence of these modulators. In in vitro studies, unidirectional fluxes of Na+ and Cl- were carried out in presence or absence of these modulators. The addition of Ca2+ ionophore A23187 along with STx further increases the amount of fluid already induced by STx. Whereas the presence of l-verapamil along with STx did not decrease the amount of fluid induced by STx. In vitro findings were in consonance with the in vivo studies. A significant increase in inositol triphosphate (IP3) levels was observed in enterocytes isolated from STx treated rabbit ileum. The addition of PMA into rabbit ileal loops in presence of STx mimicked the effect of STx while the presence of H-7 reversed the secretion caused by STx to absorption. Similar results were obtained while determining unidirectional fluxes of Na+ and Cl- in presence of PMA and also with H-7. A significant increase in PKC levels was observed in the membrane fraction of enterocytes isolated from STx treated rabbit ileum as compared to control. Further a marked decrease in PKC levels was observed in the presence of H-7 in membrane fraction of enterocytes isolated from STx treated rabbit ileum. The addition of indomethacin into rabbit ileal loops reversed the secretion (caused by STx) to absorption. In vitro findings were in consonance with in vivo studies. Besides, there was a significant increase in PG-E levels in enterocytes isolated from STx treated rabbit ileum as compared to control. These findings suggested that STx induced enteritis involves the role of PKC, intracellular calcium stores and prostaglandins. The extracellular calcium pool probably does not play a significant role in this process.