Effect of Amiloride on Electrical Activity and Electrolyte Transport in Human Colon

Abstract

Whether factors other than Na transport are involved in generating the electrical potential difference (PD) across the human colonic wall is unknown. The effect of amiloride on PD and ion transport was evaluated in the in vitro short-circuited human colon. In control periods the short-circuit current (Isc) was 2.9 .+-. 0.3 (mean .+-. SEM [standard error of the mean]) .mu.eq/h per cm2, while the corresponding net transfer of Na and Cl was 4.6 .+-. 0.4 and 1.4 .+-. 0.1, respectively. The residual flux was insignificantly different from 0. Amiloride caused a prompt, but reversible, decreasein Isc, PD and conductance when added to the mucosal side, but only a relatively small reduction of mucosa to serosa fluxes of Na occurred. Bidirectional Cl fluxes were unchanged, whie residual flux increased significantly. Some ions other than Cl (presumably mucosa to serosa fluxes of H and/or serosa to mucosa fluxes of HCO3) appear to be the main counter ions for actively transported Na in the large bowel. Experiments performed in vivo showed that rectal PD decreased exponentially from -46 mV .+-. 0.8 to -27 mV .+-. 0.3 (mean .+-. SEM) following rectal instillation of 10-3 M amiloride. Half-time required for this effect was < 13 s.