AJP - Renal Physiology, Vol 247, Issue 4 588-F595, Copyright © 1984 by American Physiological Society
Effect of ouabain on K secretion in cortical collecting tubules from adrenalectomized rabbits
C. S. Wingo
Previous studies have shown that Na-K-ATPase activity in the cortical
collecting tubule of the rabbit increases significantly with
mineralocorticoid stimulation and decreases significantly with
adrenalectomy. The present study examined the effects of 10(-4) M ouabain
on K secretion in the isolated perfused cortical collecting tubules from
normal, adrenalectomized, and mineralocorticoid-stimulated animals.
Potassium secretion was similar in the tubules from adrenalectomized (3.42
+/- 0.53 pmol X mm-1 X min-1) and from normal rabbits (3.38 +/- 0.36 pmol X
mm-1 X min-1). K secretion was greater (15.1 +/- 3.0 pmol X mm-1 X min-1)
in tubules from animals receiving 11-deoxycorticosterone acetate (DOCA).
Ouabain inhibition of K secretion was 74% for the adrenalectomized group,
86% for the normal group, and 98% for the DOCA-treated group. The degree of
inhibition was statistically equivalent among the three groups and not
statistically different from complete inhibition of K secretion. Ouabain
had no effect on the lumen-positive transepithelial voltage of the cortical
collecting tubules from adrenalectomized rabbits but reduced the
lumen-negative voltage in tubules from normal rabbits and reversed the
polarity of the transepithelial voltage in cortical collecting tubules from
DOCA-treated animals. Thus adrenal mineralocorticoids may be necessary for
maximal K secretion by the cortical collecting tubule, but they are not
essential to maintain K secretion during "normal" K intake. In all groups K
secretion is totally dependent on Na-K-ATPase. The lumen-positive
transepithelial voltage from DOCA-treated animals after addition of ouabain
suggests an additional effect of mineralocorticoid to stimulate secretion
of cations (protons) or reabsorption of anions.
