AT1 receptor for angiotensin II. Angiotensin II is a potent vasopressor hormone and a primary regulator of aldosterone secretion. It is an important effector controlling blood pressure and volume in the cardiovascular system. Mediates the major cardiovascular effects of angiotensin II. May play role in the generation of reperfusion arrhythmias following restoration of blood flow to ischemic or infarcted myocardium. Mediates its action by association with G proteins that activate a phosphatidylinositol-calcium second messenger system.