Effect of aldosterone and dexamethasone pretreatment on sodium transport in rat distal colon in vitro

Aldosterone and dexamethasone stimulate sodium absorption in the rat colon in vivo. In vitro, increased amiloride inhibitable short-circuit current (I_SC) has been demonstrated following aldosterone or dexamethasone treatment. Since I_SC bears no relationship to sodium flux (J_Na) in the untreated rat colon, we measured J_Na in partially stripped voltage clamped segments of rat distal colon. Our results demonstrate directly that continuous infusion of aldosterone or dexamethasone for 4–7 days stimulated amiloride inhibitable J_Na by stimulating J_NaM-S. The amiloride inhibitable portion of J_NaM-S was highly correlated with and approximately equal to the amiloride inhibitable I_SC. Amiloride had no effect in controls. We conclude that J_NaM-S in the rat distal colon is only sensitive to mucosal amiloride after treatment with aldosterone or dexamethasone. the amiloride sensitive I_SC in these treated tissues was a good measure of the amiloride sensitive J_Na. Small differences between aldosterone and dexamethasone treatment were noted in the effect on transepithelial resistance, potential difference, and the I_SC after amiloride.