Passive transepithelial diltiazem absorption across intestinal tissue leading to tight junction openings

Diltiazem hydrochloride fluxes were tested in side-by-side acrylic diffusion chambers using rat colon, rat duodenum, Caco-2 and T84 intestinal epithelia. Fluxes performed in traditional Ussing chambers were inaccurate due to binding of diltiazem to system components leading to loss of mass balance. For all tissues tested in the side-by-side chambers the apparent permeability coefficient (P-app) values ranged from 0.5 to 2.8 x 10(-5) cm s(-1) in both the absorptive and secretory direction. These fluxes were unsaturable and were unaffected by alterations in transepithelial resistance (TER) caused by either incubating the tissues with apical cytochalasin D (1 mu g ml(-1)) or by high concentrations of apical diltiazem (2 mM). Apical but not basolateral additions of diltiazem caused an increase in short-circuit current (I-sc) across rat colon and T84 monolayers. In addition, a concentration-dependent disruptive effect of mM concentrations of diltiazem was detected by electron microscopy (EM) in T84 cells, as defined by tight junction openings, vacuolization and cell sloughing. Using a single pass perfusion in situ method on duodenal segments in anaesthetized rats, the P-app for diltiazem was 2.58 x 10(-5) cm s(-1) at a flow rate of 3.33 x 10(-3) ml s(-1). As with the in vitro method, incubation with apical cytochalasin D in situ was without effect on the diltiazem P-app. Taken together these results indicate that diltiazem is absorbed across rat intestine by passive transcellular diffusion as shown by each of the models. The results also indicate that diltiazem is a secretagogue which may induce intestinal water secretion in association with concentration-dependent reduction of epithelial integrity.