Angiotensin II enhances beta-adrenergic receptor-mediated vasorelaxation in aortas from young but not old rats

Aging-Induced Impairment of Vascular Function: Mitochondrial Redox Contributions and Physiological/Clinical Implications

Significance: The vasculature responds to the respiratory needs of tissue by modulating luminal diameter through smooth muscle constriction or relaxation. Coronary perfusion, diastolic function, and coronary flow reserve are drastically reduced with aging. This loss of blood flow contributes to and exacerbates pathological processes such as angina pectoris, atherosclerosis, and coronary artery and microvascular disease. Recent Advances: Increased attention has recently been given to defining mechanisms behind aging-mediated loss of vascular function and development of therapeutic strategies to restore youthful vascular responsiveness. The ultimate goal aims at providing new avenues for symptom management, reversal of tissue damage, and preventing or delaying of aging-induced vascular damage and dysfunction in the first place. Critical Issues: Our major objective is to describe how aging-associated mitochondrial dysfunction contributes to endothelial and smooth muscle dysfunction via dysregulated reactive oxygen species production, the clinical impact of this phenomenon, and to discuss emerging therapeutic strategies. Pathological changes in regulation of mitochondrial oxidative and nitrosative balance (Section 1) and mitochondrial dynamics of fission/fusion (Section 2) have widespread effects on the mechanisms underlying the ability of the vasculature to relax, leading to hyperconstriction with aging. We will focus on flow-mediated dilation, endothelial hyperpolarizing factors (Sections 3 and 4), and adrenergic receptors (Section 5), as outlined in Figure 1. The clinical implications of these changes on major adverse cardiac events and mortality are described (Section 6). Future Directions: We discuss antioxidative therapeutic strategies currently in development to restore mitochondrial redox homeostasis and subsequently vascular function and evaluate their potential clinical impact (Section 7). Antioxid. Redox Signal. 35, 974-1015.

Neurohormonal Regulation of IKs in Heart Failure: Implications for Ventricular Arrhythmogenesis and Sudden Cardiac Death

Heart failure (HF) results in sustained alterations in neurohormonal signaling, including enhanced signaling through the sympathetic nervous system and renin-angiotensin-aldosterone system pathways. While enhanced sympathetic nervous system and renin-angiotensin-aldosterone system activity initially help compensate for the failing myocardium, sustained signaling through these pathways ultimately contributes to HF pathophysiology. HF remains a leading cause of mortality, with arrhythmogenic sudden cardiac death comprising a common mechanism of HF-related death. The propensity for arrhythmia development in HF occurs secondary to cardiac electrical remodeling that involves pathological regulation of ventricular ion channels, including the slow component of the delayed rectifier potassium current, that contribute to action potential duration prolongation. To elucidate a mechanistic explanation for how HF-mediated electrical remodeling predisposes to arrhythmia development, a multitude of investigations have investigated the specific regulatory effects of HF-associated stimuli, including enhanced sympathetic nervous system and renin-angiotensin-aldosterone system signaling, on the slow component of the delayed rectifier potassium current. The objective of this review is to summarize the current knowledge related to the regulation of the slow component of the delayed rectifier potassium current in response to HF-associated stimuli, including the intracellular pathways involved and the specific regulatory mechanisms.

Angiotensin II, a unique vasoactive agent dissociates myosin light chain phosphorylation from contraction

Angiotensin II (100 nM) induced bi-phasic increases in cytosolic Ca²⁺ level ([Ca²⁺]_i) through the activation of angiotensin II type 1 receptor. Pharmacological examinations using 10 µM verapamil, 30 µM La³⁺, and 1 µM thapsigargin indicated that the first phase of the [Ca²⁺]_i-increase was mediated by Ca²⁺ release from sarcoplasmic reticulum (SR) and Ca²⁺ influx independently of voltage dependent Ca²⁺ channel (VDC). In contrast, the second phase of [Ca²⁺]_i-increase was mediated by Ca²⁺ influx through VDC. Although both [Ca²⁺]_i and myosin light chain (MLC)-phosphorylation at the first phase was apparently exceeded the threshold for contraction as estimated by high K⁺-induced responses, there was no appreciable contraction, indicating the dissociation between MLC phosphorylation and force during this phase. In contrast, the second phase of [Ca²⁺]_i was associated with the increases in both MLC phosphorylation and force. These results suggest that angiotensin II is a unique agonist which dissociates MLC-phosphorylation from muscle force during the Ca²⁺ releases from SR.

Biochemical and molecular aspects of vascular adrenergic regulation of blood pressure in the elderly

Hypertension, orthostatic hypotension, arterial insufficiency, and atherosclerosis are common disorders in the elderly that lead to significant morbidity and mortality. One common factor to these conditions is an age-related decline in vascular beta-adrenergic receptor-mediated function and subsequent cAMP generation. Presently, there is no single cellular factor that can explain this age-related decline, and thus, the primary cause of this homeostatic imbalance is yet to be identified. However, the etiology is clearly associated with an age-related change in the ability of beta-adrenergic receptor to respond to agonist at the cellular level in the vasculature. This paper will review what is presently understood regarding the molecular and biochemical basis of age-impaired beta-adrenergic receptor-mediated signaling. A fundamental understanding of why β-AR-mediated vasorelaxation is impaired with age will provide new insights and innovative strategies for the management of multiple clinical disorders.

Inhibition of angiotensin II Gq signaling augments beta-adrenergic receptor mediated effects in a renal artery stenosis model of high blood pressure

Chronic ventricular pressure overload states, such as hypertension, and elevated levels of neurohormones (norepinephrine, angiotensin II, endothelin-1) initiate cardiac hypertrophy and dysfunction and share the property of being able to bind to Gq-coupled 7-transmembrane receptors. The goal of the current study was to determine the role of endogenous cardiac myocyte Gq signaling and its role in cardiac hypertrophy and dysfunction during high blood pressure (BP). We induced renal artery stenosis for 8 weeks in control mice and mice expressing a peptide inhibitor of Gq signaling (GqI) using a 2 kidney, 1 clip renal artery stenosis model. 8 weeks following chronic high BP, control mice had cardiac hypertrophy and depressed function. Inhibition of cardiomyocyte Gq signaling did not reverse cardiac hypertrophy but attenuated increases in a profile of cardiac profibrotic genes and genes associated with remodeling. Inhibition of Gq signaling also attenuated the loss of cardiac function. We determined that Gq signaling downstream of angiotensin II receptor stimulation negatively impacted beta-adrenergic receptor (AR) responses and inhibition of Gq signaling was sufficient to restore betaAR-mediated responses. Therefore, in this study we found that Gq signaling negatively impacts cardiac function during high BP. Specifically, we found that inhibition of AT1-Gq signaling augmented betaAR mediated effects in a renal artery stenosis model of hypertension. These observations may underlie additional, beneficial effects of angiotensinogen converting enzyme (ACE) inhibitors and angiotensin receptor antagonists observed during times of hemodynamic stress.

Phospholipase C and Src modulate angiotensin II-induced cyclic AMP production in preglomerular microvascular smooth-muscle cells from spontaneously hypertensive rats

Our previous study indicates that the phospholipase C family (PLC) and Src kinase family (Src) modulate adrenoceptor-induced cAMP production in a negative and positive manner, respectively, in preglomerular vascular smooth-muscle cells (PGSMCs) obtained from spontaneously hypertensive rats (SHR). Because angiotensin II (Ang II) activates PLC and Src, and because PLC and Src inhibit and augment cAMP production, respectively, it is conceivable that the balance between these signal-transduction pathways determines whether Ang II increases or decreases cAMP production in SHR PGSMCs. In SHR PGSMCs, Ang II (500 nM) did not alter cAMP production in the absence or presence of PP1 (100 nM; inhibitor of Src). In the presence of U73122 (3 microM; inhibitor of PLC), Ang II stimulated cAMP production from 2.2 +/- 0.062 to 4.7 +/- 0.73 pmol/well. In another study in U73122-pretreated SHR PGSMCs, Ang II increased cAMP from 3.0 +/- 0.07 to 6.3 +/- 0.40 pmol/well, and this response was blocked by PP1. RT-PCR of 10 isoforms of Scr (Lck, Hck, Frk Fyn, Blk, Lyn, Fgr, Yes, Yrk, and c-Src) indicated that SHR PGSMCs preferentially express Frk, Fyn, Lyn, and c-Src. We conclude that in SHR PGSMCs, inhibition of PLC uncovers a stimulatory effect of Ang II on cAMP production that is mediated by Src family kinases, most likely Frk, Fyn, Lyn, and/or c-Src.