title: Receptors for angiotensin II on platelets from man.
abstract: Platelets were prepared from peripheral venous blood on iso-osmotic density gradients of Percoll, resulting in a good recovery of cells (50-80%) which were relatively free of contaminating blood cells (erythrocyte less than 0.1%, leucocyte less than 1%). At 22 degrees C, specific binding of 125I-labelled angiotensin II (300 pmol/l) was time and temperature dependent, saturable, reversible and linear with cell concentration. Scatchard analysis of saturation curves revealed a single class of binding sites with Kd 1.5 +/- 0.4 X 10(-10) mol/l and total binding capacity 6.3 +/- 1.2 receptors/platelet. Similar values (Kd 2.4 +/- 0.7 X 10(-10) mol/l and binding capacity 6.5 +/- 1.0 receptors/cell) were obtained by displacement analysis. From kinetic studies the forward and reverse rate constants were 3.1 X 10(8) mol min-1 l-1 and 3.6 X 10(-2)/min giving a Kd of 1.2 X 10(-10) mol/l. The relative binding potencies for angiotensin II and analogues were: [Sar1, Thr8]ANG II greater than ANG II greater than ANG III greater than [Sar1, Ala8]ANG II greater than ANG I. Incubation with an extracellular marker (51Cr-labelled EDTA) demonstrated that binding of angiotensin II to platelets was not due to free fluid endocytosis.
mesh_terms: D000328:Adult; D000804:Angiotensin II / Q000031:analogs & derivatives / Q000097:blood*; D001667:Binding, Competitive; D001792:Blood Platelets / Q000378:metabolism*; D002216:Captopril / Q000494:pharmacology; D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D010976:Platelet Count; D011945:Receptors, Angiotensin / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013696:Temperature
chemical_list: D011945:Receptors, Angiotensin; D011956:Receptors, Cell Surface; D000804:Angiotensin II; D002216:Captopril