Mechanism of active chloride transport by urinary bladder of the Colombian toad

In order to investigate the mechanism of active chloride transport, experiments were performed to verify the previous report that removal of potassium from the solutions bathing the urinary bladders of Colombian toads induced a reversal of short-circuit current (RSCC) and active chloride transport. The present experiments confirmed these findings. However, there was no correlation between the magnitude of the RSCC and the chloride transport. Furthermore, removal of chloride from the mucosal bathing solutions did not markedly affect the RSCC, indicating that the chloride transport was electrically silent. Removal of bicarbonate from the bathing solutions eliminated the RSCC, and acetazolamide inhibited both the RSCC and net chloride transport. These findings suggest a relationship between chloride and hydrogen ion transport. Inhibition of sodium transport by removal of sodium or addition of ouabain or amiloride has previously been shown to produce an RSCC. In the present experiments these same maneuvers caused an RSCC and induced net chloride transport. It is concluded that active chloride transport by Colombian toad bladder is stimulated by inhibition of sodium transport. The inhibition of active chloride transport by acetazolamide suggests a possible role for carbonic anhydrase in this process.