200 The ERK pathway regulates sarcolemmal Na+-HCO3-cotransport activity following intracellular acidification in the absence or presence of angiotensin II

Hypoxic injury to cardiomyocytes is a stress that causes cardiac pathology through cardiac-restricted gene expression. SRF (serum-response factor) and myocardin are important for cardiomyocyte growth and differentiation in response to myocardial injuries. Previous studies have indicated that AngII (angiotensin II) stimulates both myocardin expression and cardiomyocyte hypertrophy. In the present study, we evaluated the expression of myocardin and AngII after hypoxia in regulating gene transcription in neonatal cardiomyocytes. Cultured rat neonatal cardiomyocytes were subjected to hypoxia, and the expression of myocardin and AngII were evaluated. Different signal transduction pathway inhibitors were used to identify the pathway(s) responsible for myocardin expression. An EMSA (electrophoretic mobility-shift assay) was used to identify myocardin/SRF binding, and a luciferase assay was used to identify transcriptional activity of myocardin/SRF in neonatal cardiomyocytes. Both myocardin and AngII expression increased after hypoxia, with AngII appearing at an earlier time point than myocardin. Myocardin expression was stimulated by AngII and ERK (extracellular-signal-regulated kinase) phosphorylation, but was suppressed by an ARB (AngII type 1 receptor blocker), an ERK pathway inhibitor and myocardin siRNA (small interfering RNA). AngII increased both myocardin expression and transcription in neonatal cardiomyocytes. Binding of myocardin/SRF was identified using an EMSA, and a luciferase assay indicated the transcription of myocardin/SRF in neonatal cardiomyocytes. Increased BNP (B-type natriuretic peptide), MHC (myosin heavy chain) and [3H]proline incorporation into cardiomyocytes was identified after hypoxia with the presence of myocardin in hypertrophic cardiomyocytes. In conclusion, hypoxia in cardiomyocytes increased myocardin expression, which is mediated by the induction of AngII and the ERK pathway, to cause cardiomyocyte hypertrophy. Myocardial hypertrophy was identified as an increase in transcriptional activities, elevated hypertrophic and cardiomyocyte phenotype markers, and morphological hypertrophic changes in cardiomyocytes.

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Vascular smooth muscle Na+-H+ exchanger kinetics and its activation by angiotensin II

AJP Cell Physiology ◽

10.1152/ajpcell.1988.254.6.c751 ◽

1988 ◽

Vol 254 (6) ◽

pp. C751-C758 ◽

Cited By ~ 38

Author(s):

G. A. Vallega ◽

M. L. Canessa ◽

B. C. Berk ◽

T. A. Brock ◽

R. W. Alexander

Keyword(s):

Smooth Muscle ◽

Angiotensin Ii ◽

Maximum Velocity ◽

Kinetic Properties ◽

Ang Ii ◽

Intracellular Acidification ◽

Aortic Smooth Muscle ◽

Maximal Activation ◽

Free Media ◽

Kinetics Of

We have studied the kinetic properties of basal and angiotensin II (ANG II)-stimulated Na+-H+ exchange in cultured rat aortic smooth muscle cells. Initial rates of 22Na+ influx were measured in the presence of ouabain (1 mM) and bumetanide (0.1 mM) with and without amiloride after intracellular acidification by preincubation in Na-free media. The kinetics of amiloride (100 microM)-sensitive Na+ influx were studied under the following conditions: 1) constant intracellular pH (pHi; 6.8) and varying external Na+ (Na+o), which gave a Km of 23.6 +/- 2.0 (SD, n = 3) mM and a maximum velocity (Vmax) of 25 nmol.mg protein-1.min-1 (varying the amiloride concentration gave a Ki of 22 microM for inhibition under these conditions); and 2) constant Na+o (100 mM) and varying pHi (from 7.4 to 6.2), which indicated that amiloride-sensitive Na+ influx was stimulated by cell acidification when an outward H+ gradient was imposed. ANG II-stimulated amiloride-sensitive Na+ influx for up to 30 min with a half-maximal activation 10(-8) M. The pHi dependence from cell pH (pHi 7.2-6.2) of amiloride-sensitive Na+ influx stimulated by ANG II was similar to that of the basal values, a finding indicating that ANG II did not change the affinity of Na+-H+ exchange for intracellular H+. However, at pHi 6.8, ANG II increased the Vmax of amiloride-sensitive Na+ influx from 25 to 33 nmol.mg protein-1.min-1 and markedly decreased the Km for Na+o from 23.6 +/- 7.4 to 3.7 (SD, n = 4; P less than 0.005) mM.(ABSTRACT TRUNCATED AT 250 WORDS)

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The ERK pathway regulates Na+-HCO 3 − cotransport activity in adult rat cardiomyocytes

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.01071.2001 ◽

2002 ◽

Vol 283 (5) ◽

pp. H2102-H2109 ◽

Cited By ~ 15

Author(s):

Delphine Baetz ◽

Robert S. Haworth ◽

Metin Avkiran ◽

Danielle Feuvray

Keyword(s):

Ventricular Myocytes ◽

Immunoblot Analysis ◽

Erk Pathway ◽

Ang Ii ◽

Intracellular Acidification ◽

Rat Cardiomyocytes ◽

Adult Rat ◽

Erk Phosphorylation ◽

Acid Load

The sarcolemmal Na+-HCO[Formula: see text] cotransporter (NBC) is stimulated by intracellular acidification and acts as an acid extruder. We examined the role of the ERK pathway of the MAPK cascade as a potential mediator of NBC activation by intracellular acidification in the presence and absence of angiotensin II (ANG II) in adult rat ventricular myocytes. Intracellular pH (pHi) was recorded with the use of seminaphthorhodafluor-1. The NH[Formula: see text]method was used to induce an intracellular acid load. NBC activation was significantly decreased with the ERK inhibitors PD-98059 and U-0126. NBC activity after acidification was increased in the presence of ANG II (pHi range of 6.75–7.00). ANG II plus PD-123319 (AT2 antagonist) still increased NBC activity, whereas ANG II plus losartan (AT1 antagonist) did not affect it. ERK phosphorylation (measured by immunoblot analysis) during intracellular acidification was increased by ANG II, an effect that was abolished by losartan and U-0126. In conclusion, the MAPK(ERK)-dependent pathway facilitates the rate of pHirecovery from acid load through NBC activity and is involved in the AT1 receptor-mediated stimulation of such activity by ANG II.

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Roles of MEK/ERK Pathway in Vascular and Renal Tubular Actions of Angiotensin II

Vascular Disease Prevention ◽

10.2174/1567270001006010157 ◽

2009 ◽

Vol 6 (1) ◽

pp. 157-162

Author(s):

George Seki ◽

Hideomi Yamada ◽

Yuehong Li ◽

Shoko Horita ◽

Nobukazu Ishizaka ◽

...

Keyword(s):

Angiotensin Ii ◽

Erk Pathway ◽

Renal Tubular

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4P-1129 Role of Ras-ERK pathway and c-Src in angiotensin II-induced osteopontin expression in vascular smooth muscle cells

Atherosclerosis Supplements ◽

10.1016/s1567-5688(03)91385-7 ◽

2003 ◽

Vol 4 (2) ◽

pp. 323 ◽

Cited By ~ 1

Author(s):

H. Nakashima ◽

N. Miho ◽

M. Ishida ◽

K. Chayama ◽

T. Oshima ◽

...

Keyword(s):

Smooth Muscle ◽

Angiotensin Ii ◽

Vascular Smooth Muscle ◽

Smooth Muscle Cells ◽

Vascular Smooth Muscle Cells ◽

Muscle Cells ◽

Erk Pathway ◽

Osteopontin Expression

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Angiotensin II and the ERK pathway mediate the induction of leptin by mechanical cyclic stretch in cultured rat neonatal cardiomyocytes

Clinical Science ◽

10.1042/cs20130235 ◽

2013 ◽

Vol 126 (7) ◽

pp. 483-495 ◽

Cited By ~ 3

Author(s):

Chiung-Zuan Chiu ◽

Bao-Wei Wang ◽

Kou-Gi Shyu

Keyword(s):

Angiotensin Ii ◽

Cyclic Stretch ◽

Erk Pathway ◽

Rat Cardiomyocytes ◽

Neonatal Cardiomyocytes ◽

Leptin Expression

Cyclic stretch increases leptin expression in rat cardiomyocytes through the ERK pathway.

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Specific role of the extracellular signal-regulated kinase pathway in angiotensin II-induced cardiac hypertrophy in vitro

Biochemical Journal ◽

10.1042/bj3470275 ◽

2000 ◽

Vol 347 (1) ◽

pp. 275-284 ◽

Cited By ~ 49

Author(s):

Hiroki AOKI ◽

Mary RICHMOND ◽

Seigo IZUMO ◽

Junichi SADOSHIMA

Keyword(s):

Angiotensin Ii ◽

Cardiac Hypertrophy ◽

Specific Inhibitor ◽

Dominant Negative ◽

Neonatal Rat ◽

Specific Response ◽

Erk Pathway ◽

Ang Ii ◽

Extracellular Signal

Although MAP (mitogen-activated protein) kinases are implicated in cell proliferation and differentiation in many cell types, the role of MAP kinases in cardiac hypertrophy remains unclear. We examined the role of extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 MAP kinase in angiotensin II (Ang II)-induced hypertrophy compared with phenylephrine-induced hypertrophy in neonatal rat cardiac myocytes. Both Ang II and phenylephrine activated ERKs to a similar extent, whereas phenylephrine caused stronger and more sustained activation of JNK and p38 than Ang II. PD98059, a specific inhibitor of MAPK/ERK kinase (MEK),inhibited Ang II-induced, but not phenylephrine-induced, expression of atrial natriuretic factor (ANF) at both the mRNA and polypeptide levels. SB203580, a specific inhibitor of p38 and some JNK isoforms, did not show significant effects on ANF expression induced by Ang II or phenylephrine. Although PD98059 and dominant-negative MEK1 blocked Ang II-induced activation of the ANF promoter, SB203580 or dominant-negative MEK kinase 1 (MEKK1) showed no effect. Phenylephrine-induced ANF promoter activation was significantly inhibited by SB203580 and dominant-negative MEKK1, but not by PD98059 or dominant-negative MEK1. Dominant-negative Ras inhibited both ERK activation and ANF up-regulation by Ang II, whereas constitutively active forms of Ras and MEK were sufficient to activate the ANF promoter. Dominant-negative Ras also partly inhibited the phenylephrine-induced activation of ANF promoter. PD98059 did not affect other markers of Ang II-induced hypertrophy, such as skeletal α-actin and c-fos expression, increases in the rate of protein synthesis or rapid sarcomeric actin organization. These results suggest that Ang II uses ERK for ANF expression, whereas phenylephrine uses other pathways. The Ras/ERK pathway selectively mediates ANF expression in various phenotypes observed in Ang II-induced hypertrophy. The ERK pathway mediates an agonist-specific and phenotype-specific response in cardiac hypertrophy.

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