Contribution of adenosine receptors in the control of arteriolar tone and adenosine–angiotensin II interaction

Adenosine (Ado) mediates vasoconstriction via A1-Ado receptors and vasodilation via A2-Ado receptors in the kidney. It interacts with angiotensin II (Ang II), which is important for renal hemodynamics and tubuloglomerular feedback (TGF). The aim was to investigate the function of Ado receptors in the Ado–Ang II interaction in mouse microperfused, afferent arterioles. Ado (10−11–10−4mol/l) caused a biphasic response: arteriolar diameters were reduced (-7%) at Ado 10−11–10−9mol/l and returned to control values at higher concentrations. Treatment with Ang II (10−10mol/l) transformed the response into a concentration-dependent constriction. N6-cyclopentyladenosine (A1-Ado receptor agonist) reduced diameters (12% at 10−6mol/l). Application of CGS21680 (10−12–10−4mol/l, A2A receptor agonist) increased the diameter by 13%. Pretreatment with ZM241385 (A2A-Ado receptor antagonist) alone or in combination with MRS1706 (A2B-Ado receptor antagonist) resulted in a pure constriction upon Ado, whereas 8-cyclopentyltheophylline (CPT) (A1-Ado receptor antagonist) inhibited the constrictor response. Afferent arterioles of mice lacking A1-Ado receptor did not show constriction upon Ado. Treatment with Ado (10−8mol/l) increased the response upon Ang II, which was blocked by CPT. Ado (10−5mol/l) did not influence the Ang II response, but an additional blockade of A2-Ado receptors enhanced it. The action of Ado on constrictor A1-Ado receptors and dilatory A2-Ado receptors modulates the interaction with Ang II. Both directions of Ado–Ang II interaction, which predominantly leads to an amplification of the contractile response, are important for the operation of the TGF.