PASSIVE TRANSEPITHELIAL DILTIAZEM ABSORPTION ACROSS INTESTINAL TISSUELEADING TO TIGHT JUNCTION OPENINGS

Diltiazem hydrochloride fluxes were tested in side-by-side acrylic dif fusion chambers using rat colon, rat duodenum, Caco-2 and T84 intestin al epithelia. Fluxes performed in traditional Ussing chambers were ina ccurate due to binding of diltiazem to system components leading to lo ss of mass balance. For all tissues tested in the side-by-side chamber s 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 directi on. These fluxes were unsaturable and were unaffected by alterations i n transepithelial resistance (TER) caused by either incubating the tis sues with apical cytochalasin D (1 mu g ml(-1)) or by high concentrati ons of apical diltiazem (2 mM). Apical but not basolateral additions o f diltiazem caused an increase in short-circuit current (I-sc) across rat colon and T84 monolayers. In addition, a concentration-dependent d isruptive effect of mM concentrations of diltiazem was detected by ele ctron microscopy (EM) in T84 cells, as defined by tight junction openi ngs, vacuolization and cell sloughing. Using a single pass perfusion i n situ method on duodenal segments in anaesthetized rats, the P-app fo r 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 cytocha lasin D in situ was without effect on the diltiazem P-app. Taken toget her these results indicate that diltiazem is absorbed across rat intes tine 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-d ependent reduction of epithelial integrity.