title: Angiotensin receptors in resting smooth muscle are the low affinity sites observed in binding studies.
abstract: Angiotensin receptors in rat uterine smooth muscle have been investigated by [125I]angiotensin II binding studies in membrane preparations. Scatchard analysis of binding data has demonstrated the presence of low and high affinity angiotensin binding sites with KLD = 3.0 X 10(-8) and KHD = 5.0 X 10(-10)M respectively. These values are identical to our previously reported values for the EC50 and dissociation constant, respectively, obtained from bioassays on intact uterine tissues. The antagonist [Sar1, Ile8]angiotensin II also demonstrates a binding affinity in uterine membranes (pKD = 8.7) which is not significantly different from its apparent binding affinity (pA2 = 8.6) in responding tissues. Taken in conjunction with our previously published bioassay data the present binding studies suggest that the resting state of the angiotensin receptor in smooth muscle is a low affinity state, and that interaction with ANG II induces a portion of the receptors into a high affinity "excited" state. The antagonist [Sar1, Ile8]angiotensin II apparently binds with higher affinity than angiotensin II to the low affinity (resting) state of the receptor.
mesh_terms: D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D004054:Diethylstilbestrol / Q000494:pharmacology; D005260:Female; D007700:Kinetics; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011945:Receptors, Angiotensin / Q000378:metabolism*; D014599:Uterus / Q000378:metabolism
chemical_list: D011945:Receptors, Angiotensin; D000804:Angiotensin II; D004054:Diethylstilbestrol