Bile salts regulate ion transport in the intestine of Senegalese sole

The regulatory role of taurocholic acid (TC) and taurolithocholic acid (TLC) in ion transport was investigated with the short-circuit current (Isc) technique in the intestine of Senegalese sole (Solea senegalensis). Under voltage clamp conditions, Isc was stable for over 3 h and averaged −15.42 ± 2.75 μA/cm2 and −65.28 + 7.69 μA/cm2 in the anterior and posterior intestine, respectively. Only bumetanide (200 μM), a loop diuretic that inhibits Na+/K+/2Cl− co-transporters, inhibited the absorptive Isc, and apical application of NPPB (200 μM), EIPA (200 μM), glibenclamide (200 μM) and DIDS (200 μM) were without effect in the absorptive current. Apical application of TC and TLC induced rapid (<1 min) increases in the absorptive current in the anterior and the posterior intestine. The responses were dose dependent in the range of physiological levels of TC or TLC previously detected in the intestine of Senegalese sole, 0.4-4 mM, with higher responses in the posterior intestine at the same doses. The response to apical application of TC and TLC was completely abolished by bumetanide (200 μM). In addition, the effect of TC or TLC in preparations with bilateral reduction of chloride (from 146 to 6 mM) in the chamber saline was reduced by 80%. Conclusions of this study indicate that the bile salts TC and TLC alter ionic transport in the intestine of marine fish enhancing the absorptive pathway. These changes revealed by regulation of Isc are characterized by their dose-dependent action, intestinal region dependency, reversibility, chloride dependence and bumetanide sensitivity.