Cortical collecting tubule potassium secretion: Effect of amiloride, ouabain, and luminal sodium concentration

Cortical collecting tubule potassium secretion: Effect of amiloride, ouabain, and luminal sodium concentration. The present study examined the effect of sodium transport inhibition by amiloride, ouabain, and luminal sodium removal on potassium secretion in isolated cortical collecting tubules from adrenalectomized and DOCA-stimulated rabbits. Collecting tubules from adrenalectomized rabbits had a mean potassium secretion of 3.62 ± 0.37 pmoles·mm -1 ·min -1 , which significantly decreased to 1.52 ± 0.21 pmoles·mm -1 ·min -1 after addition of amiloride, but no additional effect was observed after the addition of ouabain. The transepithelial voltage (V T ) became less positive after exposure to amiloride. Cortical collecting tubules from DOCA-treated animals exhibited significantly greater potassium secretion (28.6 ± 9.4 pmoles·mm -1 ·mm -1 ). Amiloride totally inhibited potassium secretion, and V T reversed polarity in these tubules. In tubules from adrenalectomized rabbits the removal of luminal sodium inhibited potassium secretion by approximately 44% but had no effect on V T . There remained, however, a substantial amount of potassium secretion in the absence of transepithelial sodium flux. Thus, potassium secretion in the cortical collecting tubule is highly dependent on sodium reabsorption under conditions of mineralocorticoid stimulation but significantly less so in adrenalectomized animals. Potassium secretion in the cortical collecting tubule of adrenalectomized rabbits is inhibited independent of V T and occurs, in part, by an apparent electroneutral process. Chronic exposure to mineralocorticoids appears to stimulate electrogenie sodium reabsorption and potassium secretion. Secretion de potassium dans le tubule collecteur cortical: effets de la concentration de l'amiloride, de l'ouabaine et du sodium luminal. Cette etude a permis d'examiner l'effet de l'inhibition du transport de sodium (Na) par l'amiloride, l'ouabaine et la supression du Na luminal sur la secretion de potassium (K) dans des tubules collecteurs corticaux isoles de lapins surrenalectomises et stimules par la DOCA. Les tubules collecteurs de lapins surrenalectomises avaient une secretion moyenne de K de 3,62 ± 0,37 pmoles·mm -1 ·min -1 , qui diminuait significativement a 1,52 ± 0,21 pmoles·mm -1 ·min -1 apres addition d'amiloride, mais aucun effet supplementaire n'etait observe apres addition d'ouabaine. Le voltage transepithelial (V T ) devenait moins positif apres exposition a l'amiloride. Les tubules collecteurs corticaux des animaux traites a la DOCA presentaient une secretion de K significativement plus elevee (28,6 ± 9,4 pmoles·mm -1 min -1 . L'amiloride inhibait totalement la secretion de K, et V T inversait sa polarite dans ces tubules. Dans les tubules de lapins surrenalectomises, la suppression de Na luminal inhibait la secretion de K d'environ 44% mais n'avait pas d'effet sur V T . Il restait, cependant, une quantite substantielle de K secrete en l'absence de flux transepithelial de Na. Ainsi, la secretion de K dans le tubule collecteur cortical est tres dependante de la reabsorption de Na dans des conditions de stimulation mineralocorticoide, mais significativement moins chez les animaux surrenalectomises. La secretion de K dans le tubule collecteur cortical de lapins surrenalectomises est inhibee independamment de V T et se produit en partie par un processus apparemment electroneutre. L'exposition chronique aux mineralocorticoides parait stimuler la reabsorption electrogene de Na et la secretion de K.