Further observations on the uptake and effects of phosphonates in perfused rat liver studied by (31)P-NMR.
We examined the route of uptake of 2-aminoethylphosphonate (NEthPo) and of phenylphosphonate (PhePo; 10 mM each) in perfused liver by (31)P-NMR. Uptake of NEthPo 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 mM) reduced NEthPo uptake to 38 +/- 6% (n = 3). The data are consistent with uptake of NEthPo by the Na(+)-coupled Cl(-)-dependent beta-amino acid transporter. A small fraction of NEthPo was incorporated into phospholipid. PhePo uptake evolved over 1 h towards levels of the membrane-permeant volume marker dimethyl methylphosphonate. Uptake depended on H(+), and was inhibited by 4, 4'-diisothiocyanato-stilbene-2,2'-disulphonic acid (100 microM), bumetanide and furosemide (1 mM each) and alpha-cyano-4-OH-cinnamic acid (5 mM) to 31 +/- 4% (n = 4), 28 +/- 4% (n = 4), 27 +/- 5% (n = 6) and 40 +/- 7% (n = 4), respectively. These characteristics of PhePo uptake are reminiscent of H(+)-coupled monocarboxylate transport. The monocarboxylates, lactate and acetate (20 mM), and the substrate analogue, phenylalanine (20 mM), were not inhibitory, while benzoic acid (20 mM) slightly inhibited (to 82 +/- 5%; n = 4) PhePo uptake. The tested phosphonates (10 mM) did not significantly affect hepatic extraction of [(3)H]-cholate or [(3)H]-taurocholate (25 microM each; 1:3 bile salt:albumin). The monocarboxylate analogue, PhePo (10 mM), did not significantly interfere with disposal of lactate (0.3-5 mM).
Bruynseels
K
K
Biomedical NMR Unit, Department of Radiology, Faculteit Geneeskunde, Katholieke Universiteit Leuven, Herestraat 49, B-3000, Leuven, Belgium.
Van Hecke
P
P
Vanstapel
F
F
D000615:Aminoethylphosphonic Acid / Q000037:antagonists & inhibitors / Q000493:pharmacokinetics* / Q000494:pharmacology*; D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D002934:Cinnamates / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D019344:Lactic Acid / Q000378:metabolism; D008099:Liver / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D027501:Monocarboxylic Acid Transporters; D019906:Nuclear Magnetic Resonance, Biomolecular; D009943:Organophosphorus Compounds / Q000037:antagonists & inhibitors / Q000493:pharmacokinetics* / Q000494:pharmacology*; D010477:Perfusion; D051381:Rats; D017208:Rats, Wistar; D015203:Reproducibility of Results; D000099247:Taurine Transporters
D000615:Aminoethylphosphonic Acid; D001647:Bile Acids and Salts; D002352:Carrier Proteins; D002934:Cinnamates; D019344:Lactic Acid; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D027501:Monocarboxylic Acid Transporters; D009943:Organophosphorus Compounds; D000099247:Taurine Transporters; C018253:alpha-cyanocinnamate; C023604:phenylphosphonic acid