PMC

mRNA expression of AT₁, AT₂, and selected sodium transporters in the distal colon of control rats (CON), rats in CRF, and CRF rats treated with losartan (10 mg/kg) for 1 wk before study (+LOS). *Significant difference compared with control, P ≤ 0.05. †Significant difference compared with CRF, P ≤ 0.05. NHE, sodium-hydrogen exchanger; ENaC, epithelial sodium channel.

Mucosal amiloride (10⁻⁴ M) partially reduces net sodium absorption and I_sc in the distal colon of CRF rats (n = 7). Error bars represent ±1 SE above or below the mean of data in each group. An asterisk indicates a significant difference between Per I (CRF) and Per II (+Amiloride), using a paired t-test, P ≤ 0.05. Transepithelial conductance (G_T) was not significantly changed in Per II (9.58 ± 1.09 mS/cm²) compared with Per I (10.13 ± 1.13 mS/cm²).

Acute serosal losartan (10⁻⁴ M) does not alter sodium fluxes across distal colonic tissues removed from CON rats (n = 9), but I_sc is significantly decreased. Error bars represent ±1 SE above or below the mean of data in each group. An asterisk indicates a significant difference between Per I (CON) and Per II (+LOS), using a paired t-test, P ≤ 0.05. Transepithelial conductance (G_T) was not significantly changed in Per II (9.94 ± 1.05 mS/cm²) compared with Per I (10.37 ± 1.08 mS/cm²).

Immunoblot analyses of Na⁺/H⁺ exchangers (NHE1, NHE2, NHE3), Na⁺ channel subunits (ENaC-α, ENaC-β, ENaC-γ), ATPase, and AT₂ receptor in protein extracts of distal colon from CON, CRF, and + LOS rats. Membranes were reprobed for GAPDH as an internal loading control. Results were quantitated by densitometry from n = 4 to 6 tissues in each group and given in arbitrary units. Significant differences in CRF and + LOS from CON rats were established by a one-way ANOVA followed by Bonferroni's t-test and are indicated by an asterisk.

Acute serosal losartan (10⁻⁴ M) reduces net sodium absorption and I_sc across distal colonic tissues removed from CRF rats (n = 11). Error bars represent ±1 SE above or below the mean of data in each group. An asterisk indicates a significant difference between the control period of 45 min (Per I) (CRF) and the second 45-min flux period (Per II) (+LOS), using a paired t-test, P ≤ 0.05. Transepithelial conductance (G_T) was not significantly changed in Per II (8.23 ± 0.66 mS/cm²) compared with Per I (9.00 ± 0.62 mS/cm²).

Mucosal EIPA (50 μM) partially reduces net sodium absorption in the distal colon of CRF rats (n = 7). Indomethacin was present in this series (5 μM, serosal) to better resolve any changes in I_sc that might result from EIPA inhibition of electrogenic Na⁺ absorption. Error bars represent ±1 SE above or below the mean of data in each group. An asterisk indicates a significant difference between Per I (CRF) and Per II (+EIPA), using a paired t-test, P ≤ 0.05. Transepithelial conductance (G_T) was not significantly changed in Per II (7.82 ± 0.90 mS/cm²) compared with Per I (8.62 ± 0.77 mS/cm²).

Angiotensin II (ANG II) stimulation of sodium transport by rat distal colon in vitro. ANG II (10⁻⁷ M) was added at the end of Per I (CON) to the serosal side of control rat colonic tissue (n = 7). Error bars represent ±1 SE above or below the mean of data in each group. An asterisk indicates a significant difference between Per I and II using a paired t-test, P ≤ 0.05. Transepithelial conductance (G_T) was not significantly affected in Per II (8.00 ± 0.57 mS/cm²) compared with Per I (8.57 ± 0.48 mS/cm²).

Comparison of Na⁺ transport and short-circuit current (I_sc) across isolated, short-circuited distal colon from control rats with 2 intact kidneys (CON, n = 7), 5/6 nephrectomized rats with chronic renal failure (CRF, n = 11), and rats with renal failure that were treated with losartan (10 mg/kg) for 7 days before euthanasia (+LOS, n = 10). Error bars represent ±1 SE of the mean of data in each group. An asterisk indicates a significant difference compared with CON, and § indicates a significant difference from CRF in a one-way ANOVA (P ≤ 0.05). Transepithelial conductance (G_T) was not significantly affected in CRF (9.00 ± 0.62 mS/cm²) or + LOS (8.23 ± 0.66 mS/cm²) compared with CON (8.79 ± 0.83 mS/cm²). The fluxes and electrical parameters measured in + LOS are not significantly different compared with CON. J, mucosal to serosal flux; J, serosal to mucosal flux; J, net flux.