NO upregulation of a cyclic nucleotide-gated channel contributes to calcium elevation in endothelial cells

Transcriptomic profile of cationic channels in human pulmonary arterial hypertension

The dysregulation of K⁺ channels is a hallmark of pulmonary arterial hypertension (PAH). Herein, the channelome was analyzed in lungs of patients with PAH in a public transcriptomic database. Sixty six (46%) mRNA encoding cationic channels were dysregulated in PAH with most of them downregulated (83%). The principal component analysis indicated that dysregulated cationic channel expression is a signature of the disease. Changes were very similar in idiopathic, connective tissue disease and congenital heart disease associated PAH. This analysis 1) is in agreement with the widely recognized pathophysiological role of TASK1 and K_V1.5, 2) supports previous preliminary reports pointing to the dysregulation of several K⁺ channels including the downregulation of K_V1.1, K_V1.4, K_V1.6, K_V7.1, K_V7.4, K_V9.3 and TWIK2 and the upregulation of K_Ca1.1 and 3) points to other cationic channels dysregulated such as Kv7.3, TALK2, Ca_V1 and TRPV4 which might play a pathophysiological role in PAH. The significance of other changes found in Na⁺ and TRP channels remains to be investigated.

Causality analysis reveals the link between cerebrovascular control and acute kidney dysfunction after coronary artery bypass grafting

BACKGROUND

Patients undergoing coronary artery bypass graft (CABG) surgery might experience postoperative complications and some of them, such as acute kidney dysfunction (AKD), are the likely consequence of hypoperfusion. We hypothesized that an impaired cerebrovascular control is a hallmark of a vascular damage that might favor AKD after CABG.

OBJECTIVE

Our aim is to characterize cerebrovascular control in CABG patients through the assessment of the relationship between mean arterial pressure (MAP) and mean cerebral blood flow velocity (MCBFV) and to check whether markers describing MCBFV-MAP dynamical interactions could identify subjects at risk to develop postoperative AKD.

APPROACH

MAP and MCBFV beat-to-beat series were extracted from invasive arterial pressure and transcranial Doppler recordings acquired simultaneously in 23 patients just before CABG after the induction of propofol general anesthesia. Subjects were divided into AKD group (n  =  9, age: 68  ±  9, 8 males) and noAKD group (n  =  14, age: 65  ±  8, 12 males) according to whether they developed postoperative AKD or not after CABG. We computed MAP and MCBFV time-domain and spectral markers as well as MCBFV-MAP cross-spectral indexes in very-low-frequency (VLF, 0.02-0.07 Hz), low-frequency (LF, 0.07-0.15 Hz) and high-frequency (HF, 0.15-0.30 Hz) bands. We also calculated model-based transfer entropy (TE) to quantify the degree of MCBFV dependence on MAP and vice versa. The null hypothesis of MCBFV-MAP uncoupling was tested via a surrogate approach associating MAP and MCBFV in different patients.

MAIN RESULTS

Time, spectral and cross-spectral markers had a limited power in separating AKD from noAKD individuals. Conversely, TE from MAP to MCBFV was significantly above the level set by surrogates only in AKD groups and significantly larger than that computed in noAKD.

SIGNIFICANCE

The reduced cerebrovascular autoregulation in AKD patients suggest a vascular impairment likely making them more at risk of hypoperfusion during CABG and AKD after CABG.

Assessing the Role of Muscle Protein Breakdown in Response to Nutrition and Exercise in Humans

Muscle protein breakdown (MPB) is an important metabolic component of muscle remodeling, adaptation to training, and increasing muscle mass. Degradation of muscle proteins occurs via the integration of three main systems—autophagy and the calpain and ubiquitin-proteasome systems. These systems do not operate independently, and the regulation is complex. Complete degradation of a protein requires some combination of the systems. Determination of MPB in humans is technically challenging, leading to a relative dearth of information. Available information on the dynamic response of MPB primarily comes from stable isotopic methods with expression and activity measures providing complementary information. It seems clear that resistance exercise increases MPB, but not as much as the increase in muscle protein synthesis. Both hyperaminoacidemia and hyperinsulinemia inhibit the post-exercise response of MPB. Available data do not allow a comprehensive examination of the mechanisms behind these responses. Practical nutrition recommendations for interventions to suppress MPB following exercise are often made. However, it is likely that some degree of increased MPB following exercise is an important component for optimal remodeling. At this time, it is not possible to determine the impact of nutrition on any individual muscle protein. Thus, until we can develop and employ better methods to elucidate the role of MPB following exercise and the response to nutrition, recommendations to optimize post exercise nutrition should focus on the response of muscle protein synthesis. The aim of this review is to provide a comprehensive examination of the state of knowledge, including methodological considerations, of the response of MPB to exercise and nutrition in humans.

Adenosine receptors regulate gap junction coupling of the human cerebral microvascular endothelial cells hCMEC/D3 by Ca2+ influx through cyclic nucleotide-gated channels

KEY POINTS

Gap junction channels are essential for the formation and regulation of physiological units in tissues by allowing the lateral cell-to-cell diffusion of ions, metabolites and second messengers. Stimulation of the adenosine receptor subtype A_2B increases the gap junction coupling in the human blood-brain barrier endothelial cell line hCMEC/D3. Although the increased gap junction coupling is cAMP-dependent, neither the protein kinase A nor the exchange protein directly activated by cAMP were involved in this increase. We found that cAMP activates cyclic nucleotide-gated (CNG) channels and thereby induces a Ca²⁺ influx, which leads to the increase in gap junction coupling. The report identifies CNG channels as a possible physiological link between adenosine receptors and the regulation of gap junction channels in endothelial cells of the blood-brain barrier.

ABSTRACT

The human cerebral microvascular endothelial cell line hCMEC/D3 was used to characterize the physiological link between adenosine receptors and the gap junction coupling in endothelial cells of the blood-brain barrier. Expressed adenosine receptor subtypes and connexin (Cx) isoforms were identified by RT-PCR. Scrape loading/dye transfer was used to evaluate the impact of the A_2A and A_2B adenosine receptor subtype agonist 2-phenylaminoadenosine (2-PAA) on the gap junction coupling. We found that 2-PAA stimulated cAMP synthesis and enhanced gap junction coupling in a concentration-dependent manner. This enhancement was accompanied by an increase in gap junction plaques formed by Cx43. Inhibition of protein kinase A did not affect the 2-PAA-related enhancement of gap junction coupling. In contrast, the cyclic nucleotide-gated (CNG) channel inhibitor l-cis-diltiazem, as well as the chelation of intracellular Ca²⁺ with BAPTA, or the absence of external Ca²⁺ , suppressed the 2-PAA-related enhancement of gap junction coupling. Moreover, we observed a 2-PAA-dependent activation of CNG channels by a combination of electrophysiology and pharmacology. In conclusion, the stimulation of adenosine receptors in hCMEC/D3 cells induces a Ca²⁺ influx by opening CNG channels in a cAMP-dependent manner. Ca²⁺ in turn induces the formation of new gap junction plaques and a consecutive sustained enhancement of gap junction coupling. The report identifies CNG channels as a physiological link that integrates gap junction coupling into the adenosine receptor-dependent signalling of endothelial cells of the blood-brain barrier.

Toward a broader understanding of aldosterone in congestive heart failure

Discovered some 50 years ago, aldosterone (ALDO) has come to be recognised as a mineralocorticoid hormone with well-known endocrine properties in epithelial cells that contribute to the pathophysiology of congestive heart failure. This includes Na + resorption at the expense of K+ excretion in classic target tissues: kidneys, colon, sweat and salivary glands. Though less well known, Mg2+ excretion is likewise enhanced by ALDO, while adrenal ALDO secretion is regulated by extracellular Mg2+ ([Mg2+ ]o). An emerging body of information has and continues to identify other endocrine actions of ALDO receptor-ligand binding. They include: promoting an efflux of cytosolic free Mg2+, or [Mg2+]i, in exchange for Na+ in such non-epithelial cells as peripheral blood mononuclear cells; its influence on endothelial cell function; and its central actions that involve regulation of cerebrospinal fluid composition produced by epithelial cells of the choroid plexus, activity of the hypothalamic paraventricular nucleus involved in Na+ appetite, Na+ and H2O excretion and sympathetic nerve activity, and the regulation of TNF-α production from central and/or peripheral sources. Extra-adrenal steroidogenesi and auto/paracrine properties of ALDO generated de novo in the cardiovasculature are now under investigation and preliminary findings suggest they contribute to tissue repair. The past decade has witnessed a revival of interest in this steroid molecule. In years to come, an even broader understanding of ALDO's contribution to the pathophysiology of congestive heart failure will undoubtedly emerge.

Peptide-stimulated angiogenesis: Role of lung endothelial caveolar signaling and nitric oxide

Endothelial nitric oxide (NO) synthase (eNOS)-derived NO plays a critical role in the modulation of angiogenesis in the pulmonary vasculature. We recently reported that an eleven amino acid (SSWRRKRKESS) cell penetrating synthetic peptide (P1) activates caveolar signaling, caveloae/eNOS dissociation, and enhance NO production in lung endothelial cells (EC). This study examines whether P1 promote angiogenesis via modulation of caveolar signaling and the level of NO generation in EC and pulmonary artery (PA) segments. P1-enhanced tube formation and cell sprouting were abolished by caveolae disruptor Filipin (FIL) in EC and PA, respectively. P1 enhanced eNOS activity and angiogenesis were attenuated by inhibition of eNOS as well as PLCγ-1, PKC-α but not PI3K-mediated caveolar signaling in intact EC and/or PA. P1 failed to enhance the catalytic activity of eNOS and angiogenesis in caveolae disrupted EC by FIL. Lower (0.01 mM) concentration of NOC-18 enhanced angiogenesis without inhibition of eNOS activity whereas higher concentration of NOC-18 (1.0 mM) inhibited eNOS activity and angiogenesis in EC. Inhibition of eNOS by l-NAME in the presence of P1 resulted in near total loss of tube formation in EC. Although P1 enhanced angiogenesis mimicked only by lower concentrations of NO generated by NOC-18, this response is independent of caveolar signaling/integrity. These results suggest that P1-enhanced angiogenesis is regulated by dynamic process involving caveolar signaling-mediated increased eNOS/NO activity or by the direct exposure to NOC-18 generating only physiologic range of NO independent of caveolae in lung EC and PA segments.

Calcium signalling in pericytes

Recent advances in pericyte research have contributed to our understanding of the physiology and pathophysiology of microvessels. The microvasculature consists of arteriolar and venular networks located upstream and downstream of the capillaries. Arterioles are surrounded by a monolayer of spindle-shaped myocytes, while terminal branches of precapillary arterioles, capillaries and all sections of postcapillary venules are encircled by a monolayer of morphologically diverse pericytes. There are physiological differences in the response of pericytes and myocytes to vasoactive molecules, suggesting that these two vascular cell types could have different functional roles in the regulation of local blood flow. The contractile activity of pericytes and myocytes is controlled by changes of cytosolic free Ca(2+) concentration. In this short review, we summarize our results and those of other authors on the contractility of pericytes and their Ca(2+) signalling. We describe results regarding sources of Ca(2+) and mechanisms of Ca(2+) release and Ca(2+) entry in control of the spatiotemporal characteristics of the Ca(2+) signals in pericytes.

Nitric oxide-mediated protein modification in cardiovascular physiology and pathology

Nitric oxide (NO) is a key regulator of cardiovascular functions including the control of vascular tone, anti-inflammatory properties of the endothelium, cardiac contractility, and thrombocyte activation and aggregation. Numerous experimental data support the view that NO not only acts via cyclic guanosine monophosphate (cGMP)-dependent mechanisms but also modulates protein function by nitrosation, nitrosylation, glutathiolation, and nitration, respectively. To understand how NO regulates all of these diverse biological processes on the molecular level a comprehensive assessment of NO-mediated cGMP-dependent and independent targets is required. Novel proteomic approaches allow the simultaneous identification of large quantities of proteins modified in an NO-dependent manner and thereby will considerably deepen our understanding of the role NO plays in cardiovascular physiology and pathophysiology.

Hypoxia-induced endothelial CX3CL1 triggers lung smooth muscle cell phenotypic switching and proliferative expansion

Distal arterioles with limited smooth muscles help maintain the high blood flow and low pressure in the lung circulation. Chronic hypoxia induces lung distal vessel muscularization. However, the molecular events that trigger alveolar hypoxia-induced peripheral endothelium modulation of vessel wall smooth muscle cell (SMC) proliferation and filling of nonmuscular areas are unclear. Here, we investigated the role of CX3CL1/CX3CR1 system in endothelial-SMC cross talk in response to hypoxia. Human lung microvascular endothelial cells responded to alveolar oxygen deficiency by overproduction of the chemokine CX3CL1. The CX3CL1 receptor CX3CR1 is expressed by SMCs that are adjacent to the distal endothelium. Hypoxic release of endothelial CX3CL1 induced SMC phenotypic switching from the contractile to the proliferative state. Inhibition of CX3CR1 prevented CX3CL1 stimulation of SMC proliferation and monolayer expansion. Furthermore, CX3CR1 deficiency attenuated spiral muscle expansion, distal vessel muscularization, and pressure elevation in response to hypoxia. Our findings indicate that the capillary endothelium relies on the CX3CL1-CX3CR1 axis to sense alveolar hypoxia and promote peripheral vessel muscularization. These results have clinical significance in the development of novel therapeutics that target mechanisms of distal arterial remodeling associated with pulmonary hypertension induced by oxygen deficiency that is present in people living at high altitudes and patients with obstructive lung diseases.

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.

Expression of olfactory-type cyclic nucleotide-gated channels in rat cortical astrocytes

Cyclic nucleotide-gated (CNG) channels are nonselective cation channels activated by cyclic AMP (cAMP) or cyclic GMP (cGMP). They were originally identified in retinal and olfactory receptors, but evidence has also emerged for their expression in several mammalian brain areas. Because cGMP and cAMP control important aspects of glial cell physiology, we wondered whether CNG channels are expressed in astrocytes, the most functionally relevant glial cells in the CNS. Immunoblot and immunofluorescence experiments demonstrated expression of the CNG channel olfactory-type A subunit, CNGA2, in cultured rat cortical astrocytes. In patch-clamp experiments, currents elicited in these cells by voltage ramps from -100 to +100 mV in the presence of the cGMP analogue, dB-cGMP, were significantly reduced by the CNG channel blockers, L-cis-diltiazem (LCD) and Cd(2+) . The reversal potentials of the LCD- and Cd(2+) -sensitive currents were more positive than that of K(+) , as expected for a mixed cation current. Noninactivating, voltage-independent currents were also elicited by extracellular application of the membrane permeant cGMP analogue, 8-Br-cGMP. These effects were blocked by LCD and were mimicked by natriuretic peptide receptor activation and inhibition of phosphodiesterase activity. Voltage-independent, LCD-sensitive currents were also elicited by 8-Br-cGMP in astrocytes of hippocampal and neocortical brain slices. Immunohistochemistry confirmed a broad distribution of CNG channels in astrocytes of the rat forebrain, midbrain, and hindbrain. These findings suggest that CNG channels are downstream targets of cyclic nucleotides in astrocytes, and they may be involved in the glial-mediated regulation of CNS functions under physiological and pathological conditions.

Role of reactive oxygen species and redox in regulating the function of transient receptor potential channels

Cellular redox status, regulated by production of reactive oxygen species (ROS), greatly contributes to the regulation of vascular smooth muscle cell contraction, migration, proliferation, and apoptosis by modulating the function of transient receptor potential (TRP) channels in the plasma membrane. ROS functionally interact with the channel protein via oxidizing the redox-sensitive residues, whereas nitric oxide (NO) regulates TRP channel function by cyclic GMP/protein kinase G-dependent and -independent pathways. Based on the structural differences among different TRP isoforms, the effects of ROS and NO are also different. In addition to regulating TRP channels in the plasma membrane, ROS and NO also modulate Ca(2+) release channels (e.g., IP(3) and ryanodine receptors) on the sarcoplasmic/endoplasmic reticulum membrane. This review aims at briefly describing (a) the role of TRP channels in receptor-operated and store-operated Ca(2+) entry, and (b) the role of ROS and redox status in regulating the function and structure of TRP channels.

Cellular magnesium homeostasis

Magnesium, the second most abundant cellular cation after potassium, is essential to regulate numerous cellular functions and enzymes, including ion channels, metabolic cycles, and signaling pathways, as attested by more than 1000 entries in the literature. Despite significant recent progress, however, our understanding of how cells regulate Mg(2+) homeostasis and transport still remains incomplete. For example, the occurrence of major fluxes of Mg(2+) in either direction across the plasma membrane of mammalian cells following metabolic or hormonal stimuli has been extensively documented. Yet, the mechanisms ultimately responsible for magnesium extrusion across the cell membrane have not been cloned. Even less is known about the regulation in cellular organelles. The present review is aimed at providing the reader with a comprehensive and up-to-date understanding of the mechanisms enacted by eukaryotic cells to regulate cellular Mg(2+) homeostasis and how these mechanisms are altered under specific pathological conditions.

Cyclic nucleotide-gated channels: a familiar channel family with a new function?

The cyclic nucleotide-gated (CNG) channel is a family of nonselective cation channels that open in response to an elevated cyclic nucleotide level. Cyclic nucleotides, particularly cAMP and cGMP, govern a great diversity of cellular functions. While the pivotal roles of CNG channels in the visual and olfactory systems have been well established in the past decade, relatively few studies were performed regarding the functional roles of CNG channels in non-neuronal systems. Cyclic nucleotides and Ca2+ are key signaling molecules in cardiovascular systems. Given that CNG channels are expressed in vascular tissues, several recent studies have explored the possible functional role of CNG channels in cardiovascular systems. This article intends to summarize some recent developments regarding the expression and functional role of CNG channels in the cardiovascular system.

Introduction to TRP channels: structure, function, and regulation

Transient receptor potential or TRP families of ion channels demonstrate great diversity in activation and inhibition, and they are diverse in selectivity of ion conductance. TRP ion channels function as signal integrators through their ion conductance properties, and in some cases kinase activity. They mediate processes such as vision, taste, olfaction, hearing, touch, and thermo- and osmosensation. TRP cation channels function by mediating the flux of Na(+) and Ca(2+) across the plasma membrane and into the cytoplasm. The influx of cations into the cytoplasm depolarizes cells and is necessary for action potentials in excitable cells such as neurons. In non-excitable cells, membrane depolarization by TRP ) and-channels stimulates voltage- dependent channels (Ca(2+), K(+), Cl(-) influences many cellular events, such as transcription, translation, contraction, and migration. TRP channels are important in human physiology, and mutations in TRP genes are associated with at least four diseases. Furthermore, altered expression, function, and/or regulation of TRP channels have been implicated in diseases such as pulmonary hypertension.

Store-operated calcium entry channels in pulmonary endothelium: the emerging story of TRPCS and Orai1

Cells of diverse origin utilize shifts in cytosolic calcium concentrations as intracellular signals to elicit physiological responses. In endothelium, inflammatory first messengers increase cytosolic calcium as a signal to disrupt cell-cell borders and produce inter-cellular gaps. Calcium influx across the plasma membrane is required to initiate barrier disruption, although the calcium entry mechanism responsible for this effect remains poorly understood. This chapter highlights recent efforts to define the molecular anatomy of the ion channel responsible for triggering endothelial cell gap formation. Resolving the identity and function of this calcium channel will pave the way for new anti-inflammatory therapeutic targets.

Impact of matrine on inflammation related factors in rat intestinal microvascular endothelial cells

ETHNOPHARMACOLOGICAL RELEVANCE

Matrine (MT) is a main active ingredient of Sophora flavescens roots, which is used in Traditional Chinese Medicine (TCM) for the treatment of inflammations like enteritis, hepatitis and atopic dermatitis.

AIMS OF THE STUDY

Aim of the study is to gain insight into the effects of MT on nitric oxide (NO) release, intracellular NO production, and endothelial nitric oxide synthase (eNOS) level in second generation rat intestinal microvascular endothelial cells (RIMECs). Moreover, the effects of MT on soluble intercellular adhesion molecule-1 (sICAM-1), interleukin-6 (IL-6) and interleukin-8 (IL-8) production induced by lipopolysaccharide (LPS) in these cells were evaluated.

MATERIAL AND METHODS

Isolated and identified RIMECs cultures were exposed to different concentrations of matrine, and changes in extra- and intracellular NO concentrations were measured in dependance of time by Griess reaction or DAF-FM diacetate. Obtained cell cultures were solitude treated with lypopolysaccharide (LPS) or combined with MT to observe impacts on sICAM-1, IL-6 and IL-8 concentration in culture supernatants by ELISA.

RESULTS

Matrine dose-dependently increased the concentration of NO in culture supernatant of RIMECs. Exposure of MT resulted in a steady intracellular NO increase pattern under different concentrations with different values and has an increasing effect on eNOS concentration at a long time exposure. Additionally, matrine reduced the increasing effect of LPS on the production of IL-6, IL-8, and sICAM-1 in RIMECs.

CONCLUSION

These results show that matrine may serve as a protective agent against tissue damage in inflammation by improving NO-dependent vasomotion and inhibiting inflammatory cytokines induced by LPS.

A Role for Erythropoietin in the Attenuation of Radiocontrast-Induced Acute Renal Failure in Rats

BACKGROUND

Radiocontrast-induced nephropathy (CIN) remains an important iatrogenic cause of acute renal failure in high-risk patients, despite the development of safer contrast media, the improvement of hydration protocols, and the introduction of additional preventive strategies. Erythropoietin (EPO) pretreatment may confer protection against acute renal failure through the induction of stress response genes.

METHODS

The effect of EPO has been evaluated in a rat model of CIN, induced by iothalamate, following the inhibition of nitric oxide- and prostaglandin-synthesis with indomethacin and N(omega) nitro-L-arginine methyl ester (L-NAME). Twenty-two male Sprague-Dawley rats were subjected to saline (CTR) or EPO injections (3000 U/kg and 600 U/kg, 24 and 2 h before the induction of CIN, respectively).

RESULTS

The decline in creatinine clearance in CTR animals from 0.38 +/- 0.03 to 0.28 +/- 0.03 mL/min/100 g (p < 0.005), was prevented by EPO pretreatment (from 0.34 +/- 0.02 to 0.32 +/- 0.03 mL/min/100 g, NS). The extent of medullary thick ascending limb- and S3-tubular damage in the outer medulla, however, was comparable in the two experimental groups.

CONCLUSIONS

EPO pretreatment prevents renal dysfunction in a rat model of CIN. Further experimental and clinical studies are required to confirm these preliminary conclusions regarding a potential protective potency of EPO against CIN.

Role of cyclic nucleotides in the control of cytosolic Ca2+ levels in vascular endothelial cells

1. Endothelial cells have a key role in the cardiovascular system. Most endothelial cell functions depend on changes in cytosolic Ca(2+) concentrations ([Ca(2+)](i)) to some extent and Ca2+ signalling acts to link external stimuli with the synthesis and release of regulatory factors in endothelial cells. The [Ca(2+)](i) is maintained by a well-balanced Ca(2+) flux across the endoplasmic reticulum and plasma membrane. 2. Cyclic nucleotides, such as cAMP and cGMP, are very important second messengers. The cyclic nucleotides can affect [Ca(2+)](i) directly or indirectly (via the actions of protein kinase (PK) A or PKG-mediated phosphorylation) by regulating Ca(2+) mobilization and Ca(2+) influx. Fine-tuning of [Ca(2+)](i) is also fundamental to protect endothelial cells against damaged caused by the excessive accumulation of Ca(2+). 3. Therapeutic agents that control cAMP and cGMP levels have been used to treat various cardiovascular diseases. 4. The aim of the present review is to discuss: (i) the functions of endothelial cells; (ii) the importance of [Ca(2+)](i) in endothelial cells; (iii) the impact of excessive [Ca(2+)](i) in endothelial cells; and (iv) the balanced control of [Ca(2+)](i) in endothelial cells via involvement of cyclic nucleotides (cAMP and cGMP) and their general effectors.

cGMP in the vasculature

Cyclic guanosine 3', 5'-monophosphate (cGMP) plays an integral role in the control of vascular function. Generated from guanylate cyclases in response to the endogenous ligands, nitric oxide (NO) and natriuretic peptides (NPs), cGMP influences a number of vascular cell types and regulates vasomotor tone, endothelial permeability, cell growth and differentiation, as well as platelet and blood cell interactions. Reciprocal regulation of the NO-cGMP and NP-cGMP pathways is evident in the vasculature such that one cGMP generating system may compensate for the dysfunction of the other. Indeed, aberrant cGMP production and/or signalling accompanies many vascular disorders such as hypertension, atherosclerosis, coronary artery disease and diabetic complications. This chapter highlights the main vascular functions of cGMP, its role in disease and the resulting current and potential therapeutic applications. With respect to pulmonary hypertension, heart failure and erectile dysfunction, as well as cGMP signal transduction, the reader is specifically referred to other dedicated chapters.

Organic anion transporter OAT1 undergoes constitutive and protein kinase C-regulated trafficking through a dynamin- and clathrin-dependent pathway

Organic anion transporter 1 (OAT1) mediates the body disposition of a diverse array of environmental toxins and clinically important drugs. Therefore, understanding the regulation of this transporter has profound clinical significance. We previously demonstrate that OAT1 activity was down-regulated by activation of protein kinase C (PKC), kinetically revealed as a decrease in the maximum transport velocity V(max) without significant change in the substrate affinity K(m) of the transporter. In the current study, we showed that OAT1 constitutively internalized from and recycled back to the plasma membrane, and PKC activation accelerated OAT1 internalization without affecting OAT1 recycling. We further showed that treatment of OAT1-expressing cells with concanavalin A, depletion of K(+) from the cells, or transfection of dominant negative mutants of dynamin-2 or Eps15 into the cells, all of which block the clathrin-dependent endocytotic pathway, significantly blocked constitutive and PKC-regulated OAT1 internalization. We finally showed that OAT1 colocalized with transferrin, a marker for clathrin-dependent endocytosis, at the cell surface and in the EEA1-positive early endosomes. Together, our findings demonstrated for the first time that (i) OAT1 constitutively traffics between plasma membrane and recycling endosomes, (ii) PKC activation down-regulates OAT1 activity by altering already existent OAT1 trafficking, and (iii) OAT1 internalization occurs partly through a dynamin- and clathrin-dependent pathway.

Epinephrine-induced Ca2+ influx in vascular endothelial cells is mediated by CNGA2 channels

Epinephrine, through its action on beta-adrenoceptors, may induce endothelium-dependent vascular dilation, and this action is partly mediated by a cytosolic Ca(2+) ([Ca(2+)](i)) change in endothelial cells. In the present study, we explored the molecular identity of the channels that mediate epinephrine-induced endothelial Ca(2+) influx and subsequent vascular relaxation. Patch clamp recorded an epinephrine- and cAMP-activated cation current in the primary cultured bovine aortic endothelial cells (BAECs) and H5V endothelial cells. L-cis-diltiazem and LY-83583, two selective inhibitors for cyclic nucleotide-gated channels, diminished this cation current. Furthermore, this cation current was greatly reduced by a CNGA2-specific siRNA in H5V cells. With the use of fluorescent Ca(2+) dye, it was found that epinephrine and isoprenaline, a beta-adrenoceptor agonist, induced endothelial Ca(2+) influx in the presence of bradykinin. This Ca(2+) influx was inhibited by L-cis-diltiazem and LY-83583, and by a beta(2)-adrenoceptor antagonist ICI-118551. CNGA2-specific siRNA also diminished this Ca(2+) influx in H5V cells. Furthermore, L-cis-diltiazem and LY-83583 inhibited the endothelial Ca(2+) influx in isolated mouse aortic strips. L-cis-diltiazem also markedly reduced the endothelium-dependent vascular dilation to isoprenaline in isolated mouse aortic segments. In summary, CNG channels, CNGA2 in particular, mediate beta-adrenoceptor agonist-induced endothelial Ca(2+) influx and subsequent vascular dilation.

CNGA2 channels mediate adenosine-induced Ca2+ influx in vascular endothelial cells

OBJECTIVE

Adenosine is a cAMP-elevating vasodilator that induces both endothelium-dependent and -independent vasorelaxation. An increase in cytosolic Ca(2+) ([Ca(2+)](i)) is a crucial early signal in the endothelium-dependent relaxation elicited by adenosine. This study explored the molecular identity of channels that mediate adenosine-induced Ca(2+) influx in vascular endothelial cells.

METHODS AND RESULTS

Adenosine-induced Ca(2+) influx was markedly reduced by L-cis-diltiazem and LY-83583, two selective inhibitors for cyclic nucleotide-gated (CNG) channels, in H5V endothelial cells and primary cultured bovine aortic endothelial cells (BAECs). The Ca(2+) influx was also inhibited by 2 adenylyl cyclase inhibitors MDL-12330A and SQ-22536, and by 2 A(2B) receptor inhibitors MRS-1754 and 8-SPT, but not by an A(2A) receptor inhibitor SCH-58261 or a guanylyl cyclase inhibitor ODQ. Patch clamp experiments recorded an adenosine-induced current that could be inhibited by L-cis-diltiazem and LY-83583. A CNGA2-specific siRNA markedly decreased the Ca(2+) influx and the cation current in H5V cells. Furthermore, L-cis-diltiazem inhibited the endothelial Ca(2+) influx in mouse aortic strips, and it also reduced 5-N-ethylcarboxamidoadenosine (NECA, an A(2) adenosine receptor agonist)-induced vasorelaxation.

CONCLUSIONS

CNGA2 channels play a key role in adenosine-induced endothelial Ca(2+) influx and vasorelaxation. It is likely that adenosine acts through A(2B) receptors and adenylyl cyclases to stimulate CNGA2.

Disturbance of the Ca(2+)/calmodulin-dependent signalling pathway is responsible for the resistance of Arabidopsis dnd1 against Pectobacterium carotovorum infection

SUMMARY Arabidopsis thaliana wild-type Col-0 and its mutant, 'defence, no death' (dnd) 1-1, were infected with biotrophic Pseudomonas syringae pv. tomato strain DC3000 and necrotrophic Pectobacterium carotovorum strain KACC 10228, and cellular and molecular responses among them were then analysed. Col-0 wild-type was susceptible to both pathogens. By contrast, neither DC3000 nor KACC 10228 infected dnd1-1 (Yu et al., 1998. Proc. Natl. Acad. Sci. USA 95: 7819-7824). Neither of the pathogens triggered cell death or accumulation of active oxygen species in dnd1-1. KACC 10228 induced accelerated transcriptions of PDF1.2 and AtEBP genes in wild-type Col-0, while DC3000-induced transcriptions of them were relatively retarded. Neither of the pathogens modified the constitutive transcription of PR1 in dnd1-1. PDF1.2 and AtEBP transcriptions were not induced by the same treatments. Hydrogen peroxide scavengers, catalase and ascorbic acid, and LaCl(3), an inhibitor of Ca(2+) influx, diminished cell death and protected the wild-type plant from KACC 10228 infection, while EGTA inhibited cell death and pathogen growth. Exogenous Ca(2+) nullified resistance against KACC 10228 challenge in dnd1-1. W-7 and chloropromazine, two calmodulin antagonists, also triggered cell death in dnd1-1 and abolished resistance against KACC 10228. In summary, cell death is correlated with KACC 10228 infection and disease development. Furthermore, the resistance of dnd1-1 against P. carotovorum is dependent on calmodulin and inhibition of cytosolic Ca(2+) increment.

Reduced store-operated Ca2+ entry in pulmonary endothelial cells from chronically hypoxic rats

Chronic hypoxia (CH)-induced pulmonary hypertension may influence basal endothelial cell (EC) intracellular Ca(2+) concentration ([Ca(2+)](i)). We hypothesized that CH decreases EC [Ca(2+)](i) associated with membrane depolarization and reduced Ca(2+) entry. To test this hypothesis, we assessed 1) basal endothelial Ca(2+) in pressurized pulmonary arteries and freshly isolated ECs, 2) EC membrane potential (E(m)), 3) store-operated Ca(2+) current (I(SOC)), and 4) store-operated Ca(2+) (SOC) entry in arteries from control and CH rats. We found that basal EC Ca(2+) was significantly lower in pressurized pulmonary arteries and freshly isolated ECs from CH rats compared with controls. Similarly, ECs in intact arteries from CH rats were depolarized compared with controls, although no differences were observed between groups in isolated cells. I(SOC) activation by 1 muM thapsigargin displayed diminished inward current and a reversal potential closer to 0 mV in cells from CH rats compared with controls. In addition, SOC entry determined by fura 2 fluorescence and Mn(2+) quenching revealed a parallel reduction in Ca(2+) entry following CH. We conclude that differences in the magnitude of SOC entry exist between freshly dispersed ECs from CH and control rats and correlates with the decrease in basal EC [Ca(2+)](i). In contrast, basal EC Ca(2+) influx is unaffected and membrane depolarization is limited to intact arteries, suggesting that E(m) may not play a major role in determining basal EC [Ca(2+)](i) following CH.

Diurnal regulation of microsomal triglyceride transfer protein and plasma lipid levels

Plasma lipids are maintained within a narrow physiologic range and exhibit circadian rhythmicity. Plasma triglyceride and cholesterol levels were high in the night due to changes in apolipoprotein B-lipoproteins in ad libitum fed rats and mice maintained in a 12-h photoperiod. Absorption of [(3)H]triolein or [(3)H]cholesterol was higher at 2400 h than at 1200 h, indicating that intestinal lipoprotein production shows diurnal variation. Moreover, intestinal microsomal triglyceride transfer protein (MTP) activity, protein, mRNA, and gene transcription showed diurnal variations and were high at 2400 h. Similar to the small intestine, hepatic MTP activity, protein, and mRNA levels also changed significantly within a day. MTP was induced in fasted animals soon after refeeding. When mice were subjected to restricted feeding, MTP expression was high at the expected time of food availability. In contrast, extended exposures to light and dark completely abolished rhythmicity in MTP expression and plasma lipid levels. These studies show that MTP expression and plasma lipid undergo diurnal regulation and exhibit peaks and nadirs at similar times and suggest that diurnal modulation of MTP is a major determinant of daily changes in plasma lipids. Furthermore, environmental factors, such as food and light, play an important role in MTP regulation.

Nitric oxide upregulation of caspase-8 mRNA expression in lung endothelial cells: role of JAK2/STAT-1 signaling

We recently reported that nitric oxide (NO) modulates expression of multiple genes associated with apoptotic pathways, including expression of caspase-8. The objective of the present study is to determine whether the NO-induced expression of the caspase-8 gene is regulated via signal transducers and activators of transcription-1 (STAT-1) signaling. The confluent monolayers of pulmonary artery endothelial cells (PAEC) were incubated with or without (control) 1 mM NOC-18, a NO donor, at 37 degrees C for 0-24 h. In some experiments PAEC were pretreated with a Janus kinase (JAK-2) inhibitor, AG490 (20 microM). Exposure of PAEC to NO-increased relative levels of caspase-8 mRNA as determined using quantitative real time PCR. Relative levels of phosphorylated STAT-1 at Serine (Ser)-727, but not total STAT-1 expression in NO-exposed cells, were upregulated significantly compared to control cells. AG490 attenuated NO-induced phosphorylation of STAT-1 at Ser 727 and expression of caspase-8 mRNA, suggesting JAK2 plays a role in the induction of caspase-8 mRNA. The promoter of caspase-8 has four gamma-activated sequence (GAS) and two interferon-stimulated response element (ISRE) transcription factor-binding sites. NO enhanced the STAT-1 binding activity to GAS/ISRE. Suppression of STAT-1 expression attenuated NO-induced elevation of caspase-8 mRNA. These studies demonstrate that a NO-dependent increase in caspase-8 mRNA levels is associated with phosphorylation of STAT-1 at Ser-727 and STAT1 binding to the caspase-8 promoter in cultured PAEC.

TRPC1 Ca(2+)-permeable channels in animal cells

The full-length transient receptor (TRPC)1 polypeptide is composed of about 790 amino acids, and several splice variants are known. The predicted structure and topology is of an integral membrane protein composed of six transmembrane domains, and a cytoplasmic C- and N-terminal domain. The N-terminal domain includes three ankyrin repeat motifs. Antibodies which recognise TRPC1 have been developed, but it has been difficult to obtain antibodies which have high affinity and specificity for TRPC1. This has made studies of the cellular functions of TRPC1 somewhat difficult. The TRPC1 protein is widely expressed in different types of animal cells, and within a given cell is found at the plasma membrane and at intracellular sites. TRPC1 interacts with calmodulin, caveolin-1, the InsP3 receptor, Homer, phospholipase C and several other proteins. Investigations of the biological roles and mechanisms of action of TRPC1 have employed ectopic (over-expression or heterologous expression) of the polypeptide in addition to studies of endogenous TRPC1. Both approaches have encountered difficulties. TRPC1 forms heterotetramers with other TRPC polypeptides resulting in cation channels which are non-selective. TRPC1 may be: a component of the pore of store-operated Ca2+ channels (SOCs); a subsidiary protein in the pathway of activation of SOCs; activated by interaction with InsP3R; and/or activated by stretch. Further experiments are required to resolve the exact roles and mechanisms of activation of TRPC1. Cation entry through the TRPC1 channel is feed-back inhibited by Ca2+ through interaction with calmodulin, and is inhibited by Gd3+, La3+, SKF96365 and 2-APB, and by antibodies targeted to the external mouth of the TRPC1 pore. Activation of TRPC1 leads to the entry to the cytoplasmic space of substantial amounts of Na+ as well as Ca2+. A requirement for TRPC1 is implicated in numerous downstream cellular pathways. The most clearly described roles are in the regulation of growth cone turning in neurons. It is concluded that TRPC1 is a most interesting protein because of the apparent wide variety of its roles and functions and the challenges posed to those attempting to elucidate its primary intracellular functions and mechanisms of action.

Mitogen-activated Protein Kinase Kinase-4 Promotes Cell Survival by Decreasing PTEN Expression through an NFκB-dependent Pathway

Mitogen-activated protein kinase kinase-4 (MKK4/SEK1) cooperates with phosphatidylinositol 3-kinase to maintain the survival of non-small cell lung cancer (NSCLC) cells, but the biochemical basis of this phenomenon has not been elucidated. Here we used genetic approaches to modulate MKK4 expression in mouse embryo fibroblasts (MEF cells) and NSCLC cells to identify prosurvival signals downstream of MKK4. Relative to wild-type MEF cells, MKK4-null MEF cells were highly susceptible to apoptosis by LY294002, paclitaxel, or serum starvation. MKK4 promoted the survival of MEF cells by decreasing the expression of phosphatase and tensin homologue deleted from chromosome 10 (PTEN). MKK4 inhibited PTEN transcription by activating NFkappaB, a transcriptional suppressor of PTEN. MKK4 was required for nuclear translocation of RelA/p65 and processing of the NFkappaB2 precursor (p100) into the mature form (p52). Studies on a panel of NSCLC cell lines revealed a subset with high MKK4/high NFkappaB/low PTEN that was relatively resistant to apoptosis. Thus, MKK4 promotes cell survival by activating phosphatidylinositol 3-kinase through an NFkappaB/PTEN-dependent pathway.

The pro-inflammatory cytokines, IL-1beta and TNF-alpha, inhibit intestinal alkaline phosphatase gene expression

High levels of the pro-inflammatory cytokines, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), are present in the gut mucosa of patients suffering form various diseases, most notably inflammatory bowel diseases (IBD). Since the inflammatory milieu can cause important alterations in epithelial cell function, we examined the cytokine effects on the expression of the enterocyte differentiation marker, intestinal alkaline phosphatase (IAP), a protein that detoxifies bacterial lipopolysaccharides (LPS) and limits fat absorption. Sodium butyrate (NaBu), a short-chain fatty acid and histone deacetylase (HDAC) inhibitor, was used to induce IAP expression in HT-29 cells and the cells were also treated +/- the cytokines. Northern blots confirmed IAP induction by NaBu, however, pretreatment (6 h) with either cytokine showed a dose-dependent inhibition of IAP expression. IAP Western analyses and alkaline phosphatase enzyme assays corroborated the Northern data and confirmed that the cytokines inhibit IAP induction. Transient transfections with a reporter plasmid carrying the human IAP promoter showed significant inhibition of NaBu-induced IAP gene activation by the cytokines (100 and 60% inhibition with IL-1beta and TNF-alpha, respectively). Western analyses showed that NaBu induced H4 and H3 histone acetylation, and pretreatment with IL-1beta or TNF-alpha did not change this global acetylation pattern. In contrast, chromatin immunoprecipitation showed that local histone acetylation of the IAP promoter region was specifically inhibited by either cytokine. We conclude that IL-1beta and TNF-alpha inhibit NaBu-induced IAP gene expression, likely by blocking the histone acetylation within its promoter. Cytokine-mediated IAP gene silencing may have important implications for gut epithelial function in the setting of intestinal inflammatory conditions.

Regulation of Calpain Activity in Rat Brain with Altered Ca2+ Homeostasis

Activation of calpain occurs as an early event in correlation with an increase in [Ca2+]i induced in rat brain upon treatment with a high salt diet for a prolonged period of time. The resulting sequential events have been monitored in the brain of normal and hypertensive rats of the Milan strain, diverging for a constitutive alteration in the level of [Ca2+]i found to be present in nerve cells of hypertensive animals. After 2 weeks of treatment, the levels of the plasma membrane Ca2+-ATPase and of native calpastatin are profoundly decreased. These degradative processes, more pronounced in the brain of hypertensive rats, are progressively and efficiently compensated in the brain of both rat strains by different incoming mechanisms. Along with calpastatin degradation, 15-kDa still-active inhibitory fragments are accumulated, capable of efficiently replacing the loss of native inhibitor molecules. A partial return to a more efficient control of Ca2+ homeostasis occurs in parallel, assured by an early increase in the expression of Ca2+-ATPase and of calpastatin, both producing, after 12 weeks of a high salt (sodium) diet, the restoration of almost original levels of the Ca2+ pump and of significant amounts of native inhibitor molecules. Thus, conservative calpastatin fragmentation, associated with an increased expression of Ca2+-ATPase and of the calpain natural inhibitor, has been demonstrated to occur in vivo in rat brain. This represents a sequential adaptive response capable of overcoming the effects of calpain activation induced by a moderate long term elevation of [Ca2+]i.

Renal oxygen delivery: matching delivery to metabolic demand

The kidneys are second only to the heart in terms of O2 consumption; however, relative to other organs, the kidneys receive a very high blood flow and oxygen extraction in the healthy kidney is low. Despite low arterial-venous O2 extraction, the kidneys are particularly susceptible to hypoxic injury and much interest surrounds the role of renal hypoxia in the development and progression of both acute and chronic renal disease. Numerous regulatory mechanisms have been identified that act to maintain renal parenchymal oxygenation within homeostatic limits in the in vivo kidney. However, the processes by which many of these mechanisms act to modulate renal oxygenation and the factors that influence these processes remain poorly understood. A number of such mechanisms specific to the kidney are reviewed herein, including the relationship between renal blood flow and O2 consumption, pre- and post-glomerular arterial-venous O2 shunting, tubulovascular cross-talk, the differential control of regional kidney blood flow and the tubuloglomerular feedback mechanism. The roles of these mechanisms in the control of renal oxygenation, as well as how dysfunction of these mechanisms may lead to renal hypoxia, are discussed.

Regulation of magnesium homeostasis and transport in mammalian cells

Magnesium is the second most abundant cation within the cell after potassium and plays an important role in numerous biological functions. Several pieces of experimental evidence indicate that mammalian cells tightly regulate Mg(2+) content by precise control mechanisms operating at the level of Mg(2+) entry and efflux across the cell membrane, as well as at the level of intracellular Mg(2+) buffering and organelle compartmentation under resting conditions and following hormonal stimuli. This review will attempt to elucidate the mechanisms involved in hormonal-mediated Mg(2+) extrusion and accumulation, as well as the physiological implications of changes in cellular Mg(2+) content following hormonal stimuli.

Dot1a-AF9 complex mediates histone H3 Lys-79 hypermethylation and repression of ENaCalpha in an aldosterone-sensitive manner

Aldosterone is a major regulator of epithelial Na(+) absorption and acts in large part through induction of the epithelial Na(+) channel (ENaC) gene in the renal collecting duct. We previously identified Dot1a as an aldosterone early repressed gene and a repressor of ENaCalpha transcription through mediating histone H3 Lys-79 methylation associated with the ENaCalpha promoter. Here, we report a novel aldosterone-signaling network involving AF9, Dot1a, and ENaCalpha. AF9 and Dot1a interact in vitro and in vivo as evidenced in multiple assays and colocalize in the nuclei of mIMCD3 renal collecting duct cells. Overexpression of AF9 results in hypermethylation of histone H3 Lys-79 at the endogenous ENaCalpha promoter at most, but not all subregions examined, repression of endogenous ENaCalpha mRNA expression and acts synergistically with Dot1a to inhibit ENaCalpha promoter-luciferase constructs. In contrast, RNA interference-mediated knockdown of AF9 causes the opposite effects. Chromatin immunoprecipitation assays reveal that overexpressed FLAG-AF9, endogenous AF9, and Dot1a are each associated with the ENaCalpha promoter. Aldosterone negatively regulates AF9 expression at both mRNA and protein levels. Thus, Dot1a-AF9 modulates histone H3 Lys-79 methylation at the ENaCalpha promoter and represses ENaCalpha transcription in an aldosterone-sensitive manner. This mechanism appears to be more broadly applicable to other aldosterone-regulated genes because overexpression of AF9 alone or in combination with Dot1a inhibited mRNA levels of three other known aldosterone-inducible genes in mIMCD3 cells.

Interaction between prostaglandin E2 and l-cis-diltiazem, a specific blocker of cyclic nucleotide gated channels in bovine aortic endothelial cells

Prostaglandins are known to transduce their signals via 7 transmembrane prostanoid receptors, which typically signal through coupling to G proteins and downstream second messenger molecules and protein kinase activation. Recently we have shown that cyclic nucleotides affect prostaglandins binding to bovine aortic endothelial cells independent of protein kinases. Here we show that incubation of bovine aortic endothelial cells with permeable analogs of cAMP or cGMP leads to a rapid and reversible reduction in PGE(2) binding to the cells. Since cyclic nucleotides are known modulators of cyclic nucleotide gated channels, we examined the effect of a specific cyclic nucleotide gated channel blocker l-cis-diltiazem on prostaglandin E(2) (PGE(2)) binding to bovine aortic endothelial cells. L-cis-diltiazem is shown to displace PGE(2) binding to bovine aortic endothelial cells in a dose dependent manner. In addition the effect of PGE(2) and l-cis-diltiazem on thapsigargin induced calcium elevation in the cells was compared. Both agents reduced in bovine aortic endothelial cells the thapsigargin induced calcium elevation by about half. PGE(2) also retarded the time course of the response to thapsigargin. Simultaneous treatment of the cells with both PGE(2) and l-cis-diltiazem did not yield an inhibitory effect beyond that observed with l-cis-diltiazem alone. Together our data point at the cyclic nucleotide gated channels as a feasible candidate for association with the PGE(2) binding site in bovine aortic endothelial cells.

An introduction to TRP channels

The aim of this review is to provide a basic framework for understanding the function of mammalian transient receptor potential (TRP) channels, particularly as they have been elucidated in heterologous expression systems. Mammalian TRP channel proteins form six-transmembrane (6-TM) cation-permeable channels that may be grouped into six subfamilies on the basis of amino acid sequence homology (TRPC, TRPV, TRPM, TRPA, TRPP, and TRPML). Selected functional properties of TRP channels from each subfamily are summarized in this review. Although a single defining characteristic of TRP channel function has not yet emerged, TRP channels may be generally described as calcium-permeable cation channels with polymodal activation properties. By integrating multiple concomitant stimuli and coupling their activity to downstream cellular signal amplification via calcium permeation and membrane depolarization, TRP channels appear well adapted to function in cellular sensation. Our review of recent literature implicating TRP channels in neuronal growth cone steering suggests that TRPs may function more widely in cellular guidance and chemotaxis. The TRP channel gene family and its nomenclature, the encoded proteins and alternatively spliced variants, and the rapidly expanding pharmacology of TRP channels are summarized in online supplemental material.

Atrial natriuretic peptide administered just prior to reperfusion limits infarction in rabbit hearts

We investigated whether atrial natriuretic peptide (ANP) given just prior to reperfusion reduces infarction in rabbit hearts and whether protection is related to activation of protein kinase G (PKG). Isolated rabbit hearts were subjected to a 30-min period of regional ischemia; treated hearts received a 20-min infusion of ANP (0.1 microM) starting 5 min before 2 h of reperfusion. ANP infusion decreased infarction from 31.5+/-2.4% of the risk zone in untreated hearts to 12.5+/-2.0% (P<0.001). To explore mechanisms of protection ischemic hearts were treated simultaneously with ANP and isatin, a blocker of the natriuretic peptide receptor, shortly before reperfusion. ANP's protective effect was aborted (36.8+/-2.9% infarction). There is no acceptable blocker of protein kinase G that can be used in intact organs. However, 8-(4-chlorophenylthio)-guanosine 3', 5'-cyclic monophosphate (10 microM), a cell-permeable cGMP analog that directly activates PKG, was infused from 5 min before to 15 min after reperfusion. The PKG activator mimicked ANP's protection with only 18.2+/-3.6% infarction (P<0.001). 5-Hydroxyde-canoate (5-HD), a putative mitochondrial KATP channel (mKATP) inhibitor, abrogated ANP's protection (34.4+/-2.6% infarction). Unexpectedly, 1H-[1,2,4]oxadiazole- [4,3-a]quinoxalin-1-one (ODQ), a blocker of soluble guanylyl cyclase also prevented ANP's infarct-sparing effect. It is unclear whether this observation implicated participation of soluble guanylyl cyclase in the mechanism or simply a lack of selectivity of ODQ. Finally the reperfusion injury salvage kinases (RISK), phosphatidylinositol 3-kinase and extracellular signal-regulated kinase, were implicated in ANP's mechanism since either wortmannin or PD98059 infused at reperfusion prevented ANP's infarct-sparing effect. ANP administered just prior to reperfusion protects hearts against infarction, likely by activation of PKG, opening of mKATP, and stimulation of downstream kinases.

Angiotensin IV enhances phosphorylation of 4EBP1 by multiple signaling events in lung endothelial cells

Angiotensin IV (Ang IV)-stimulated cell proliferation is regulated through activation of multiple signaling modules in lung endothelial cells (EC). Because eukaryotic intitiation factor 4E (eIF4E) binding protein 1 (4EBP1) plays a critical role in the RNA translation and the regulation of cell growth, we examined whether Ang IV modulates expression and/or phosphorylation of eIF4E and 4EBP1 as well as the role of multiple signaling events associated with 4EBP1 phosphorylation in EC. Ang IV stimulation increased phosphorylation but not expression of eIF4E and 4EBP1 proteins. Ang IV stimulation selectively phosphorylated Thr46 > Thr70 > Ser65 but not Thr37 residues in 4EBP1. Pretreatment of cells with PD-98059 and rapamycin, inhibitors of mitogen-activated protein kinase (ERK1/2) and mammalian target for rapamycin (mTOR), respectively, partially blocked Ang IV-mediated phosphorylation of 4EBP1. In contrast, overexpression of p70 ribosomal S6 kinase (p70S6K) and protein kinase B (Akt) enhanced phosphorylation of 4EBP1 and eIF4E binding affinity to the cap region of mRNA. These results support critical roles of multiple signaling and phosphorylation of 4EBP1 by Ang IV in translation process and protein synthesis.

Role of protein kinase G in barrier-protective effects of cGMP in human pulmonary artery endothelial cells

Increases in endothelial cGMP prevent oxidant-mediated endothelial barrier dysfunction, but the downstream mechanisms remain unclear. To determine the role of cGMP-dependent protein kinase (PKG)(I), human pulmonary artery endothelial cells (HPAEC) lacking PKG(I) expression were infected with a recombinant adenovirus encoding PKG(Ibeta) (Ad.PKG) and compared with uninfected and control-infected (Ad.betagal) HPAEC. Transendothelial electrical resistance (TER), an index of permeability, was measured after H(2)O(2) (250 microM) exposure with or without pretreatment with 8-(4-chlorophenylthio)guanosine 3',5'-cyclic monophosphate (CPT-cGMP). HPAEC infected with Ad.PKG, but not Ad.betagal, expressed PKG(I) protein and demonstrated Ser(239) and Ser(157) phosphorylation of vasodilator-stimulated phosphoprotein after treatment with CPT-cGMP. Adenoviral infection decreased basal permeability equally in Ad.PKG- and Ad.betagal-infected HPAEC compared with uninfected cells. Treatment with CPT-cGMP (100 microM) caused a PKG(I)-independent decrease in permeability (8.2 +/- 0.6%). In all three groups, H(2)O(2) (250 microM) caused a similar approximately 35% increase in permeability associated with increased actin stress fiber formation, intercellular gaps, loss of membrane VE-cadherin, and increased intracellular Ca(2+) concentration ([Ca(2+)](i)). In uninfected and Ad.betagal-infected HPAEC, pretreatment with CPT-cGMP (100 microM) partially blocked the increased permeability induced by H(2)O(2). In Ad.PKG-infected HPAEC, CPT-cGMP (50 microM) prevented the H(2)O(2)-induced TER decrease, cytoskeletal rearrangement, and loss of junctional VE-cadherin. CPT-cGMP attenuated the peak [Ca(2+)](i) caused by H(2)O(2) similarly (23%) in Ad.betagal- and Ad.PKG-infected HPAEC, indicating a PKG(I)-independent effect. These data suggest that cGMP decreased HPAEC basal permeability by a PKG(I)-independent process, whereas the ability of cGMP to prevent H(2)O(2)-induced barrier dysfunction was predominantly mediated by PKG(I) through a Ca(2+)-independent mechanism.

Efficacy of aldosterone receptor antagonism in heart failure: potential mechanisms

Results of the Randomized Aldactone Evaluation Study and the Eplerenone Post-acute Myocardial Infarction Heart Failure Efficacy and Survival Study indicate aldosterone receptor antagonism, together with angiotensin-converting enzyme inhibition and loop diuretics, is a most effective strategy in reducing risk for all-cause and cardiovascular-related mortality and morbidity in patients with symptomatic heart failure. Responsible mechanisms are likely multifactoral. As a circulating hormone, aldosterone has well-known endocrine properties that contribute to the pathophysiology of congestive heart failure. This includes Na+ resorption at the expense of K+ excretion in such tissues as kidneys, colon, sweat, and salivary glands. Mg2+ excretion at these sites is likewise enhanced by aldosterone, whereas adrenal aldosterone secretion is regulated by extracellular Mg2+. Other endocrine actions of aldosterone receptor-ligand binding include: a reduction in biologically active cytosolic-free Mg2+, with intracellular Ca2+ loading in nonepithelial cells such as peripheral blood mononuclear cells; its influence on endothelial cell function; and its central actions, including the choroid plexus, activity of the hypothalamic paraventricular nucleus, and autonomic nervous system. De novo generation of aldosterone within the cardiovasculature is recognized and findings suggest its auto/paracrine properties contribute to tissue repair. Each of these actions is interrupted by aldosterone receptor antagonism and therefore may contribute to its salutary response in heart failure.

Regulation of noncapacitative calcium entry by arachidonic acid and nitric oxide in endothelial cells

Several peptides, including vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF), activate the release of arachidonic acid (AA) and nitric oxide (NO) in endothelial cells (ECs). Both messengers are involved in EC proliferation and vascular permeability and control calcium homeostasis in different ways. Interestingly, it has been recently suggested that NO acts as a downstream mediator of AA-induced calcium entry in smooth muscle cells and isolated mouse parotid cells. In this paper, we have investigated the complex relationships that link intracellular calcium, AA, and NO in cultured endothelial cells. Using different experimental approaches, mainly simultaneous Ca2+ and NO fluorimetric confocal imaging, we provide evidence for a complex pathway leading to noncapacitative calcium entry (NCCE) in bovine aortic endothelial cells (BAECs). In particular, AA is able to induce NCCE through two different pathways: one dependent on eNOS recruitment and NO release, the other NO-independent. Finally, we show that NO increase is involved in the control of BAEC proliferation.

Fibroblast Growth Factor-1 Induces Heme Oxygenase-1 via Nuclear FactorErythroid 2-related Factor 2 (Nrf2) in Spinal Cord Astrocytes

Fibroblast growth factor-1 (FGF-1) is highly expressed in motor neurons and can be released in response to sublethal cell injury. Because FGF-1 potently activates astroglia and exerts a direct neuroprotection after spinal cord injury or axotomy, we examined whether it regulated the expression of inducible and cytoprotective heme oxygenase-1 (HO-1) enzyme in astrocytes. FGF-1 induced the expression of HO-1 in cultured rat spinal cord astrocytes, which was dependent on FGF receptor activation and prevented by cycloheximide. FGF-1 also induced Nrf2 mRNA and protein levels and prompted its nuclear translocation. HO-1 induction was abolished by transfection of astrocytes with a dominant-negative mutant Nrf2, indicating that FGF-1 regulates HO-1 expression through Nrf2. FGF-1 also modified the expression of other antioxidant genes regulated by Nrf2. Both Nrf2 and HO-1 levels were increased and co-localized with reactive astrocytes in the degenerating lumbar spinal cord of rats expressing the amyotrophic lateral sclerosis-linked SOD1 G93A mutation. Overexpression of Nrf2 in astrocytes increased survival of co-cultured embryonic motor neurons and prevented motor neuron apoptosis mediated by nerve growth factor through p75 neurotrophin receptor. Taken together, these results emphasize the key role of astrocytes in determining motor neuron fate in amyotrophic lateral sclerosis.

Effect of nicotine on the renal microcirculation in anesthetized rats: a potential for medullary hypoxic injury?

BACKGROUND

Cigarette smoking has been associated with accelerated renal dysfunction among patients with chronic renal disease. Conceivably, repeated parenchymal hypoxic injury, induced by nicotine-related vasomotor changes, might contribute to the progression of renal failure in smokers.

METHODS

Renal blood flow and selective cortical and outer medullary blood flows were determined in anesthetized rats. Changes in total renal, cortical and medullary vascular resistance were calculated. Nicotine was repeatedly infused at rising doses (50-200 microg/kg) to intact (CTR) animals and to rats chronically administered with nicotine in their drinking water (NIC). In a complementary study, nicotine-treated and control rats were subjected to medullary hypoxic stress, induced by radiocontrast and indomethacin.

RESULTS

Chronic nicotine exposure led to lower baseline renal blood flow and creatinine clearance. Nicotine infusion induced a transient dose-dependent rise in blood pressure, renal blood flow and cortical flow, with a corresponding decline in renal vascular resistance and cortical resistance in both experimental groups. However, while medullary flow increased in CTR by up to 16 +/- 6%, it remained unchanged or even somewhat declined in the NIC group. Calculated medullary resistance reciprocally declined in CTR while it rose in the NIC group (p < 0.001). In animals subjected to radiocontrast and indomethacin, nicotine intensified renal dysfunction, associated with focal medullary hypoxic damage.

CONCLUSIONS

Chronic exposure to nicotine selectively compromises the outer medullary microcirculation, blunting a local vasodilatory response to acute nicotine administration. Repeated acute-on-chronic exposure to nicotine may predispose to hypoxic medullary injury.

Nitric oxide-induced persistent inhibition and nitrosylation of active site cysteine residues of mitochondrial cytochrome-c oxidase in lung endothelial cells

Persistent inhibition of cytochrome- c oxidase, a terminal enzyme of the mitochondrial electron transport chain, by excessive nitric oxide (NO) derived from inflammation, polluted air, and tobacco smoke contributes to enhanced oxidant production and programmed cell death or apoptosis of lung cells. We sought to determine whether the long-term exposure of pulmonary artery endothelial cells (PAEC) to pathophysiological concentrations of NO causes persistent inhibition of complex IV through redox modification of its key cysteine residues located in a putative NO-sensitive motif. Prolonged exposure of porcine PAEC to 1 mM 2,2′-(hydroxynitrosohydrazino)-bis-ethanamine (NOC-18; slow-releasing NO donor, equivalent to 1–5 μM NO) resulted in a gradual, persistent inhibition of complex IV concomitant with a reduction in ratios of mitochondrial GSH and GSSG. Overexpression of thioredoxin in mitochondria of PAEC attenuated NO-induced loss of complex IV activities, suggesting redox regulation of complex IV activity. Sequence analysis of complex IV subunits revealed a novel putative NO-sensitive motif in subunit II (S2). There are only two cysteine residues in porcine complex IV S2, located in the putative motif. Immunoprecipitation and Western blot analysis and “biotin switch” assay demonstrated that exposure of PAEC to 1 mM NOC-18 increased S-nitrosylation of complex IV S2 by 200%. Site-directed mutagenesis of these two cysteines of complex IV S2 attenuated NO-increased nitrosylation of complex IV S2. These results demonstrate for the first time that NO nitrosylates active site cysteines of complex IV, which is associated with persistent inhibition of complex IV. NO inhibition of complex IV via nitrosylation of NO-sensitive cysteine residues can be a novel upstream event in NO-complex IV signaling for NO toxicity in lung endothelial cells.

Intracellular calcium signals and control of cell proliferation: how many mechanisms?

The progression through the cell cycle in non-transformed cells is under the strict control of extracellular signals called mitogens, that act by eliciting complex cascades of intracellular messengers. Among them, increases in cytosolic free calcium concentration have been long realized to play a crucial role; however, the mechanisms coupling membrane receptor activation to calcium signals are still only partially understood, as are the pathways of calcium entry in the cytosol. This article centers on the role of calcium influx from the extracellular medium in the control of proliferative processes, and reviews the current understanding of the pathways responsible for this influx and of the second messengers involved in their activation.

Nitric oxide-modulated marker gene expression of signal transduction pathways in lung endothelial cells

Nitric oxide (NO) is a signal molecule involved in regulation of physiological and pathophysiological functions of the vascular endothelium such as apoptosis. We examined whether NO-modulates marker gene expression of signal transduction pathways in cultured pulmonary artery endothelial cell (PAEC). Cells were exposed to a NO donor, 1 mM NOC-18, for 0.5, 5, and 24 h, thereafter, expression levels of 96 marker genes associated with 18 signal transduction pathways were assessed using a signal transduction pathway-finder microarray analysis system. NO modulation of apoptotic pathways and nuclear factor (NF) microarray were further analyzed. Gene array analyses revealed that 17 genes in 13 signal pathways were up- or down-regulated in cells exposed to NO, four of which were significantly altered by NO and are associated with apoptotic pathways. Apoptotic pathways resulted in identification of 11 genes in this group. Nuclear factor microarray studies demonstrated that NO-modulated expression of these signal transduction genes was associated with regulation of NF-binding activities. Gel shift analysis verified the effects of NO on DNA-binding activity of NF. These results demonstrated that NO signaling modulates at least 13 signal transduction pathways including apoptosis-related families in PAEC.

Peptide blockers of PKG inhibit ROS generation by acetylcholine and bradykinin in cardiomyocytes but fail to block protection in the whole heart

Bradykinin and acetylcholine (ACh) trigger preconditioning by ATP-sensitive K(+) (K(ATP)) channel-dependent production of reactive oxygen species (ROS). Recent evidence suggests that ROS production may in turn be influenced by cGMP-dependent protein kinase (PKG). This study utilized DT-2 and DT-3 peptides, highly specific membrane-permeable blockers of PKG. Rabbit cardiomyocytes were incubated for 15 min in reduced MitoTracker red, which becomes fluorescent only after exposure to ROS. Bradykinin (400 nM) and ACh (250 microM) caused a 49.9 +/- 5.9% and 46.8 +/- 1.7% increase in ROS production, respectively (P < 0.005 vs. untreated cells). Coincubation with DT-3 (250 nM) abolished both the ACh- and bradykinin-induced ROS signal, whereas a nonpermeable form of the peptide (W45) had no effect on ACh-induced ROS production. DT-3 was unable to block ROS production from diazoxide (100 microM), a selective opener of mitochondrial K(ATP) channels, suggesting that these channels are downstream of PKG. DT-2 (125 nM) also prevented ACh from triggering ROS production. 8-(4-Chlorophenylthio)-guanosine 3',5'-cyclic monophosphate (100 microM), a cGMP analog and potent direct activator of PKG, increased ROS production of cardiomyocytes by 44.7 +/- 7.1% (P < 0.001 vs. untreated cells). This increase was blocked by DT-2. Neither DT-2 nor DT-3 could block the anti-infarct effect of bradykinin in isolated rabbit hearts. Studies with fluorescent-tagged DT-3 revealed that it was confined to endothelial cells and never reached the myocytes. We conclude that both bradykinin and ACh trigger ROS generation by a pathway that includes PKG. Although the peptides may be inappropriate for a whole heart model, they are likely to become important tool drugs for elucidation of signal transduction pathways in cell preparations.

Carbon monoxide differentially modulates STAT1 and STAT3 and inhibits apoptosis via a phosphatidylinositol 3-kinase/Akt and p38 kinase-dependent STAT3 pathway during anoxia-reoxygenation injury

Carbon monoxide (CO), previously considered a toxic waste product of heme catabolism, is emerging as an important gaseous molecule. In addition to its important role in neurotransmission, exogenous CO protects against vascular injury, transplant rejection, and acute lung injury. However, little is known regarding the precise signaling mechanisms of CO. We have recently shown that CO attenuates endothelial cell apoptosis during anoxia-reoxygenation injury by activating MKK3/p38alpha mitogen-activated protein kinase (MAPK) pathways. Our current study is the first to demonstrate that CO can differentially modulate STAT1 and STAT3 activation and, specifically, that STAT3 activation by CO is responsible for the anti-apoptotic effect in endothelial cells. In addition, we show that the anti-apoptotic effects of CO depend upon both phosphatidylinositol 3-kinase/Akt and p38 MAPK signaling pathways in endothelial cells, whereas previous reports have implicated only the MKK3/p38 MAPK pathway. Using chemical inhibitors and dominant negative constructs, we show that CO enhances STAT3 activation via phosphatidylinositol 3-kinase/Akt and p38 MAPK pathways with subsequent attenuation of Fas expression and caspase 3 activity. These data highlight the anti-apoptotic signaling mechanisms of CO and, importantly, delineate potential therapeutic strategies to prevent ischemia-reperfusion or anoxia-reoxygenation injury in the vasculature.

Regulation of organic cation transport

Transport of organic cations (OC) is important for the recycling of endogenous OC and also a necessary step for detoxification of exogenous OC in the body. Even though the identification and characterisation of numerous OC transporters in recent years has allowed the elucidation of molecular mechanisms underlying OC transport, elucidation of the regulation of this transport is just beginning. This review summarises the general properties of OC transport and then analyses the literature on the regulation of these processes. Studies on short- and long-term regulation of OC transport are considered separately. Important aspects of short-term regulation have been clarified and the regulatory pathways of several OC transporters have been characterised. Short-term regulation appears to be transporter subtype-, tissue- and species-dependent and to involve transporter phosphorylation. Transporter phosphorylation may alter the affinity for substrates or/and expression on the plasma membrane. Even though several studies have shown long-term regulation of OC transport, the pathophysiological meaning of these changes are not well understood. In this case, regulation seems to be subtype-, tissue- and gender-specific. Further research is necessary to clarify this important issue of regulation of OC transport.