Effects of secretagogues on the K+ permeability of mucosal and serosal borders of rabbit colonic mucosa.
(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 Ca2+. Ca2+-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 Ca2+. (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.
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D001726:Bisacodyl / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D003106:Colon / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology; D006571:Heterocyclic Compounds / Q000494:pharmacology; D007097:Imines / Q000494:pharmacology; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D013806:Theophylline / Q000494:pharmacology; D014268:Trifluoperazine / Q000494:pharmacology
D006571:Heterocyclic Compounds; D007097:Imines; D001726:Bisacodyl; D014268:Trifluoperazine; D010042:Ouabain; D000584:Amiloride; C014925:RMI 12330A; D002217:Carbachol; D013806:Theophylline; D000242:Cyclic AMP; D011188:Potassium; D002118:Calcium