Potassium secretion by neonatal rat distal colon

Abstract

Electrogenic K⁺ secretion across the distal colon of young rats was investigated by measuring the sensitivity of the short-circuit current to Ba²⁺ added to the mucosal side of the tissue. Ba²⁺-sensitive short-circuit current (I ^Ba_sc ) was high during the suckling and weaning periods but very low in adult animals. Increasing the mucosal K⁺ concentration was accompanied by the inhibition of the serosa-to-mucosaI ^Ba_sc and the induction of the mucosa-to-serosaI ^Ba_sc . TheI ^Ba_sc was decreased by serosal omission of either Na⁺ or Cl⁻ as well as by serosal addition of furosemide or ouabain. Mucosal omission of Na⁺ did not changeI ^Ba_sc . By increasing the plasma level of aldosterone (low-sodium diet)I ^Ba_sc rose by 95% whereas treatment decreasing this level (high-sodium diet) reducedI ^Ba_sc by 76%. Bilateral adrenalectomy loweredI ^Ba_sc by 59% and treatment of adrenalectomized rats with deoxycorticosterone acetate prevented the reduction ofI ^Ba_sc . Tetraethylammonium and quinidine had similar effects onI _sc as Ba²⁺. These data are consistent with the presence of a high level of K⁺ secretion in the distal colon of neonatal rats. This secretory pathway is electrogenic and independent of Na⁺ absorption. It appears to be mediated by the Na−K-ATPase as well as a furosemide-sensitive Na−Cl or Na−Cl−K cotransport on the basolateral side and by Ba²⁺-sensitive K⁺ conductive pathways on the mucosal side. The results suggest that this K⁺ secretion can be regulated by mineralocorticoids. The mineralocorticoids are necessary for “stimulated” K⁺ secretion but they are not essential for maintaining “basal” K⁺ secretion.