INDUCTION OF EPITHELIAL CHLORIDE SECRETION BY CHANNEL-FORMING CRYPTDIN-2 AND CRYPTDIN-3

Salt and water secretion from intestinal epithelia requires enhancemen t of anion permeability across the apical membrane of Cl- secreting ce lls lining the crypt, the secretory gland of the intestine, Paneth cel ls located at the base of the small intestinal crypt release enteric d efensins (cryptdins) apically into the lumen, Because cryptdins are ho mologs of molecules known to form anion conductive pores in phospholip id bilayers, we tested whether these endogenous antimicrobial peptides could act as soluble inducers of channel-like activity when applied t o apical membranes of intestinal Cl- secreting epithelial cells in cul ture, Of the six peptides tested, cryptdins 2 and 3 stimulated Cl- sec retion from polarized monolayers of human intestinal T84 cells, The re sponse was reversible and dose dependent, In contrast, cryptdins 1, 4, 5, and 6 lacked this activity, demonstrating that Paneth cell defensi ns with very similar primary structures may exhibit a high degree of s pecificity in their capacity to elicit Cl- secretion, The secretory re sponse was not inhibited by pretreatment with 8-phenyltheophyline (1 m u M), or dependent on a concomitant rise in intracellular cAMP or cGMP , indicating that the apically located adenosine and guanylin receptor s were not involved, On the other hand, cryptdin 3 elicited a secretor y response that correlated with the establishment of an apically locat ed anion conductive channel permeable to carboxyfluorescein, Thus cryp tdins 2 and 3 can selectively permeabilize the apical cell membrane of epithelial cells in culture to elicit a physiologic Cl- secretory res ponse, These data define the capability of cryptdins 2 and 3 to functi on as novel intestinal secretagogues, and suggest a previously undescr ibed mechanism of paracrine signaling that in vivo may involve the rev ersible formation of ion conductive channels by peptides released into the crypt microenvironment.