Angiotensin II stimulates the release of phospholipid-derived second messengers through multiple receptor subtypes in heart cells.

The octapeptide angiotensin II (Ang-II) induces both acute functional changes and longer lasting molecular changes in cultured mammalian heart myocytes, yet the underlying molecular mechanisms are poorly understood. In this study, Ang-II was found to stimulate a sustained release (> 30 min) of arachidonic acid (ARA) from cultured neonatal rat cardiac myocytes, with a half-maximal response observed at 0.1 nM. Mass spectroscopy analysis showed that Ang-II stimulated a specific release equivalent to 104 fmol of ARA/micrograms of protein in 10 min. Only Ang-II type 1 (AT1) receptor-specific antagonists were potent inhibitors of hormone-evoked [3H]inositol phosphate accumulation (DuP 753 IC50 approximately 7 nM compared to CGP 42112A IC50 > 1 microM). In contrast, only AT2 receptor-specific antagonists were potent inhibitors of [3H]ARA release (CGP 42112A IC50 approximately 7 nM, EXP 3880 IC50 approximately 2 nM, and PD 123177 IC50 approximately 10 nM). Further studies with phospholipase inhibitors (p-amylcinnamoylanthranilic acid and U73122) revealed that the production of [3H]-inositol phosphates and [3H]ARA occurs through parallel and independent pathways involving phospholipase C and phospholipase A2, respectively. Ang-II also increased the level of lysophosphatidylcholine by 49%, direct evidence that this peptide activated phospholipase A2. Thus, Ang-II stimulates distinct phospholipases in parallel through AT1 and AT2 receptors. These results reveal coordinate signaling roles for multiple Ang-II receptor subtypes in heart.