Effects of barium Chloride on electrolyte transport across isolated colons from normal and Aldosterone-treated lizards (Gallotia Galloti)

Addition of BaCl₂ to the solution bathing colons of normal lizards did not alter the absorptive Na⁺ flux, but did reverse the net absorption of Cl⁻ to become net secretion. Cl⁻ secretion resulted from an increase in its serosal-to-mucosal movement and was positively correlated to an increase in short-circuit current. Ba²⁺-induced short-circuit current was dependent on the presence of both Na⁺ and Cl⁻ in the serosal medium. Ba²⁺-induced Cl⁻ secretion could be reversed by serosal amiloride (10⁻⁴ mmol l⁻¹). Colons from acutely or chronically aldosterone-treated lizards exhibited a considerably higher short-circuit current, potential difference and net Na⁺ absorption than did untreated colons. Net Cl⁻ transport was unaltered by acute treatment, but was totally abolished after chronic treatment. BaCl₂ rapidly decreased the potential difference, short-circuit current and tissue conductance across colons from aldosterone-treated lizards. Net Na⁺ transport was markedly inhibited by Ba²⁺ in both acutely and chronically treated tissues, but barium did not change unidirectional or net Cl⁻ fluxes in these. The present results support the following hypotheses: (1) that BaCl₂ inhibits electrogenic Na⁺ absorption induced by acute or chronic aldosterone treatment and (2) that Ba²⁺ induces an electrogenic Cl⁻ secretion by stimulating a basolateral Na⁺-dependent Cl⁻ intake in normal but not in aldosterone-treated colons. This also suggests that aldosterone could exert an antisecretory influence in colonic epithelia.