Intracellular angiotensin II increases the total potassium current and the resting potential of arterial myocytes from vascular resistance vessels of the rat. Physiological and pathological implications

Dysregulation of the Renin-Angiotensin System and the Vasopressinergic System Interactions in Cardiovascular Disorders

Purpose of Review

In many instances, the renin-angiotensin system (RAS) and the vasopressinergic system (VPS) are jointly activated by the same stimuli and engaged in the regulation of the same processes.

Recent Findings

Angiotensin II (Ang II) and arginine vasopressin (AVP), which are the main active compounds of the RAS and the VPS, interact at several levels. Firstly, Ang II, acting on AT1 receptors (AT1R), plays a significant role in the release of AVP from vasopressinergic neurons and AVP, stimulating V1a receptors (V1aR), regulates the release of renin in the kidney. Secondly, Ang II and AVP, acting on AT1R and V1aR, respectively, exert vasoconstriction, increase cardiac contractility, stimulate the sympathoadrenal system, and elevate blood pressure. At the same time, they act antagonistically in the regulation of blood pressure by baroreflex. Thirdly, the cooperative action of Ang II acting on AT1R and AVP stimulating both V1aR and V2 receptors in the kidney is necessary for the appropriate regulation of renal blood flow and the efficient resorption of sodium and water. Furthermore, both peptides enhance the release of aldosterone and potentiate its action in the renal tubules.

Summary

In this review, we (1) point attention to the role of the cooperative action of Ang II and AVP for the regulation of blood pressure and the water-electrolyte balance under physiological conditions, (2) present the subcellular mechanisms underlying interactions of these two peptides, and (3) provide evidence that dysregulation of the cooperative action of Ang II and AVP significantly contributes to the development of disturbances in the regulation of blood pressure and the water-electrolyte balance in cardiovascular diseases.

Angiotensin peptides in the non-gravid uterus: Paracrine actions beyond circulation

The renin-angiotensin system (RAS) involves a complex network of precursors, peptides, enzymes and receptors comprising a systemic (endocrine) and a local (paracrine/autocrine) system. The local RAS plays important roles in tissue modulation and may operate independently of or in close interaction with the circulatory RAS, acting in a complementary fashion. Angiotensin (Ang) II, its receptor AT₁ and Ang-(1-7) expression in the endometrium vary with menstrual cycle, and stromal cell decidualization in vitro is accompanied by local synthesis of angiotensinogen and prorenin. Mas receptor is unlikely to undergo marked changes accompanying the cyclic ovarian steroid hormone fluctuations. Studies investigating the functional relevance of the RAS in the non-gravid uterus show a number of paracrine effects beyond circulation and suggest that RAS peptides may be involved in the pathophysiology of proliferative and fibrotic diseases. Endometrial cancer is associated with increased expression of Ang II, Ang-converting enzyme 1 and AT₁ in the tumoral tissue compared to neighboring non-neoplastic endometrium, and also with a gene polymorphism that enhances AT₁ signal. Ang II induces human endometrial cells to transdifferentiate into cells with myofibroblast phenotype and to synthetize extracellular matrix components that might contribute to endometrial fibrosis. Altogether, these findings point to a fully operating RAS within the uterus, but since many concepts rely on preliminary evidence further studies are needed to clarify the role of the local RAS in uterine physiology and pathophysiology.

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.

Intracellular renin increases the inward calcium current in smooth muscle cells of mesenteric artery of SHR. Implications for hypertension and vascular remodeling

The influence of intracellular renin on the inward calcium current in isolated smooth muscle cells from SHR mesenteric arteries was investigated. Measurements of calcium current were performed using the whole cell configuration of pCLAMP. The results indicated that: 1) renin (100nM) dialyzed into smooth muscle cells, increased the inward calcium current; 2) verapamil (10-9M) administered to the bath inhibited the effect of renin on the inward calcium current; 3) concurrently with the increase of calcium current a depolarization of 6.8+/-2.1mV (n=16)(P<0.05) was found in cells dialyzed with renin; 4) intracellular dialysis of renin (100nM) into smooth muscle cells isolated from mesenteric arteries of normal Wystar Kyoto rats showed no significant change on calcium current; 5) aliskiren (10-9M) dialyzed into the cell together with renin (100nM) abolished the effect of the enzyme on the calcium current in SHR; 6) Ang II (100nM) dialyzed into the smooth muscle cell from mesenteric artery of SHR in absence of renin, decreased the calcium current-an effect greatly reduced by valsartan (10-9M) added to the cytosol; 7) administration of renin (100nM) plus angiotensinogen (100nM) into the cytosol of muscles cells from SHR rats reduced the inward calcium current; 8) extracellular administration of Ang II (100nM) increased the inward calcium current in mesenteric arteries of SHR.

CONCLUSIONS

intracellular renin in vascular resistance vessels from SHR due to internalization or expression, contributes to the regulation of vascular tone and control of peripheral resistance-an effect independently of Ang II. Implications for hypertension and vascular remodeling are discussed.

Intracellular angiotensin II as a regulator of muscle tone in vascular resistance vessels. Pathophysiological implications

The influence of intracellular angiotensin II on the regulation of potassium current and membrane potential of smooth muscle cells of mesenteric arteries and its relevance for the regulation of vascular tone was reviewed. The presence of components of the renin angiotensin system (RAS) in different cells of the cardiovascular system, was discussed including their presence in the nuclei and mitochondria. Emphasis was given to the opposite effects of intracellular and extracellular angiotensin II (Ang II) on the regulation of potassium current, membrane potential and contractility of vascular resistance vessels and its implication to vascular physiology and pathology and the possible role of epigenetic factors on the expression of angiotensin II (Ang II) and renin in vascular resistance vessels as well as its possible pathophysiological role in hypertension and other cardiovascular diseases.

Intracellular angiotensin II disrupts chemical communication and impairs metabolic cooperation between cardiac myocytes

The influence of intracellular angiotensin II (Ang II) on the process of chemical communication and metabolic cooperation between cardiac cells is discussed. Emphasis is given to the influence of pathological conditions like heart failure, myocardial ischemia or hyperglycemia on the activation of the intracrine renin angiotensin aldosterone system (RAAS) and its consequence for the metabolic cooperation between heart cells. Furthermore, the influence of high glucose on the process of chemical communication was described as well as its implication for the failing and diabetic heart. The major conclusion is that the activation of the intracrine renin angiotensin induced by heart failure, hyperglycemia, aldosterone or myocardial ischemia generates metabolic imbalance in the heart with serious consequences for the cardiac function.

Voltage-gated potassium+ channel expression in coronary artery smooth muscle cells of SHR and WKY

This study aims to compare the expression of genes and the molecular characteristic of voltage-gated K(+) channels, which make great effort in maintaining and controlling smooth muscle contraction, cellular membrane potential, and intracellular calcium ion currents in artery smooth muscle cells of SHR and WKY. Expression of potassium ions family in coronary artery was detected through reverse transcription polymerase chain reaction quantitatively. Significant levels of voltage-gated K(+) channels α1.2, α1.5, and β1.1 expression were all proved to be significantly higher in smooth muscles of SHR than WKY. Whole-cell voltage-gated K(+) channel currents were larger in SHR artery smooth muscles than the ones of WKY. Moreover, the voltage dependence of voltage-gated potassium channel activation was more negative in artery smooth muscle of SHR than that of WKY, while voltage dependence of availability was not different. The above diversity of voltage-gated potassium channel detected in gene expression and electrical character in coronary artery smooth muscle of SHR than that of WKY might be an underling mechanism associated with the membrane potential depolarization in artery smooth muscle of SHR.

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.

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.

Angiotensin (1-7) increases the potassium current and the resting potential of arterial myocytes from vascular resistance vessels of normal adult rats: Pathophysiological implications

The influence of angiotensin (Ang) (1-7) on potassium current (Kv) and resting potential of smooth muscle cells isolated from mesenteric artery of Sprague Dawley rats was investigated. Measurements of potassium current were performed using the whole cell configuration of pCLAMP. The results indicated that Ang (1-7) (10(-9) M) increased the potassium current by 120% ± 2.6% (P < .05) and the resting potential of smooth muscle cells by 8 ± 2.8 mV (n = 23; P < .05). Ang II (10(-9) M) administered to the bath reduced the potassium current by 35% ± 3.6% (n = 23; P < .05) and depolarized the arterial myocytes by 7.8 ± 2.1 mV (n = 25; P < .05). The effect of the heptapeptide on potassium current was inhibited by a Mas receptor inhibitor (A779; 10(-8) M) as well as by a protein kinase A (PKA) inhibitor (10(-9) M) dialyzed into the cell. Intracellular dialysis of the catalytic subunit of PKA (5 × 10(-8) M) enhanced the potassium current by 38% ± 3.4% (n = 14; P < .05) but did not abolish the effect of Ang (1-7). On the other hand, Bis-1 (10(-9) M), which is a specific inhibitor of PKC, suppressed the effect of Ang (1-7) on potassium current. In conclusion, Ang (1-7) counteracts the effect of Ang II on potassium current and membrane potential of smooth muscle cells from mesenteric arteries, which are resistance vessels involved in the regulation of peripheral resistance and blood pressure. The activation of the cAMP/PKA cascade is essential for the effect of the heptapeptide. Pathophysiological implications are discussed.