Third-generation β-blockers stimulate nitric oxide release from endothelial cells through ATP efflux: A novel mechanism for antihypertensive action

Background - Nebivolol and carvedilol are third-generation β-adrenoreceptor antagonists, which unlike classic β-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 [³H]-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 β-blocker-induced glomerular vasorelaxations and β-blocker-stimulated NO release from GECs. Both β-blocker-induced vasorelaxations were in the micromolar concentration range identical to that required for the β-blocker stimulation of ATP and NO release from GECs. The maximum of NO release for nebivolol and carvedilol was very similar (188±14 and 226±17, respectively). Blockade of ATP release by a mechanosensitive ion channel blocker, Gd³⁺, inhibited the β-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 release from GECs.