Adenosine and hypoxanthine transport in horse erythrocytes: evidence for a polymorphism in the transport of hypoxanthine via a sodium-dependent cotransporter.
The inward transport of two purines, adenosine and hypoxanthine, at 37 degrees C by horse erythrocytes was compared. No mediated transport of adenosine was detected in horse erythrocytes, nor was saturable, high-affinity binding of the potent facilitated-diffusion inhibitor nitrobenzylthioinosine demonstrable in horse erythrocyte membranes. In contrast, erythrocytes from most horses possessed a saturable sodium-dependent hypoxanthine transporter (apparent K(m), 100 +/- 28 microM; Vmax, 0.20 +/- 0.08 mmol (l cells)-1 h-1; means +/- S.E.M., n = 5). Guanine inhibited hypoxanthine influx (apparent Ki, 24 +/- 6 microM), but adenine and xanthine had no effect. Unlike human erythrocytes, no sodium-independent hypoxanthine transporter was detected in horse erythrocytes. There are, however, a small number of animals (approximately 15%) whose erythrocytes fail to transport hypoxanthine. This variation appears to be under genetic control, but the precise nature of the control is unknown.
Jarvis
S M
SM
Research School of Biosciences, University of Kent, Canterbury, UK. s.m.jarvis@ukc.ac.uk
Harris
R C
RC
D000241:Adenosine / Q000097:blood*; D000818:Animals; D002352:Carrier Proteins / Q000097:blood; D004910:Erythrocyte Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism*; D006736:Horses; D019271:Hypoxanthine / Q000097:blood*; D007700:Kinetics; D026901:Membrane Transport Proteins; D011485:Protein Binding; D012964:Sodium / Q000097:blood; D013868:Thioinosine / Q000031:analogs & derivatives / Q000097:blood
D002352:Carrier Proteins; D026901:Membrane Transport Proteins; C065171:cif nucleoside transporter; D019271:Hypoxanthine; D013868:Thioinosine; D012964:Sodium; C001789:4-nitrobenzylthioinosine; D000241:Adenosine