Influence of cations on kinetics of angiotensin II binding to Adrenal, Renal, and Smooth Muscle Receptors

A number of biological responses to angiotensin II have been demonstrated to be modulated acutely by cations, but the exact mechanism has not been elucidated. We have utilized a radioreceptor assay for angiotensin II to determine whether this acute regulatory mechanism could be related to a change in either number or affinity of angiotensin II binding to receptors. Three target tissues were used (adrenal glomerulosa, glomeruli, and uterine smooth muscle). Both mono- and divalent cations influence the kinetics of angiotensin II binding in a similar manner in all tissues. Divalent cations increase the number of receptor sites to a greater extent than did monovalent cations, while monovalent cations changed binding affinity to a greater extent than did divalent cations. These studies demonstrate that both the number and affinity of angiotensin receptors can be rapidly modulated by a variety of cations. The physiologic importance of this observation is as yet unknown.