AJP - Renal Physiology, Vol 259, Issue 5 823-F831, Copyright © 1990 by American Physiological Society
cAMP mediates the increase in apical membrane Na+ conductance produced in rat CCD by vasopressin
J. A. Schafer and S. L. Troutman
Department of Physiology and Biophysics, University of Alabama, Birmingham 35294.
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.
