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Further observations on the uptake and effects of phosphonates in perfused rat liver studied by 31 P‐NMR
Author(s) -
Bruynseels Koenraad,
Van Hecke Paul,
Vanstapel Florent
Publication year - 1999
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/(sici)1099-1492(199908)12:5<275::aid-nbm567>3.0.co;2-s
Subject(s) - chemistry , taurine , choline , dids , bumetanide , cholic acid , benzoic acid , bile acid , chromatography , biochemistry , membrane , amino acid , ion transporter
We examined the route of uptake of 2‐aminoethylphosphonate ( N Eth Po ) and of phenylphosphonate (Phe Po; 10 m M each) in perfused liver by 31 P‐NMR. Uptake of N Eth Po was concentrative. The rate of uptake was reduced to 21 ± 2% ( n = 3; all percentages refer to control rates) by substituting choline for Na + , and to 21 ± 4% ( n = 3), 32 ± 6% ( n = 5) and 70 ± 5% ( n = 3) by replacing Cl − by gluconate, SO 4 2− or NO 3 − , respectively. Taurine (20 m M ) reduced N Eth Po uptake to 38 ± 6% ( n = 3). The data are consistent with uptake of N Eth Po by the Na + ‐coupled Cl − ‐dependent β‐amino acid transporter. A small fraction of N Eth Po was incorporated into phospholipid. Phe Po uptake evolved over 1 h towards levels of the membrane‐permeant volume marker dimethyl methylphos‐phonate. Uptake depended on H + , and was inhibited by 4,4′‐diisothiocyanato‐stilbene‐2,2′‐disulphonic acid (100 µ M ), bumetanide and furosemide (1 m M each) and α‐cyano‐4‐OH‐cinnamic acid (5 m M ) to 31 ± 4% ( n = 4), 28 ± 4% ( n = 4), 27 ± 5% ( n = 6) and 40 ± 7% ( n = 4), respectively. These characteristics of Phe Po uptake are reminiscent of H + ‐coupled monocarboxylate transport. The monocarboxylates, lactate and acetate (20 m M ), and the substrate analogue, phenylalanine (20 m M ), were not inhibitory, while benzoic acid (20 m M ) slightly inhibited (to 82 ± 5%; n = 4) Phe Po uptake. The tested phosphonates (10 m M ) did not significantly affect hepatic extraction of [ 3 H]‐cholate or [ 3 H]‐taurocholate (25 µ M each; 1:3 bile salt:albumin). The monocarboxylate analogue, Phe Po (10 m M ), did not significantly interfere with disposal of lactate (0.3–5 m M ). Copyright © 1999 John Wiley & Sons, Ltd.