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Transport and epithelial secretion of the cardiac glycoside, digoxin, by human intestinal epithelial (Caco‐2) cells
Author(s) -
Cavet Megan E.,
West Mike,
Simmons Nicholas L.
Publication year - 1996
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1996.tb15550.x
Subject(s) - digitoxin , digoxin , ouabain , medicine , endocrinology , cardiac glycoside , chemistry , verapamil , apical membrane , biology , biochemistry , calcium , sodium , heart failure , organic chemistry , membrane
1 Human intestinal epithelial Caco‐2 cells have been used to investigate the transepithelial permeation of the cardiac glycoside, digoxin. 2 Transepithelial basal to apical [ 3 H]‐digoxin flux exceeds apical to basal flux, a net secretion of [ 3 H]‐digoxin being observed. At 200 μ m digoxin, net secretory flux (J net ) was 10.8 ± 0.6 nmol cm −2 h −1 . Maximal secretory flux (J max ) of vinblastine was 1.3 ± 0.1 nmol cm −2 h −1 . Cellular uptake of digoxin was different across apical and basal cell boundaries. It was greatest across the basal surface at 1 μ m , whereas at 200 μ m , apical uptake exceeded basal uptake. 3 Net secretion of [ 3 H]‐digoxin was subject to inhibition by digitoxin and bufalin but was not inhibited by ouabain, convallatoxin, and strophanthidin (all 100 μ m ). Inhibition was due to both a decrease in J b‐a and an increase in J a‐b . Uptake of [ 3 H]‐digoxin at the apical surface was increased by digitoxin and bufalin. All cardiac glycosides decreased [ 3 H]‐digoxin uptake at the basal cell surface (except for 100 μ m digitoxin). 4 The competitive P‐glycoprotein inhibitors, verapamil (100 μ m ), nifedipine (50 μ m ) and vinblastine (50 μ m ) all abolished net secretion of [ 3 H]‐digoxin due to both a decrease in J b‐a and an increase in J a‐b . Cellular accumulation of [ 3 H]‐digoxin was also increased across both the apical and basal cell surfaces. 1‐Chloro‐2,4,‐dinitrobenzene (10 μ m ), a substrate for glutathione‐S‐transferase and subsequent ATP‐dependent glutathione‐S‐conjugate secretion, failed to inhibit net secretion of [ 3 H]‐digoxin. The increase in absorptive permeability P a‐b (= J a‐b /C a ) and cellular [ 3 H]‐digoxin uptake upon P‐glycoprotein inhibition, showed that the intestinal epithelium was rendered effectively impermeable by ATP‐dependent extrusion at the apical surface. 5 A model for [ 3 H]‐digoxin secretion by the intestinal epithelium is likely to involve both diffusional uptake and Na + ‐K + pump‐mediated endocytosis, followed by active extrusion at the apical membrane.