Stereospecific Inhibition by Ozolinone of Stimulated Chloride Secretion in Rabbit Colon Descendens

The effects of the diuretic drug ozolinone on electrogenic Cl- secretion by rabbit colonic mucosa were investigated in vitro. Electrical properties and unidirectional Cl- fluxes were measured in stripped preparations mounted in Ussing-type chambers. After abolition of electrogenic Na+ absorption by amiloride (10(-4) mol/l) on the mucosal side electrogenic Cl- secretion was induced by addition of PGE1 (10(-6) mol/l, serosal side) and theophylline (10(-2) mol/l, both sides). Under these conditions, the monitored short-circuit current (Isc) equals the amount of Cl- secreted as evidenced by determination of unidirectional Cl- fluxes. After establishing a stable Cl- secretion its sensitivity to the enantiomers of the diuretic was studied. Only levorotatory (-)-ozolinone, but not the dextrorotatory (+)form, inhibited Cl- secretion on serosal application. This effect was fully accounted for by a reduction in the serosal-to-mucosal Cl- fluxes (JClsm). It was readily reversible and concentration-dependent with a Ki value of 6 x 10(-4) mol/l, but absent when the drug was added to the mucosal side. The results are in agreement with the hypothesis that loop diuretics inhibit a coupled NaCl entry mechanism across the baso-lateral membrane into colonic epithelial cells. This mechanism is though to account for Cl- influx into the cells.