Effects of detergents on sodium transport in toad urinary bladder

The effects of ionic, nonionic and zwitterionic detergents (zwittergents) on apical sodium permeability of toad urinary bladder were investigated. Applied to the mucosal side at concentrations less than 1/100 of their respective critical micellar concentration (CMC), sodium lauryl sulfate, Triton X-100 and a series of sulfobetaine zwittergents reversibly increased amiloride-sensitive sodium current. These detergents decreased the current at concentrations higher than 1/100 of the CMC and caused large, irreversible increases of tissue electrical conductance at a concentration close to the CMC. Nonionic detergent Tween 80, however, stimulated the current at concentrations from 1/100 to 10,000 of its CMC. The maximum stimulation of current by each zwittergent occurred at 1/100 of its CMC, and the larger the CMC, the greater the stimulation attainable. Analysis of the dependence of current on mucosal sodium concentration in the presence of stimulating doses of a zwittergent and Tween 80 showed that the increase in current was not the result of increased apical maximum sodium permeability, but the consequence of removal of sodium self-inhibition. The amiloride dose-response curve in the presence of stimulating dose of zwittergent was shown to shift to the left and yield a smaller apparent inhibition constant as predicted on the basis of such a removal and an unaltered intrinsic amiloride blocking kinetic.