KINETICS OF POTASSIUM IN COLONIC MUCOSA OF NORMAL AND SODIUM-DEPLETED RATS

1. The transport of K across the mucosal epithelium of the colon of normal and Na‐depleted rats has been investigated in vivo by methods involving I.V. administration of solutions containing 42K and by labelling the mucosa with 42K from the lumen and observing the ‘soaking‐out’ rates into radionucleide‐free solutions. 2. During the infusions, the specific activity of the mucosal K was always less than the simultaneous specific activity of the secreted K. On stopping the infusion the specific activity of the mucosal K fell although the plasma specific activity remained at all times greater than that of the mucosa. The blood flow rate to the mucosa estimated from these results was 0·95 ml./min.g wet wt. 3. Experiments with 42K in the lumen showed that the steady‐state specific activity of the mucosal K was considerably less than expected if the K had been in a single compartment. The 42K efflux curves were also consistent in showing two components. The curves were analysed on the basis of a model having two compartments in the mucosa with half‐times of 6 and 33 min. 4. Na depletion produced two significant changes, (a) K secretion rate doubled, (b) the steady‐state specific activity of the mucosal K after luminal exposure to 42K was increased. The half‐times of the compartments were unaffected. 5. The results were discussed in terms of a working hypothesis which represented the mucosal K in two compartments. Most of the K exchanges across the mucosa took place through the smaller compartment which probably contained 5% or less of the mucosal K, but which had a rapid turnover rate. The change of K permeability of the luminal face produced by Na depletion and probably due to increased aldosterone action, may well be an important factor in producing the rise of K secretion rate. © 1969 The Physiological Society