Adenosine and hypoxanthine transport in horse erythrocytes: evidence for a polymorphism in the transport of hypoxanthine via a sodium-dependent cotransporter.

This study explores the differing transport methods of two purines, adenosine and hypoxanthine, by horse erythrocytes at body temperature. The research reveals unique elements of hypoxanthine transport in horse erythrocytes, with approximately 15% of horses’ erythrocytes unable to transport hypoxanthine, possibly due to genetic factors.

Research Methodology and Findings

• The research involved comparing the inward transport of adenosine and hypoxanthine by horse erythrocytes at 37 degrees Celsius.
• The researchers found that there is no mediated transport of adenosine in horse erythrocytes. They also could not detect any saturable, high-affinity binding of the powerful facilitated-diffusion inhibitor nitrobenzylthioinosine in horse erythrocyte membranes.
• Unlike adenosine, the researchers discovered that erythrocytes from most horses have a saturable sodium-dependent hypoxanthine transporter with an apparent K(m) of 100 +/- 28 microM and a Vmax of 0.20 +/- 0.08 mmol (l cells)-1 h-1; these results were averaged out from the five trials undertaken (means +/- S.E.M., n = 5).
• Guanine was discovered to inhibit hypoxanthine influx with an apparent Ki of 24 +/- 6 microM, while adenine and xanthine showed no effect.

Comparison with Human Erythrocytes

• One notable conclusion from this study pertains to the lack of sodium-independent hypoxanthine transporter found in horse erythrocytes, in contrast with human erythrocytes where one is present.

Genetic Considerations

• Furthermore, an interesting genetic component was uncovered by this study – a small percentage of tested horses (around 15%) had erythrocytes that were incapable of transporting hypoxanthine, indicating a possible variation of genetic control among different horses. The exact nature of this genetic control, however, remains under investigation.