Effect of valinomycin on membrane vesicle aggregation of porcine intestinal brush borders.

It has been found in the brush border membrane vesicles from porcine small intestine that valinomycin causes vesicle aggregation and that Ca2+-induced aggregation of the vesicles is saturably stimulated in the presence of valinomycin. The apparent half-maximal concentration of valinomycin required to enhance the Ca2+ effect on the membrane aggregation is approximately 40 microM. Results of a fluorometric study using 1-anilino-8-naphthalene sulfonate (ANS) showed that the addition of valinomycin to the membranes induces slight decreases in the ANS-binding affinities for the membranes in the presence and absence of Ca2+. On the other hand, measurements of the incorporation rate of 1,6-diphenyl-1,3,5-hexatriene (DPH) into the vesicles and of anisotropies of DPH-labeled membranes suggested that the lipid organization of the membranes was not altered upon the addition of valinomycin. From these results, it was suggested that the valinomycin effect on the membrane aggregation is mainly related to the nature of the membrane surface charge.