CalDAG-GEFI is at the nexus of calcium-dependent platelet activation.

The importance of the second messengers calcium (Ca(2+)) and diacylglycerol (DAG) in platelet signal transduction was established more than 30 years ago. Whereas protein kinase C (PKC) family members were discovered as the targets of DAG, little is known about the molecular identity of the main Ca(2+) sensor(s). We here identify Ca(2+) and DAG-regulated guanine nucleotide exchange factor I (CalDAG-GEFI) as a critical molecule in Ca(2+)-dependent platelet activation. CalDAG-GEFI, through activation of the small GTPase Rap1, directly triggers integrin activation and extracellular signal-regulated kinase-dependent thromboxane A(2) (TxA(2)) release. CalDAG-GEFI-dependent TxA(2) generation provides crucial feedback for PKC activation and granule release, particularly at threshold agonist concentrations. PKC/P2Y12 signaling in turn mediates a second wave of Rap1 activation, necessary for sustained platelet activation and thrombus stabilization. Our results lead to a revised model for platelet activation that establishes one molecule, CalDAG-GEFI, at the nexus of Ca(2+)-induced integrin activation, TxA(2) generation, and granule release. The preferential activation of CalDAG-GEFI over PKC downstream of phospholipase C activation, and the different kinetics of CalDAG-GEFI- and PKC/P2Y12-mediated Rap1 activation demonstrate an unexpected complexity to the platelet activation process, and they challenge the current model that DAG/PKC-dependent signaling events are crucial for the initiation of platelet adhesion.

Mobile-to-mobile MIMO transmit-receive diversity systems: analysis and performance in three-dimensional double-correlated channels

Mobile-to-mobile (M-to-M) communications are expected to play a crucial role in future wireless systems and networks. In this paper, we consider M-to-M multiple-input multiple-output (MIMO) maximal ratio combining system and assess its performance in spatially correlated channels. The analysis assumes double-correlated Rayleigh-and-Lognormal fading channels and is performed in terms of average symbol error probability, outage probability, and ergodic capacity. To obtain the receive and transmit spatial correlation functions needed for the performance analysis, we used a three-dimensional (3D) M-to-M MIMO channel model, which takes into account the effects of fast fading and shadowing. The expressions for the considered metrics are derived as a function of the average signal-to-noise ratio per receive antenna in closed-form and are further approximated using the recursive adaptive Simpson quadrature method. Numerical results are provided to show the effects of system parameters, such as distance between antenna elements, maximum elevation angle of scatterers, orientation angle of antenna array in the x–y plane, angle between the x–y plane and the antenna array orientation, and degree of scattering in the x–y plane, on the system performance. Copyright © 2011 John Wiley & Sons, Ltd.

Cross-layer design for MIMO systems over spatially correlated and keyhole Nakagami-m fading channels

Cross-layer design is a generic designation for a set of efficient adaptive transmission schemes, across multiple layers of the protocol stack, that are aimed at enhancing the spectral efficiency and increasing the transmission reliability of wireless communication systems. In this paper, one such cross-layer design scheme that combines physical layer adaptive modulation and coding (AMC) with link layer truncated automatic repeat request (T-ARQ) is proposed for multiple-input multiple-output (MIMO) systems employing orthogonal space--time block coding (OSTBC). The performance of the proposed cross-layer design is evaluated in terms of achievable average spectral efficiency (ASE), average packet loss rate (PLR) and outage probability, for which analytical expressions are derived, considering transmission over two types of MIMO fading channels, namely, spatially correlated Nakagami-m fading channels and keyhole Nakagami-m fading channels. Furthermore, the effects of the maximum number of ARQ retransmissions, numbers of transmit and receive antennas, Nakagami fading parameter and spatial correlation parameters, are studied and discussed based on numerical results and comparisons. Copyright © 2009 John Wiley & Sons, Ltd.

Performance analysis of MIMO MRC in 3D mobile-to-mobile double-correlated channels

In this paper, we consider multiple-input multiple- output (MIMO) maximal ratio combining (MRC) systems and assess the system performance in terms of average symbol error probability (SEP), outage probability and ergodic capacity in double-correlated Rayleigh-and-Lognormal fading channels. In order to derive the receive and transmit correlation functions needed for the performance analysis, a three-dimensional (3D) MIMO mobile-to-mobile (M-to-M) channel model, which takes into account the effects of fast fading and shadowing is used. Numerical results are provided to show the effects of system parameters, such as maximum elevation angle of scatterers, orientation angle of antenna array in the x-y plane, angle between x-y plane and the antenna array orientation, and degree of scattering in the x-y plane, on the system performance.

A cross-calibration of GMS-5 thermal channels against ATSR-2

Motivated by the importance to weather and climate of the Indo-Pacific seas, we present a new calibration of the Visible Infrared Spin-Scan Radiometer (VISSR) on the geostationary meteorological satellite, GMS-5. VISSR imagery has significant potential for exploring the dynamics of the ocean and air–sea interactions in this poorly characterized region, by virtue of the VISSR's surface temperature retrieval capability and hourly sampling. However, the calibration of the thermal imagery supplied by the Japanese Meteorological Agency (JMA) is inconsistent with the spectral characteristics of the channels, and published details of the JMA calibration procedure are scant. We use the well-characterized Along-Track Scanning Radiometer 2 (ATSR-2) as a reference, and determine calibration corrections for GMS-5 VISSR. We obtain more credible VISSR brightness temperatures and demonstrate sea surface temperature (SST) retrieval that validates well against in situ measurements (bias ∼0.3 and scatter ∼0.4 K). Comparison with a widely used sea surface temperature analysis shows that the GMS-5 VISSR SST fields capture important spatial structure, absent in the analysis.

Variation in the shoot calcium content of angiosperms

This study describes the variation in the mean relative shoot Ca content within the angiosperms at the ordinal level. Data were derived from studies in the literature in which the shoot Ca content of two or more species had been compared, and from a hydroponic experiment in which plants were selected to represent the relative number of species within each angiosperm order. Across all angiosperms, most of the variation in shoot Ca content occurred at and above the level of the order. Relative shoot Ca contents and variances correlated between literature and experimental data. In general, orders of commelinoid monocots had lower Ca contents than other monocot or eudicot orders. These results are used to illustrate how physiological and ecological hypotheses can be formulated using literature data.

Shoot calcium and magnesium concentrations differ between subtaxa, are highly heritable, and associate with potentially pleiotropic loci in Brassica oleracea

Calcium (Ca) and magnesium (Mg) are the most abundant group II elements in both plants and animals. Genetic variation in shoot Ca and shoot Mg concentration (shoot Ca and Mg) in plants can be exploited to biofortify food crops and thereby increase dietary Ca and Mg intake for humans and livestock. We present a comprehensive analysis of within-species genetic variation for shoot Ca and Mg, demonstrating that shoot mineral concentration differs significantly between subtaxa (varietas). We established a structured diversity foundation set of 376 accessions to capture a high proportion of species-wide allelic diversity within domesticated Brassica oleracea, including representation of wild relatives (C genome, 1n = 9) from natural populations. These accessions and 74 modern F-1 hybrid cultivars were grown in glasshouse and field environments. Shoot Ca and Mg varied 2- and 2.3-fold, respectively, and was typically not inversely correlated with shoot biomass, within most subtaxa. The closely related capitata (cabbage) and sabauda (Savoy cabbage) subtaxa consistently had the highest mean shoot Ca and Mg. Shoot Ca and Mg in glasshouse-grown plants was highly correlated with data from the field. To understand and dissect the genetic basis of variation in shoot Ca and Mg, we studied homozygous lines from a segregating B. oleracea mapping population. Shoot Ca and Mg was highly heritable (up to 40). Quantitative trait loci (QTL) for shoot Ca and Mg were detected on chromosomes C2, C6, C7, C8, and, in particular, C9, where QTL accounted for 14 to 55 of the total genetic variance. The presence of QTL on C9 was substantiated by scoring recurrent backcross substitution lines, derived from the same parents. This also greatly increased the map resolution, with strong evidence that a 4-cM region on C9 influences shoot Ca. This region corresponds to a 0.41-Mb region on Arabidopsis (Arabidopsis thaliana) chromosome 5 that includes 106 genes. There is also evidence that pleiotropic loci on C8 and C9 affect shoot Ca and Mg. Map-based cloning of these loci will reveal how shoot-level phenotypes relate to Ca 21 and Mg 21 uptake and homeostasis at the molecular level.

Distribution of calcium (Ca) and magnesium (Mg) in the leaves of Brassica rapa under varying exogenous Ca and Mg supply

Background and Aims Leafy vegetable Brassica crops are an important source of dietary calcium (Ca) and magnesium (Mg) and represent potential targets for increasing leaf Ca and Mg concentrations through agronomy or breeding. Although the internal distribution of Ca and Mg within leaves affects the accumulation of these elements, such data are not available for Brassica. The aim of this study was to characterize the internal distribution of Ca and Mg in the leaves of a vegetable Brassica and to determine the effects of altered exogenous Ca and Mg supply on this distribution. Methods Brassica rapa ssp. trilocularis ‘R-o-18’ was grown at four different Ca:Mg treatments for 21 d in a controlled environment. Concentrations of Ca and Mg were determined in fully expanded leaves using inductively coupled plasma-mass spectrometry (ICP-MS). Internal distributions of Ca and Mg were determined in transverse leaf sections at the base and apex of leaves using energy-dispersive X-ray spectroscopy (EDS) with cryo-scanning electron microscopy (cryo-SEM). Key Results Leaf Ca and Mg concentrations were greatest in palisade and spongy mesophyll cells, respectively, although this was dependent on exogenous supply. Calcium accumulation in palisade mesophyll cells was enhanced slightly under high Mg supply; in contrast, Mg accumulation in spongy mesophyll cells was not affected by Ca supply. Conclusions The results are consistent with Arabidopsis thaliana and other Brassicaceae, providing phenotypic evidence that conserved mechanisms regulate leaf Ca and Mg distribution at a cellular scale. The future study of Arabidopsis gene orthologues in mutants of this reference B. rapa genotype will improve our understanding of Ca and Mg homeostasis in plants and may provide a model-to-crop translation pathway for targeted breeding.

On the Nusselt number for frazil ice growth—a correction to ”Frazil evolution in channels“ by Lars Hammar and Hung-Tao Shen

The growth (melt) rate of frazil ice is governed by heat transfer away from (towards) the ice crystal, which can be represented by the Nusselt number. We discuss choices for the Nusselt number and turbulent length scale appropriate for frazil ice and note an inaccuracy in the study ”Frazil evolution in channels“ by Lars Hammar and Hung-Tao Shen, which has also led to potentially significant errors in several other papers. We correct this error and suggest an appropriate strategy for determining the Nusselt number applicable to frazil ice growth and melting.

Transient receptor potential ion channels V4 and A1 contribute to pancreatitis pain in mice.

The mechanisms of pancreatic pain, a cardinal symptom of pancreatitis, are unknown. Proinflammatory agents that activate transient receptor potential (TRP) channels in nociceptive neurons can cause neurogenic inflammation and pain. We report a major role for TRPV4, which detects osmotic pressure and arachidonic acid metabolites, and TRPA1, which responds to 4-hydroxynonenal and cyclopentenone prostaglandins, in pancreatic inflammation and pain in mice. Immunoreactive TRPV4 and TRPA1 were detected in pancreatic nerve fibers and in dorsal root ganglia neurons innervating the pancreas, which were identified by retrograde tracing. Agonists of TRPV4 and TRPA1 increased intracellular Ca(2+) concentration ([Ca(2+)](i)) in these neurons in culture, and neurons also responded to the TRPV1 agonist capsaicin and are thus nociceptors. Intraductal injection of TRPV4 and TRPA1 agonists increased c-Fos expression in spinal neurons, indicative of nociceptor activation, and intraductal TRPA1 agonists also caused pancreatic inflammation. The effects of TRPV4 and TRPA1 agonists on [Ca(2+)](i), pain and inflammation were markedly diminished or abolished in trpv4 and trpa1 knockout mice. The secretagogue cerulein induced pancreatitis, c-Fos expression in spinal neurons, and pain behavior in wild-type mice. Deletion of trpv4 or trpa1 suppressed c-Fos expression and pain behavior, and deletion of trpa1 attenuated pancreatitis. Thus TRPV4 and TRPA1 contribute to pancreatic pain, and TRPA1 also mediates pancreatic inflammation. Our results provide new information about the contributions of TRPV4 and TRPA1 to inflammatory pain and suggest that channel antagonists are an effective therapy for pancreatitis, when multiple proinflammatory agents are generated that can activate and sensitize these channels.

Protease-activated receptors: mechanisms by which proteases sensitize TRPV channels to induce neurogenic inflammation and pain

Proteolytic enzymes comprise approximately 2 percent of the human genome [1]. Given their abundance, it is not surprising that proteases have diverse biological functions, ranging from the degradation of proteins in lysosomes to the control of physiological processes such as the coagulation cascade. However, a subset of serine proteases (possessing serine residues within their catalytic sites), which may be soluble in the extracellular fluid or tethered to the plasma membrane, are signaling molecules that can specifically regulate cells by cleaving protease-activated receptors (PARs), a family of four G-protein-coupled receptors (GPCRs). These serine proteases include members of the coagulation cascade (e.g., thrombin, factor VIIa, and factor Xa), proteases from inflammatory cells (e.g., mast cell tryptase, neutrophil cathepsin G), and proteases from epithelial tissues and neurons (e.g., trypsins). They are often generated or released during injury and inflammation, and they cleave PARs on multiple cell types, including platelets, endothelial and epithelial cells, myocytes, fibroblasts, and cells of the nervous system. Activated PARs regulate many essential physiological processes, such as hemostasis, inflammation, pain, and healing. These proteases and their receptors have been implicated in human disease and are potentially important targets for therapy. Proteases and PARs participate in regulating most organ systems and are the subject of several comprehensive reviews [2, 3]. Within the central and peripheral nervous systems, proteases and PARs can control neuronal and astrocyte survival, proliferation and morphology, release of neurotransmitters, and the function and activity of ion channels, topics that have also been comprehensively reviewed [4, 5]. This chapter specifically concerns the ability of PARs to regulate TRPV channels of sensory neurons and thereby affect neurogenic inflammation and pain transmission [6, 7].

Heme oxygenase-1 regulates cell proliferation via carbon monoxide-mediated inhibition of T-type Ca2+ channels

Induction of the antioxidant enzyme heme oxygenase-1 (HO-1) affords cellular protection and suppresses proliferation of vascular smooth muscle cells (VSMCs) associated with a variety of pathological cardiovascular conditions including myocardial infarction and vascular injury. However, the underlying mechanisms are not fully understood. Over-expression of Cav3.2 T-type Ca2+ channels in HEK293 cells raised basal [Ca2+]i and increased proliferation as compared with non-transfected cells. Proliferation and [Ca2+]i levels were reduced to levels seen in non-transfected cells either by induction of HO-1 or exposure of cells to the HO-1 product, carbon monoxide (CO) (applied as the CO releasing molecule, CORM-3). In the aortic VSMC line A7r5, proliferation was also inhibited by induction of HO-1 or by exposure of cells to CO, and patch-clamp recordings indicated that CO inhibited T-type (as well as L-type) Ca2+ currents in these cells. Finally, in human saphenous vein smooth muscle cells, proliferation was reduced by T-type channel inhibition or by HO-1 induction or CO exposure. The effects of T-type channel blockade and HO-1 induction were non-additive. Collectively, these data indicate that HO-1 regulates proliferation via CO-mediated inhibition of T-type Ca2+ channels. This signalling pathway provides a novel means by which proliferation of VSMCs (and other cells) may be regulated therapeutically.

Diverse mechanisms underlying the regulation of ion channels by carbon monoxide

Carbon monoxide is firmly established as an important, physiological signalling molecule as well as a potent toxin. Through its ability to bind metal-containing proteins it is known to interfere with a number of intracellular signalling pathways, and such actions can account for its physiological and pathological effects. In particular, CO can modulate the intracellular production of reactive oxygen species, nitric oxide and cGMP levels, as well as regulate MAP kinase signalling. In this review, we consider ion channels as more recently discovered effectors of CO signalling. CO is now known to regulate a growing number of different ion channel types, and detailed studies of the underlying mechanisms of action are revealing unexpected findings. For example, there are clear areas of contention surrounding its ability to increase the activity of high conductance, Ca2+ -sensitive K+ channels. More recent studies have revealed the ability of CO to inhibit T-type Ca2+ channels and have unveiled a novel signalling pathway underlying tonic regulation of this channel. It is clear that the investigation of ion channels as effectors of CO signalling is in its infancy, and much more work is required to fully understand both the physiological and the toxic actions of this gas. Only then can its emerging use as a therapeutic tool be fully and safely exploited.

Enhancement in corneal permeability of riboflavin using calcium sequestering compounds

Ethylenediaminetetraacetic acid, ethylenediamine-N,N′-disuccinic acid and ethylene glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid are polyaminocarboxylic acids that are able to sequester metal ions. Calcium is implicated in maintenance of intercellular matrix, zonula occludens (tight junctions) and zonula adherens of epithelium and endothelium cells. Corneal epithelium is impervious to many aqueous formulations due to it being lipophilic, whereby transcellular drug transit is resisted, whilst tight junctions restrict access via the paracellular route. Research has shown that integrity of tight junctions breaks down through loss of Ca2+ for endothelial and epithelial cells. This study investigates different Ca2+ sequestering compounds and their effect on corneal permeability of riboflavin at physiological pH. Riboflavin is a topically administered ocular drug applied during UV-induced corneal cross-linking for the treatment of keratoconus.

Regulation of KCa2.3 andendothelium-dependent hyperpolarization (EDH) in the rat middle cerebral artery: the role of lipoxygenase metabolites and isoprostanes

Background and Purpose. In rat middle cerebral arteries, endothelium-dependent hyperpolarization (EDH) is mediated by activation of calcium-activated potassium(KCa) channels specifically KCa2.3 and KCa3.1. Lipoxygenase (LOX) products function as endothelium-derived hyperpolarizing factors (EDHFs) in rabbit arteries by stimulating KCa2.3. We investigated if LOX products contribute to EDH in rat cerebral arteries. Methods. Arachidonic acid (AA) metabolites produced in middle cerebral arteries were measured using HPLC and LC/MS. Vascular tension and membrane potential responses to SLIGRL were simultaneously recorded using wire myography and intracellular microelectrodes. Results. SLIGRL, an agonist at PAR2 receptors, caused EDH that was inhibited by a combination of KCa2.3 and KCa3.1 blockade. Non-selective LOX-inhibition reduced EDH, whereas inhibition of 12-LOX had no effect. Soluble epoxide hydrolase (sEH) inhibition enhanced the KCa2.3 component of EDH. Following NO synthase (NOS) inhibition, the KCa2.3 component of EDH was absent. Using HPLC, middle cerebral arteries metabolized 14C-AA to 15- and 12-LOX products under control conditions. With NOS inhibition, there was little change in LOX metabolites, but increased F-type isoprostanes. 8-iso-PGF2α inhibited the KCa2.3 component of EDH. Conclusions. LOX metabolites mediate EDH in rat middle cerebral arteries. Inhibition of sEH increases the KCa2.3 component of EDH. Following NOS inhibition,loss of KCa2.3 function is independent of changes in LOX production or sEH inhibition but due to increased isoprostane production and subsequent stimulation of TP receptors. These findings have important implications in diseases associated with loss of NO signaling such as stroke; where inhibition of sEH and/or isoprostane formation may of benefit.