Acetylcholine induces intracellular Ca2+ oscillations and nitric oxide release in mouse brain endothelial cells

Basal forebrain neurons increase cortical blood flow by releasing acetylcholine (Ach), which stimulates endothelial cells (ECs) to produce the vasodilating gasotransmitter, nitric oxide (NO). Surprisingly, the mechanism whereby Ach induces NO synthesis in brain microvascular ECs is unknown. An increase in intracellular Ca²⁺ concentration recruits a multitude of endothelial Ca²⁺-dependent pathways, such as Ca²⁺/calmodulin endothelial NO synthase (eNOS). The present investigation sought to investigate the role of intracellular Ca²⁺ signaling in Ach-induced NO production in bEND5 cells, an established model of mouse brain microvascular ECs, by conventional imaging of cells loaded with the Ca²⁺-sensitive dye, Fura-2/AM, and the NO-sensitive fluorophore, DAF-DM diacetate. Ach induced dose-dependent Ca²⁺ oscillations in bEND5 cells, 300 μM being the most effective dose to generate a prolonged Ca²⁺ burst. Pharmacological manipulation revealed that Ach-evoked Ca²⁺ oscillations required metabotropic muscarinic receptor (mAchR) activation and were patterned by a complex interplay between repetitive ER Ca²⁺ release via inositol-1,4,5-trisphosphate receptors (InsP₃Rs) and store-operated Ca²⁺ entry (SOCE). A comprehensive real time-polymerase chain reaction analysis demonstrated the expression of the transcripts encoding for M3-mAChRs, InsP₃R1 and InsP₃R3, Stim1-2 and Orai2. Next, we found that Ach-induced NO production was hindered by L-NAME, a selective NOS inhibitor, and BAPTA, a membrane permeable intracellular Ca²⁺ buffer. Moreover, Ach-elicited NO synthesis was blocked by the pharmacological abrogation of the accompanying Ca²⁺ spikes. Overall, these data shed novel light on the molecular mechanisms whereby neuronally-released Ach controls neurovascular coupling in blood microvessels.

Lung Beractant Increases Free Cytosolic Levels of Ca2+ in Human Lung Fibroblasts

Beractant, a natural surfactant, induces an antifibrogenic phenotype and apoptosis in normal human lung fibroblasts (NHLF). As intracellular Ca2+ signalling has been related to programmed cell death, we aimed to assess the effect of beractant on intracellular Ca2+ concentration ([Ca2+]i) in NHLF in vitro. Cultured NHLF were loaded with Fura-2 AM (3 μM) and Ca2+ signals were recorded by microfluorimetric techniques. Beractant causes a concentration-dependent increase in [Ca2+]i with a EC50 of 0.82 μg/ml. The application of beractant, at a concentration of 500 μg/ml, which has been shown to exert an apoptotic effect in human fibroblasts, elicited different patterns of Ca2+ signals in NHLF: a) a single Ca2+ spike which could be followed by b) Ca2+ oscillations, c) a sustained Ca2+ plateau or d) a sustained plateau overlapped by Ca2+ oscillations. The amplitude and pattern of Ca2+ transients evoked by beractant were dependent on the resting [Ca2+]i. Pharmacological manipulation revealed that beractant activates a Ca2+ signal through Ca2+ release from intracellular stores mediated by phospholipase Cβ (PLCβ), Ca2+ release from inositol 1,4,5-trisphosphate receptors (IP3Rs) and Ca2+ influx via a store-operated pathway. Moreover, beractant-induced Ca2+ release was abolished by preventing membrane depolarization upon removal of extracellular Na+ and Ca2+. Finally, the inhibition of store-operated channels prevented beractant-induced NHLF apoptosis and downregulation of α1(I) procollagen expression. Therefore, beractant utilizes SOCE to exert its pro-apoptotic and antifibrinogenic effect on NHLF.

Stim and Orai proteins in neuronal Ca(2+) signaling and excitability

Stim1 and Orai1 are ubiquitous proteins that have long been known to mediate Ca²⁺ release-activated Ca²⁺ (CRAC) current (I_CRAC) and store-operated Ca²⁺ entry (SOCE) only in non-excitable cells. SOCE is activated following the depletion of the endogenous Ca²⁺ stores, which are mainly located within the endoplasmic reticulum (ER), to replete the intracellular Ca²⁺ reservoir and engage specific Ca²⁺-dependent processes, such as proliferation, migration, cytoskeletal remodeling, and gene expression. Their paralogs, Stim2, Orai2 and Orai3, support SOCE in heterologous expression systems, but their physiological role is still obscure. Ca²⁺ inflow in neurons has long been exclusively ascribed to voltage-operated and receptor-operated channels. Nevertheless, recent work has unveiled that Stim1–2 and Orai1-2, but not Orai3, proteins are also expressed and mediate SOCE in neurons. Herein, we survey current knowledge about the neuronal distribution of Stim and Orai proteins in rodent and human brains; we further discuss that Orai2 is the main pore-forming subunit of CRAC channels in central neurons, in which it may be activated by either Stim1 or Stim2 depending on species, brain region and physiological stimuli. We examine the functions regulated by SOCE in neurons, where this pathway is activated under resting conditions to refill the ER, control spinogenesis and regulate gene transcription. Besides, we highlighted the possibility that SOCE also controls neuronal excitation and regulate synaptic plasticity. Finally, we evaluate the involvement of Stim and Orai proteins in severe neurodegenerative and neurological disorders, such as Alzheimer’s disease and epilepsy.

A functional transient receptor potential vanilloid 4 (TRPV4) channel is expressed in human endothelial progenitor cells

Endothelial progenitor cells (EPCs) are mobilized into circulation to replace damaged endothelial cells and recapitulate the vascular network of injured tissues. Intracellular Ca(2+) signals are key to EPC activation, but it is yet to be elucidated whether they are endowed with the same blend of Ca(2+) -permeable channels expressed by mature endothelial cells. For instance, endothelial colony forming cells (ECFCs), the only EPC subset truly committed to acquire a mature endothelial phenotype, lack canonical transient receptor potential channels 3, 5 and 6 (TRPC3, 5 and 6), which are widely distributed in vascular endothelium; on the other hand, they express a functional store-operated Ca(2+) entry (SOCE). The present study was undertaken to assess whether human circulating EPCs possess TRP vanilloid channel 4 (TRPV4), which plays a master signalling role in mature endothelium, by controlling both vascular remodelling and arterial pressure. We found that EPCs express both TRPV4 mRNA and protein. Moreover, both GSK1016790A (GSK) and phorbol myristate acetate and, two widely employed TRPV4 agonists, induced intracellular Ca(2+) signals uniquely in presence of extracellular Ca(2+). GSK- and PMA-induced Ca(2+) elevations were inhibited by RN-1734 and ruthenium red, which selectively target TRPV4 in mature endothelium. However, TRPV4 stimulation with GSK did not cause EPC proliferation, while the pharmacological blockade of TRPV4 only modestly affected EPC growth in the presence of a growth factor-enriched culture medium. Conversely, SOCE inhibition with BTP-2, La(3+) and Gd(3+) dramatically decreased cell proliferation. These data indicate that human circulating EPCs possess a functional TRPV4 protein before their engraftment into nascent vessels.

Endothelial remodelling and intracellular calcium machinery

Rather being an inert barrier between vessel lumen and surrounding tissues, vascular endothelium plays a key role in the maintenance of cardiovascular homeostasis. The de-endothelialization of blood vessels is regarded as the early event that results in the onset of severe vascular disorders, including atherosclerosis, acute myocardial infarction, brain stroke, and aortic aneurysm. Restoration of the endothelial lining may be accomplished by the activation of neighbouring endothelial cells (ECs) freed by contact inhibition and by circulating endothelial progenitor cells (EPCs). Intracellular Ca(2+) signalling is essential to promote wound healing: however, the molecular underpinnings of the Ca(2+) response to injury are yet to be fully elucidated. Similarly, the components of the Ca(2+) toolkit that drive EPC incorporation into denuded vessels are far from being fully elucidated. The present review will survey the current knowledge on the role of Ca(2+) signalling in endothelial repair and in EPC activation. We propose that endothelial regeneration might be boosted by intraluminal release of specific Ca(2+) channel agonists or by gene transfer strategies aiming to enhance the expression of the most suitable Ca(2+) channels at the wound site. In this view, connexin (Cx) channels/hemichannels and store-operated Ca(2+) entry (SOCE) stand amid the most proper routes to therapeutically induce the regrowth of denuded vessels. Cx stimulation might trigger the proliferative and migratory behaviour of ECs facing the lesion site, whereas activation of SOCE is likely to favour EPC homing to the wounded vessel.

Ca2+ signalling in endothelial progenitor cells: a novel means to improve cell-based therapy and impair tumour vascularisation

Endothelial progenitor cells (EPCs) have recently been employed in cell-based therapy (CBT) to promote regeneration of ischemic organs, such as heart and limbs. Furthermore, EPCs may sustain tumour vascularisation and provide an additional target for anticancer therapies. CBT is limited by the paucity of cells harvested from peripheral blood and suffers from several pitfalls, including the low rate of engrafted EPCs, whereas classic antiangiogenic treatments manifest a number of side effects and may induce resistance into the patients. CBT will benefit of a better understanding of the signal transduction pathway(s) which drive(s) EPC proliferation, trafficking, and incorporation into injured tissues. At the same time, this information might outline alternative molecular targets to impair tumor neovascularisation and improve the therapeutic outcome of antiangiogenic strategies. An increase in intracellular Ca(2+) concentration is the key signal in the regulation of cellular replication, migration, and differentiation. In particular, Ca(2+) signalling may regulate cellcycle progression, due to the Ca(2+)-sensitivity of a number of cycline-dependent kinases, and gene expression, owing to the Ca(2+)-dependence of several transcription factors. Recent work has outlined the role of the so-called store-operated Ca(2+) entry in driving EPC proliferation and migration. Unravelling the mechanisms guiding EPC engraftment into neovessels might supply the biological bases required to improve CBT and anticancer treatments. For example, genetic manipulation of the Ca(2+) signalling machinery could provide a novel approach to increase the extent of limb regeneration or preventing tumour vascularisation by EPCs.

Orai1 and transient receptor potential channels as novel molecular targets to impair tumor neovascularization in renal cell carcinoma and other malignancies

The term "angiogenic switch" describes one of the earlier events of tumorigenesis, that occurs when the balance between pro-and anti-angiogenic factors shifts towards a pro-angiogenic outcome. This leads to the transition from a microscopic indolent lesion to a macroscopic and vascularised primary tumor, that may eventually metastasize and spread to distant sites. The molecular mechanisms underlying such a critical step in the carcinogenetic process have been extensively investigated. Both local endothelial cells (ECs) and endothelial progenitor cells (EPCs), recruited from bone marrow, have been implicated in the angiogenic switch, which is ultimately triggered by a plethora of growth factors released by cancer cells, pivotal among which is vascular endothelial growth factor (VEGF); indeed, VEGF both activates ECs nearby the growing tumor, and leads to EPC mobilization into the circulation. In kidney, in particular, the frequent mutation of the Von Hippel Lindau tumor suppressor gene leads to an overproduction of pro-angiogenic factors which makes this neoplasm quite sensitive to antiangiogenic drugs. However, it is now evident that the use of VEGF(Rs) inhibitors in everyday clinical practice is not as effective as observed in murine models. The investigation of alternative signaling pathways involved in the angiogenic switch is, therefore, imperative in order to induce tumor regression whereby preventing harmful drawback consequences. Ca(2+) entry across the plasma membrane has long been known to stimulate mature ECs to undergo angiogenesis. Recent work from several groups worldwide has then outlined that members of the Transient Receptor Potential (TRP) super-family of cationic channels and Orai1 provide the pathway for such proangiogenic Ca(2+) signal. In addition, Canonical TRP 1 (TRPC1) and Orai1 channels control proliferation and tubulogenesis in both normal EPCs and EPCs isolated from peripheral blood of tumor patients. As a consequence, TRP channels and Orai1 might serve as novel molecular targets to develop alternative and more effective strategies of angiogenesis inhibition.

Hydrogen sulphide triggers VEGF-induced intracellular Ca²⁺ signals in human endothelial cells but not in their immature progenitors

Hydrogen sulphide (H2S) is a newly discovered gasotransmitter that regulates multiple steps in VEGF-induced angiogenesis. An increase in intracellular Ca(2+) concentration ([Ca(2+)]i) is central to endothelial proliferation and may be triggered by both VEGF and H2S. Albeit VEGFR-2 might serve as H2S receptor, the mechanistic relationship between VEGF- and H2S-induced Ca(2+) signals in endothelial cells is unclear. The present study aimed at assessing whether and how NaHS, a widely employed H2S donor, stimulates pro-angiogenic Ca(2+) signals in Ea.hy926 cells, a suitable surrogate for mature endothelial cells, and human endothelial progenitor cells (EPCs). We found that NaHS induced a dose-dependent increase in [Ca(2+)]i in Ea.hy926 cells. NaHS-induced Ca(2+) signals in Ea.hy926 cells did not require extracellular Ca(2+) entry, while they were inhibited upon pharmacological blockade of the phospholipase C/inositol-1,4,5-trisphosphate (InsP3) signalling pathway. Moreover, the Ca(2+) response to NaHS was prevented by genistein, but not by SU5416, which selectively inhibits VEGFR-2. However, VEGF-induced Ca(2+) signals were suppressed by dl-propargylglycine (PAG), which blocks the H2S-producing enzyme, cystathionine γ-lyase. Consistent with these data, VEGF-induced proliferation and migration were inhibited by PAG in Ea.hy926 cells, albeit NaHS alone did not influence these processes. Conversely, NaHS elevated [Ca(2+)]i only in a modest fraction of circulating EPCs, whereas neither VEGF-induced Ca(2+) oscillations nor VEGF-dependent proliferation were affected by PAG. Therefore, H2S-evoked elevation in [Ca(2+)]i is essential to trigger the pro-angiogenic Ca(2+) response to VEGF in mature endothelial cells, but not in their immature progenitors.

The importance of calcium in the regulation of megakaryocyte function

Platelet release by megakaryocytes is regulated by a concert of environmental and autocrine factors. We previously showed that constitutively released adenosine diphosphate by human megakaryocytes leads to platelet production. Here we show that adenosine diphosphate elicits, in human megakaryocytes, an increase in cytosolic calcium concentration, followed by a plateau, which is lowered in the absence of extracellular calcium, suggesting the involvement of Store-Operated Calcium Entry. Indeed, we demonstrate that megakaryocytes express the major candidates to mediate Store-Operated Calcium Entry, stromal interaction molecule 1, Orai1 and canonical transient receptor potential 1, which are activated upon either pharmacological or physiological depletion of the intracellular calcium pool. This mechanism is inhibited by phospholipase C or inositol-3-phosphate receptor inhibitors and by a specific calcium entry blocker. Studies on megakaryocyte behavior, on extracellular matrix proteins that support proplatelet extension, show that calcium mobilization from intracellular stores activates signaling cascades that trigger megakaryocyte adhesion and proplatelet formation, and promotes extracellular calcium entry which is primarily involved in the regulation of the contractile force responsible for megakaryocyte motility. These findings provide the first evidence that both calcium mobilization from intracellular stores and extracellular calcium entry specifically regulate human megakaryocyte functions.

Ca²⁺-dependent nitric oxide release in the injured endothelium of excised rat aorta: a promising mechanism applying in vascular prosthetic devices in aging patients

Background

Nitric oxide is key to endothelial regeneration, but it is still unknown whether endothelial cell (EC) loss results in an increase in NO levels at the wound edge. We have already shown that endothelial damage induces a long-lasting Ca²⁺ entry into surviving cells though connexin hemichannels (CxHcs) uncoupled from their counterparts on ruptured cells. The physiological outcome of injury-induced Ca²⁺ inflow is, however, unknown.

Methods

In this study, we sought to determine whether and how endothelial scraping induces NO production (NOP) in the endothelium of excised rat aorta by exploiting the NO-sensitive fluorochrome, DAF-FM diacetate and the Ca²⁺-sensitive fluorescent dye, Fura-2/AM.

Results

We demonstrated that injury-induced NOP at the lesion site is prevented in presence of the endothelial NO synthase inhibitor, L-NAME, and in absence of extracellular Ca²⁺. Unlike ATP-dependent NO liberation, the NO response to injury is insensitive to BTP-2, which selectively blocks store-operated Ca²⁺ inflow. However, injury-induced NOP is significantly reduced by classic gap junction blockers, and by connexin mimetic peptides specifically targeting Cx37Hcs, Cx40HCs, and Cx43Hcs. Moreover, disruption of caveolar integrity prevents injury-elicited NO signaling, but not the accompanying Ca²⁺ response.

Conclusions

The data presented provide the first evidence that endothelial scraping stimulates NO synthesis at the wound edge, which might both exert an immediate anti-thrombotic and anti-inflammatory action and promote the subsequent re-endothelialization.

How to utilize Ca²⁺ signals to rejuvenate the repairative phenotype of senescent endothelial progenitor cells in elderly patients affected by cardiovascular diseases: a useful therapeutic support of surgical approach?

Endothelial dysfunction or loss is the early event that leads to a host of severe cardiovascular diseases, such as atherosclerosis, hypertension, brain stroke, myocardial infarction, and peripheral artery disease. Ageing is regarded among the most detrimental risk factor for vascular endothelium and predisposes the subject to atheroscleorosis and inflammatory states even in absence of traditional comorbid conditions. Standard treatment to restore blood perfusion through stenotic arteries are surgical or endovascular revascularization. Unfortunately, ageing patients are not the most amenable candidates for such interventions, due to high operative risk or unfavourable vascular involvement. It has recently been suggested that the transplantation of autologous bone marrow-derived endothelial progenitor cells (EPCs) might constitute an alternative and viable therapeutic option for these individuals. Albeit pre-clinical studies demonstrated the feasibility of EPC-based therapy to recapitulate the diseased vasculature of young and healthy animals, clinical studies provided less impressive results in old ischemic human patients. One hurdle associated to this kind of approach is the senescence of autologous EPCs, which are less abundant in peripheral blood and display a reduced pro-angiogenic activity. Conversely, umbilical cord blood (UCB)-derived EPCs are more suitable for cellular therapeutics due to their higher frequency and sensitivity to growth factors, such as vascular endothelial growth factor (VEGF). An increase in intracellular Ca²⁺ concentration is central to EPC activation by VEGF. We have recently demonstrated that the Ca²⁺ signalling machinery driving the oscillatory Ca²⁺ response to this important growth factor is different in UCB-derived EPCs as compared to their peripheral counterparts. In particular, we focussed on the so-called endothelial colony forming cells (ECFCs), which are the only EPC population belonging to the endothelial lineage and able to form capillary-like structures in vitro and stably integrate with host vasculature in vivo. The present review provides a brief description of how exploiting the Ca²⁺ toolkit of juvenile EPCs to restore the repairative phenotype of senescent EPCs to enhance their regenerative outcome in therapeutic settings.

Canonical transient receptor potential 3 channel triggers vascular endothelial growth factor-induced intracellular Ca2+ oscillations in endothelial progenitor cells isolated from umbilical cord blood

Endothelial colony-forming cells (ECFCs) are the only endothelial progenitor cells (EPCs) that are capable of acquiring a mature endothelial phenotype. ECFCs are mainly mobilized from bone marrow to promote vascularization and represent a promising tool for cell-based therapy of severe ischemic diseases. Vascular endothelial growth factor (VEGF) stimulates the proliferation of peripheral blood-derived ECFCs (PB-ECFCs) through oscillations in intracellular Ca(2+) concentration ([Ca(2+)]i). VEGF-induced Ca(2+) spikes are driven by the interplay between inositol-1,4,5-trisphosphate (InsP3)-dependent Ca(2+) release and store-operated Ca(2+) entry (SOCE). The therapeutic potential of umbilical cord blood-derived ECFCs (UCB-ECFCs) has also been shown in recent studies. However, VEGF-induced proliferation of UCB-ECFCs is faster compared with their peripheral counterpart. Unlike PB-ECFCs, UCB-ECFCs express canonical transient receptor potential channel 3 (TRPC3) that mediates diacylglycerol-dependent Ca(2+) entry. The present study aimed at investigating whether the higher proliferative potential of UCB-ECFCs was associated to any difference in the molecular underpinnings of their Ca(2+) response to VEGF. We found that VEGF induces oscillations in [Ca(2+)]i that are patterned by the interaction between InsP3-dependent Ca(2+) release and SOCE. Unlike PB-ECFCs, VEGF-evoked Ca(2+) oscillations do not arise in the absence of extracellular Ca(2+) entry and after pharmacological (with Pyr3 and flufenamic acid) and genetic (by employing selective small interference RNA) suppression of TRPC3. VEGF-induced UCB-ECFC proliferation is abrogated on inhibition of the intracellular Ca(2+) spikes. Therefore, the Ca(2+) response to VEGF in UCB-ECFCs is shaped by a different Ca(2+) machinery as compared with PB-ECFCs, and TRPC3 stands out as a promising target in EPC-based treatment of ischemic pathologies.

Store-dependent Ca(2+) entry in endothelial progenitor cells as a perspective tool to enhance cell-based therapy and adverse tumour vascularization

Endothelial progenitor cells (EPCs) have recently been employed in cell-based therapy (CBT) to promote neovascularization and regeneration of ischemic organs, such as heart and limbs. Furthermore, EPCs may be recruited from bone marrow by growing tumors to drive the angiogenic switch through physical engrafting into the lumen of nascent vessels or paracrine release of pro-angiogenic factors. CBT is hampered by the paucity of EPCs harvested from peripheral blood and suffered from several pitfalls, including the differentiation outcome of transplanted cells and low percentage of engrafted cells. Therefore, CBT will benefit from a better understanding of the signal transduction pathway(s) which govern(s) EPC homing, proliferation and incorporation into injured tissues. At the same time, this information might outline alternative molecular targets to combat tumoral neovascularization. We have recently found that store-operated Ca(2+) entry, a Ca(2+)-permeable membrane pathway that is activated upon depletion of the inositol-1,4,5-trisphosphate-sensitive Ca(2+) pool, is recruited by vascular endothelial growth factor to support proliferation and tubulogenesis in human circulating endothelial colony forming cells (ECFCs). ECFCs are a subgroup of EPCs that circulate in the peripheral blood of adult individuals and are able to proliferate and differentiate into endothelial cells and form capillary networks in vitro and contribute to neovessel formation in vivo. The present review will discuss the relevance of SOCE to ECFC-based cell therapy and will address the pharmacological inhibition of store-dependent Ca(2+) channels as a promising target for anti-angiogenic treatments.

Store-operated Ca2+ entry is remodelled and controls in vitro angiogenesis in endothelial progenitor cells isolated from tumoral patients

BACKGROUND

Endothelial progenitor cells (EPCs) may be recruited from bone marrow to sustain tumor vascularisation and promote the metastatic switch. Understanding the molecular mechanisms driving EPC proliferation and tubulogenesis could outline novel targets for alternative anti-angiogenic treatments. Store-operated Ca(2+) entry (SOCE), which is activated by a depletion of the intracellular Ca(2+) pool, regulates the growth of human EPCs, where is mediated by the interaction between the endoplasmic reticulum Ca(2+)-sensor, Stim1, and the plasmalemmal Ca(2+) channel, Orai1. As oncogenesis may be associated to the capability of tumor cells to grow independently on Ca(2+) influx, it is important to assess whether SOCE regulates EPC-dependent angiogenesis also in tumor patients.

METHODOLOGY/PRINCIPAL FINDINGS

The present study employed Ca(2+) imaging, recombinant sub-membranal and mitochondrial aequorin, real-time polymerase chain reaction, gene silencing techniques and western blot analysis to investigate the expression and the role of SOCE in EPCs isolated from peripheral blood of patients affected by renal cellular carcinoma (RCC; RCC-EPCs) as compared to control EPCs (N-EPCs). SOCE, activated by either pharmacological (i.e. cyclopiazonic acid) or physiological (i.e. ATP) stimulation, was significantly higher in RCC-EPCs and was selectively sensitive to BTP-2, and to the trivalent cations, La(3+) and Gd(3+). Furthermore, 2-APB enhanced thapsigargin-evoked SOCE at low concentrations, whereas higher doses caused SOCE inhibition. Conversely, the anti-angiogenic drug, carboxyamidotriazole (CAI), blocked both SOCE and the intracellular Ca(2+) release. SOCE was associated to the over-expression of Orai1, Stim1, and transient receptor potential channel 1 (TRPC1) at both mRNA and protein level The intracellular Ca(2+) buffer, BAPTA, BTP-2, and CAI inhibited RCC-EPC proliferation and tubulogenesis. The genetic suppression of Stim1, Orai1, and TRPC1 blocked CPA-evoked SOCE in RCC-EPCs.

CONCLUSIONS

SOCE is remodelled in EPCs from RCC patients and stands out as a novel molecular target to interfere with RCC vascularisation due to its ability to control proliferation and tubulogenesis.

Update on vascular endothelial Ca2+ signalling: A tale of ion channels, pumps and transporters

A monolayer of endothelial cells (ECs) lines the lumen of blood vessels and forms a multifunctional transducing organ that mediates a plethora of cardiovascular processes. The activation of ECs from as state of quiescence is, therefore, regarded among the early events leading to the onset and progression of potentially lethal diseases, such as hypertension, myocardial infarction, brain stroke, and tumor. Intracellular Ca²⁺ signals have long been know to play a central role in the complex network of signaling pathways regulating the endothelial functions. Notably, recent work has outlined how any change in the pattern of expression of endothelial channels, transporters and pumps involved in the modulation of intracellular Ca²⁺ levels may dramatically affect whole body homeostasis. Vascular ECs may react to both mechanical and chemical stimuli by generating a variety of intracellular Ca²⁺ signals, ranging from brief, localized Ca²⁺ pulses to prolonged Ca²⁺ oscillations engulfing the whole cytoplasm. The well-defined spatiotemporal profile of the subcellular Ca²⁺ signals elicited in ECs by specific extracellular inputs depends on the interaction between Ca²⁺ releasing channels, which are located both on the plasma membrane and in a number of intracellular organelles, and Ca²⁺ removing systems. The present article aims to summarize both the past and recent literature in the field to provide a clear-cut picture of our current knowledge on the molecular nature and the role played by the components of the Ca²⁺ machinery in vascular ECs under both physiological and pathological conditions.

Old and new gasotransmitters in the cardiovascular system: focus on the role of nitric oxide and hydrogen sulfide in endothelial cells and cardiomyocytes

The functional relevance of nitric oxide (NO) in the cardiovascular system is well established since the end of the 80', when it was firstly proposed as a key controller of vasodilation. More recent evidences, still debated and partly conflicting, point to a role of NO in the angiogenic progression. On the other hand hydrogen sulfide is a new entry as a gasotransmitter in the cardiovascular system. The variety of its biological functions seems to grow day after day. The first to be described is surely its reversible and poisoning binding of the cytochrome c oxidase that leads to impairment of the respiratory chain in mitochondria. However, sub-toxic concentrations have been later proved to be essential to maintain fundamental physiological functions in several tissues. The basal production of H2S is determined by the activity of, at least, three constitutively expressed enzymes (CBS, CSE, and 3-MPT) with tissue specificity for CBS and CSE in the central nervous and cardiovascular system, respectively. The assumption of a pivotal role of H2S in regulating physiological function is supported by the demonstration that reduced production of this gaseous molecule by CSE induces hypertension in mice. The increasing number of studies showing the regulatory functions of H2S reveals that maintaining the normal blood pressure levels is only one of its multiple biological actions. In this review, we would like to explore the recent literature on NO and H2S roles on cardiovascular system and to elucidate potential outcomes in the use of pharmacological drugs interfering with their metabolism.

Hydrogen sulfide regulates intracellular Ca2+ concentration in endothelial cells from excised rat aorta

Hydrogen sulphide (H2S) is a recently discovered gasotransmitter that may regulate a growing number of endothelial functions, including nitric oxide (NO) release, proliferation, adhesion and migration, which are the key steps of angiogenesis. The mechanism whereby H2S impacts on endothelial physiology is still unclear: however, the aforementioned processes are driven by an increase in intracellular Ca2+ concentration ([Ca2+]i). In the present study, we exploited the excised rat aorta to gain insights into the regulation of [Ca2+]i by H2S within in situ endothelial cells (ECs). Sodium hydrosulphide (NaHS), a H2S donor, caused an elevation in [Ca2+]i, which disappeared in absence of extracellular Ca2+. NaHSinduced Ca2+ inflow was sensitive to high doses of Gd3+, but not BTP-2. Inhibition of the reverse-mode of the Na+-Ca2+ exchanger (NCX), with KB-R7943 or upon removal of extracellular Na+, abrogated the Ca2+ response to NaHS. Moreover, NaHS-elicited Ca2+ entry was significantly reduced by TEA and glybenclamide, which hinted at the involvement of ATP-dependent K+ (KATP) channels. Conversely, NaHS-evoked Ca2+ signal was not affected by the reducing agent, dithiothreitol. Acute addition of NaHS hindered both Ca2+ release and Ca2+ entry induced by ATP, a physiological agonist of ECs. Consistently, inhibition of endogenous H2S synthesis with DL-propargylglycine impaired ATP-induced Ca2+ inflow, whereas it did not affect Ca2+ mobilization. These data provide the first evidence that H2S may stimulate Ca2+ influx into ECs by recruiting the reverse-mode of NCX and KATP channels. In addition, they show that such gasotransmitter may modulate the Ca2+ signals elicited by physiological stimuli in intact endothelium.

Vascular endothelial growth factor stimulates endothelial colony forming cells proliferation and tubulogenesis by inducing oscillations in intracellular Ca2+ concentration

Endothelial progenitor cells (EPCs) home from the bone marrow to the site of tissue regeneration and sustain neovascularization after acute vascular injury and upon the angiogenic switch in solid tumors. Therefore, they represent a suitable tool for cell-based therapy (CBT) in regenerative medicine and provide a novel promising target in the fight against cancer. Intracellular Ca(2+) signals regulate numerous endothelial functions, such as proliferation and tubulogenesis. The growth of endothelial colony forming cells (ECFCs), which are EPCs capable of acquiring a mature endothelial phenotype, is governed by store-dependent Ca(2+) entry (SOCE). This study aimed at investigating the nature and the role of VEGF-elicited Ca(2+) signals in ECFCs. VEGF induced asynchronous Ca(2+) oscillations, whose latency, amplitude, and frequency were correlated to the growth factor dose. Removal of external Ca(2+) (0Ca(2+)) and SOCE inhibition with N-(4-[3,5-bis(trifluoromethyl)-1H-pyrazol-1-yl]phenyl)-4-methyl-1,2,3-thiadiazole-5-carboxamide (BTP-2) reduced the duration of the oscillatory signal. Blockade of phospholipase C-γ with U73122, emptying the inositol-1,4,5-trisphosphate (InsP(3))-sensitive Ca(2+) pools with cyclopiazonic acid (CPA), and inhibition of InsP(3) receptors with 2-APB prevented the Ca(2+) response to VEGF. VEGF-induced ECFC proliferation and tubulogenesis were inhibited by the Ca(2+)-chelant, BAPTA, and BTP-2. NF-κB activation by VEGF was impaired by BAPTA, BTP-2, and its selective blocker, thymoquinone. Thymoquinone, in turn, suppressed VEGF-dependent ECFC proliferation and tubulogenesis. These data indicate that VEGF-induced Ca(2+) oscillations require the interplay between InsP(3)-dependent Ca(2+) release and SOCE, and promote ECFC growth and tubulogenesis by engaging NF-κB. This novel signaling pathway might be exploited to enhance the outcome of CBT and chemotherapy.

Hydrogen sulfide promotes calcium signals and migration in tumor-derived endothelial cells

Hydrogen sulfide (H(2)S) is a gasotransmitter that plays several roles in various tissues, including the cardiovascular system. Because it has been recently proposed to act as a mediator of angiogenesis progression, here we investigate the effects of H(2)S in a well-established model of tumor angiogenesis: endothelial cells obtained from human breast carcinoma (B-TECs). Ca(2+) imaging and patch-clamp experiments reveal that acute perfusion with NaHS, a widely employed H(2)S donor, activates cytosolic calcium (Ca(c)) increase, as well as potassium and nonselective cationic currents, in B-TECs. Stimulation with NaHS in the same concentration range (1 nM-200 μM) evoked Ca(c) signals also in "normal" human microvascular endothelial cells (HMVECs), but the amplitude was significantly lower. Moreover, although NaHS failed to promote either migration or proliferation on HMVECs, B-TEC migration was enhanced at low-micromolar NaHS concentrations (1-10 μM). Remarkably H(2)S mediates tumor proangiogenic signaling triggered by vascular endothelial growth factor (VEGF). B-TECs pretreated with dl-propargylglycine (5mM, 30 min), an inhibitor of the H(2)S-producing enzyme cystathionine γ-lyase, showed drastically reduced migration and Ca(c) signals induced by VEGF (20 ng/ml). We conclude that H(2)S plays a role in proangiogenic signaling of tumor-derived but not normal human ECs. Furthermore the ability of this gasotransmitter to interfere with B-TEC responsiveness to VEGF suggests that it could be an interesting target for antiangiogenic strategies in tumor treatment.

The mechanism of injury-induced intracellular calcium concentration oscillations in the endothelium of excised rat aorta

Endothelial injury is the primary event that leads to a variety of severe vascular disorders. Mechanical injury elicits a Ca(2+) response in the endothelium of excised rat aorta, which comprises an initial Ca(2+) release from inositol-1,4,5-trisphosphate (InsP(3))-sensitive stores followed by a long-lasting decay phase due to Ca(2+) entry through uncoupled connexons. The Ca(2+) signal may also adopt an oscillatory pattern, the molecular underpinnings of which are unclear. In the light of the role played by Ca(2+) spiking in tissue regeneration, this study aimed to unveil the mechanisms underlying injury-induced Ca(2+) oscillations. The latter reversibly ceased upon removal of extracellular Ca(2+) or addition of the gap junction blockers heptanol, 18 α,β-glycyrrhetinic acid, La(3+) and Ni(2+), but were insensitive to BTP-2 and SKF 96365. The spiking response was abolished by inhibiting the Ca(2+) entry mode of the Na(+)/Ca(2+) exchanger (NCX). The InsP(3)-producing agonist ATP resumed Ca(2+) oscillations in silent cells, while the phospholipase C inhibitor U73122 suppressed them. Injury-induced Ca(2+) transients were prevented by the sarcoplasmic-endoplasmic reticulum calcium ATPase (SERCA) blockers thapsigargin and cyclopiazonic acid, while they were unaffected by suramin and genistein. These data show for the first time that the coordinated interplay between NCX-mediated Ca(2+) entry and InsP(3)-dependent Ca(2+) release contributes to injury-induced intracellular Ca(2+) concentration oscillations.

Genistein effects on Ca2+ handling in human umbilical artery: inhibition of sarcoplasmic reticulum Ca2+ release and of voltage-operated Ca2+ channels

Isoflavones are a group of natural phytoestrogens including the compound genistein. Health beneficial effects have been attributed to the consumption of this compound, but the fact that it has estrogen-like activity has raised doubts regarding its potential risk in infants, newborns, or in the fetus and placenta during pregnancy. This work is aimed at studying genistein effects on Ca2+ handling by smooth muscle cells of the human umbilical artery (HUA). Using fluorometric techniques, we found that in these cells genistein reduces the intracellular Ca2+ peak produced by serotonin. The same result could be demonstrated in absence of extracellular Ca2+, suggesting that the isoflavone reduces Ca2+ release from the sarcoplasmic reticulum. Force measurement experiments strengthen these results, since genistein reduced the peak force attained by intact HUA rings stimulated by serotonin in a Ca2+-free solution. Moreover, genistein induced the relaxation of HUA rings precontracted either with serotonin or a depolarizing high-extracellular K+ solution, hinting at a reduction of extracellular Ca2+ entry to the cell. This was confirmed by whole-cell patch-clamp experiments where it was shown that the isoflavone inhibits ionic currents through voltage-operated Ca2+ channels. In summary, we show that genistein inhibits two mechanisms that could increase intracellular Ca2+ in human umbilical smooth muscle cells, behaving in this way as a potential vasorelaxing substance of fetal vessels. Taking into account that genistein is able to cross the placental barrier, these data show that isoflavones may have important implications in the regulation of feto-maternal blood flow in pregnant women who consume soy-derived products as part of their meals.

Ca2+ signaling in injured in situ endothelium of rat aorta

The inner wall of excised rat aorta was scraped by a microelectrode and Ca2+ signals were investigated by fluorescence microscopy in endothelial cells (ECs) directly coupled with injured cells. The injury caused an immediate increase in the intracellular Ca2+ concentration ([Ca2+]i), followed by a long-lasting decay phase due to Ca2+ influx from extracellular space. The immediate response was mainly due to activation of purinergic receptors, as shown by the effect of P2X and P2Y receptors agonists and antagonists, such as suramin, alpha,beta-MeATP, MRS-2179 and 2-MeSAMP. Inhibition of store-operated Ca2+ influx did not affect either the peak response or the decay phase. Furthermore, the latter was: (i) insensitive to phospholipase C inhibition, (ii) sensitive to the gap junction blockers, palmitoleic acid, heptanol, octanol and oleamide, and (iii) sensitive to La3+ and Ni2+, but not to Gd3+. Finally, ethidium bromide or Lucifer Yellow did not enter ECs facing the scraped area. These results suggest that endothelium scraping: (i) causes a short-lasting stimulation of healthy ECs by extracellular nucleotides released from damaged cells and (ii) uncouples the hemichannels of the ECs facing the injury site; these hemichannels do not fully close and allow a long-lasting Ca2+ entry.

Genistein inhibits contractile force, intracellular Ca2+ increase and Ca2+ oscillations induced by serotonin in rat aortic smooth muscle

The soy-derived isoflavones genistein and daidzein affect the contractile state of different kinds of smooth muscle. We describe acute effects of genistein and daidzein on contractile force and intracellular Ca2+ concentration ([Ca2+]i) in in situ smooth muscle of rat aorta. Serotonin (5-HT) (2 microM) or a depolarizing high K+ solution produced the contraction of aortic rings, which were immediately relaxed by 20 microM genistein and by 20 microM daidzein. Accordingly, both 5-HT and a high K+ solution increased the [Ca2+]i in in situ smooth muscle cells. Genistein strongly inhibited the [Ca2+]i increase evoked by 5-HT (74.0 +/- 7.3%, n = 11, p < 0.05), and had a smaller effect on high K+ induced [Ca2+]i increase (19.9 +/- 4.0%, n = 7, p < 0.05). The K+ channels blocker tetraethylammonium (TEA) (0.5 mM) diminished genistein effects on 5-HT-induced [Ca2+]i increase. Interestingly, during prolonged application of 5-HT, the [Ca2+]i oscillated and a short (90 s) preincubation with genistein (20 microM) significantly diminished the frequency of the oscillations. This effect was totally abolished by TEA. In conclusion, in rat aortic smooth muscle, genistein is capable of diminishing the increase in [Ca2+]i and in force evoked by 5-HT and high K+ solution, and of decreasing the frequency of [Ca2+]i oscillations induced by 5-HT. The short time required by genistein, and the relaxing effect of daidzein suggest that tyrosine kinases inhibition is not involved. The small inhibiting effect of genistein on the [Ca2+]i increase evoked by high K+ and the effect of TEA point to the activation by genistein of calcium-activated K+ channels.

Prediction of hip fracture risk by quantitative ultrasound in more than 7000 Swiss women > or =70 years of age: comparison of three technologically different bone ultrasound devices in the SEMOF study

To compare the prediction of hip fracture risk of several bone ultrasounds (QUS), 7062 Swiss women > or =70 years of age were measured with three QUSs (two of the heel, one of the phalanges). Heel QUSs were both predictive of hip fracture risk, whereas the phalanges QUS was not.

INTRODUCTION

As the number of hip fracture is expected to increase during these next decades, it is important to develop strategies to detect subjects at risk. Quantitative bone ultrasound (QUS), an ionizing radiation-free method, which is transportable, could be interesting for this purpose.

MATERIALS AND METHODS

The Swiss Evaluation of the Methods of Measurement of Osteoporotic Fracture Risk (SEMOF) study is a multicenter cohort study, which compared three QUSs for the assessment of hip fracture risk in a sample of 7609 elderly ambulatory women > or =70 years of age. Two QUSs measured the heel (Achilles+; GE-Lunar and Sahara; Hologic), and one measured the heel (DBM Sonic 1200; IGEA). The Cox proportional hazards regression was used to estimate the hazard of the first hip fracture, adjusted for age, BMI, and center, and the area under the ROC curves were calculated to compare the devices and their parameters.

RESULTS

From the 7609 women who were included in the study, 7062 women 75.2 +/- 3.1 (SD) years of age were prospectively followed for 2.9 +/- 0.8 years. Eighty women reported a hip fracture. A decrease by 1 SD of the QUS variables corresponded to an increase of the hip fracture risk from 2.3 (95% CI, 1.7, 3.1) to 2.6 (95% CI, 1.9, 3.4) for the three variables of Achilles+ and from 2.2 (95% CI, 1.7, 3.0) to 2.4 (95% CI, 1.8, 3.2) for the three variables of Sahara. Risk gradients did not differ significantly among the variables of the two heel QUS devices. On the other hand, the phalanges QUS (DBM Sonic 1200) was not predictive of hip fracture risk, with an adjusted hazard risk of 1.2 (95% CI, 0.9, 1.5), even after reanalysis of the digitalized data and using different cut-off levels (1700 or 1570 m/s).

CONCLUSIONS

In this elderly women population, heel QUS devices were both predictive of hip fracture risk, whereas the phalanges QUS device was not.

The Na+/Ca2+ exchanger is active and working in the reverse mode in human umbilical artery smooth muscle cells

The data presented in this work suggest that in human umbilical artery (HUA) smooth muscle cells, the Na(+)/Ca(2+) exchanger (NCX) is active and working in the reverse mode. This supposition is based on the following results: (i) microfluorimetry in HUA smooth muscle cells in situ showed that a Ca(2+)-free extracellular solution diminished intracellular Ca(2+) ([Ca(2+)](i)), and KB-R7943 (5microM), a specific inhibitor of the Ca(2+) entry mode of the exchanger, also decreased [Ca(2+)](i) (40.6+/-4.5% of Ca(2+)-free effect); (ii) KB-R7943 produced the relaxation of HUA rings (-24.7+/-7.3gF/gW, n=8, p<0.05); (iii) stimulation of the NCX by lowering extracellular Na(+) increases basal [Ca(2+)](i) proportionally to Na(+) reduction (Delta fluorescence ratio=0.593+/-0.141 for Na(+)-free solution, n=8) and HUA rings' contraction (peak force=181.5+/-39.7 for 130mM reduction, n=8), both inhibited by KB-R7943 and a Ca(2+)-free extracellular solution. In conclusion, the NCX represents an important Ca(2+) entry route in HUA smooth muscle cells.

The duration and amplitude of the plateau phase of ATP- and ADP-evoked Ca(2+) signals are modulated by ectonucleotidases in in situ endothelial cells of rat aorta

ATP has a long-lasting vasodilatory effect, possibly due to its capability to induce a prolonged increase in the intracellular Ca(2+) concentration ([Ca(2+)](i)) in endothelial cells (EC) and activate constitutive nitric oxide synthase. However, contradictory data have been reported regarding the time course of ATP-evoked Ca(2+) signals in in situ EC. In particular, short-duration Ca(2+) signals have been reported, which might be thought to be unable to sustain a prolonged, NO-induced vasodilation. The current experiments were therefore performed in in situ EC of rat aorta in order to more fully define the time course of ATP-evoked Ca(2+) signals. 20 microM ATP evoked a short-lasting Ca(2+) signal. However, medium stirring, high agonist concentrations, inhibition of ectonucleotidases and application of a poorly hydrolyzable agonist evoked long-lasting Ca(2+) signals (up to 20 min at 37 degrees C). These studies suggest that ATP is able to sustain a prolonged [Ca(2+)](i) increase, unless ectonucleotidase activity reduces the agonist concentration near the EC surface to subthreshold values, quickly cutting the Ca(2+) signal. Furthermore, the amplitude of the long-lasting phase of the Ca(2+) signal depended on the balance between agonist degradation by ectonucleotidases and agonist transport, by diffusion and convection, from bulk solution to the EC surface.

Cu2+, Co2+, and Mn2+ modify the gating kinetics of high-voltage-activated Ca2+ channels in rat palaeocortical neurons

The effects of three divalent metal cations (Mn2+, Co2+, and Cu2+) on high-voltage-activated (HVA) Ca2+ currents were studied in acutely dissociated pyramidal neurons of rat piriform cortex using the patch-clamp technique. Cu2+, Mn2+, and Co2+ blocked HVA currents conducted by Ba2+ ( IBa) with IC50 of approximately 920 nM, approximately 58 micro M, and approximately 65 micro M, respectively. Additionally, after application of non-saturating concentrations of the three cations, residual currents activated with substantially slower kinetics than control IBa. As a consequence, the current fraction abolished by the blocking cations typically displayed, in its early phase, an unusually fast-decaying transient. The latter phenomenon turned out to be a subtraction artifact, since none of the pharmacological components (L-, N-, P/Q-, and R-type) that constitute the total HVA currents under study showed a similarly fast early decay: hence, the slow activation kinetics of residual currents was not due to the preferential inhibition of a fast-activating/inactivating component, but rather to a true slowing effect of the blocker cations. The percent IBa-amplitude inhibition caused by Mn2+, Co2+, and Cu2+ was voltage-independent over the whole potential range explored (up to +30 mV), hence the slowing of IBa activation kinetics was not due to a mechanism of voltage- and time-dependent relief from block. Moreover, Mn2+, Co2+, and Cu2+ significantly reduced I(Ba) deactivation speed upon repolarization, which also is not compatible with a depolarization-dependent unblocking mechanism. The above results show that 1) Cu2+ is a particularly potent HVA Ca2+-channel blocker in rat palaeocortical neurons; and 2) Mn2+, Co2+, and Cu2+, besides exerting a blocking action on HVA Ca2+-channels, also modify Ca2+-current activation and deactivation kinetics, most probably by directly interfering with channel-state transitions.

Expression and function of neuronal nicotinic ACh receptors in rat microvascular endothelial cells

The expression and function of nicotinic ACh receptors (nAChRs) in rat coronary microvascular endothelial cells (CMECs) were examined using RT-PCR and whole cell patch-clamp recording methods. RT-PCR revealed expression of mRNA encoding for the subunits alpha(2), alpha(3), alpha(4), alpha(5), alpha(7), beta(2), and beta(4) but not beta(3). Focal application of ACh evoked an inward current in isolated CMECs voltage clamped at negative membrane potentials. The current-voltage relationship of the ACh-induced current exhibited marked inward rectification and a reversal potential (E(rev)) close to 0 mV. The cholinergic agonists nicotine, epibatidine, and cytisine activated membrane currents similar to those evoked by ACh. The nicotine-induced current was abolished by the neuronal nAChR antagonist mecamylamine. The direction and magnitude of the shift in E(rev) of nicotine-induced current as a function of extracellular Na(+) concentration indicate that the nAChR channel is cation selective and follows that predicted by the Goldman-Hodgkin-Katz equation assuming K(+)/Na(+) permeability ratio of 1.11. In fura-2-loaded CMECs, application of ACh, but not of nicotine, elicited a transient increase in intracellular free Ca(2+) concentration. Taken together, these results demonstrate that neuronal nAChR activation by cholinergic agonists evokes an inward current in CMECs carried primarily by Na(+), which may contribute to the plasma nicotine-induced changes in microvascular permeability and reactivity induced by elevations in plasma nicotine.

Comparison of three bone ultrasounds for the discrimination of subjects with and without osteoporotic fractures among 7562 elderly women

Bone ultrasound measures (QUSs) can assess fracture risk in the elderly. We compared three QUSs and their association with nonvertebral fracture history in 7562 Swiss women 70-80 years of age. The association between nonvertebral fracture was higher for heel than phalangeal QUS.

INTRODUCTION

Because of the high morbidity and mortality associated with osteoporotic fractures, it is essential to detect subjects at risk for such fractures with screening methods. Because quantitative bone ultrasound (QUS) discriminated subjects with osteoporotic fractures from controls in several cross-sectional studies and predicted fractures in prospective studies, QUS could be more practical than DXA for screening.

MATERIAL AND METHODS

This cross-sectional and retrospective multicenter (10 centers) study was performed to compare three QUSs (two heel ultrasounds: Achilles+ [GE-Lunar] and Sahara [Hologic]; the phalanges: ultrasound DBM sonic 1200 [IGEA]) for determining by logistic regression nonvertebral fracture odds ratio (OR) in a sample of 7562 Swiss women, 75.3 +/- 3.1 years of age. The two heel QUSs measured the broadband ultrasound attenuation (BUA) and the speed of sound (SOS). In addition, Achilles+ calculated the stiffness index (SI) and the Sahara calculated the quantitative ultrasound index (QUI) from BUA and SOS. The DBM sonic 1200 measured the amplitude-dependent SOS (AD-SOS).

RESULTS

Eighty-six women had a history of a traumatic hip fracture after the age of 50, 1594 had a history of forearm fracture, and 2016 had other nonvertebral fractures. No fracture history was reported by 3866 women. Discrimination for hip fracture was higher than for the other nonvertebral fractures. The two heel QUSs had a significantly higher discrimination power than the QUSs of the phalanges, with standardized ORs, adjusted for age and body mass index, ranging from 2.1 to 2.7 (95% CI = 1.6, 3.5) compared with 1.4 (95% CI = 1.1, 1.7) for the AD-SOS of DBM sonic 1200.

CONCLUSION

This study showed a high association between heel QUS and hip fracture history in elderly Swiss women. This could justify integration of QUS among screening strategies for identifying elderly women at risk for osteoporotic fractures.

Dual effect of Zn2+ on multiple types of voltage-dependent Ca2+ currents in rat palaeocortical neurons

The effects of Zn(2+) were evaluated on high-voltage-activated Ca(2+) currents expressed by pyramidal neurons acutely dissociated from rat piriform cortex. Whole-cell, patch-clamp experiments were carried out using Ba(2+) (5 mM) as the charge carrier. Zn(2+) blocked total high-voltage-activated Ba(2+) currents with an IC(50) of approximately 21 microM. In addition, after application of non-saturating Zn(2+) concentrations, residual currents activated with substantially slower kinetics than control Ba(2+) currents. Both of the above-mentioned effects of Zn(2+) were also observed in high-voltage-activated currents recorded in the presence of nearly-physiological concentrations of extracellular Ca(2+) (1 and 2 mM) rather than Ba(2+). Under the latter conditions, 30 microM Zn(2+) inhibited high-voltage-activated currents somewhat less than observed in extracellular Ba(2+) (approximately 47% and approximately 41%, respectively, vs. approximately 59%), but slowed Ca(2+)-current activation to very similar degrees. All of the pharmacological components in which Ba(2+) currents could be dissected (L-, N-, P/Q-, and R-type) were inhibited by Zn(2+), the percentage of current blocked by 30 microM Zn(2+) ranging from 34 to 57%. Moreover, the activation kinetics of all pharmacological Ba(2+) current components were slowed by Zn(2+). Hence, the lower activation speed observed in residual Ba(2+) currents after Zn(2+) block is due to a true slowing of macroscopic Ca(2+)-current activation kinetics and not to the preferential inhibition of a fast-activating current component. The inhibitory effect of Zn(2+) on Ba(2+) current amplitude was voltage-independent over the whole voltage range explored (-60 to +30 mV), hence the Zn(2+)-dependent decrease of Ba(2+) current activation speed is not the consequence of a voltage- and time-dependent relief from block. Zn(2+) also caused a slight, but significant, reduction of Ba(2+) current deactivation speed upon repolarization, which is further evidence against a depolarization-dependent unblocking mechanism. Finally, the slowing effect of Zn(2+) on Ca(2+)-channel activation kinetics was found to result in a significant, extra reduction of Ba(2+) current amplitude when action-potential-like waveforms, rather than step pulses, were used as depolarizing stimuli. We conclude that Zn(2+) exerts a dual action on multiple types of voltage-gated Ca(2+) channels, causing a blocking effect and altering the speed at which channels are delivered to conducting states, with mechanism(s) that could be distinct.

Epidermal growth factor induces intracellular Ca2+ oscillations in microvascular endothelial cells

An increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) may play a role in the proliferative effect of several growth factors. In this study, the changes in [Ca(2+)](i) elicited by epidermal growth factor (EGF) in rat cardiac microvascular endothelial cells (CMEC) have been investigated by using fura-2 conventional and confocal microscopy. A large heterogeneity in the latency and in the pattern of the Ca(2+) response was found at each dose of EGF (2.5-100 ng/ml), whereas some cells displayed a non-oscillatory behavior and others exhibited a variable number of Ca(2+) oscillations. On average, the fraction of responsive cells, the total number of oscillations and the duration of the Ca(2+) signal were higher at around 10 ng/ml EGF, while there was no dose-dependence in the lag time and in the amplitude of the [Ca(2+)](i) increase. EGF-induced Ca(2+) spikes were abolished by the tyrosine kinase inhibitor genistein, but not by its inactive analogue daidzein, and by the phospholipase C blocker NCDC. Only 1-2 transients could be elicited in Ca(2+)-free solution, while re-addition of extracellular Ca(2+) recovered the spiking activity. The oscillatory signal was prevented by the SERCA inhibitor thapsigargin and abolished by the calcium entry blockers Ni(2+) and La(3+). Moreover, EGF-induced Ca(2+) transients were abolished by the InsP(3) receptor blocker caffeine, while ryanodine was without effect. Confocal imaging microscopy showed that the Ca(2+) response to EGF was localized both in the cytoplasm and in the nucleus. We suggest that EGF-induced [Ca(2+)](i) increase may play a role in the proliferative action of EGF on endothelial cells.

Basal nonselective cation permeability in rat cardiac microvascular endothelial cells

The presence of a basal nonselective cation permeability was mainly investigated in primary cultures of rat cardiac microvascular endothelial cells (CMEC) by applying both the patch-clamp technique and Fura-2 microfluorimetry. With low EGTA in the pipette solution, the resting membrane potential of CMEC was -21.2 +/- 1.1 mV, and a Ca(2+)-activated Cl(-) conductance was present. When the intracellular Ca(2+) was buffered with high EGTA, the membrane potential decreased to 5.5 +/- 1.2 mV. In this condition, full or partial substitution of external Na(+) by NMDG(+) proportionally reduced the inward component of the basal I-V relationship. This current was dependent on extracellular monovalent cations with a permeability sequence of K(+) > Cs(+) > Na(+) > Li(+) and was inhibited by Ca(2+), La(3+), Gd(3+), and amiloride. The K(+)/Na(+) permeability ratio, determined using the Goldman-Hodgkin-Katz equation, was 2.01. The outward component of the basal I-V relationship was reduced when intracellular K(+) was replaced by NMDG(+), but was not sensitive to substitution by Cs(+). Finally, microfluorimetric experiments indicated the existence of a basal Ca(2+) entry pathway, inhibited by La(3+) and Gd(3+). The basal nonselective cation permeability in CMEC could be involved both in the control of myocardial ionic homeostasis, according to the model of the blood-heart barrier, and in the modulation of Ca(2+)-dependent processes.

Protein Kinase C Facilitation of Acetylcholine Release at the Rat Neuromuscular Junction

Protein kinase C (PKC) is a Ca2+-dependent enzyme involved in synaptic transmission, which can be experimentally activated by the phorbol ester, phorbol 12-myristate-13-acetate (TPA). We studied the effects of TPA application on acetylcholine (ACh) release at the rat neuromuscular junction by means of the focal recording technique; possible effects of TPA at the postsynaptic site had been ruled out in preliminary studies. In extracellular solutions containing 2 mM Ca2+ and at the stimulation frequency of 0.1 Hz, TPA increased endplate current (EPC) amplitude. In non-stimulated preparations spontaneous current frequency was increased at a similar rate. The similar time course of TPA action on evoked and spontaneous currents suggests that an increased presynaptic Ca2+ efficacy can be considered to be the probable mechanism of action. The interactions of PKC with ACh release were further investigated. In 0.1 mM Ca2+ extracellular solutions, TPA enhanced evoked currents only at stimulation frequencies (e.g. 40 Hz) that were themselves capable of inducing facilitation. This facilitation is classically associated with presynaptic Ca2+ accumulation, indicating that PKC interacts synergistically with Ca2+ to facilitate ACh release. In particular, since mean quantum size and release probability remained almost unchanged during TPA facilitation, it was concluded that PKC acted by enlarging the immediately available store. Interestingly, TPA also increased the presynaptic currents that were observed to be largely brought about by Ca2+-dependent K+ currents: evidence was obtained to suggest that increases in these currents provide negative feedback against excess release activation rather than being an expression of enhanced Ca2+ influx.

Ca2+ uptake by the endoplasmic reticulum Ca2+-ATPase in rat microvascular endothelial cells

In non-excitable cells, many agonists increase the intracellular Ca(2+) concentration ([Ca(2+)](i)) by inducing an inositol 1,4,5-trisphosphate (IP(3))-mediated Ca(2+) release from the intracellular stores. Ca(2+) influx from the extracellular medium may then sustain the Ca(2+) signal. [Ca(2+)](i) recovers its resting level as a consequence of Ca(2+)-removing mechanisms, i.e. plasma-membrane Ca(2+)-ATPase (PMCA) pump, Na(+)/Ca(2+) exchanger (NCX) and sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA) pump. In a study performed in pancreatic acinar cells, evidence has been provided suggesting that, during the decay phase of the agonist-evoked Ca(2+) transients, the Ca(2+) concentration within the intracellular stores remains essentially constant [Mogami, Tepikin and Petersen (1998) EMBO J. 17, 435-442]. It was therefore hypothesized that, in such a situation, intracellular Ca(2+) is not only picked up by the SERCA pump, but is also newly released through IP(3)-sensitive Ca(2+) channels, with the balance between these two processes being approximately null. The main aim of the present work was to test this hypothesis by a different experimental approach. Using cardiac microvascular endothelial cells, we found that inhibition of the SERCA pump has no effect on the time course of agonist-evoked Ca(2+) transients. This result was not due to a low capacity of the SERCA pump since, after agonist removal, this pump proved to be very powerful in clearing the excess of intracellular Ca(2+). We showed further that: (i) in order to avoid a rapid removal of Ca(2+) by the SERCA pump, continuous IP(3) production appears to be required throughout all of the decay phase of the Ca(2+) transient; and (ii) Ca(2+) picked up by the SERCA pump can be fully and immediately released by agonist application. All these results support the model of Mogami, Tepikin and Petersen [(1998) EMBO J. 17, 435-442]. Since the SERCA pump did not appear to be involved in shaping the decay phase of the agonist-evoked Ca(2+) transient, we inhibited the PMCA pump with carboxyeosin, and NCX with benzamil and by removing extracellular Na(+). The results indicate that, during the decay phase of the agonist-evoked Ca(2+) transient, the intracellular Ca(2+) is removed by both the PMCA pump and NCX. Finally, we provide evidence indicating that mitochondria have no role in clearing intracellular Ca(2+) during agonist-evoked Ca(2+) transients.

A new method to assess the fluidodynamic behaviour of an angiographic contrast agent

PURPOSE

To propose a new method for the assessment of the fluidodynamic behaviour of angiographic contrast agents. The method enables measurement of the spatial distribution and time dependence of the contrast agent along a pseudo-vessel on images obtained with an X-ray image intensifier.

MATERIAL AND METHODS

A particular phantom was devised consisting of a plexiglas box with an insert into which a latex tube with a 0.4 cm in diameter was placed in order to simulate the tortuous flow of a blood vessel. The box, which is filled with water to simulate the thickness of a normal patient, is connected to an injection and pumping system which serve to keep the contrast agent flowing in the pseudo-vessel tube. The pseudo-vessel tube was filled with plain water in one case and with saline solution in another case to assess their different dilution capabilities. The phantom and the flow of contrast agent were imaged with a conventional X-ray image intensifier system and the images were stored in digital format during 35 second acquisitions at a speed of 4 frames per second; for any frame it is possible to measure the mathematical contrast in any position in the image. Further, a diagram showing the time dependence of the spatial distribution of the mathematical contrast is proposed. The X axis shows the spatial distribution of the mathematical contrast, whereas the Y axis shows its temporal variation with a gray level proportional to the mathematical contrast value. By building an horizontal profile of this diagram one can obtain the spatial distribution at a fixed time, while by building a vertical profile one can obtain the temporal variation at a fixed point. Several different contrast agents were so tested.

RESULTS

The proposed method allows different fluido-dynamic behaviour patterns of contrast agents and flowing media to be shown. Owing to the different chemical characteristics of water and saline solution these media have different dilution capabilities (higher for water) and this is well demonstrated by the diagram profiles obtained for each. The system has also allowed the detection of a particular behaviour of some contrast agents, whose spatial distribution was non uniform even in the last frames, thus showing a tendency to maintain their bolus-nature over time. An interesting feature which can be noticed in all the temporal profiles is the presence of a "pre-bolus", i.e. the contrast is higher at the very beginning of the flow, then decreases and after some time starts to increase again. Though the initial contrast value obviously depends on the iodine concentration employed, the method shows the contrast variation as a function of time is different for different contrast agents.

CONCLUSIONS

The method and the equipment proposed provide a good description of the fluidodynamic behaviour of different contrast agents, but do not constitute a reference method for testing haemodynamic behaviour which, "in vivo", is obviously affected by several other chemical and metabolic factors. However, the method allows evaluation of the contrast agents from a physical and fluidodynamic point of view, showing that the iodine content is not the only feature affecting their behaviour. The method can be used in quality control to test the constancy of the physical behaviour of different contrast agents.

Quality controls for two heel bone ultrasounds used in the Swiss Evaluation of the Methods of Measurement of Osteoporotic Fracture Risk Study

Because of the important morbidity and mortality associated with osteoporosis, it is essential to detect subjects at risk by screening methods, such as bone quantitative ultrasounds (QUSs). Several studies showed that QUS could predict fractures. None, however, compared prospectively different QUS devices, and few data of quality controls (QCs) have been published. The Swiss Evaluation of the Methods of Measurement of Osteoporotic Fracture Risk is a prospective multicenter study that compared three QUSs for the assessment of hip fracture risk in a population of 7609 women age >/=70 yr. Because the inclusion phase lasted 20 mo, and because 10 centers participated in this study, QC became a major issue. We therefore developed a QC procedure to assess the stability and precision of the devices, and for their cross-calibration. Our study focuses on the two heel QUSs. The water bath system (Achilles+) had a higher precision than the dry system (Sahara). The QC results were highly dependent on temperature. QUS stability was acceptable, but Sahara must be calibrated regularly. A sufficient homogeneity among all the Sahara devices could be demonstrated, whereas significant differences were found among the Achilles+ devices. For speed of sound, 52% of the differences among the Achilles+ was explained by the water s temperature. However, for broadband ultrasound attenuation, a maximal difference of 23% persisted after adjustment for temperature. Because such differences could influence measurements in vivo, it is crucial to develop standardized phantoms to be used in prospective multicenter studies.

Patient effective dose from endovascular brachytherapy with 192Ir sources

The growing use of endovascular brachytherapy has been accompanied by the publication of a large number of studies in several fields, but few studies on patient dose have been found in the literature. Moreover, these studies were carried out on the basis of Monte Carlo simulation. The aim of the present study was to estimate the effective dose to the patient undergoing endovascular brachytherapy treatment with 112Ir sources, by means of experimental measurements. Two standard treatments were taken into account: an endovascular brachytherapy of the coronary artery corresponding to the activity x time product of 184 GBq.min and an endovascular brachytherapy of the renal artery (898 GBq.min). Experimental assessment was accomplished by thermoluminescence dosemeters positioned in more than 300 measurement points in a properly adapted Rqndo phantom. A method has been developed to estimate the mean organ doses for all tissues and organs concerned in order to calculate the effective dose associated with intravascular brachytherapy. The normalised organ doses resulting from cronary treatment were 2.4 x 10(-2) mSv.GBq(-1).min(-1) for lung, 0.9 x 10(-2) mSv.GBSq(-1).min(-1) for oesophagus and 0.48 x 10(-2) mS.GBq(-1).min(-1) for bone marrow. During brachytherapy of the renal artery, the corresponding normalised doses were 4.2 x 10(-2) mS.GBq(-1).min(-1) for colon, 7.8 x 10(-2) mSv.GBq(-1).min(-1) for stomach and 1.7 x 10(-2) mSv.GBq(-1).min(-1) for liver. Coronary treatment iJnvlled an efl'fective dose of (0.046 mSv.GBq(-1).min(-1), whereas the treatment of the renal artery resulted in an effective dose of 0.15 mSv.GBq(-1).min(-1); there were many similarities with data from former studies. Based on these results it can be concluded that the dose level of patients exposed during brachytherapy treatment is low.

P2y1 and P2y2 receptor-operated Ca2+ signals in primary cultures of cardiac microvascular endothelial cells

Intracellular Ca2+ signals elicited by nucleotide agonists were investigated in primary cultures of rat cardiac microvascular endothelial cells using the fura-2 technique. UTP increased the intracellular [Ca2+] in 94% of the cells, whereas 2MeSATP was active in 32%. The rank order of potency was ATP = UTP > 2MeSATP and the maximal response to 2MeSATP was lower compared to UTP and ATP. ATP and UTP showed strong homologous and heterologous desensitization. ATP fully inhibited the 2MeSATP response, while UTP abolished 2MeSATP-elicited transients in 25% of cells. 2MeSATP did not desensitize the UTP or ATP response. Adenosine 2',5'-diphosphate inhibited the response to 2MeSATP, while it did not modify the response to ATP and UTP. 2MeSATP was more sensitive to suramin than UTP and ATP. These results indicate that P(2Y1) and P(2Y2) receptors may be coexpressed in CMEC. Nucleotide-induced Ca2+ signals lacked a sustained plateau and were almost independent from extracellular Ca2+. ATP and UTP elicited Ca2+ transients longer than 2MeSATP-evoked transients. The kinetics of Ca2+ responses was not affected by bath solution stirring or ectonucleotidase inhibition. Furthermore, the nonhydrolyzable ATP analogue AMP-PNP induced Ca2+ signals similar to those elicited by ATP and UTP. These results suggest that the distinct kinetics of nucleotide-evoked Ca2+ responses do not depend on the activity of ectonucleotidases or ATP autocrine stimulation. The possibility that Ca2+ signals with different time courses may modulate different cellular responses is discussed.

[Feasibility of the use of elastographic techniques with ultrasound in the diferentiation of different tissues]

PURPOSE

To investigate the feasibility of distinguishing different tissues by detecting their different elastic properties when mechanically stimulated with an ultrasound wide beam.

MATERIAL AND METHODS

A tissue-mimicking material phantom was placed in a water filled box. Two devices (Teuco Hydrosonic) emitting two US beams (3.2 MHz) were placed on two opposite walls of the box. The US beams had a circular diameter of about 10 cm; their intensity could be set by varying the power voltage applied to the device from 0 to 12 V. The US beams caused a mechanical stimulation of both the phantom and the water surrounding it. An ATL HDI 5000 scanner was used in order to acquire tissue Color Doppler images using the fundamental frequency (Tissue Doppler Imaging, TDI), and the second harmonic (Harmonic Tissue Doppler Imaging, HTDI). The images allowed to visualize, using a color scale, the vibrational status of both the phantom and the water surrounding it. Both fundamental and second harmonic images were taken using different power values supplied to the stimulation device, with the voltage ranging from 0 to 12 V. In order to quantify the vibrational status of the water and of the tissue-mimicking phantom two Regions Of Interest (ROI) were taken on the images. A parameter describing the "color amount" in each ROI and defined by an appropriate mathematical function was proposed.

RESULTS

Differences between the values of the "color amount" parameter in the phantom and in water were statistically significant both at the fundamental frequency and at second harmonic imaging, and for each positive value of the voltage of the power supplied to the device for the stimulation. Also the differences between the parameter "color amount" at the fundamental frequency and second harmonic imaging were statistically significant; the differences were found for both water and phantom and for any positive voltage. The correlation between the intensity of the stimulation (voltage) and the "color amount" parameter is statistically significant with the second harmonic technique in the phantom, nearly significant with the second harmonic technique in water and not significant in the other cases.

CONCLUSIONS

It is possible to try to characterize a tissue by analyzing its elastic properties when an ultrasound wide beam mechanically stimulates it. The most promising technique consists in acquiring images using Harmonic Tissue Doppler Imaging, (HTDI) and measuring the vibrational status by using the "color amount" parameter proposed.