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Effect of ouabain on K secretion in cortical collecting tubules from adrenalectomized rabbits
Abstract:
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.
Insights
Mineralocorticoids enhance potassium secretion in rabbit kidney tubules, with Na-K-ATPase being crucial for this process. This study investigated ouabain
Area of Science:
- Nephrology
- Renal Physiology
- Endocrinology
Background:
- Na-K-ATPase activity in rabbit cortical collecting tubules is modulated by mineralocorticoids.
- Mineralocorticoid stimulation increases, while adrenalectomy decreases, Na-K-ATPase activity.
Purpose of the Study:
- To investigate the effects of ouabain on potassium (K) secretion in isolated rabbit cortical collecting tubules.
- To compare K secretion and ouabain's inhibitory effects across normal, adrenalectomized, and mineralocorticoid-stimulated states.
Main Methods:
- Isolated perfused cortical collecting tubules from rabbits were used.
- Animals were normal, adrenalectomized, or treated with 11-deoxycorticosterone acetate (DOCA).
- The effect of 10(-4) M ouabain on K secretion and transepithelial voltage was measured.
Main Results:
- Potassium secretion was similar in adrenalectomized and normal rabbits but significantly higher in DOCA-treated rabbits.
- Ouabain inhibited K secretion in all groups, indicating total dependence on Na-K-ATPase.
- Ouabain altered transepithelial voltage differently across groups, suggesting mineralocorticoid-specific effects beyond Na-K-ATPase.
Conclusions:
- Adrenal mineralocorticoids are essential for maximal K secretion in cortical collecting tubules but not for maintaining secretion during normal K intake.
- Potassium secretion in all tested conditions is entirely dependent on Na-K-ATPase activity.
- Mineralocorticoids may stimulate cation secretion or anion reabsorption, independent of Na-K-ATPase.