Alterations by age of calcium handling in rat resistance arteries

Functional Role of STIM-1 and Orai1 in Human Microvascular Aging

The impact of aging on vascular function is heterogeneous depending on the vascular territories. Calcium regulation plays a key role in vascular function and has been implicated in aging-related hypercontractility of corpus cavernosum. We aimed to evaluate stromal interaction molecule (STIM)/Orai system involvement in aging-related vascular alterations in the human macro and microvasculature. Aortae specimens and mesenteric arteries (MA), obtained from 45 organ donors, were functionally evaluated in organ chambers and wire myographs. Subjects were divided into groups either younger or older than 65-years old. The expressions of STIM-1, Orai1, and Orai3 were determined by immunofluorescence in the aorta and MA, and by Western blot in the aorta homogenates. The inhibition of STIM/Orai with YM-58483 (20 μM) reversed adrenergic hypercontractility in MA from older subjects but did not modify aging-related hypercontractility in the aortic strips. Aging was related to an increased expression of Orai1 in human aorta, while Orai1 and STIM-1 were upregulated in MA. STIM-1 and Orai1 protein expressions were inversely correlated to endothelial function in MA. Circulating levels of Orai1 were correlated with the inflammatory factor TNF-α and with the endothelial dysfunction marker asymmetric dimethylarginine. Aging is associated with an increased expression of the STIM/Orai system in human vessels with functional relevance only in the microvascular territory, suggesting its role in aging-related microvascular dysfunction.

Contrasting Patterns of Agonist-induced Store-operated Ca2+ Entry and Vasoconstriction in Mesenteric Arteries and Aorta With Aging

Ca is a crucial factor in the regulation of smooth muscle contraction. Store-operated Ca entry (SOCE) is one pathway that mediates Ca influx and smooth muscle contraction. Vessel contraction function usually alters with aging to cause severe vascular-related diseases. However, the underlying mechanism is still not fully understood. Here, we assessed intracellular Ca and vessel tension and found that SOCE and SOCE-mediated contraction of vascular smooth muscle cells (VSMCs) was reduced in aorta but increased in mesenteric arteries from aged rats. The results of Western blot and immunofluorescence staining show that the expression levels of Orai1, a store-operated Ca channel, were increased in VSMCs of mesenteric arteries but were reduced in VSMCs of aorta with aging. In conclusion, we demonstrated that the changing pattern of SOCE and SOCE-mediated contraction of VSMCs is completely reversed in mesenteric arteries and aorta with aging, providing a potential therapeutic target for clinical treatment in age-related vascular diseases.

Divergent effects of aging and sex on vasoconstriction to endothelin in coronary arterioles

OBJECTIVE

The risk for cardiovascular disease increases with advancing age; however, the chronological development of heart disease differs in males and females. The purpose of this study was to determine whether age-induced alterations in responses of coronary arterioles to the endogenous vasoconstrictor, endothelin, are sex-specific.

METHODS

Coronary arterioles were isolated from young and old male and female rats to assess vasoconstrictor responses to endothelin (ET), and ETa and ETb receptor inhibitors were used to assess receptor-specific signaling.

RESULTS

In intact arterioles from males, ET-induced vasoconstriction was reduced with age, whereas age increased vasoconstrictor responses to ET in intact arterioles from female rats. In intact arterioles from both sexes, blockade of either ETa or ETb eliminated age-related differences in responses to ET; however, denudation of arterioles from both sexes revealed age-related differences in ETa-mediated vasoconstriction. In arterioles from male rats, ETa receptor protein decreased, whereas ETb receptor protein increased with age. In coronary arterioles from females, neither ETa nor ETb receptor protein changed with age, suggesting age-related changes in ET signaling occur downstream of ET receptors.

CONCLUSIONS

Thus, aging-induced alterations in responsiveness of the coronary resistance vasculature to endothelin are sex-specific, possibly contributing to sexual dimorphism in the risk of cardiovascular disease with advancing age.

mTOR pathway and Ca²⁺ stores mobilization in aged smooth muscle cells

Aging is considered to be driven by the so called senescence pathways, especially the mTOR route, although there is almost no information on its activity in aged tissues. Aging also induces Ca²⁺ signal alterations, but information regarding the mechanisms for these changes is almost inexistent. We investigated the possible involvement of the mTOR pathway in the age-dependent changes on Ca²⁺ stores mobilization in colonic smooth muscle cells of young (4 month old) and aged (24 month old) guinea pigs. mTORC1 activity was enhanced in aged smooth muscle, as revealed by phosphorylation of mTOR and its direct substrates S6K1 and 4E-BP1. Mobilization of intracellular Ca²⁺ stores through IP₃R or RyR channels was impaired in aged cells, and it was facilitated by mTOR and by FKBP12, as indicated by the inhibitory effects of KU0063794 (a direct mTOR inhibitor), rapamycin (a FKBP12-mediated mTOR inhibitor) and FK506 (an FKBP12 binding immunosuppressant). Aging suppressed the facilitation of the Ca²⁺ mobilization by FKBP12 but not by mTOR, without changing the total expression of FKBP12 protein. In conclusion, or study shows that in smooth muscle aging enhances the constitutive activity of mTORC1 pathway and impairs Ca²⁺ stores mobilization by suppression of the FKBP12-induced facilitation of Ca²⁺ release.

Calcium dynamics and signaling in vascular regulation: computational models

Calcium is a universal signaling molecule with a central role in a number of vascular functions including in the regulation of tone and blood flow. Experimentation has provided insights into signaling pathways that lead to or affected by Ca(2+) mobilization in the vasculature. Mathematical modeling offers a systematic approach to the analysis of these mechanisms and can serve as a tool for data interpretation and for guiding new experimental studies. Comprehensive models of calcium dynamics are well advanced for some systems such as the heart. This review summarizes the progress that has been made in modeling Ca(2+) dynamics and signaling in vascular cells. Model simulations show how Ca(2+) signaling emerges as a result of complex, nonlinear interactions that cannot be properly analyzed using only a reductionist's approach. A strategy of integrative modeling in the vasculature is outlined that will allow linking macroscale pathophysiological responses to the underlying cellular mechanisms.

α(1D)-Adrenergic receptors constitutive activity and reduced expression at the plasma membrane

Adrenergic receptors are a heterogeneous family of the G protein-coupled receptors that mediate the actions of adrenaline and noradrenaline. Adrenergic receptors comprise three subfamilies (α(1), α(2), and β, with three members each) and the α(1D)-adrenergic receptor is one of the members of the α(1) subfamily with some interesting traits. The α(1D)-adrenergic receptor is difficult to express, seems predominantly located intracellularly, and exhibits constitutive activity. In this chapter, we will describe in detail the conditions and procedures used to determine changes in intracellular free calcium concentration which has been instrumental to define the constitutive activity of these receptors. Taking advantage of the fact that truncation of the first 79 amino acids of α(1D)-adrenergic receptors markedly increased their membrane expression, we were able to show that constitutive activity is present in receptors truncated at the amino and carboxyl termini, which indicates that such domains are dispensable for this action. Constitutive activity could be observed in cells expressing either the rat or human α(1D)-adrenergic receptor orthologs. Such constitutive activity has been observed in native rat arteries and we will discuss the possible functional implications that it might have in the regulation of blood pressure.

The ER and ageing II: calcium homeostasis

Increase in intracellular Ca(2+) concentration occurs by Ca(2+) influx through the plasma membrane and by Ca(2+) release from intracellular stores. The ER is the most important Ca(2+) store. Its stress, characterized by the impairment of Ca(2+) homeostasis and by the accumulation of misfolded proteins, can be induced by different factors. In turn, it induces defense mechanisms such as unfolded protein response, and when it is severe and prolonged, activation of the apoptotic pathway. Damage to the ER, impairment of its function, and a decreased level of its Ca(2+)-handling proteins might all play a role in physiological ageing by handicapping the ER stress response. Thus, healthy ageing is accompanied by subtle alterations of Ca(2+) homeostasis and signaling, including alterations in the ER Ca(2+) load and release. The expression and/or function of ryanodine receptors, IP3 receptors, and SERCA Ca(2+) pumps located in the ER membrane, and Ca(2+)-binding proteins within ER lumen all seem to be affected in aged cells. Data are presented on age-dependent, tissue-specific changes in ER-related Ca(2+) homeostasis in skeletal, cardiac and smooth muscles, as well as in the nervous and immune systems. Disturbances of Ca(2+) homeostasis and of signaling are potential targets for intervention in aged humans.

A mathematical model of Ca2+ dynamics in rat mesenteric smooth muscle cell: agonist and NO stimulation

A mathematical model of calcium dynamics in vascular smooth muscle cell (SMC) was developed based on data mostly from rat mesenteric arterioles. The model focuses on (a) the plasma membrane electrophysiology; (b) Ca2+ uptake and release from the sarcoplasmic reticulum (SR); (c) cytosolic balance of Ca2+, Na+, K+, and Cl ions; and (d) IP3 and cGMP formation in response to norepinephrine(NE) and nitric oxide (NO) stimulation. Stimulation with NE induced membrane depolarization and an intracellular Ca2+ ([Ca2+]i) transient followed by a plateau. The plateau concentrations were mostly determined by the activation of voltage-operated Ca2+ channels. NE causes a greater increase in [Ca2+]i than stimulation with KCl to equivalent depolarization. Model simulations suggest that the effect of[Na+]i accumulation on the Na+/Ca2+ exchanger (NCX) can potentially account for this difference.Elevation of [Ca2+]i within a concentration window (150-300 nM) by NE or KCl initiated [Ca2+]i oscillations with a concentration-dependent period. The oscillations were generated by the nonlinear dynamics of Ca2+ release and refilling in the SR. NO repolarized the NE-stimulated SMC and restored low [Ca2+]i mainly through its effect on Ca2+-activated K+ channels. Under certain conditions, Na+-K+-ATPase inhibition can result in the elevation of [Na+]i and the reversal of NCX, increasing resting cytosolic and SR Ca2+ content, as well as reactivity to NE. Blockade of the NCX's reverse mode could eliminate these effects. We conclude that the integration of the selected cellular components yields a mathematical model that reproduces, satisfactorily, some of the established features of SMC physiology. Simulations suggest a potential role of intracellular Na+ in modulating Ca2+ dynamics and provide insights into the mechanisms of SMC constriction, relaxation, and the phenomenon of vasomotion. The model will provide the basis for the development of multi-cellular mathematical models that will investigate microcirculatory function in health and disease.

Ca2+ extrusion in aged smooth muscle cells

We investigated the effects of aging in Ca(2+) extrusion mechanisms in smooth muscle bladder cells from 4 and 20-24-month-old guinea pigs using fluorescence microscopy and fura-2. Cells were challenged with a pulse of KCl immediately before perfusion with a Ca(2+) free solution containing no inhibitors (control, untreated cells) or inhibitors of plasma membrane Ca(2+) pump (PMCA, 1mM La(3+)), Na(+)/Ca(2+) exchanger (NCX, 1 microM SEA0400) or the sarcoendoplasmic Ca(2+) pump (SERCA, 1 microM thapsigargin). Treatment of young adult cells with the inhibitors allowed estimating a relative contribution of 55% for NCX, 27% for PMCA and 31% for SERCA. Combination of two inhibitors at the same time showed the presence of interaction between extrusion mechanisms. In aged cells the [Ca(2+)](i) extrusion was impaired due to decrease of PMCA activity, as revealed by the loss of effect of La(3+), and to inhibitory interactions between NCX and SERCA activities, indicated by acceleration of decay in response to their respective inhibitors. In conclusion, in smooth muscle cells aging decreases the overall Ca(2+) extrusion activity and modifies the interactions between the activities of the main Ca(2+) removing mechanisms.

Mechanisms of agonist-induced constriction in isolated human mesenteric arteries

We determined the calcium signalling pathways involved in the mechanisms of contraction of the vasoconstrictive agonists KCl, U46619 and PDBu in isolated human mesenteric arteries. The influence of gender, vessel diameter and age of the patients was also investigated. Human mesenteric arteries (n = 76) were loaded in a wire myograph and maintained at a tension equivalent to the in vivo pressure of 100 mm Hg, bubbled with 95%O2/5%CO2 to maintain pH 7.4 in physiological saline solution (PSS). Cumulative concentration-response curves were obtained to KCl (100 microM-100 mM), U46619 (1 nM-1 microM) or PDBu (1 nM-1 microM), before or after a 30 min incubation with either the voltage-gated calcium channel (VGCC) blocker nifedipine (10 microM), the store-operated calcium channel (SOCC) blocker SK&F96365 (50 microM) or in calcium-free PSS (-Ca2+ PSS). The KCl response was abolished in -Ca2+ PSS and with nifedipine. The U46619 response was partially blocked in -Ca2+ PSS and with nifedipine and predominantly blocked by SK&F96365. Incubation in -Ca2+ PSS had no effect on the response to PDBu. Arteries from male patients responded significantly higher to KCl than arteries from female patients. This study demonstrates that KCl induces mesenteric vasoconstriction via activation of VGCCs, U46619 induces mesenteric vasoconstriction via activation of SOCCs, but also VGCCs and PDBu induce mesenteric vasoconstriction via a calcium-independent pathway.

Acute and chronic captopril, but not prazosin or nifedipine, normalize alterations in adrenergic intracellular Ca2+ handling observed in the mesenteric arterial tree of spontaneously hypertensive rats

The effect of hypertension and acute (36-h) or chronic (from age 6 to 16 weeks) antihypertensive treatment with prazosin (2 mg kg(-1) per day), nifedipine (50 mg kg(-1) per day), or captopril (50 mg kg(-1) per day) on Ca2+ mobilization due to alpha1-adrenoceptor activation was analyzed in functional studies using arterial rings [four conductance/distributing vessels: aorta, main mesenteric, iliac, and tail arteries and two resistance vessels; first and second small mesenteric artery branches obtained from spontaneously hypertensive rats (SHR, 6 and 16 weeks old) and age-matched Wistar Kyoto rats (WKY)]. Maximal response to noradrenaline in the presence of extracellular Ca2+ is not affected by hypertension or by the antihypertensive treatment. The extracellular Ca2+-independent contractile responses increased with age in iliac, tail, and small mesenteric arteries (SMA) and were further increased in SHR in SMA from both young and adult animals and in the main mesenteric artery of adult SHR. In main mesenteric artery, this increased contraction in SHR was associated with a higher increase in cytosolic [Ca2+] mobilized by noradrenaline without changes in the total stored Ca2+. Acute or chronic treatment with captopril abolished the differences observed between WKY and SHR in the noradrenaline-induced contraction in mesenteric arteries loaded in Ca2+-free medium. In contrast, animals acutely treated with prazosin or chronically treated with either prazosin or nifedipine exhibit the same differences in Ca2+ handling than untreated rats. In conclusion, these differences are not a consequence of increased blood pressure but precede it and can only be normalized by inhibition of the rennin-angiotensin system.

Ageing alters the production of nitric oxide and prostanoids after IL-1beta exposure in mesenteric resistance arteries

We aimed to analyse age influence on the production of inflammatory mediators from inducible isoforms of nitric oxide synthase (iNOS) and cyclooxygenase (COX-2) in rat mesenteric resistance arteries (MRA). The second and/or third branches of MRA from young (3-month-old) and old (22-month-old) male Sprague-Dawley rats were incubated in culture medium with or without interleukin-1ss (IL-1ss; 10 ng/ml, 14 h). IL-1ss did not modify endothelial NOS (eNOS) expression or endothelial cell distribution. However, IL-1ss increased nitrite production and iNOS expression in endothelial and smooth muscle cells more in arteries from young than from old rats. IL-1ss also increased PGI(2) levels and COX-2 expression in the three layers of the vascular wall. Ageing did not affect COX-2 expression but did increase TXA(2) and PGF(2alpha) levels. The maximum contraction to phenylephrine was increased in arteries from old rats after IL-1ss treatment. Inhibition of iNOS and COX-2 with 1400 W and NS398, respectively, abolished the differences in phenylephrine contraction. In conclusion, IL-1ss induced an inflammatory response in MRA with associated increases in iNOS and COX-2 expression. The lower increase in nitrite production from iNOS together with a greater contractile prostanoid production in the old rats would be responsible for the increase observed in their contraction to phenylephrine after IL-1 ss treatment.

Attenuated noradrenergic sensitivity during local cooling in aged human skin

Reflex-mediated cutaneous vasoconstriction (VC) is impaired in older humans; however, it is unclear whether this blunted VC also occurs during local cooling, which mediates VC through different mechanisms. We tested the hypothesis that the sensitization of cutaneous vessels to noradrenaline (NA) during direct skin cooling seen in young skin is blunted in aged skin. In 11 young (18-30 years) and 11 older (62-76 years) men and women, skin blood flow was monitored at two forearm sites with laser Doppler (LD) flowmetry while local skin temperature was cooled and clamped at 24 degrees C. Cutaneous vascular conductance (CVC; LD flux/mean arterial pressure) was expressed as percentage change from baseline (% DeltaCVC(base)). At one site, five doses of NA (10(-10)-10(-2) m) were sequentially infused via intradermal microdialysis during cooling while the other 24 degrees C site served as control (Ringer solution + cooling). At control sites, VC due to cooling alone was similar in young versus older (-54 +/- 5 versus -56 +/- 3% DeltaCVC(base), P = 0.46). In young, NA infusions induced additional dose-dependent VC (10(-8), 10(-6), 10(-4) and 10(-2) m: -70 +/- 2, -72 +/- 3, -78 +/- 3 and -79 +/- 4% DeltaCVC(base); P < 0.05 versus control). In older subjects, further VC did not occur until the highest infused dose of NA (10(-2) m: -70 +/- 5% DeltaCVC(base); P < 0.05 versus control). When cutaneous arterioles are sensitized to NA by direct cooling, young skin exhibits the capacity to further constrict to NA in a dose-dependent manner. However, older skin does not display enhanced VC capacity until treated with saturating doses of NA, possibly due to age-associated decrements in Ca2+ availability or alpha2C-adrenoceptor function.

Pharmacological modulation of sarcoplasmic reticulum function in smooth muscle

The sarco/endoplasmic reticulum (SR/ER) is the primary storage and release site of intracellular calcium (Ca2+) in many excitable cells. The SR is a tubular network, which in smooth muscle (SM) cells distributes close to cellular periphery (superficial SR) and in deeper aspects of the cell (deep SR). Recent attention has focused on the regulation of cell function by the superficial SR, which can act as a buffer and also as a regulator of membrane channels and transporters. Ca2+ is released from the SR via two types of ionic channels [ryanodine- and inositol 1,4,5-trisphosphate-gated], whereas accumulation from thecytoplasm occurs exclusively by an energy-dependent sarco-endoplasmic reticulum Ca2+-ATPase pump (SERCA). Within the SR, Ca2+ is bound to various storage proteins. Emerging evidence also suggests that the perinuclear portion of the SR may play an important role in nuclear transcription. In this review, we detail the pharmacology of agents that alter the functions of Ca2+ release channels and of SERCA. We describe their use and selectivity and indicate the concentrations used in investigating various SM preparations. Important aspects of cell regulation and excitation-contractile activity coupling in SM have been uncovered through the use of such activators and inhibitors of processes that determine SR function. Likewise, they were instrumental in the recent finding of an interaction of the SR with other cellular organelles such as mitochondria. Thus, an appreciation of the pharmacology and selectivity of agents that interfere with SR function in SM has greatly assisted in unveiling the multifaceted nature of the SR.