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  • Polynuclear complexes as precursor templates for hierarchical microporous graphitic carbon: An unusual approach

    Kobielska, P.A.; Telford, Richard; Rowlandson, J.; Tian, M.; Shahin, Z.; Demessence, A.; Ting, V.P.; Nayak, Sanjit (2018-07)
    A highly porous carbon was synthesized using a coordination complex as an unusual precursor. During controlled pyrolysis, a trinuclear copper complex, [CuII3Cl4(H2L)2]·CH3OH, undergoes phase changes with melt and expulsion of different gases to produce a unique morphology of copper-doped carbon which, upon acid treatment, produces highly porous graphitic carbon with a surface area of 857 m2 g–1 and a gravimetric hydrogen uptake of 1.1 wt % at 0.5 bar pressure at 77 K.
  • Team-based Learning: Engaging learners and creating team accountability

    de Vries, J.; Tweddell, Simon; McCarter, Rebecca (2018-06)
    Team-based Learning (TBL) is a new teaching strategy that may take small group learning to a new level of effectiveness. TBL shifts the focus from content delivery by teachers to the application of course content by student teams. Teams work on authentic problems, make collaborative decisions, and develop problem-solving skills required in their future workplace. Prior to redesigning the MPharm programme according to TBL principles, several pilots were set up to research how students responded to this new way of teaching. One pilot focussed on the introduction of TBL as a phenomena and aimed to find out if and how TBL engaged students, how students were held accountable by their teams, and more importantly how that affected their lifeworld. Ashworth’s lifeworld contingencies provided the theoretical framework as it ranges from students’ selfhood, embodiment and social interactions to their ability to carry out tasks they are committed to and regard as essential (Ashworth, 2003).
  • Size dependent effects of gold nanoparticles in ISO-induced hyperthyroid rats

    Zhang, J.; Xue, Y.; Ni, Y.; Ning, F.; Shang, Lijun; Ma, A. (2018-07-19)
    In this study, we applied different sizes of gold nanoparticles (Au-NPs) to isoproterenol (ISO)-induced hyperthyroid heart disease rats (HHD rats). Single dose of 5, 40, 100 nm Au-NPs were injected intravenously. Cardiac safety tests were evaluated by cardiac marker enzymes in serum and cardiac accumulation of Au-NPs were measured by ICP-MS. Our results showed that size-dependent cardiac effects of Au-NPs in ISO-induced hyperthyroid rats. 5 nm Au-NPs had some cardiac protective effect but little accumulation in heart, probably due to smaller size Au-NPs can adapt to whole body easily in vivo. Histological analysis and TUNEL staining showed that Au-NPs can induce pathological alterations including cardiac fibrosis, apoptosis in control groups, however they can protect HHD groups from these harmful effects. Furthermore, transmission electron microscopy and western blotting employed on H9C2 cells showed that autophagy presented in Au-NPs treated cells and that Au-NPs can decrease LC3 II turning to LC3 I and decrease APG7 and caspase 12 in the process in HHD groups, while opposite effects on control groups were presented, which could be an adaptive inflammation reacts. As there are few animal studies about using nanoparticles in the treatment of heart disease, our in vivo and in vitro studies would provide valuable information before they can be considered for clinical use in general.
  • Conjugating existing clinical drugs with gold nanoparticles for better treatment of heart diseases

    Zhang, J.; Ma, A.; Shang, Lijun (2018-05-29)
    Developing new methods to treat heart diseases is always a focus for basic research and clinical applications. Existing drugs have strong side-effects and also require lifetime administration for patients. Recent attempts of using nanoparticles (NPs) in treating atherosclerosis in animals and some heart diseases such as heart failure and endocarditis have provided hopes for better drug delivery and reducing of drug side-effects. In this mini-review, we summarize the present applications of using gold nanoparticles (GNPs) as a new drug delivery system in diseased hearts and of the assessment of toxicity in using GNPs. We suggest that conjugating existing clinical drugs with GNPs is a favorable choice to provide “new and double-enhanced” potentiality to those existing drugs in treating heart diseases. Other applications of using NPs in the treatment of heart diseases including using drugs in nano-form and coating drugs with a surface of relevant NP are also discussed.
  • An explanation for the mysterious distribution of melanin in human skin ‐ a rare example of asymmetric (melanin) organelle distribution during mitosis of basal layer progenitor keratinocytes

    Joly-Tonetti, Nicolas; Wibawa, J.I.D.; Bell, M.; Tobin, Desmond J. (2018)
    Background: Melanin is synthesized by melanocytes in the basal layer of the epidermis. When transferred to surrounding keratinocytes it is the key UVR-protective biopolymer responsible for skin pigmentation. Most melanin is observable in the proliferative basal layer of the epidermis, and only sparsely distributed in the stratifying/differentiating epidermis. The latter has been explained, despite formal evidence, to ‘melanin degradation’ in supra-basal layers. Objectives: Our aim was to re-evaluate this currently-accepted basis for melanin distribution in the human skin epidermis, and whether this pattern is altered after a regenerative stimulus. Methods: Normal epidermis of adult human skin, at rest and after tape-stripping, was analysed by a range of (immuno)histochemical and high-resolution microscopy techniques. In vitro models of melanin granule uptake by human keratinocytes were attempted. Results: We propose a wholly different fate for melanin in the human epidermis. Our evidence indicates that the bulk of melanin is inherited only by the non-differentiating daughter cell post mitosis in progenitor keratinocytes, via asymmetric organelle inheritance. Moreover, this preferred pattern of melanin distribution can switch to a symmetric or equal daughter cell inheritance mode under conditions of stress including regeneration. Conclusions: We provide in this preliminary report a plausible and histologically-supportable explanation for how human skin pigmentation is efficiently organized in the epidermis. Steady state epidermis pigmentation may involve much less redox-sensitive melanogenesis than previously thought, and at least some pre-made melanin may be available for re-use. The epidermal-melanin unit may be an excellent example to study organelle distribution via asymmetric or symmetric inheritance in response to micro-environment and tissue demands.
  • Targeting HOX-PBX interactions causes death in oral potentially malignant and squamous carcinoma cells but not normal oral keratinocytes

    Platais, C.; Radhakrishnan, R.; Ebensberger, S.N.; Morgan, Richard; Lambert, D.W.; Hunter, K.D. (2018-07)
    Background: High HOX gene expression has been described in many cancers, including oral squamous cell carcinoma and the functional roles of these genes are gradually being understood. The pattern of overexpression suggests that inhibition may be useful therapeutically. Inhibition of HOX protein binding to PBX cofactors by the use of synthetic peptides, such as HXR9, results in apoptosis in multiple cancers. Methods: Activity of the HOX-PBX inhibiting peptide HXR9 was tested in immortalised normal oral (NOK), potentially-malignant (PMOL) and squamous cell carcinoma (OSCC) cells, compared to the inactive peptide CXR9. Cytotoxicity was assessed by LDH assay. Expression of PBX1/2 and c-Fos was assessed by qPCR and western blotting. Apoptosis was assessed by Annexin-V assay. Results: PMOL and OSCC cells expressed PBX1/2. HOX-PBX inhibition by HXR9 caused death of PMOL and OSCC cells, but not NOKs. HXR9 treatment resulted in apoptosis and increased expression of c-Fos in some cells, whereas CXR9 did not. A correlation was observed between HOX expression and resistance to HXR9. Conclusion: Inhibition of HOX-PBX interactions causes selective apoptosis of OSCC/PMOL, indicating selective toxicity that may be useful clinically.
  • Clinical pharmacists in primary care: a safe solution to the workforce crisis?

    Komwong, D.; Greenfield, G.; Zaman, Hadar; Majeed, A.; Hayhoe, B. (2018-04)
  • Benzodiazepines for psychosis-induced aggression or agitation

    Zaman, Hadar; Sampson, S.J.; Beck, A.L.S.; Sharma, T.; Clay, F.J.; Spyridi, S.; Zhao, S.; Gillies, D. (2017)
  • Benzodiazepines for psychosis-induced aggression or agitation

    Zaman, Hadar; Sampson, S.; Beck, A.; Sharma, T.; Clay, F.; Spyridi, S.; Zhao, S.; Gillies, D. (2018)
  • Cardiology patients' medicines management networks after hospital discharge: A mixed methods analysis of a complex adaptive system

    Fylan, Beth; Tranmer, M.; Armitage, Gerry R.; Blenkinsopp, Alison (2018)
    Introduction: The complex healthcare system that provides patients with medicines places them at risk when care is transferred between healthcare organisations, for example discharge from hospital. Consequently, under-standing and improving medicines management, particularly at care transfers, is a priority.Objectives: This study aimed to explore the medicines management system as patients experience it and determine differences in the patient-perceived importance of people in the system.Methods: We used a Social Network Analysis framework, collecting ego-net data about the importance of people patients had contact with concerning their medicines after hospital discharge. Single- and multi-level logistic regression models of patients' networks were constructed, and model residuals were explored at the patient level.This enabled us to identify patients' networks with support tie patterns different from the general patterns suggested by the model results. Qualitative data for those patients were then analysed to understand their differing experiences.Results: Networks comprised clinical and administrative healthcare staff and friends and family members.Networks were highly individual and the perceived importance of alters varied both within and between patients. Ties to spouses were significantly more likely to be rated as highly important and ties to community pharmacy staff (other than pharmacists) and to GP receptionists were less likely to be highly rated. Patients with low-value medicines management networks described having limited information about their medicines and alack of understanding or help. Patients with high-value networks described appreciating support and having confidence in staff.Conclusions: Patients experienced medicines management as individual systems within which they interacted with healthcare staff and informal support to manage their treatment. Multilevel models indicated that there are unexplained variables impacting on patients' assessments of their medicines management networks. Qualitative exploration of the model residuals can offer an understanding of networks that do not have the typical range of support ties.
  • Can optical recordings of membrane potential be used to screen for drug-induced action potential prolongation in single cardiac myocytes?

    Hardy, Matthew E.; Lawrence, C.L.; Standen, N.B.; Rodrigo, G.C. (2006)
    Introduction: Potential-sensitive dyes have primarily been used to optically record action potentials (APs) in whole heart tissue. Using these dyes to record drug-induced changes in AP morphology of isolated cardiac myocytes could provide an opportunity to develop medium throughout assays for the pharmaceutical industry. Ideally, this requires that the dye has a consistent and rapid response to membrane potential, is insensitive to movement, and does not itself affect AP morphology. Materials and methods: We recorded the AP from isolated adult guinea-pig ventricular myocytes optically using di-8-ANEPPS in a single-excitation dual-emission ratiometric system, either separately in electrically field stimulated myocytes, or simultaneously with an electrical AP recorded with a patch electrode in the whole-cell bridge mode. The ratio of di-8-ANEPPS fluorescence signal was calibrated against membrane potential using a switch-clamp to voltage clamp the myocyte. Results: Our data show that the ratio of the optical signals emitted at 560/620 nm is linearly related to voltage over the voltage range of an AP, producing a change in ratio of 7.5% per 100mV, is unaffected by cell movement and is identical to the AP recorded simultaneously with a patch electrode. However, the APD90 recorded optically in myocytes loaded with di-8-ANEPPS was significantly longer than in unloaded myocytes recorded with a patch electrode (355.6 ± 13.5 vs. 296.2 ± 16.2ms; p< 0.01). Despite this effect, the apparent IC50 for cisapride, which prolongs the AP by blocking IKr, was not significantly different whether determined optically or with a patch electrode (91 ± 46 vs. 81 ± 20 nM). Discussion: These data show that the optical AP recorded ratiometrically using di-8- ANEPPS from a single ventricular myocyte accurately follows the action potential morphology. This technique can be used to estimate the AP prolonging effects of a compound, although di-8-ANEPPS itself prolongs APD90. Optical dyes require less technical skills and are less invasive than conventional electrophysiological techniques and, when coupled to ventricular myocytes, decreases animal usage and facilitates higher throughput assays.
  • Validation of a voltage-sensitive dye (di-4-ANEPPS)-based method for assessing drug-induced delayed repolarisation in Beagle dog left ventricular midmyocardial myocytes

    Hardy, Matthew E.; Pollard, C.E.; Small, B.G.; Bridgland-Taylor, M.; Woods, A.J.; Valentin, J.-P.; Abi-Gerges, N. (2009)
    Evaluation of drug candidates in in-vitro assays of action potential duration (APD) is one component of preclinical safety assessment. Current assays are limited by technically-demanding, time-consuming electrophysiological methods. This study aimed to assess whether a voltage-sensitive dye-based assay could be used instead. Methods Optical APs were recorded using di-4-ANEPPS in electrically field stimulated Beagle left ventricular midmyocardial myocytes (LVMMs). Pharmacological properties of di-4-ANEPPS on the main cardiac ion channels that shape the ventricular AP were investigated using IonWorks™ and conventional electrophysiology. Effects of 9 reference drugs (dofetilide, E4031, d-sotalol, ATXII, cisapride, terfenadine, alfuzosin, diltiazem and pinacidil) with known APD-modulating effects were assessed on optically measured APD at 1 Hz. Results Under optimum conditions, 0.1 μM di-4-ANEPPS could be used to monitor APs paced at 1 Hz during nine, 5 s exposures without altering APD. di-4-ANEPPS had no effect on either hIERG, hINa, hIKs and hIto currents in transfected CHO cells (up to 10 µM) or ICa,L current in LVMMs (at 16 µM). di-4-ANEPPS had no effect on APs recorded with microelectrodes at 1 or 0.5 Hz over a period of 30 min di-4-ANEPPS displayed the sensitivity to record changes in optically measured APD in response to altered pacing frequencies and sequential vehicle additions did not affect the optically measured APD. APD data obtained with 9 reference drugs were as expected except (i) d-sotalol-induced increases in duration were smaller than those caused by other IKr blockers and (ii) increases in APD were not detected using low concentrations of terfenadine. Discussion Early in drug discovery, the di-4-ANEPPS-based method can reliably be used to assess drug effects on APD as part of a cardiac risk assessment strategy.
  • Glucose reduces endothelin inhibition of voltage-gated potassium channels in rat arterial smooth muscle cells

    Rainbow, R.D.; Hardy, Matthew E.; Standen, N.B.; Davies, N.W. (2006-09)
    Prolonged hyperglycaemia impairs vascular reactivity and inhibits voltage-activated K+ (Kv) channels. We examined acute effects of altering glucose concentration on the activity and inhibition by endothelin-1 (ET-1) of Kv currents of freshly isolated rat arterial myocytes. Peak Kv currents recorded in glucose-free solution were reversibly reduced within 200 s by increasing extracellular glucose to 4 mm. This inhibitory effect of glucose was abolished by protein kinase C inhibitor peptide (PKC-IP), and Kv currents were further reduced in 10 mm glucose. In current-clamped cells, membrane potentials were more negative in 4 than in 10 mm glucose. In 4 mmd-glucose, 10 nm ET-1 decreased peak Kv current amplitude at +60 mV from 23.5 ± 3.3 to 12.1 ± 3.1 pA pF−1 (n = 6, P < 0.001) and increased the rate of inactivation, decreasing the time constant around fourfold. Inhibition by ET-1 was prevented by PKC-IP. When d-glucose was increased to 10 mm, ET-1 no longer inhibited Kv current (n = 6). Glucose metabolism was required for prevention of ET-1 inhibition of Kv currents, since fructose mimicked the effects of d-glucose, while l-glucose, sucrose or mannitol were without effect. Endothelin receptors were still functional in 10 mmd-glucose, since pinacidil-activated ATP-dependent K+ (KATP) currents were reduced by 10 nm ET-1. This inhibition was nearly abolished by PKC-IP, indicating that endothelin receptors could still activate PKC in 10 mmd-glucose. These results indicate that changes in extracellular glucose concentration within the physiological range can reduce Kv current amplitude and can have major effects on Kv channel modulation by vasoconstrictors.
  • Electrophysiological and structural determinants of electrotonic modulation of repolarization by the activation sequence

    Walton, R.D.; Benson, A.P.; Hardy, Matthew E.; White, E.; Bernus, O. (2013-10-08)
    Spatial dispersion of repolarization is known to play an important role in arrhythmogenesis. Electrotonic modulation of repolarization by the activation sequence has been observed in some species and tissue preparations, but to varying extents. Our study sought to determine the mechanisms underlying species- and tissue-dependent electrotonic modulation of repolarization in ventricles. Epi-fluorescence optical imaging of whole rat hearts and pig left ventricular wedges were used to assess epicardial spatial activation and repolarization characteristics. Experiments were supported by computer simulations using realistic geometries. Tight coupling between activation times (AT) and action potential duration (APD) were observed in rat experiments but not in pig. Linear correlation analysis found slopes of −1.03 ± 0.59 and −0.26 ± 0.13 for rat and pig, respectively (p < 0.0001). In rat, maximal dispersion of APD was 11.0 ± 3.1 ms but dispersion of repolarization time (RT) was relatively homogeneous (8.2 ± 2.7, p < 0.0001). However, in pig no such difference was observed between the dispersion of APD and RT (17.8 ± 6.1 vs. 17.7 ± 6.5, respectively). Localized elevations of APD (12.9 ± 8.3%) were identified at ventricular insertion sites of rat hearts both in experiments and simulations. Tissue geometry and action potential (AP) morphology contributed significantly to determining influence of electrotonic modulation. Simulations of a rat AP in a pig geometry decreased the slope of AT and APD relationships by 70.6% whereas slopes were increased by 75.0% when implementing a pig AP in a rat geometry. A modified pig AP, shortened to match the rat APD, showed little coupling between AT and APD with greatly reduced slope compared to the rat AP. Electrotonic modulation of repolarization by the activation sequence is especially pronounced in small hearts with murine-like APs. Tissue architecture and AP morphology play an important role in electrotonic modulation of repolarization.
  • Endocytosis of hERG Is Clathrin-Independent and Involves Arf6

    Karnik, R.; Ludlow, M.J.; Abuarab, N.; Smith, A.J.; Hardy, Matthew E.; Elliott, D.J.S.; Sivaprasadarao, A. (2013-12-31)
    The hERG potassium channel is critical for repolarisation of the cardiac action potential. Reduced expression of hERG at the plasma membrane, whether caused by hereditary mutations or drugs, results in long QT syndrome and increases the risk of ventricular arrhythmias. Thus, it is of fundamental importance to understand how the density of this channel at the plasma membrane is regulated. We used antibodies to an extracellular native or engineered epitope, in conjunction with immunofluorescence and ELISA, to investigate the mechanism of hERG endocytosis in recombinant cells and validated the findings in rat neonatal cardiac myocytes. The data reveal that this channel undergoes rapid internalisation, which is inhibited by neither dynasore, an inhibitor of dynamin, nor a dominant negative construct of Rab5a, into endosomes that are largely devoid of the transferrin receptor. These results support a clathrin-independent mechanism of endocytosis and exclude involvement of dynamin-dependent caveolin and RhoA mechanisms. In agreement, internalised hERG displayed marked overlap with glycosylphosphatidylinositol-anchored GFP, a clathrin-independent cargo. Endocytosis was significantly affected by cholesterol extraction with methyl-β-cyclodextrin and inhibition of Arf6 function with dominant negative Arf6-T27N-eGFP. Taken together, we conclude that hERG undergoes clathrin-independent endocytosis via a mechanism involving Arf6.
  • Effects of superoxide donor menadione in adult Rat myocardium are associated with increased diastolic intracellular calcium

    Rogers, L.J.; Lake, A.J.; White, K.; Hardy, Matthew E.; White, E. (2014-02-12)
    Superoxide anions have been associated with many aspects of cardiovascular disease. Menadione is a superoxide anion donor that alters the heart’s electrical and mechanical functions. The aim of this study was to demonstrate simultaneous changes in intracellular Ca2+ ([Ca2+]i) and mechanical activity in intact adult cardiac myocytes, and mechanical activity and electrical activity in isolated whole hearts in order to provide greater insight into the mechanisms associated with the detrimental effects of menadione on the myocardium. Isolated hearts from adult male Wistar rats (n = 11, 200–250 g) were Langendorff perfused at 38°C with a Krebs–Henseleit solution. A saline-filled balloon was placed in the left ventricle (LV) in order to measure diastolic and developed pressure. Monophasic action potentials were simultaneously recorded from the epicardial surface. External stimulation at 5 Hz and intrinsic pacing were used throughout a 10 min control period and 30 min exposure to 50 μM menadione. Single LV myocytes (n = 7 from n = 4 animals) were loaded with the Ca2+-indicator Fura4-AM, stimulated at 1 Hz and exposed to 50 μM menadione. Myocyte length was simultaneously measured with [Ca2+]i using a video edge detection system. In isolated hearts, exposure to menadione significantly decreased contractility and action potential duration (with a similar time course); intrinsic heart rate and rhythmicity. Diastolic pressure was significantly increased. In single adult myocytes, menadione caused a significant increase in diastolic [Ca2+]i and a decrease in resting cell length and led to spontaneous release of [Ca2+]i. We conclude that the effects of menadione upon electrical and mechanical activity of the heart are at least in part a consequence of dysregulation of [Ca2+]i handling and the subsequent increase in diastolic [Ca2+] alterations in [Ca2+]i are consistent with the generation of delayed after depolarization arrhythmias.
  • Systems approach to the study of stretch and arrhythmias in right ventricular failure induced in rats by monocrotaline

    Benoist, D.; Stones, R.; Benson, A.P.; Fowler, E.D.; Drinkhill, M.J.; Hardy, Matthew E.; Saint, D.A.; Cazorla, O.; Bernus, O.; White, E. (2014-08)
    We demonstrate the synergistic benefits of using multiple technologies to investigate complex multi-scale biological responses. The combination of reductionist and integrative methodologies can reveal novel insights into mechanisms of action by tracking changes of in vivo phenomena to alterations in protein activity (or vice versa). We have applied this approach to electrical and mechanical remodelling in right ventricular failure caused by monocrotaline-induced pulmonary artery hypertension in rats. We show arrhythmogenic T-wave alternans in the ECG of conscious heart failure animals. Optical mapping of isolated hearts revealed discordant action potential duration (APD) alternans. Potential causes of the arrhythmic substrate; structural remodelling and/or steep APD restitution and dispersion were observed, with specific remodelling of the Right Ventricular Outflow Tract. At the myocyte level, [Ca2+]i transient alternans were observed together with decreased activity, gene and protein expression of the sarcoplasmic reticulum Ca2+-ATPase (SERCA). Computer simulations of the electrical and structural remodelling suggest both contribute to a less stable substrate. Echocardiography was used to estimate increased wall stress in failure, in vivo. Stretch of intact and skinned single myocytes revealed no effect on the Frank-Starling mechanism in failing myocytes. In isolated hearts acute stretch-induced arrhythmias occurred in all preparations. Significant shortening of the early APD was seen in control but not failing hearts. These observations may be linked to changes in the gene expression of candidate mechanosensitive ion channels (MSCs) TREK-1 and TRPC1/6. Computer simulations incorporating MSCs and changes in ion channels with failure, based on altered gene expression, largely reproduced experimental observations.
  • The Golgi apparatus is a functionally distinct Ca2+ store regulated by PKA and Epac branches of the β1-adrenergic signaling pathway.

    Yang, Z.; Kirton, H.M.; MacDougall, D.A.; Boyle, J.P.; Deuchars, J.; Frater, B.; Ponnambalam, S.; Hardy, Matthew E.; White, M.; Calaghan, S.C.; Peers, C.; Steele, D.S. (2015-10-13)
    Ca2+ release from the Golgi apparatus regulates key functions of the organelle, including vesicle trafficking. However, the signaling pathways that control this form of Ca2+ release are poorly understood and evidence of discrete Golgi Ca2+ release events is lacking. Here, we identified the Golgi apparatus as the source of prolonged Ca2+ release events that originate from the nuclear ‘poles’ of primary cardiac cells. Once initiated, Golgi Ca2+ release was unaffected by global depletion of sarcoplasmic reticulum Ca2+, and disruption of the Golgi apparatus abolished Golgi Ca2+ release without affecting sarcoplasmic reticulum function, suggesting functional and anatomical independence of Golgi and sarcoplasmic reticulum Ca2+ stores. Maximal activation of β1-adrenoceptors had only a small stimulating effect on Golgi Ca2+ release. However, inhibition of phosphodiesterase (PDE) 3 or 4, or downregulation of PDE 3 and 4 in heart failure markedly potentiated β1-adrenergic stimulation of Golgi Ca2+ release, consistent with compartmentalization of cAMP signaling within the Golgi apparatus microenvironment. β1-adrenergic stimulation of Golgi Ca2+ release involved activation of both Epac and PKA signaling pathways and CaMKII. Interventions that stimulated Golgi Ca2+ release induced trafficking of vascular growth factor receptor-1 (VEGFR-1) from the Golgi apparatus to the surface membrane. These data establish the Golgi apparatus as a juxtanuclear focal point for Ca2+ and β1-adrenergic signaling, which functions independently from the sarcoplasmic reticulum and the global Ca2+ transients that underlie the primary contractile function of the cell.
  • Inward rectifier potassium current (IK1) and Kir2 composition of the zebrafish (Danio rerio) heart

    Hassinen, M.; Haverinen, J.; Hardy, Matthew E.; Sheils, H.A.; Vornanen, M. (2015-12)
    Electrophysiological properties and molecular background of the zebrafish (Danio rerio) cardiac inward rectifier current (IK1) were examined. Ventricular myocytes of zebrafish have a robust (−6.7±1.2 pA pF−1 at −120 mV) strongly rectifying and Ba2+-sensitive (IC50=3.8 μM) IK1. Transcripts of six Kir2 channels (drKir2.1a, drKir2.1b, drKir2.2a, drKir2.2b, drKir2.3, and drKir2.4) were expressed in the zebrafish heart. drKir2.4 and drKir2.2a were the dominant isoforms in both the ventricle (92.9±1.5 and 6.3±1.5 %) and the atrium (28.9±2.9 and 64.7±3.0 %). The remaining four channels comprised together less than 1 and 7 % of the total transcripts in ventricle and atrium, respectively. The four main gene products (drKir2.1a, drKir2.2a, drKir2.2b, drKir2.4) were cloned, sequenced, and expressed in HEK cells for electrophysiological characterization. drKir2.1a was the most weakly rectifying (passed more outward current) and drKir2.2b the most strongly rectifying (passed less outward current) channel, whilst drKir2.2a and drKir2.4 were intermediate between the two. In regard to sensitivity to Ba2+ block, drKir2.4 was the most sensitive (IC50=1.8 μM) and drKir2.1a the least sensitive channel (IC50=132 μM). These findings indicate that the Kir2 isoform composition of the zebrafish heart markedly differs from that of mammalian hearts. Furthermore orthologous Kir2 channels (Kir2.1 and Kir2.4) of zebrafish and mammals show striking differences in Ba2+- sensitivity. Structural and functional differences needs to be taken into account when zebrafish is used as a model for human cardiac electrophysiology, cardiac diseases, and in screening cardioactive substances.
  • Advances in archaeomagnetic dating in Britain: New data, new approaches and a new calibration curve

    Batt, Catherine M.; Brown, M.C.; Clelland, Sarah-Jane; Korte, M.; Linford, P.; Outram, Zoe (2017-09)
    Archaeomagnetic dating offers a valuable chronological tool for archaeological investigations, particularly for dating fired material. The method depends on the establishment of a dated record of secular variation of the Earth's magnetic field and this paper presents new and updated archaeomagnetic directional data from the UK and geomagnetic secular variation curves arising from them. The data are taken from publications from the 1950's to the present day; 422 dated entries derived from existing archaeo and geomagnetic databases are re-evaluated and 487 new directions added, resulting in 909 entries with corresponding dates, the largest collection of dated archaeomagnetic directions from a single country. An approach to improving the largest source of uncertainty, the independent dating, is proposed and applied to the British Iron Age, resulting in 145 directions from currently available databases being updated with revised ages and/or uncertainties, and a large scale reassessment of age assignments prior to inclusion into the Magnetic Moments of the Past and GEOMAGIA50 databases. From the significantly improved dataset a new archaeomagnetic dating curve for the UK is derived through the development of a temporally continuous geomagnetic field model, and is compared with previous UK archaeomagnetic dating curves and global field models. The new model, ARCH-UK.1 allows model predictions for any location in the UK with associated uncertainties. It is shown to improve precision and accuracy in archaeomagnetic dating, and to provide new insight into past geomagnetic field changes.

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