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J. Biol. Chem., Vol. 261, Issue 27, 12562-12567, Sep, 1986
alpha-Amanitin uptake into hepatocytes. Identification of hepatic membrane transport systems used by amatoxins
KD Kroncke, G Fricker, PJ Meier, W Gerok, T Wieland and G Kurz
Hepatic transport studies with amatoxins, toxic bicyclic octapeptides from
poisonous mushrooms of the genus Amanita were performed, using
[(6'-O,1'-N-di[3H]methyl)trp4]-alpha-amanitin and [(6'-O,1'-N-di-
methyl)trp4]-[4-[3H]desmethyl)hyi3]-gamma-ama nitin. Uptake into
hepatocytes from rat liver was inhibited by taurocholate and antamanide.
Photoaffinity labeling studies with isolated hepatocytes and basolateral
plasma membranes, using the sodium salt of (7,7-azo-3 alpha, 12
alpha-dihydroxy-5 beta-[3 beta-3H]cholan-24-oyl)-2- aminoethanesulfonic
acid demonstrated that the presence of alpha- amanitin decreased the
labeling of the two sinusoidal bile salt-binding membrane polypeptides with
the apparent molecular weights of 54,000 and 48,000. In basolateral plasma
membrane vesicles amanitin uptake was temperature-dependent and could be
stimulated 1.5 to 2-fold by an out to in Na+ gradient as compared to a K+
gradient or sucrose and 2 to 2.5- fold as compared to amanitin
equilibration (overshoot). Kinetic studies proved saturability of amanitin
uptake in the presence and absence of a Na+ gradient. Membrane transport
could be inhibited by taurocholate, antamanide, phalloidin, prednisolone,
and silybin, but not by penicillin G or thioctic acid. Hepatic uptake of
amatoxins is mediated by the sinusoidal bile salt-transport systems which
are also involved in the uptake of antamanide and phalloidin. This supports
the concept of a multispecificity of hepatic transport systems for a wide
variety of amphipathic molecules.

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Copyright © 1986 by the American Society for Biochemistry and Molecular Biology.
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