Figure 4. The effect of a high K⁺ diet on adrenaline-stimulated ion secretion in mouse distal colonic mucosa from BK^+/+ and BK^−/− mice (SV129×C57Bl6 hybrid background).

A and B, two original Ussing chamber recordings in BK^+/+ (A) and in BK^−/− tissue (B). Note the difference of a larger V_te effect in the BK^−/− tissue. Note also that adrenaline induces a biphasic change of V_te with an initial change into the lumen-positive direction in the BK^+/+ tissue. C, summary of adrenaline-induced V_te effects (n= 8). D, summary of adrenaline-induced R_te effects. E, summary of calculated adrenaline-induced I_sc effects. The positive-directed difference I_sc curve was obtained by subtracting ΔI_sc BK^−/− from ΔI_sc BK^+/+. This positive current indicates electrogenic K⁺ secretion. For comparison with the data in Fig. 2E the grey line shows this differential current from control mice. Note the up-regulation of apparent BK conducted electrogenic K⁺ secretion in mice treated on a high K⁺ diet. Note also the inset to enlarge the initial period of the adrenaline-induced I_sc effect. * indicates statistical significance (P < 0.05) between BK^+/+ and BK^−/− curves.