Potassium secretion by neonatal rat distal colon

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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 sc Ba ) 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 sc Ba and the induction of the mucosa-to-serosaI sc Ba . TheI sc Ba 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 sc Ba . By increasing the plasma level of aldosterone (low-sodium diet)I sc Ba rose by 95% whereas treatment decreasing this level (high-sodium diet) reducedI sc Ba by 76%. Bilateral adrenalectomy loweredI sc Ba by 59% and treatment of adrenalectomized rats with deoxycorticosterone acetate prevented the reduction ofI sc Ba . 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.