Adaptative mechanism of the equilibrative nucleoside transporter 1 (ENT-1) and blood adenosine levels in elite freedivers.

Purpose: Long static or intense dynamic apnoea-like high-altitude exposure is inducing hypoxia. Adenosine is known to participate to the adaptive response to hypoxia leading to the control of heart rate, blood pressure and vasodilation. Extracellular adenosine level is controlled through the equilibrative nucleoside transporter 1 (ENT-1) and the enzyme adenosine deaminase (ADA). The aim of this study was to determine the control of adenosine blood level (ABL) via ENT-1 and ADA during apnoea-induced hypoxia in elite freedivers was similar to high-altitude adaptation.
Methods: Ten freediver champions and ten controls were studied. Biological (e.g. ENT-1, ADA, ABL, PaO ₂ , PaCO ₂ and pH) and cardiovascular (e.g. heart rate, arterial pressure) parameters were measured at rest and after a submaximal dry static apnoea.
Results: In freedivers, ABL was higher than in control participants in basal condition and increased more in response to apnoea. Also, freedivers showed an ADA increased in response to apnoea. Finally, ENT-1 level and function were reduced for the free divers.
Conclusion: Our results suggest in freedivers the presence of an adaptive mechanism similar to the one observed in human exposed to chronic hypoxia induced by high-altitude environment.