ANGIOTENSIN-II STIMULATES THE RELEASE OF PHOSPHOLIPID-DERIVED 2ND 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 hea rt myocytes, yet the underlying molecular mechanisms are poorly unders tood. In this study, Ang-II was found to stimulate a sustained release (>30 min) of arachidonic acid (ARA) from cultured neonatal rat cardia c myocytes, with a half-maximal response observed at 0.1 nM. Mass spec troscopy analysis showed that Ang-II stimulated a specific release equ ivalent to 104 fmol of ARA/mu g of protein in 10 min. Only Ang-II type 1 (AT(1)) receptor-specific antagonists were potent inhibitors of hor mone-evoked [H-3]inositol phosphate accumulation (DuP 753 IC50 approxi mate to 7 nM compared to CGP 42112A IC50 > 1 mu M). In contrast, only AT(2) receptor-specific antagonists were potent inhibitors of [H-3]ARA release (CGP 42112A IC50 approximate to 7 nM) EXP 3880 IC50 approxima te to 2 nM and PD 123177 IC50 approximate to 10 nM). Further studies w ith phospholipase inhibitors (p-amylcinnamoylanthranilic acid and U731 22) revealed that the production of [H-3]inositol phosphates and [H-3] ARA occurs through parallel and independent pathways involving phospho lipase C and phospholipase Az, respectively. Ang-II also increased the level of lysophosphatidylcholine by 49%, direct evidence that this pe ptide activated phospholipase Az. Thus, Ang-II stimulates distinct pho spholipases in parallel through AT(1) and AT(2) receptors. These resul ts reveal coordinate signaling roles for multiple Ang-II receptor subt ypes in heart.