Position of Src tyrosine kinases in the interaction between angiotensin II and endothelin in in vivo vascular protein synthesis

Endothelin signalling regulates volume-sensitive Cl- current via NADPH oxidase and mitochondrial reactive oxygen species

AIMS

We assessed regulation of volume-sensitive Cl(-) current (I(Cl,swell)) by endothelin-1 (ET-1) and characterized the signalling pathway responsible for its activation in rabbit atrial and ventricular myocytes.

METHODS AND RESULTS

ET-1 elicited I(Cl,swell) under isosmotic conditions. Outwardly rectified Cl(-) current was blocked by the I(Cl,swell)-selective inhibitor DCPIB or osmotic shrinkage and involved ET(A) but not ET(B) receptors. ET-1-induced current was abolished by inhibiting epidermal growth factor receptor (EGFR) kinase or phosphoinositide-3-kinase (PI-3K), indicating that these kinases were downstream. Regarding upstream events, activation of I(Cl,swell) by osmotic swelling or angiotensin II (AngII) was suppressed by ET(A) blockade, whereas AngII AT(1) receptor blockade failed to alter ET-1-induced current. Reactive oxygen species (ROS) produced by NADPH oxidase (NOX) stimulate I(Cl,swell). As expected, blockade of NOX suppressed ET-1-induced I(Cl,swell), but blockade of mitochondrial ROS production with rotenone also suppressed I(Cl,swell). I(Cl,swell) was activated by augmenting complex III ROS production with antimycin A or diazoxide; in this case, I(Cl,swell) was insensitive to NOX inhibitors, indicating that mitochondria were downstream from NOX. ROS generation in HL-1 cardiomyocytes measured by flow cytometry confirmed the electrophysiological findings. ET-1-induced ROS production was inhibited by blocking either NOX or mitochondrial complex I, whereas complex III-induced ROS production was insensitive to NOX blockade.

CONCLUSION

ET-1-ET(A) signalling activated I(Cl,swell) via EGFR kinase, PI-3K, and NOX ROS production, which triggered mitochondrial ROS production. ET(A) receptors were downstream effectors when I(Cl,swell) was elicited by osmotic swelling or AngII. These data suggest that ET-1-induced ROS-dependent I(Cl,swell) is likely to participate in multiple physiological and pathophysiological processes.

Endothelin-1, but not Ang II, activates MAP kinases through c-Src independent Ras-Raf dependent pathways in vascular smooth muscle cells

OBJECTIVE

Endothelin-1 (ET-1) and angiotensin II (Ang II) activate common signaling pathways to promote changes in vascular reactivity, remodeling, inflammation, and oxidative stress. Here we sought to determine whether upstream regulators of mitogen-activated protein kinases (MAPKs) are differentially regulated by ET-1 and Ang II focusing on the role of c-Src and the small GTPase Ras.

METHODS AND RESULTS

Mesenteric vascular smooth muscle cells (VSMCs) from mice with different disruption levels in the c-Src gene (c-Src(+/-) and c-Src(-/-)) and wild-type (c-Src(+/+)) were used. ET-1 and Ang II induced extracellular signal-regulated kinase (ERK) 1/2, SAPK/JNK, and p38MAPK phosphorylation in c-Src(+/+) VSMCs. In VSMCs from c-Src(+/-) and c-Src(-/-), Ang II effects were blunted, whereas c-Src deficiency had no effect in ET-1-induced MAPK activation. Ang II but not ET-1 induced c-Src phosphorylation in c-Src(+/+) VSMCs. Activation of c-Raf, an effector of Ras, was significantly increased by ET-1 and Ang II in c-Src(+/+) VSMCs. Ang II but not ET-1-mediated c-Raf phosphorylation was inhibited by c-Src deficiency. Knockdown of Ras by siRNA inhibited both ET-1 and Ang II-induced MAPK phosphorylation.

CONCLUSIONS

Our data indicate differential regulation of MAPKs by distinct G protein-coupled receptors. Whereas Ang II has an obligatory need for c-Src, ET-1 mediates its actions through a c-Src-independent Ras-Raf-dependent pathway for MAPK activation. These findings suggest that Ang II and ET-1 can activate similar signaling pathways through unrelated mechanisms. MAP kinases are an important point of convergence for Ang II and ET-1.

Sex-related differences in NMDA-evoked rat masseter muscle afferent discharge result from estrogen-mediated modulation of peripheral NMDA receptor activity

In the present study, the hypothesis that sex-related differences in glutamate-evoked rat masseter muscle afferent discharge may result from estrogen-related modulation of peripheral N-methyl-d-aspartate (NMDA) receptor activity and/or expression was tested by examining afferent fiber discharge in response to masseter injection of NMDA and the expression of NR2A/B subunits by masseter ganglion neurons in male and female rats. The results showed that injection of NMDA into the masseter muscle evoked discharges in putative mechanonociceptive afferent fibers and increased blood pressure that was concentration-dependent, however, a systemic action of NMDA appeared responsible for increased blood pressure. NMDA-evoked afferent discharge was significantly greater in female than in male rats, was positively correlated with plasma estrogen levels in females and was significantly greater in ovariectomized female rats treated with a high dose (5 mug/day) compared with a low dose (0.5 mug/day) of estrogen. Pre-treatment of high dose estrogen-treated-ovariectomized female rats with the Src tyrosine kinase inhibitor PP2 did not affect NMDA-evoked afferent discharge. NMDA-evoked afferent discharge was attenuated by the antagonists ketamine and ifenprodil, which is selective for NR2B containing NMDA receptors. Fewer masseter ganglion neurons expressed the NR2A (16%) subunit as compared with the NR2B subunit (38%), which was expressed at higher frequencies in intact female (46%) and high dose estrogen-treated ovariectomized female (60%) rats than in male (31%) rats. Taken together, these results suggest that sex-related differences in NMDA-evoked masseter afferent discharge are due, at least in part, to an estrogen-mediated increase in expression of peripheral NMDA receptors by masseter ganglion neurons in female rats.

The interrelation of the angiotensin and endothelin systems on the modulation of NAD(P)H oxidaseThis paper is one of a selection of papers published in this Special issue, entitled Young Investigator's Forum

The NAD(P)H oxidase is an enzyme assembled at the cellular membrane able to produce superoxide anion from NADH or NAD(P)H (nicotinamide adenine dinucleotide phosphate). It is one of the main sources of superoxide anion in cardiovascular tissues and its role in a variety of cardiovascular disorders such as atherosclerosis, cardiac hypertrophy, and endothelial dysfunction was recently proposed. Although, many factors and receptors were shown to lead to the activation of the enzyme, particulary the type 1 angiotensin receptor, the pathways involved are still widely unknown. Despite the identification of factors such as c-Src and protein kinase C implicated in the acute activation of NAD(P)H oxidase, the signalling involved in the sustained activation of the enzyme is probably far more complex than was previously envisioned. In this review, we describe the role of endothelin-1 in NAD(P)H oxidase signalling after a sustained stimulation by angiotensin II. Since most pathologies caused by an NAD(P)H oxidase overactivation develop over a relatively long period of time, it is necessary to better understand the long-term signalling of the enzyme for the development or use of more specific therapeutic tools.