cAMP mediates the increase in apical membrane Na+ conductance produced in rat CCD by vasopressin

Experiments were conducted to determine if adenosine 3',5'-cyclic monophosphate (cAMP) mediates the stimulation of Na+ absorption by arginine vasopressin (AVP) in isolated perfused cortical collecting ducts (CCD) from rats treated with deoxycorticosterone pivalate (5 mg im) 5-9 days before study. AVP (220 pM) in the bathing solution hyperpolarized the transepithelial voltage (PDT) from -4.0 +/- 0.8 (SE) to -15.1 +/- 1.4 mV (n = 9, P less than 0.001) and decreased the transepithelial resistance (RT) from 40 +/- 8 to 33 +/- 6 omega.cm2 (n = 5, P less than 0.025). Bath addition of 0.2 mM dibutyryl cAMP (DBcAMP), 0.1 mM isobutylmethylxanthine (IBMX), 0.1 mM DBcAMP plus 0.1 mM IBMX, and 10 or 50 microM forskolin produced the same effects, reversibly hyperpolarizing PDT by 7.0-11.5 mV and decreasing RT by 6-12 omega.cm2. Addition of 10 microM amiloride to the luminal perfusate reduced PDT from -0.9 to +2.0 mV and increased RT in the presence or absence of any of the test agents. Addition of DBcAMP + IBMX or 50 microM forskolin to the bathing solution also reversibly depolarized the basolateral membrane voltage of principal cells by 1-2 mV and decreased the apical membrane fractional resistance from 0.82-0.84 to 0.72-0.77. Both effects were reversed by addition of amiloride to the luminal perfusate. These results demonstrate that cAMP is the intracellular mediator of the increase in apical membrane Na+ conductance produced by AVP in the rat CCD.