[(125)I]-(Pyr(1))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.
1. We have determined the binding characteristics of [(125)I]-(Pyr(1))Apelin-13, a putative ligand for the APJ orphan receptor in human cardiovascular and rat tissue and investigated the functional properties of (Pyr(1))Apelin-13 in human saphenous vein. 2. The binding of [(125)I]-(Pyr(1))Apelin-13 to sections of human heart tissue was time dependent and rapid at 23 degrees C. Data were fitted to a single site model with an association rate constant (k(obs)) of 0.115 min(-1). [(125)I]-(Pyr(1))Apelin-13 also dissociated from a single site with a dissociation rate constant of 0.0105 min(-1). 3. In saturation binding experiments [(125)I]-(Pyr(1))Apelin-13 bound to human left ventricle with a K(D) value of 0.35+/-0.08 nM, B(max) 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 K(D) of 0.33+/-0.09 nM, B(max) of 3.1+/-0.6 fmol mg(-1) protein and a Hill slope of 0.93+/-0.05. 4. [(125)I]-(Pyr(1))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. 2. (Pyr(1))Apelin-13 potently contracted human saphenous vein with a pD(2) value of 8.4+/-0.2 (n=8). The maximum response elicited by the peptide was 22.6+/-6% of 100 mM KCl. 6. We provide the first evidence of APJ receptor expression, relative densities and functional properties of (Pyr(1))Apelin-13 in human cardiovascular tissue.
Clinical Pharmacology Unit, University of Cambridge, Level 6, Centre for Clinical Investigation, Box 110, Addenbrooke's Hospital, Cambridge, CB2 2QQ. sdk23@hermes.cam.ac.uk
S D
SD
Katugampola
J J
JJ
Maguire
S R
SR
Matthewson
A P
AP
Davenport
D000328:Adult; D000368:Aged; D000818:Animals; D000073861:Apelin; D000075244:Apelin Receptors; D001345:Autoradiography; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D005260:Female; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D007457:Iodine Radioisotopes; D008875:Middle Aged; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000378:metabolism* / Q000502:physiology; D043562:Receptors, G-Protein-Coupled; D012501:Saphenous Vein / Q000187:drug effects / Q000378:metabolism; D014662:Vasoconstrictor Agents / Q000378:metabolism*
C115436:APLN protein, human; C104575:APLNR protein, human; D000073861:Apelin; D000075244:Apelin Receptors; C498579:Apln protein, rat; C491284:Aplnr protein, rat; D002352:Carrier Proteins; D036341:Intercellular Signaling Peptides and Proteins; D007457:Iodine Radioisotopes; D017448:Receptors, Dopamine D2; D043562:Receptors, G-Protein-Coupled; D014662:Vasoconstrictor Agents