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Angiotensin II receptor type I (AT₁R) is a G-protein coupled receptor involved in regulation of body water-electrolyte balance and blood pressure. Oxidative stress promotes AT₁R oligomerization and hyper-responsiveness to its cognate ligand Ang II. In this study, bivalent Ang II, synthesized by linking with aminocaproic acid (Acp) at the N-terminus, was used to induce AT₁R dimerization and hyper-responsiveness in AT₁R-expressed human embryonic kidney (AT₁R-HEK) cells, determined using image correlation spectroscopy (ICS) and by measuring AT₁R-mediated change in intracellular Ca²⁺ concentration, respectively. In addition, ICS was employed to determine distribution pattern of cell-surface AT₁R and its degree of aggregation when stimulated by monomeric (monovalent) and bivalent Ang II under oxidative stress (100 μM H₂O₂) condition in comparison with normal (unoxidized) AT₁R-HEK cells. Bivalent …