Intracellular Angiotensin II and cell growth of vascular smooth muscle cells

1. We recently demonstrated that intracellular application of Angiotensin II (Angiotensin II(intr)) induces rat aorta contraction independent of plasma membrane Angiotensin II receptors. In this study we investigated the effects of Angiotensin II(intr) on cell growth in A7r5 smooth muscle cells. 2. DNA-synthesis was increased dose-dependently by liposomes filled with Angiotensin II as measured by [(3)H]-thymidine incorporation at high (EC(50)=27+/-6 pM) and low (EC(50)=14+/-5 nM) affinity binding sites with increases in E(max) of 58+/-4 and 37+/-4% above quiescent cells, respectively. Cell growth was corroborated by an increase in cell number. 3. Extracellular Angiotensin II (10 pM - 10 microM) did not modify [(3)H]-thymidine incorporation. 4. Growth effects of Angiotensin II(intr) mediated via high affinity sites were inhibited by liposomes filled with 1 microM of the non-peptidergic antagonists losartan (AT(1)-receptor) or PD123319 (AT(2)-receptor) or with the peptidergic agonist CGP42112A (AT(2)-receptor). E(max) values were decreased to 30+/-3, 29+/-4 and 4+/-2%, respectively, without changes in EC(50). The Angiotensin II(intr) effect via low affinity sites was only antagonized by CGP42112A (E(max)=11+/-3%), while losartan and PD123319 increased E(max) to 69+/-4%. Intracellular applications were ineffective in the absence of Angiotensin II(intr). 5. Neither intracellular nor extracellular Angiotensin I (1 microM) were effective. 6. The Angiotensin II(intr) induced growth response was blocked by selective inhibition of phosphatidyl inositol 3-kinase (PI-3K) by wortmannin (1 microM) and of the mitogen-activated protein kinase (MAPK/ERK) pathway by PD98059 (1 microM) to 61+/-14 and 4+/-8% of control, respectively. 7. These data demonstrate that Angiotensin II(intr) induces cell growth through atypical AT-receptors via a PI-3K and MAPK/ERK -sensitive pathway.