Figure 6. Prolonged exposure of colon tissue to low apical Na⁺ results in an up-regulation of ENaC which is preserved in Liddle mice.

Representative traces are shown in A for one wild-type animal (WT; top traces) and one L/L animal (bottom traces). Paired colon tissue preparations obtained from the same animal were mounted into Ussing chambers and were exposed either to an apical solution containing 4 mm Na⁺ (low sodium) or to an apical solution containing 123 mm Na⁺ (high sodium). The basolateral compartment contained standard mouse Ringer solution. Tissue preparations were maintained under these conditions for 8 h. At the time indicated by the bar below the traces, the apical bath solution was switched to a bath solution containing 63.5 mm NaCl. This was achieved either by replacing 50% of the low sodium bath solution by high sodium bath solution (I_SC traces with continuous lines) or by replacing 50% of the high sodium bath solution by low sodium bath solution (I_SC traces with dashed lines). Application of 10⁻⁴m amiloride (Ami), as indicated by the black bar, revealed the ENaC-mediated I_SC component (ΔI_SC-Ami). B, summary of ΔI_SC-Ami values obtained in similar experiments as shown in A. Each circle or square represents an individual ΔI_SC-Ami value measured either in colon tissue pre-incubated in high sodium (123 mm; open symbols) or in low sodium (4 mm; filled symbols), using colon tissue from WT (circles) or L/L (squares) animals. ΔI_SC-Ami values measured in matched tissue preparations from the same animal are connected by dotted lines. In addition to the individual values, medians with interquartiles are shown.