No involvement of system N, system y+ and the oligopeptide-H+ transport system in the uptake of methylmercury in rat erythrocytes.
Previous studies have investigated a number of possible transport systems for the uptake of methylmercury (MeHg) in erythrocytes. In the present study, three additional systems were studied. The uptake of MeHg by isolated erythrocytes from rats was studied at 5 degrees C and 20 degrees C. Glutamine was used to test system N and system y+, and glycylglycine was used to test the oligopeptide-H+ transport system. The Hill equation was used in kinetic analysis. The results show that both glutamine and glycylglycine stimulated the uptake of MeHg, but the stimulation by glycylglycine is stronger than by glutamine, and the stimulation at 5 degrees C is stronger than at 20 degrees C (mean values are 167.98% and 83.68% in the glycylglycine group at 5 degrees C and 20 degrees C versus 26.28% and 19.23% in the glutamine group at 5 degrees C and 20 degrees C). The kinetic analysis shows that: the Michaelis-Menten constant Km increased as temperature increased in both groups and was larger in experimental groups than in control groups; the Hill constants increased as temperature increased in both groups and were smaller in experimental groups than in control groups; and as temperature increased, maximum velocity Vmax increased in control groups and decreased in experimental groups, and was larger in experimental groups than in control groups, with the exception of the glycylglycine group at 20 degrees C. The results demonstrated that system N, system y+ and oligopeptide-H+ transport systems were not involved in the in vitro uptake of MeHg into erythrocytes. The stimulation by glutamine and glycylglycine might be related to some signalling pathways, through which nitric oxide and oligopeptide serve as messengers and cause functional alterations in the uptake of MeHg.
Wu
G
G
Biochemistry Section, National Institute for Minamata Disease, Kumamoto, Japan.
D026905:Amino Acid Transport Systems; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism*; D005973:Glutamine / Q000097:blood / Q000494:pharmacology; D006033:Glycylglycine / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008767:Methylmercury Compounds / Q000378:metabolism* / Q000633:toxicity; D000074011:Peptide Transporter 1; D051381:Rats; D017208:Rats, Wistar; D027981:Symporters; D013696:Temperature
D026905:Amino Acid Transport Systems; D002352:Carrier Proteins; D008767:Methylmercury Compounds; D000074011:Peptide Transporter 1; C489940:Slc15a1 protein, rat; D027981:Symporters; D005973:Glutamine; D006033:Glycylglycine