Changes in the membrane surface charge density and/or membrane potential of the porcine intestinal brush-border membrane vesicles induced by treatment with neuraminidase.

Abstract

The effects of neuraminidase treatment on the membrane surface charge density and/or membrane potential of the porcine intestinal brush-border membrane vesicles were studied by using three fluorescent dyes, 1,6-diphenyl-1,3,5-hexatriene (DPH), 1-anilino-8-naphthalene sulfonate (ANS), and 3,3'-dipropyl-2,2'-thiadicarbocyanine iodide (DiS-C3(5]. The results of quenching studies of DPH-labeled membranes using cationic (T1+) and anionic (I-) quenchers suggested an increase of negative charge on the membrane surface by desialylation upon neuraminidase treatment. This interpretation was further supported by a decrease of ANS-binding affinity of the membranes after treatment with the enzyme. In addition, the degree of valinomycin-induced fluorescence change of DiS-C3(5)-probed membranes in the presence of various concentrations of KCl was reduced by treatment of the membranes with neuraminidase. This suggests that penetration of the dye molecules into the vesicle interior is facilitated by the treatment. The membrane potentials estimated from the null point of valinomycin-induced changes in the DiS-C3(5) fluorescence of the control and neuraminidase-treated membranes were -25 to -29.7 and -40 to -48.8 mV, respectively. From these results, it is suggested that the membrane surface charge density and/or membrane potential of the intestinal brush-border membranes are susceptible to modification of carbohydrate moieties on the membrane surface by neuraminidase treatment.