INHIBITORY EFFECT OF ACETAZOLAMIDE ON ACTIVE CHLORIDE AND BICARBONATE TRANSPORT MECHANISMS ACROSS SHORT-CIRCUITED TURTLE BLADDERS

Acetazolamide added to the serosal fluid, at a final concentration of 0.1 mM, inhibits the active transport of Cl- and HCO3- across the short-circuited turlte bladder. When bladders are bathed on both mucosal and serosal surfaces by Na+-free choline Ringer solutions containing Cl- and HCO3-, the net Cl- flux (m to s) accounts for only half of the short-circuiting current. If HCO3- is removed from the mucosal fluid the net Cl- flux accounts for all of the short-circuiting current. In the experiments presented in this report both the net Cl- flux and the short-circuiting current were inhibited by acetazolamide. When Cl- was replaced by SO42- in the Na+-free choline Ringer the short-circuiting current associated with the presence of HCO3- in the bathing fluids was also inhibited by addition of acetazolamide to the serosal fluid. These inhibitory effects could be reversed in most of the experiments. Previous work has shown that ouabain-treated bladders in Na+-rich ambient media were indistinguishable from untreated bladders in Na+-free (choline) ambient media. This finding was confirmed. In this connection, acetazolamide inhibited, in the same quantitative and qualitative fashion, the active transport of Cl- and HCO3- in ouabain-treated Na+-rich preparations as well as in Na+-free preparations. Acetazolamide fails to inhibit both moieties, the Mg2+-dependent and the (Na+ + K+-stimulated, of the ATPase activity found in the microsomes of the turtle bladder. A relation between the active transport of Cl- and HCO3- and the enzyme carbonic anhydrase is difficult to entertain at this poitn since homogenates of the turtle bladder do not possess carbonic anhydrase activity. © 1969.