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_sm^Cl). 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.