Third-Generation β-Blockers Stimulate Nitric Oxide Release From Endothelial Cells Through ATP Efflux

Abstract

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 [ 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 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, Gd 3+ , 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.