Ion permeability of rabbit intestinal brush border membrane vesicles

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Abstract
The ion permeability of rabbit jejunal brush border membrane vesicles was studied by measuring unidirectional fluxes with radioactive tracers and bi-ionic diffusion potentials with the potential-sensitive fluorescent dye, diS−C3-(5). Tracer measurements provide estimates of the absolute magnitudes of permeability coefficients, while fluorescence measurements provide estimates of relative and absolute ion permeabilities. The magnitudes of the permeability coefficients for Na+, K+, Rb+, and Br− were approximately 5 nanoliters/(mg protein × sec) or 10−5 cm/sec as determined by radioactive tracer measurements. The apparent selectivity sequence, relative to Na+, as determined by bi-ionic potential measurements was: F−, isetheionate, gluconate, choline (+(1.0)−(1.5)=NO 3 − (1.5)−(2.3)+(2.4)+(2.5)+(2.6)+(3.9) 4 − +(12)−(40). The origin of this selectivity sequence and its relationship to the ion permeability of the brush border membrane in the intact epithelium are discussed.