Potassium secretion by rat distal colon during acute potassium loading: effect of sodium, potassium intake and aldosterone.

Abstract

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.

The effect of dietary sodium and potassium intake on potassium secretion and kinetics in rat distal colon.

“…In all groups the secretion rate increased by two-to threefold during the potassium infusion, a change comparable to that observed previously (Edmonds & Willis, 1988a). The particular interest of these experiments, however, was the effect of the acute potassium load on chloride secretion.…”

“…Rubidium-86 has been widely used as an analogue of potassium and it was shown previously that 86Rb+ behaved similarly to potassium in the distal colon (Edmonds & Willis, 1988a). In the present experiments, we used 86Rb+ to examine epithelial secretion under various experimental conditions.…”

“…But in rats fed a potassium-rich diet, sodium absorption is unchanged and, providing dietary potassium is not in gross excess, the PD is also unchanged (Fisher et al 1976;Budinger, Foster, Hayslett & Binder, 1986;Edmonds & Willis, 1988a). A further difference is in the effect of amiloride at low concentration (10-4 M or less in the lumen) which abolishes the PD by completely blocking active sodium absorption in sodium-depleted rats but which only partially reduces the PD in the rats fed a potassium-rich diet (Will, Lebowitz & Hopfer, 1980;Edmonds & Willis, 1988a). There is a substantial body of evidence showing that the adrenal secretion of aldosterone plays a major part in these epithelial adaptations (Edmonds & Marriott, 1967;Bastl, Binder & Hayslett, 1980;Foster, Jones, Hayslett & Binder, 1985;Martin, Oszi, Brocca, Arrizurietta & Hayslett, 1986).…”

Effects of Eimeria separata infections on Na + and Cl - transport in the rat large intestine

“…Edmonds and Willis 1988). In the present experiment, the disturbed sodium balance due to reduced sodium net absorption in the infested caecum and colon may have been responsible for increased aldosterone synthesis.…”

Aldosterone in colonic potassium adaptation in rats

“…One of these is potassium intake, potassium being secreted at an increased rate when the animal takes a potassium-rich diet (Fisher, Binder & Hayslett, 1976). Moreover, the adminis¬ tration of an acute potassium load results in a brisk rise of colonie potassium secretion (Basti, Kliger, Binder & Hayslett, 1978), and this is considerably enhanced if the animal is taking a potassium-rich diet (Edmonds & Willis, 1988). Thus colonie epithelium behaves similarly to that of the kidney.…”