Effect of lanthanum on urinary acidification and sodium transport by the turtle and toad bladder

Lanthanum has been extensively used to evaluate the role of extracellular and membrane-bound calcium on several aspects of cell function. In the present study we evaluated the effect of mucosal or serosal addition of lanthanum on Na and H+ transport by the turtle bladder, in vitro, to gain insight concerning the role of calcium on these processes. Mucosal addition of lanthanum was associated with a decrease in Na transport and H+ secretion. The inhibition was of rapid onset, achieving a maximal inhibition at 10(-3) M for H+ secretion and 5 X 10(-4) for Na transport. The effect was rapidly and totally reversible with the removal of lanthanum. The mucosal effect of lanthanum addition was observed only at pH 7.4 for H+ secretion and at pH 7.4, 6.4, and 5.4 for Na transport. Agents capable of 'screening' the negative change of membrane proteins, such as cadmium or zinc, could neither elicit nor prevent the effect of lanthanum on H+ secretion. The effect of serosal addition of lanthanum on H+ or Na transport was different from that observed with mucosal addition; it was of slow onset, smaller magnitude, partially reversible, and only elicited by high concentrations (10 mM) of lanthanum. Serosal addition of lanthanum caused an early increase and a late decrease in radioactive calcium efflux. Mucosal addition of lanthanum caused an increase in calcium efflux. The data demonstrate that lanthanum inhibits Na and H+ transport in the turtle bladder and suggest that the mechanism of action of lanthanum is the result of either displacement of membrane-bound calcium or altered cell membrane permeability to calcium.