Figure 1. Effect of secretagogues on wild-type mouse colon mucosa.

The traces show continuous recordings of transepithelial potential (V_te) as function of time obtained in Ussing chamber experiments of mouse distal colon. The voltage deflections are caused by current pulse injection. Addition of 100 μm isobutylmethylxanthine (IBMX) plus 1 μm forskolin in both experiments, induces a negative change in V_te that was fully reversed by 10 μm chromanol 293B. Addition of 100 μm carbachol (black boxes) yielded fast negative changes in V_te that were maintained during repeated application (lower panel). Carbachol effect was almost completely blocked by the Kcnn4 inhibitor clotrimazole (CTZ, 3 μm) and totally blocked by further addition of 5 mm serosal Ba²⁺ (upper panel). In both experiments apical 10 μm amiloride was used to inhibit ENaC-mediated sodium currents. Apical and bl indicate additions to the mucosal and serosal compartment, respectively. Tissue resistances were, respectively, 86 and 83 Ω cm² at the beginning and end of the experiment shown in the upper panel. The respective numbers for the lower panel experiment were 78 and 75 Ω cm².