Potassium secretion by rat distal colon during acute potassium loading: effect of sodium, potassium intake and aldosterone
1. Potassium secretion by the distal colon before and during intravenous infusion of a potassium load was measured in vivo in groups of rats treated in various ways: A, normal control; B, adrenalectomized; C, sodium depleted; D, on potassium-rich diet for 7 days; E, after 72 h aldosterone (1 microgr...
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Veröffentlicht in: | The Journal of physiology 1988-07, Vol.401 (1), p.39-51 |
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Zusammenfassung: | 1. Potassium secretion by the distal colon before and during intravenous infusion of a potassium load was measured in vivo
in groups of rats treated in various ways: A, normal control; B, adrenalectomized; C, sodium depleted; D, on potassium-rich
diet for 7 days; E, after 72 h aldosterone (1 microgram/h); F, after 72 h aldosterone (10 micrograms/h). 2. Potassium infusion
produced no increase of secretion in the adrenalectomized rats but in all the other groups it increased by 2- to 3-fold. Secretion
during infusion correlated well with the basal (pre-infusion) rate and in groups C and D reached 140 +/- 15 and 173 +/- 17
nmol min-1 cm-1 respectively compared with 28 +/- 6 nmol min-1 cm-1 in the controls (A). The passive paracellular pathway
for potassium was unaffected by the infusion. Amiloride (100 mumol/l) did not significantly affect potassium secretion rate
either before or during the acute potassium infusion. The potassium channel blocker, tetraethylammonium chloride, reduced
both basal and the secretion rate during infusion. 3. Transepithelial potential difference (PD), active sodium absorption
and sodium fluxes were similar in normal controls and rats fed the potassium-rich diet. However, the PD was partially amiloride
sensitive in the latter group although amiloride insensitive in the normal group. In sodium-depleted rats, the PD was elevated
and totally amiloride insensitive. 4. In both aldosterone-treated groups (E and F), basal potassium secretion rate was high
and similar, and during potassium infusion rose 3-fold to 114 +/- 24 (E) and 105 +/- 5 (F) nmol min-1 cm-1. However, the PD
was not elevated significantly in group E and was only partially amiloride sensitive, whereas in those infused at the higher
rate (F) the PD was increased and was totally amiloride sensitive. 5. The high potassium secretion rates developed by this
epithelium in sodium-restricted and potassium-enriched dietary states appear to depend on the presence of an amiloride-insensitive
transcellular potassium pathway which is induced at a lower level of aldosterone stimulation than is the amiloride-sensitive
transcellular sodium pathway. |
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ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.1988.sp017150 |