EFFECT OF CYCLIC-AMP ON HYDROGEN-ION SECRETION BY TURTLE URINARY-BLADDER

Parathyroid hormone and its intracellular mediator cyclic AMP play a role in acid excretion by the mammalian kidney. To investigate this effect, we studied cyclic AMP in turtle bladder with the pH-stat method. In carbon dioxide-free and bicarbonate-free solutions, where neither hydrogen ion nor bicarbonate ion gradients existed, serosal cyclic AMP (10 mM) promptly decreased hydrogen ion secretion to 74% of the control value, from 1.22 ± 0.16 to 0.90 ± 0.14 μmoles/hr (P < 0.01). The combination of cyclic AMP and theophylline, an inhibitor of phosphodiesterase, decreased hydrogen ion secretion further, to 45% of the control value. The effect of cyclic AMP was additive to that of benzolamide, a known carbonic anhydrase inhibitor. Direct assay of tissue carbonic anhydrase activity demonstrated complete inhibition of the enzyme by benzolamide, but no inhibition by cyclic AMP and theophylline. The decreases in hydrogen ion secretion produced by cyclic AMP and theophylline were not linked to decreased active sodium transport. The results of the present study demonstrate a significant role of intracellular cyclic AMP in the control of hydrogen ion secretion by the turtle bladder. Cyclic AMP decreases active hydrogen ion secretion independently of passive hydrogen ion or bicarbonate ion movement and without coupled decreases in sodium transport. The data also indicate that cyclic AMP does not inhibit carbonic anhydrase in this tissue.