Pathways of Transepithelial Potassium Movement in the Epithelium of Distal Colon in Man

Abstract

1. Methods for studying the kinetics of movement of radioactive tracers across human distal colonic epithelium have been developed for use in vivo and applied to examination of transepithelial transfers of potassium. 2. During absorption of 43K from the lumen, two potassium pools, A and B, in the epithelium were identified, having mean turnover half-times of 16 and 87 min respectively. On average about 50% of the potassium lumen-to-plasma flux and most, if not all, of the potassium plasma-to-lumen flux took place through pool A. The transcellular pathway (equated with pool B) appeared to be of relatively little significance in transepithelial movement of potassium in the human distal colon. 3. Sodium and chloride movements were unaffected when lithium was present in the luminal solution, but the potassium secretion rate was nearly trebled due to increased plasma-to-lumen flux through the fast turnover pool A. 4. The permeability of the epithelium to potassium, as judged by the plasma-to-lumen fluxes, greatly exceeded that to sodium. This appeared to depend on a special highly selective potassium channel which differed from the shunt pathway in possessing definite capacity.

Active potassium transport by rabbit descending colon epithelium

“…However, the mechanism of potassium transport across this epithelium has been disputed. In some studies potassium secretion was greater than expected from transepithelial electrical or chemical driving forces (cf Archampong, Harris & Clark, 1972;Yorio & Bentley, 1977;Powell, 1979;Kermode & Edmonds, 1980;Kliger, Binder, Bastl & Hayslett, 1981), suggesting active transport mechanisms. In contrast other investigations have shown evidence against active potassium transport.…”

Fluid and Electrolyte Transport in Human Colon in Health and Disease

“…It is likely that colonic potassium secretion in vivo reflects, at least in part, passive movement of potassium from plasma to lumen secondary to the high, lumen-negative pd. However, 43K tracer studies have suggested that the passive component may be relatively small (Kermode and Edmonds 1980), and intraluminal amiloride has been shown to have no effect on net potassium secretion in the proximal rectum despite decreasing transmucosal pd by 30% (SandIe et al 1986b). Microelectrode studies also indicate that paracellular pathways in human proximal and distal colonic epithelia possess no significant potassium selectivity (Sandie and McGlone 1987).…”