Selective stimulation of epithelial cells in colonic crypts: relation to active chloride secretion

D. R. Halm, S. T. Halm, D. R. DiBona, R. A. Frizzell and R. D. Johnson Department of Physiology, Ohio State University, Columbus 43210, USA. Stimulation of Cl secretion by prostaglandin E2 (PGE2) was measured as the short-circuit current (Isc) across isolated epithelium of the rabbit distal colon. Cellular morphology of columnar and goblet cells during secretion was monitored using light and electron microscopy. Stimulation by PGE2 altered epithelial cell morphology only by a reduction of vacuolar space in the apical pole of crypt columnar cells, consistent with release of vacuole contents. Imaging of isolated crypts using differential interference microscopy confirmed the release of material from columnar cells during the onset of secretion. Inhibition of Cl secretion with the loop diuretic bumetanide did not block vacuole release. The actin filament-disrupting agent, cytochalasin, reduced the PGE2-stimulated Isc by 40% and blocked emptying of the vacuolar space. These electrical and morphological results indicate that the process of active ion secretion is associated with release of the macromolecular contents from apical vacuoles through a mechanism involving the cytoskeleton. In addition, this relationship supports the concept that vacuolated columnar cells of the crypts of Lieberkuhn are the cell type that secretes Cl in response to PGE2.