Regulation of ⁸⁶Rb⁺ ion transport across polarized human colonocytes by bis‐phenolic compounds

Abstract

1. Phenolphthalein, a well-known laxative, stimulates the secretion of Na+ and Cl- ions and accompanying water into the intestinal tract. Measurement of 86Rb+ efflux from several, but not all, cell types indicates that phenolphthalein also results in release of cellular K+ ions. 2. In the present study, the transport of 86Rb+ across human colonocyte cells (T84) cultured on trans-well inserts was examined. The T84 cells were cultured until they developed tight junctions and a high trans-epithelial resistance. 3. Results show that phenolphthalein applied to the apical, but not the basolateral, surface of cells causes the release of 86Rb+ from the apical surface. Basolateral treatment of cells with phenolphthalein had no effect on the release of 86Rb+. 4. Simultaneously with the increased 86Rb+ efflux, indirect evidence of enhanced Na+/K+-ATPase activity was also observed. 5. Although ouabain inhibited the increased Na+ pump activity, it did not affect apical 86Rb+ release. 6. As evidenced by near steady state 86Rb+ uptake data, the increased Na+/K+-ATPase activity was insufficient to restore intracellular concentrations of K+ in the presence of phenolphthalein. 7. 4,4(9-Fluorenylidene)diphenol, a homologue of phenolphthalein, had a similar effect on 86Rb+ transport by T84 cells. 8. These results indicate a primary stimulation of 86Rb+ efflux from the apical surface of polarized T84 cells by apically applied bis-phenolic compounds. 9. A secondary stimulation of the basolateral Na+/K+-ATPase is thought to result from intracellular Na+ increase, as documented in several other cell types exposed to bis-phenolic compounds, although not directly measured in these experiments. 10. The results also indicate that bis-phenolic compounds interact specifically with some apical but not basolateral membrane structures in regulating 86Rb+ efflux from polarized T84 cells.

Nitric Oxide Does Not Mediate Promotion of Cellular Potassium Release by Phenolphthalein in Cos‐7 Cells

“…This led to the hypothesis that NO is an important mediator of laxative action and that NO may be an important regulator of ion transport by intestinal epithelial cells. We have shown previously that phenolphthalein stimulates 86 Rb + and K + release from a range of epithelial cells, including COS‐7 cells and T84 intestinal epithelial cells, in vitro 13,16,17 and here test the hypothesis that NO mediates this cation release.…”

“…We conclude that the effect of phenolphthalein on cellular release of 86 Rb + and K + ions is probably distinct from its laxative action. A direct effect of phenolphthalein on the cell surface seems likely, because we have shown that phenolphthalein exerts its effect on the apical face of polarized epithelial cells and clofilium, a potassium channel blocker, partially abrogates the effect of the laxative 17 . The identity of the channel involved has not yet been determined.…”

Intestinal epithelial secretion and barrier function: from bench to bedside

“…Similarly, ligustrazine, the active constituent of a traditional Chinese medicine for postmenopausal women, was shown to activate CFTR-dependent chloride secretion in intestinal epithelial cells while improving barrier function secondary to upregulation of the tight junctional proteins ZO-1 and ZO-2 [131], implying it might be useful to alleviate symptoms of constipation in the elderly. Finally, yet another laxative, phenophthalein, evokes epithelial potassium secretion, which would also be expected to drive fluid transport into the intestinal lumen [132]. In total, studies of the type described may spur the development of new treatments for constipation, a very common yet neglected condition.…”