Superoxide anion triggers the angiotensin II intracellular pathway leading to release/production of endothelin-1 and positive inotropism.

AIELLO EA; ENNIS IL; VILLA –ABRILLE MC; GARCIARENA CD; CALDIZ CI; CHIAPPE DE CINGOLANI GE; CINGOLANI HE.

Colby-Sawyer College, New London, New Hampshire, EEUU

Congreso; Gordon Research Conference, Cardiac Regulatory Mechanisms.; 2006

Colby-Sawyer College

Doses of angiotensin II (Ang II) as low as 1 nmol/L induce a positive inotropic effect (PIE) entirely due to the action of endogenous endothelin-1 (ET-1) released/produced by Ang II. However the mechanism by which Ang II releases/produces ET-1 remains unknown. In the present work we used isolated cat cardiomyocytes for measuring sarcomere shortening (SS) with a video-camera and preproET-1 mRNA levels by RT-PCR, and cat left ventricular slices for superoxide anions (O2-.) production by the lucigenin-chemiluminescence method. These parameters were measured in control and after 15 min treatment with 1 nmol/L Ang II. Ang II increased the level of preproET-1 mRNA from 100±3.4 % (n=15) to 173.3±28.1 % (n=11, p<0.05) as an indicator of the replenishment of the ET-1 intracellular pool that might have been reduced after the release of this peptide by Ang II. This increase in the level of preproET-1 mRNA was abrogated by the AT1 receptor blocker losartan (1 mmol/L; 90.5±21.4 %, n=4), the NADPH oxidase inhibitor apocinin (0.3 mmol/L; 77.7±15.8 %, n=5) and the reactive oxygen species (ROS) scavenger mercapto-propionyl-glycine (MPG, 1 mmol/L; 115.7±15.6 %, n=3), but not by the non-specific ET-1 receptor blocker TAK044 (1 mmol/L, 190±10.9 %, n=4). The production of O2-. increased from 123±7.7 (in arbitrary units/min mg dry weight) in control (n=20) to 163±11.7 with Ang II (n=17, p<0.05). This effect was inhibited by losartan (104±19.8, n=3), TAK044 (104±5.1, n=10), and apocinin (104±19.9, n=8). These blockers did not affect the basal O2-. production. The PIE of Ang II (29.2±3.1 %, n=15, p<0.05) was abrogated by losartan (-1±4.9 %, n=6) and by TAK044 (-4.5±4.9 %, n=6). This PIE was also abolished by apocinin (8.7±7.3 %, n=8) and by MPG (-8.4±3.8 %, n=6). The fact that apocinin and MPG abrogated the increase in ET-1 mRNA induced by Ang II whereas the increase in O2-. production and the PIE induced by this peptide was also abolished by ET-1 receptors blockade could be explained by a two steps mechanism: 1) Ang II, by stimulating NADPH oxidase, induces a slight increase in O2-. that in spite of not being detected by our measurements trigger the production of ET-1 and 2) Endogenous ET-1 released by Ang II induce the measurable increase in O2-., which in turn produces the increase in contractility.