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 (PD(T)) from -4.0 +/- 0.8 (SE) to -15.1 +/- 1.4 mV (n = 9, P < 0.001) and decreased the transepithelial resistance (R(T)) from 40 +/- 8 to 33 +/- 6 OMEGA-.cm2 (n = 5, P < 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-mu-M forskolin produced the same effects, reversibly hyperpolarizing PD(T) by 7.0-11.5 mV and decreasing R(T) by 6-12 OMEGA-.cm2. Addition of 10-mu-M amiloride to the luminal perfusate reduced PD(T) from -0.9 to +2.0 mV and increased R(T) in the presence or absence of any of the test agents. Addition of DBcAMP + IBMX or 50-mu-M 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.