Cell swelling, impulse conduction, and cardiac arrhythmias in the failing heart. Opposite effects of angiotensin II and angiotensin (1–7) on cell volume regulation

The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7)

The renin-angiotensin system (RAS) is a key player in the control of the cardiovascular system and hydroelectrolyte balance, with an influence on organs and functions throughout the body. The classical view of this system saw it as a sequence of many enzymatic steps that culminate in the production of a single biologically active metabolite, the octapeptide angiotensin (ANG) II, by the angiotensin converting enzyme (ACE). The past two decades have revealed new functions for some of the intermediate products, beyond their roles as substrates along the classical route. They may be processed in alternative ways by enzymes such as the ACE homolog ACE2. One effect is to establish a second axis through ACE2/ANG-(1-7)/MAS, whose end point is the metabolite ANG-(1-7). ACE2 and other enzymes can form ANG-(1-7) directly or indirectly from either the decapeptide ANG I or from ANG II. In many cases, this second axis appears to counteract or modulate the effects of the classical axis. ANG-(1-7) itself acts on the receptor MAS to influence a range of mechanisms in the heart, kidney, brain, and other tissues. This review highlights the current knowledge about the roles of ANG-(1-7) in physiology and disease, with particular emphasis on the brain.

Losartan counteracts the effects of cardiomyocyte swelling on glucose uptake and insulin receptor substrate-1 levels

A growing body of evidence demonstrates an association between Angiotensin II (Ang II) receptor blockers (ARBs) and enhanced glucose metabolism during ischemic heart disease. Despite these encouraging results, the mechanisms responsible for these effects during ischemia remain poorly understood. In this study we investigated the influence of losartan, an AT1 receptor blocker, and secreted Ang II (sAng II) on glucose uptake and insulin receptor substrate (IRS-1) levels during cardiomyocyte swelling. H9c2 cells were differentiated to cardiac muscle and the levels of myogenin, Myosin Light Chain (MLC), and membrane AT1 receptors were measured using flow cytometry. Intracellular Ang II (iAng II) was overexpressed in differentiated cardiomyocytes and swelling was induced after incubation with hypotonic solution for 40min. Glucose uptake and IRS-1 levels were monitored by flow cytometry using 2-NBDG fluorescent glucose (10μM) or an anti-IRS-1 monoclonal antibody in the presence or absence of losartan (10^-7M). Secreted Angiotensin II was quantified from the medium using a specific Ang II-EIA kit. To evaluate the relationship between sAng II and losartan effects on glucose uptake, transfected cells were pretreated with the drug for 24h and then exposed to hypotonic solution in the presence or absence of the secreted peptide. The results indicate that: (1) swelling of transfected cardiomyocytes decreased glucose uptake and induced the secretion of Ang II to the extracellular medium; (2) losartan antagonized the effects of swelling on glucose uptake and IRS-1 levels in transfected cardiomyocytes; (3) the effects of losartan on glucose uptake were observed during swelling only in the presence of sAng II in the culture medium. Our study demonstrates that both losartan and sAng II have essential roles in glucose metabolism during cardiomyocyte swelling.

Local Renin Angiotensin Aldosterone Systems and Cardiovascular Diseases

The presence of local renin angiotensin aldosterone systems (RAAS) in the cardiovascular and renal tissues and their influence in cardiovascular and renal diseases are described. The fundamental role of ACE/Ang II/AT1 receptor axis activation as well the counterregulatory role of ACE2/Ang (1-7)/Mas receptor activation on cardiovascular and renal physiology and pathology are emphasized. The presence of a local RAS and its influence on hypertension is discussed, and finally, the hypothesis that epigenetic factors change the RAAS in utero and induce the expression of renin or Ang II inside the cells of the cardiovascular system is presented.

The hidden hand of chloride in hypertension

Among the environmental factors that affect blood pressure, dietary sodium chloride has been studied the most, and there is general consensus that increased sodium chloride intake increases blood pressure. There is accruing evidence that chloride may have a role in blood pressure regulation which may perhaps be even more important than that of Na⁺. Though more than 85 % of Na⁺ is consumed as sodium chloride, there is evidence that Na⁺ and Cl⁻ concentrations do not go necessarily hand in hand since they may originate from different sources. Hence, elucidating the role of Cl⁻ as an independent player in blood pressure regulation will have clinical and public health implications in addition to advancing our understanding of electrolyte-mediated blood pressure regulation. In this review, we describe the evidence that support an independent role for Cl⁻ on hypertension and cardiovascular health.

Chemical Communication between Heart Cells is Disrupted by Intracellular Renin and Angiotensin II: Implications for Heart Development and Disease

HighlightsIntracellular renin and angiotensin disrupts chemical communication in heart.Epigenetic modification of renin angiotensin aldosterone system (RAAS) and heart disease.Intracrine renin angiotensin and metabolic cooperation.Gap junction, intracellular renin and angiotensin, cellular patterns, and heart development. The finding that intracellular renin and angiotensin II (Ang II) disrupts chemical communication and impairs metabolic cooperation between cardiomyocytes induced by aldosterone, hyperglycemia, and pathological conditions like myocardial ischemia is discussed. The hypothesis is presented that epigenetic changes of the renin angiotensin aldosterone system (RAAS) are responsible for cardiovascular abnormalities, including the expression of RAAS components inside cardiac myocytes (intracrine RAAS) with serious consequences including inhibition of electrical and chemical communication in the heart, resulting in metabolic disarrangement and cardiac arrhythmias. Moreover, the inhibition of gap junctional communication induced by intracellular Ang II or renin can contribute to the selection of cellular patterns during heart development.

Regulation of cell volume and water transport--an old fundamental role of the renin angiotensin aldosterone system components at the cellular level

The expression and the role of renin angiotensin aldosterone system (RAAS) components on regulation of cell volume and water transport on vertebrates and invertebrates were reviewed. The presence of these components even in simple organisms like leeches and their relevance for the control of cellular volume and water transport supports the view that the expression of these components, at cellular level, is an acquisition which was preserved throughout evolution.

An evolving story of angiotensin-II-forming pathways in rodents and humans

Lessons learned from the characterization of the biological roles of Ang-(1-7) [angiotensin-(1-7)] in opposing the vasoconstrictor, proliferative and prothrombotic actions of AngII (angiotensin II) created an underpinning for a more comprehensive exploration of the multiple pathways by which the RAS (renin-angiotensin system) of blood and tissues regulates homoeostasis and its altered state in disease processes. The present review summarizes the progress that has been made in the novel exploration of intermediate shorter forms of angiotensinogen through the characterization of the expression and functions of the dodecapeptide Ang-(1-12) [angiotensin-(1-12)] in the cardiac production of AngII. The studies reveal significant differences in humans compared with rodents regarding the enzymatic pathway by which Ang-(1-12) undergoes metabolism. Highlights of the research include the demonstration of chymase-directed formation of AngII from Ang-(1-12) in human left atrial myocytes and left ventricular tissue, the presence of robust expression of Ang-(1-12) and chymase in the atrial appendage of subjects with resistant atrial fibrillation, and the preliminary observation of significantly higher Ang-(1-12) expression in human left atrial appendages.

Mechanisms of cardiac conduction: a history of revisions

Cardiac conduction is the process by which electrical excitation spreads through the heart, triggering individual myocytes to contract in synchrony. Defects in conduction disrupt synchronous activation and are associated with life-threatening arrhythmias in many pathologies. Therefore, it is scarcely surprising that this phenomenon continues to be the subject of active scientific inquiry. Here we provide a brief review of how the conceptual understanding of conduction has evolved over the last century and highlight recent, potentially paradigm-shifting developments.

Clinical perspectives and fundamental aspects of local cardiovascular and renal Renin-Angiotensin systems

Evidence for the potential role of organ specific cardiovascular renin-angiotensin systems (RAS) has been demonstrated experimentally and clinically with respect to certain cardiovascular and renal diseases. These findings have been supported by studies involving pharmacological inhibition during ischemic heart disease, myocardial infarction, cardiac failure; hypertension associated with left ventricular ischemia, myocardial fibrosis and left ventricular hypertrophy; structural and functional changes of the target organs associated with prolonged dietary salt excess; and intrarenal vascular disease associated with end-stage renal disease. Moreover, the severe structural and functional changes induced by these pathological conditions can be prevented and reversed by agents producing RAS inhibition (even when not necessarily coincident with alterations in arterial pressure). In this review, we discuss specific fundamental and clinical aspects and mechanisms related to the activation or inhibition of local RAS and their implications for cardiovascular and renal diseases. Fundamental aspects involving the role of angiotensins on cardiac and renal functions including the expression of RAS components in the heart and kidney and the controversial role of angiotensin-converting enzyme 2 on angiotensin peptide metabolism in humans, were discussed.

Osmotic swelling and residual stress in cardiovascular tissues

Osmotic swelling (OS) and residual stress (RS) significantly affect the function of cardiovascular (CVS) tissues and organs. The physical mechanisms of OS and RS are reviewed and analyzed with focus on the theoretical background and related experimental evidence. It will be shown that swelling of CVS tissues stems from the presence of charged proteoglycan macro-molecules in these tissues, and that this swelling is a key determinant of RS. In view of OS and RS functional significance in mechanical function, modeling attempts which incorporate them in CVS stress analysis will be presented and discussed.

Angiotensin (1-7) reduces the cell volume of swollen cardiac cells and decreases the swelling-dependent chloride current. Implications for cardiac arrhythmias and myocardial ischemia

The influence of angiotensin II and angiotensin (1-17) on cell volume and on the activation of ionic channels including the swelling-dependent chloride channel was reviewed. Particular emphasis was given to the influence of the balance between the ACE-angiotensin II and of the ACE2-angiotensin (1-7)-Mas receptor axis on heart cell volume regulation and on the swelling-dependent chloride current. The implications for myocardial ischemia and cardiac arrhythmias are discussed.

Angiotensin-(1-7) attenuates hyposmolarity-induced ANP secretion via the Na+-K+ pump

The alteration in osmolarity challenges cell volume regulation, a vital element for cell survival. Hyposmolarity causes an increase in cell volume. Recently, it has been reported that the renin-angiotensin system (RAS) plays a role in cell volume regulation. We investigated the effect of angiotensin-(1-7) [Ang-(1-7)] on hyposmolarity-induced atrial natriuretic peptide (ANP) secretion in normal and diabetic (DM) rat atria and modulation of the effect of Ang-(1-7) by the Na(+)-K(+) pump. Using isolated control rat atria, we observed that perfusion of hyposmotic solution into the atria increased ANP secretion. When Ang-(1-7) [0.1 microM or 1 microM] was perfused in a hyposmolar solution, it decreased the hyposmolarity-induced ANP secretion in a dose-dependent manner. This effect of Ang-(1-7) could be mediated by the Na(+)-K(+) pump, since ouabain, an Na(+)-K(+) pump inhibitor, significantly decreased the effect of Ang-(1-7) on hyposmolarity-induced ANP secretion. In contrast, N(omega) Nitro-l-arginine methyl ester hydrochloride (l-NAME) did not modify the effect of Ang-(1-7) on the hyposmolarity-induced ANP secretion. Interestingly, the ANP secretion was increased robustly by the perfusion of the hyposmolar solution in the DM atria, as compared to the control atria. However, the inhibitory effect of Ang-(1-7) on the hyposmolarity-induced ANP secretion was not observed in the DM atria. In the DM atria, atrial contractility was significantly increased. Taken together, we concluded that Ang-(1-7) attenuated hyposmolarity-induced ANP secretion via the Na(+)-K(+) pump and a lack of Ang-(1-7) response in DM atria may partly relate to change in Na(+)-K(+) pump activity.

Further studies on the effects of intracrine and extracellular angiotensin II on the regulation of heart cell volume. On the influence of aldosterone and spironolactone

The influence of extracellular and intracellular angiotensin II (Ang II) on the cell volume in the failing heart of cardiomyopathic hamsters (TO2) was further investigated as well as the influence of aldosterone and spironolactone on the Ang II action on cell volume. Measurements of cell width and area of quiescent ventricular cardiomyocytes were performed using a video camera and computer analysis and the relative cell volume was calculated. All measurements of cell volume were performed in the same cell before and after the administration of Ang II (10⁻⁸M). The results indicated that: a) the increase in cell volume caused by extracellular Ang II(10⁻⁸ M) was enhanced in cells incubated with aldosterone (100 nM) for 48 h; b) the effect of aldosterone was abolished by spironolactone (10⁻⁸ M); c) the decline in cell volume elicited by intracellular administration of Ang II (10⁻⁸ M) was increased by aldosterone and inhibited by spironolactone; d) the effects of aldosterone and spironolactone were related, in part, to a change in expression of AT1 receptors; and e) the intracellular administration of Ang II reduced the swelling-dependent chloride current (I(Clswell)). The implications of these findings to the failing heart and myocardial ischemia are discussed.

KCNE1-KCNQ1 osmoregulation by interaction of phosphatidylinositol-4,5-bisphosphate with Mg2+ and polyamines

KCNQ1 osmosensitivity is of physiological and pathophysiological relevance in epithelial and cardiac cells, but the mechanism involved remains elusive. In COS-7 cells expressing the KCNE1-KCNQ1 fusion protein, extracellular hypoosmolarity and hyperosmolarity modify the channel biophysical parameters. These changes are consistent with hypoosmolarity increasing the level of membrane phosphatidylinositol-4,5-bisphosphate (PIP(2)), which in turn upregulates KCNE1-KCNQ1 channels. We showed that increasing PIP(2) levels with a water-soluble PIP(2) analogue prevented channel upregulation in hypoosmotic condition, suggesting a variation of the channel-PIP(2) interaction during channel osmoregulation. Furthermore, we showed that polyamines and Mg(2+), already known to tonically inhibit KCNQ channels by screening PIP(2) negative charges, are involved in the osmoregulatory process. Indeed, intracellular Mg(2+) removal and polyamines chelation inhibited the channel osmoregulation. Thus, the dilution of those cations during cell swelling might decrease channel inhibition and explain the channel upregulation by hypoosmolarity. To support this idea, we quantified the role of Mg(2+) in the osmodependent channel activity. Direct measurement of intracellular [Mg(2+)] variations during osmotic changes and characterization of the channel Mg(2+) sensitivity showed that Mg(2+) participates significantly to the osmoregulation. Using intracellular solutions that mimic the variation of Mg(2+) and polyamines, we were able to recapitulate the current amplitude variations in response to extracellular osmolarity changes. Altogether, these results support the idea of a modulation of the channel-PIP(2) interactions by Mg(2+) and polyamines during cell volume changes. It is likely that this mechanism applies to other channels that are sensitive to both osmolarity and PIP(2).

Risk factors and outcome of new-onset cardiac arrhythmias in vascular surgery patients

BACKGROUND

The pathophysiology of new-onset cardiac arrhythmias is complex and may bring about severe cardiovascular complications. The relevance of perioperative arrhythmias during vascular surgery has not been investigated. The aim of this study was to assess risk factors and prognosis of new-onset arrhythmias during vascular surgery.

METHODS

A total of 513 vascular surgery patients, without a history of arrhythmias, were included. Cardiac risk factors, inflammatory status, and left ventricular function (LVF; N-terminal pro-B-type natriuretic peptide and echocardiography) were assessed. Continuous electrocardiography (ECG) recordings for 72 hours were used to identify ischemia and new-onset arrhythmias: atrial fibrillation, sustained ventricular tachycardia, supraventricular tachycardia, and ventricular fibrillation. Logistic regression analysis was applied to identify preoperative risk factors for arrhythmias. Cox regression analysis assessed the impact of arrhythmias on cardiovascular event-free survival during 1.7 years.

RESULTS

New-onset arrhythmias occurred in 55 (11%) of 513 patients: atrial fibrillation, ventricular tachycardia, supraventricular tachycardia, and ventricular fibrillation occurred in 4%, 7%, 1%, and 0.2%, respectively. Continuous ECG showed myocardial ischemia and arrhythmias in 17 (3%) of 513 patients. Arrhythmia was preceded by ischemia in 10 of 55 cases. Increased age and reduced LVF were risk factors for the development of arrhythmias. Multivariate analysis showed that perioperative arrhythmias were associated with long-term cardiovascular events, irrespective of the presence of perioperative ischemia (hazard ratio 2.2, 95% CI 1.3-3.8, P = .004).

CONCLUSION

New-onset perioperative arrhythmias are common after vascular surgery. The elderly and patients with reduced LVF show arrhythmias. Perioperative continuous ECG monitoring helps to identify this high-risk group at increased risk of cardiovascular events and death.

Cell swelling impairs dye coupling in adult rat ventricular myocytes. Cell volume as a regulator of cell communication

The influence of cell swelling on cell communication was investigated in cardiomyocytes isolated from the ventricle of adult rats. Measurements of dye coupling were performed in cell pairs using intracellular dialysis of Lucifer Yellow CH. The pipette was attached to one cell of the pair and after a gig ohm seal was achieved, the membrane was ruptured by a brief suction allowing the dye to diffuse from the pipette into the cell. Fluorescence of the dye in the injected as well as in non-dialyzed cell of the pair was continuously monitored. The results indicate that in cell pairs exposed to hypotonic solution the cell volume was increased by about 60% within 35 min and the dye coupling was significantly reduced by cell swelling. Calculation of gap junction permeability (P(j)) assuming an the intracellular volume accessible to intracellular diffusion of the dye as 12% of total cell volume, showed an average P(j) value of 0.16 ± 0.04 × 10(-4) cm/s (n = 35) in the control and 0.89 ± 1.1 × 10(-5) cm (n = 40) for cells exposed to hypotonic solution (P < 0.05). Similar results were found assuming intracellular volumes accessible to the dye of 20 and 30% of total cell volume, respectively. Cell swelling did not change the rate of intracellular diffusion of the dye. The results which indicate that cell volume is an important regulator of gap junction permeability, have important implications to myocardial ischemia and heart failure as well as to heart pharmacology because changes in cell volume caused by drugs and transmitters can impair cell communication with consequent generation of slow conduction and cardiac arrhythmias.

Advances in the renin angiotensin system focus on angiotensin-converting enzyme 2 and angiotensin-(1-7)

The contribution of the renin angiotensin system to physiology and pathology is undergoing a rapid reconsideration of its mechanisms from emerging new concepts implicating angiotensin-converting enzyme 2 and angiotensin-(1-7) as new elements negatively influencing the vasoconstrictor, trophic, and pro-inflammatory actions of angiotensin II. This component of the system acts to oppose the vasoconstrictor and proliferative effects on angiotensin II through signaling mechanisms mediated by the mas receptor. In addition, a reduced expression of the vasodepressor axis composed by angiotensin-converting enzyme 2 and angiotensin-(1-7) may contribute to the expression of essential hypertension, the remodeling of heart and renal function associated with this disease, and even the physiology of pregnancy and the development of eclampsia.