Inhibitory effects of monovalent cations on the Ca2+-induced aggregation of porcine intestinal brush border membranes.

J-STAGE
  • OHYASHIKI Takao
    Department of Physiological Chemistry, School of Pharmacy, Hokuriku University
  • KODERA Michiyo
    Department of Physiological Chemistry, School of Pharmacy, Hokuriku University
  • MOHRI Tetsuro
    Department of Physiological Chemistry, School of Pharmacy, Hokuriku University

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説明

The Cat2+-induced aggregation of porcine intestinal brush border membranes could be inhibited by addition of monovalent cations to the medium or by increasing the ionic strength of the medium, as measured by the change in optical density of the membrane suspension. The relative effectiveness of monovalent cations at 100mM in the inhibition was in the order, Na+ NH4+>K+ Rb+ Li+>choline+. The Ca2+ concentration dependence profile of the membrane aggregation showed that the Ca2+ threshold at which the aggregation began was distinctly shifted to a higher concentration by the addition of KCl. In addition, the results of fluorometric studies with 1-anilino-8-naphthalane sulfonate suggested that the inhibition of the membrane aggregation by extravesicular KCl is due to a decrease of the binding affinity of Ca2+ for the membranes as a result of neutralization of the surface charges. On the other hand, measurements of the incorporation of 1, 6-diphenyl-1, 3, 5-hex-atrience (DPH) into the membrane vesicles and of the anisotropy of DPH-labeled membranes suggested that the imposition of a salt gradient across the membrane vesicles (out>in) causes an increase of lipid fluidity of the membranes. Based on these results, a possible contribution of membrane surface charges and/or membrane fluidity to the Ca2+-induced aggregation of the membranes is discussed.

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