Effects of secretagogues on the K + permeability of mucosal and serosal borders of rabbit colonic mucosa

Abstract

(1) K + efflux rates from the mucosal and serosal surfaces of sheets of rabbit colonic mucosa have been determined by measuring net K + loss into K +-free Ringer solution bathing each side of the tissue. (2) Initially, there is a high rate of K + loss from the tissue, this falls to a lower steady-state rate after 20 min. Loss of K + from the tissue into the serosal bath is 6–8-fold faster than loss to the mucosal bath. (3) A number of intestinal secretagogues, e.g. theophylline, cyclic AMP, carbachol, ionophore A23187, as well as the laxative bisacodyl, raise the K + efflux rate across the mucosal border by 200–300%. In the case of K + efflux induced by carbachol the effect is shown to be dependent on raised levels of intracellular Ca 2+. Ca 2+-calmodulin complex does not appear to be be involved in activation of K + efflux across the mucosal border. (4) Amiloride does not block mucosal K + efflux, but tetraethyl-ammonium does inhibit K + efflux across the mucosal border, induced by either bisacodyl or raised intracellular Ca 2+. (5) The results suggest that laxatives may increase the rate of K + secretion into the colonic lumen by raising the K + permeability of the mucosal border.