Abstract
Salt (sodium chloride) and A2A adenosine receptors (A2AR) have both been implicated in blood pressure regulation. While high salt consumption raises blood pressure, A2AR is a key mediator of coronary vasodilation. Although a sodium ion binding pocket has been identified in A2AR, the physiological link between salt and A2AR remains poorly investigated. Hereby, we explored how salt modulates its expression and function in vitro.
Using Adonis, an IgM mouse monoclonal antibody against A2AR with agonist properties, or CGS21680, an organic agonist, we evaluated the effects of distinct sodium chloride concentrations (low = 120 mM and high = 194 mM, compared to control = 133 mM) on A2AR protein expression, ligand binding affinity (KD) and function (cAMP production and EC50). We used peripheral blood mononuclear cells, a cellular model mimicking the behavior of A2AR expressed in the cardiovascular system.
After 24h salt supplementation in culture medium, high salt concentration is associated with A2AR increased expression (mean ± SD: +131% ± 25.63 compared with control, p<0.05). Upon Adonis activation, KD and EC50 values inversely correlated to salt concentration: the higher salt concentration, the lower KD and EC50 are. High salt concentration is also associated with higher cAMP production upon CGS21680 activation (mean +42%). None of these changes was observed when salt and Adonis were simultaneously added (competition condition).
These results demonstrate that salt promotes A2AR increased expression, binding to Adonis as well as activation. We hypothesize that Adonis binding, potentially due to its large size or to induced conformational changes, allosterically prevents sodium ion from accessing or modulating its binding pocket. This is supported by our competition experiments where simultaneous addition abrogates the salt effect. Our results imply the presence of a novel beneficial compensatory mechanism, via A2AR, that responds to elevated blood salt levels and influences blood pressure regulation.
Keywords
Adenosine A2A receptors, Salt, Sodium ion, Blood pressure