[125I]-(Pyr1)Apelin-13 is a novel radioligand for localizing the APJ orphan receptor in human and rat tissues with evidence for a vasoconstrictor role in man

摘要

We have determined the binding characteristics of [125I]-(Pyr1)Apelin-13, a putative ligand for the APJ orphan receptor in human cardiovascular and rat tissue and investigated the functional properties of (Pyr1)Apelin-13 in human saphenous vein.The binding of [125I]-(Pyr1)Apelin-13 to sections of human heart tissue was time dependent and rapid at 23°C. Data were fitted to a single site model with an association rate constant (kobs) of 0.115 min−1. [125I]-(Pyr1)Apelin-13 also dissociated from a single site with a dissociation rate constant of 0.0105 min−1.In saturation binding experiments [125I]-(Pyr1)Apelin-13 bound to human left ventricle with a KD value of 0.35±0.08 nM, Bmax of 4.3±0.9 fmol mg−1 protein with a Hill slope of 0.97±0.04 and to the right atria with a KD of 0.33±0.09 nM, Bmax of 3.1±0.6 fmol mg−1 protein and a Hill slope of 0.93±0.05.[125I]-(Pyr1)Apelin-13 binding sites were localized using autoradiography to human cardiovascular tissue, including coronary artery, aorta and saphenous vein grafts. In rat tissue a high density of receptors were localized to the molecular layer of the rat cerebellum, rat lung, rat heart and low levels in the rat kidney cortex.(Pyr1)Apelin-13 potently contracted human saphenous vein with a pD2 value of 8.4±0.2 (n=8). The maximum response elicited by the peptide was 22.6±6% of 100 mM KCl.We provide the first evidence of APJ receptor expression, relative densities and functional properties of (Pyr1)Apelin-13 in human cardiovascular tissue.