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Adenosine is known to exert dual actions on the afferent arteriole, eliciting vasoconstriction, by activating A1 receptors, and vasodilation at higher concentrations, by activating lower-affinity A2 receptors. We could demonstrate both of these known adenosine responses in the in vitro perfused hydronephrotic rat kidney. Thus, 1.0 μM adenosine elicited a transient vasoconstriction blocked by 8-cyclopentyl-1,3- dipropylxanthine (DPCPX), and 10-30 μM adenosine reversed KCl- induced vasoconstriction. However, when we examined the effects of adenosine on pressure-induced afferent arteriolar vasoconstriction, we observed a third action. In this setting, a high-affinity adenosine vasodilatory response was observed at concentrations of 10-300 nM. This response was blocked by both 4- (2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-yl- amino]ethyl)phenol (ZM-241385) and glibenclamide and was mimicked by 2-phenylaminoadenosine (CV-1808) (IC50 of 100 nM), implicating adenosine A(2a) receptors coupled to ATP-sensitive K channels (K(ATP)). Like adenosine, 5'-N-ethylcarboxamidoadenosine (NECA) elicited both glibenclamide-sensitive and glibenclamide- insensitive vasodilatory responses. The order of potency for the glibenclamide-sensitive component was NECA > adenosine = CV-1808. Our findings suggest that, in addition to the previously described adenosine A1 and low-affinity A(2b) receptors, the renal microvasculature is also capable of expressing high- affinity adenosine A(2a) receptors. This renal adenosine receptor elicits afferent arteriolar vasodilation at submicromolar adenosine levels by activating K(ATP).

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Journal article


American Journal of Physiology - Renal Physiology

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