Effects of taurine-conjugated bile salts on ionic transport of the rabbit esophageal mucosa.

Bile salts have been implicated as a cause of esophageal injury. We examined in vitro the changes in ionic transport of the rabbit esophagus resulting from taurine-conjugated bile salts at neutral pH to define and characterize their actions independent of hydrogen ion. In an Ussing chamber changes in potential difference (PD, mV), short-circuit current (SCC, microA X cm-2) and resistance (R, omega X cm2) resulting from taurocholate (TC), taurodeoxycholate (TDC) and taurochenodeoxycholate (TCDC) were studied. Transport properties were unaffected by TC at 5 and 10 mM. With TDC (5 mM) there was an initial rise in SCC and PD. After 60 min PD and R declined in association with an increase in paracellular permeability as measured by [14C]sucrose flux. TCDC (5.0 and 7.5 mM) caused a sustained rise in PD and SCC with a greater rise seen at 7.5 mM. The rise in SCC after TCDC was secondary to an increase in net sodium absorption as basal net sodium absorption increased threefold from 0.15 +/- 0.03 to 0.44 +/- 0.10 mu eq X cm-2 X h-1. Increased net sodium absorption accounted for 73% of the TCDC-induced rise in SCC. Amiloride (10(-4) M) added to the mucosal solution significantly inhibited this bile salt-induced rise in SCC. We conclude that bile salts alter ionic transport in the esophageal mucosa independent of hydrogen ion. These changes are characterized by an early selective increase in apical membrane cation conductance and with longer exposure, particularly in the presence of more hydrophobic bile salts, there is a marked increase in paracellular conductance.