Characterization of avian angiotensin II cardiac receptors: coupling to mechanical activity and phosphoinositide metabolism.

We have characterized the avian angiotensin II (AII) cardiac receptor and provide data that this receptor couples to both mechanical activity and phospholipid metabolism in the avian heart. In 10-day-old chicks, 125I-AII bound to a high affinity site (Kd = 10 nmol) and a low affinity site (Kd = 79.4 nmol) with estimated binding capacities of 531 and 1330 fmol/mg protein, respectively. The 125I-AII binding was rapid, saturable, reversible and modulated by divalent cations and guanine nucleotides. The potency order for the competitive binding of angiotensin I and II paralleled that observed for in vitro contractile force development in bioassays utilizing left atrial tissue. In avian heart, AII also produced a dose-dependent accumulation of inositol-1-phosphate which was inhibited by the angiotensin antagonist [Sar1, Ile8]AII. The data demonstrate specific avian AII cardiac receptors and provide the first evidence that these receptors couple to both mechanical activity and phosphoinositide metabolism in avian heart.