Stereospecific inhibition by ozolinone of stimulated chloride secretion in rabbit colon descendens

Summary

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 (10⁻⁶mol/l, serosal side) and theophylline (10⁻²mol/l, both sides). Under these conditions, the monitored short-circuit current (I_sc) 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 (J ^Cl_sm ). It was readily reversible and concentration-dependent with a K _i value of 6×10⁻⁴mol/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.