Characterization of the angiotensin receptor in guinea-pig aorta.

The binding of 14C-angiotensin to the subcellular fractions of guinea-pig aorta was compared to the known physiological data as obtained from the intact preparation. Results show that only the plasma membrane fraction possesses binding characteristics consistent with the physiological data. Equilibrium of specific binding occurs at 10(-7) M 14C-angiotensin which is the physiological maximal dose. This equilibrium is achieved after 3 minutes of incubation, the time required to develop maximal response. 8-Leu-angiotensin, a specific competitive antagonist of angiotensin, blocks the binding of 14C-angiotensin in a manner similar to nonradioactive angiotensin. Neither bradykinin nor angiotensin I has a significant effect on the binding of 14C-angiotensin to plasma membranes. The dissociation constant (Ka) as calculated from the 50% inhibition of the specific binding is 2.2 X 10(-8) M. This value corresponds to the apparent Ka estimated from both the physiological dose-response curve (6.3 X 10(-8) M) and the reversibility of binding curve (4.7 X 10(-8) M). Specific binding of 14C-angiotensin is pH dependent with maximal binding occurring at pH 7.4. The rate of dissociation of 14C-angiotensin bound to plasma membranes is compatible with the recovery of the physiological response. These results indicate that the angiotensin receptor is located in the cell membrane.