Background-Nebivolol and carvedilol are third-generation ␤-adrenoreceptor antagonists, which unlike classic ␤-blockers, have additional endothelium-dependent vasodilating properties specifically related to microcirculation by a molecular mechanism that still remains unclear. We hypothesized that nebivolol and carvedilol stimulate NO release from microvascular endothelial cells by extracellular ATP, which is a well-established potent autocrine and paracrine signaling factor modulating a variety of cellular functions through the activation of P2-purinoceptors. Methods and Results-Contraction and relaxation of renal glomerular vasculature were measured by determination of intracapillary volume with [ 3 H]-inulin. Biologically active NO was measured with highly sensitive porphyrinic NO microsensors in a single glomerular endothelial cell (GEC). Extracellular ATP was measured by a luciferin-luciferase assay. Enzymatic degradation of extracellular ATP by apyrase and blockade of P2Y-purinoceptors by suramin or reactive blue 2 inhibited both ␤-blocker-induced glomerular vasorelaxations and ␤-blocker-stimulated NO release from GECs. Both ␤-blocker-induced vasorelaxations were in the micromolar concentration range identical to that required for the ␤-blocker stimulation of ATP and NO release from GECs. The maximum of NO release for nebivolol and carvedilol was very similar (188Ϯ14 and 226Ϯ17, respectively). Blockade of ATP release by a mechanosensitive ion channel blocker, Gd 3ϩ , inhibited the ␤-blocker-dependent release of ATP and NO from GECs. Conclusions-These results demonstrate for the first time that nebivolol and carvedilol induce relaxation of renal glomerular microvasculature through ATP efflux with consequent stimulation of P2Y-purinoceptor-mediated NO

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The relaxing effect of extracellular ATP on renal glomeruli has been investigated by applying ATP and its analogues to suspensions of angiotensin II‐precontracted rat renal glomeruli. Based on changes of glomerular [3H]inulin space (GIS) the relaxation of glomeruli was analysed in the presence of agonists: ATP, ADP, AMP, UTP, 2‐methylthio‐ATP (P2Y agonist), β,γ‐methylene‐ATP (P2X agonist) and adenosine. ATP, 2‐methylthio‐ATP, ADP and UTP induced concentration‐dependent relaxation whereas AMP, β,γ‐methylene‐ATP and adenosine had no effect. The rank order of relaxation potency was 2‐methylthio‐ATP > ATP > ADP > UTP. An inhibitor of constitutive nitric oxide synthase (NOS), Nω‐nitro‐L‐arginine (NNA) prevented the ATP‐induced increased accumulation of L‐citrulline and the relaxation effect of ATP. An inhibitor of the neuronal isoform of NOS, 7‐nitroindazole, had no effect on the relaxation effect of ATP. The relaxing effect of ATP was prevented in the presence of inhibitors of cyclic guanylyl cyclase: methylene blue (MB) and the more specific inhibitor 1H‐[1,2,4]oxadiazolo‐[4,3‐a]quinoxalin‐1‐one (ODQ). ATP stimulated an accumulation of cGMP that was diminished in the presence of MB. We indicated that extracellular ATP may relax the glomeruli via activation of P2Y receptors with the subsequent activation of the endothelial isoform of nitric oxide synthase and soluble guanylyl cyclase. We suggest that, based on the described mechanism, extracellular ATP may increase the filtration surface which, in turn, may influence the glomerular filtration rate.