Antidiuretic hormone decreases the intracellular pH in distal nephron epithelium (A6) by inhibiting Na+/H+ exchange.

1. To clarify the effect of arginine vasotocin (AVT) on intracellular pH (pHi) of A6 cells (an amphibian renal cell line), we measured pHi with a single-cell fluorescent imaging system in an HCO3(-)-nominally-free medium. 2. AVT (40 mU/ml) significantly decreased pHi from 7.44 +/- 0.11 to 7.19 +/- 0.22 (mean +/- SE) by inhibiting the Na+/H+ exchanger. 3. A membrane-permeable analogue of cAMP, dibutyryl cAMP (1 mM), significantly decreased pHi from 7.40 +/- 0.02 to 7.17 +/- 0.02, a response similar to that of AVT. 4. These data indicate that, in A6 cells, AVT suppresses the Na+/H+ exchanger via a cAMP-dependent pathway and the Na+/H+ exchanger maintains pHi under HCO3(-)-nominally-free conditions.