Multi-phase volcanic resurfacing at Loki Patera on Io.

The Jovian moon Io hosts the most powerful persistently active volcano in the Solar System, Loki Patera. The interior of this volcanic, caldera-like feature is composed of a warm, dark floor covering 21,500 square kilometres surrounding a much cooler central 'island'. The temperature gradient seen across areas of the patera indicates a systematic resurfacing process, which has been seen to occur typically every one to three years since the 1980s. Analysis of past data has indicated that the resurfacing progressed around the patera in an anti-clockwise direction at a rate of one to two kilometres per day, and that it is caused either by episodic eruptions that emplace voluminous lava flows or by a cyclically overturning lava lake contained within the patera. However, spacecraft and telescope observations have been unable to map the emission from the entire patera floor at sufficient spatial resolution to establish the physical processes at play. Here we report temperature and lava cooling age maps of the entire patera floor at a spatial sampling of about two kilometres, derived from ground-based interferometric imaging of thermal emission from Loki Patera obtained on 8 March 2015 ut as the limb of Europa occulted Io. Our results indicate that Loki Patera is resurfaced by a multi-phase process in which two waves propagate and converge around the central island. The different velocities and start times of the waves indicate a non-uniformity in the lava gas content and/or crust bulk density across the patera.

Accreting protoplanets in the LkCa 15 transition disk.

Exoplanet detections have revolutionized astronomy, offering new insights into solar system architecture and planet demographics. While nearly 1,900 exoplanets have now been discovered and confirmed, none are still in the process of formation. Transition disks, protoplanetary disks with inner clearings best explained by the influence of accreting planets, are natural laboratories for the study of planet formation. Some transition disks show evidence for the presence of young planets in the form of disk asymmetries or infrared sources detected within their clearings, as in the case of LkCa 15 (refs 8, 9). Attempts to observe directly signatures of accretion onto protoplanets have hitherto proven unsuccessful. Here we report adaptive optics observations of LkCa 15 that probe within the disk clearing. With accurate source positions over multiple epochs spanning 2009-2015, we infer the presence of multiple companions on Keplerian orbits. We directly detect Hα emission from the innermost companion, LkCa 15 b, evincing hot (about 10,000 kelvin) gas falling deep into the potential well of an accreting protoplanet.

A role for the AKT1 potassium channel in plant nutrition.

In plants, potassium serves an essential role as an osmoticum and charge carrier. Its uptake by roots occurs by poorly defined mechanisms. To determine the role of potassium channels in planta, we performed a reverse genetic screen and identified an Arabidopsis thaliana mutant in which the AKT1 channel gene was disrupted. Roots of this mutant lacked inward-rectifying potassium channels and displayed reduced potassium (rubidium-86) uptake. Compared with wild type, mutant plants grew poorly on media with a potassium concentration of 100 micromolar or less. These results and membrane potential measurements suggest that the AKT1 channel mediates potassium uptake from solutions that contain as little as 10 micromolar potassium.

Collection and determinants of patient reported outcome measures in haemodialysis patients in Scotland.

BACKGROUND/INTRODUCTION: Patient reported outcome measures (PROMs) can evaluate the quality of health in patients with established renal failure. There is limited experience of their use within national renal registries. AIM: To describe the Scottish Renal Registry's (SRR) experience of collecting PROMS in the haemodialysis population and correlate PROMS to demographic and clinical parameters. DESIGN: Retrospective observational cross-sectional study. METHODS: Haemodialysis patients in Scotland were invited to complete the KDQOL™-36 questionnaire on the day of the annual SRR census in 2015 and 2016. Questionnaires were linked to census demographic and clinical variables. RESULTS: In 2016, 738 questionnaires were linked to census data (39% of prevalent haemodialysis population). Response rates differed with age (≥ 65 years 42%, < 65 years 36%) [χ2P = 0.006]; duration of renal replacement therapy (<1 year 46%, ≥1 < 5 years 38%, ≥ 5 years 33%) [χ2P = 0.002] and social class (Scottish Index of Multiple Deprivation (SIMD) Class 1 32%, Class 2 41%, Class 3 40%, Class 4 48%, Class 5 40%) [χ2P < 0.001]. There were significant differences in PROMs with age, SIMD quintile and primary renal diagnosis. Achieving a urea reduction ratio of >65% and dialysing through arteriovenous access were associated with significantly higher PROMs. PROMs were not affected by haemoglobin or phosphate concentration. DISCUSSION/CONCLUSIONS: Routine collection of PROMs is feasible and can identify potentially under-recognized and treatable determinants to quality of life. The association between attaining recommended standards of care and improved PROMs is striking. Individual and population-wide strategies are required to improve PROMs.

Activation of K+ Channels in the Plasma Membrane of Arabidopsis by ATP Produced Photosynthetically.

Light activates a K+ channel and transiently depolarizes the plasma membrane of Arabidopsis mesophyll cells. Genetically or chemically impairing photosynthesis abolished this electrical response to light. These results indicate that illuminated chloroplasts produce a factor that activated K+ channels in the plasma membrane. By patch clamping at the single-channel level, we have obtained evidence that ATP is one such factor. Application of 0.2 to 2 mM ATP to the cytoplasmic side of excised patches of membrane reversibly activated the type of channel that was activated by light in cell-attached patches. In addition, an outward-rectifying K+ channel and an outward-rectifying nonselective cation channel were similarly activated by ATP, whereas a nonselective stretch-activated channel was unaffected by this treatment. This novel mechanism for controlling the permeability of the plasma membrane to K+ may be important to photosynthetic metabolism.

Investigation of outbreaks of Pneumocystis jirovecii pneumonia in two Scottish renal units.

Pneumocystis jirovecii is recognized as an opportunistic pathogen. In recent years, human-to-human transmission of P. jirovecii has been demonstrated. However, outbreaks of P. jirovecii infections are not well defined because the epidemiological setting that facilitates transmission is not fully understood. This article describes two outbreaks of P. jirovecii pneumonia (PCP) in renal transplant patients in the West of Scotland. In total, 25 patients in two geographically contiguous locations were affected. Allele B was identified as the dominant type, along with allele A3. It was not possible to determine the exact reason for clustering of cases, although the outpatient clinic setting featured in one of the outbreaks. The outbreaks ceased with the use of trimethoprim-sulphamethoxazole prophylaxis; the target populations that received prophylaxis were different in the two outbreaks. Infection control teams should be alert to the possibility of outbreaks of PCP.

Photocontrol of stem growth.

Rapid and measurable growth rate changes that occur in seedling stems upon illumination serve as an excellent means to analyze signal transduction. Growth kinetic studies have shown how red, far-red and blue light signals are transduced via the solitary and/or coordinated action of known plant photoreceptors. These reports are consistent with current findings describing light-induced photoreceptor interaction and compartmentation.

Potassium uptake supporting plant growth in the absence of AKT1 channel activity: Inhibition by ammonium and stimulation by sodium.

A transferred-DNA insertion mutant of Arabidopsis that lacks AKT1 inward-rectifying K+ channel activity in root cells was obtained previously by a reverse-genetic strategy, enabling a dissection of the K+-uptake apparatus of the root into AKT1 and non-AKT1 components. Membrane potential measurements in root cells demonstrated that the AKT1 component of the wild-type K+ permeability was between 55 and 63% when external [K+] was between 10 and 1,000 microM, and NH4+ was absent. NH4+ specifically inhibited the non-AKT1 component, apparently by competing for K+ binding sites on the transporter(s). This inhibition by NH4+ had significant consequences for akt1 plants: K+ permeability, 86Rb+ fluxes into roots, seed germination, and seedling growth rate of the mutant were each similarly inhibited by NH4+. Wild-type plants were much more resistant to NH4+. Thus, AKT1 channels conduct the K+ influx necessary for the growth of Arabidopsis embryos and seedlings in conditions that block the non-AKT1 mechanism. In contrast to the effects of NH4+, Na+ and H+ significantly stimulated the non-AKT1 portion of the K+ permeability. Stimulation of akt1 growth rate by Na+, a predicted consequence of the previous result, was observed when external [K+] was 10 microM. Collectively, these results indicate that the AKT1 channel is an important component of the K+ uptake apparatus supporting growth, even in the "high-affinity" range of K+ concentrations. In the absence of AKT1 channel activity, an NH4+-sensitive, Na+/H+-stimulated mechanism can suffice.

An apparatus for studying rapid electrophysiological responses to light demonstrated on Arabidopsis leaves.

An apparatus for making high-resolution measurements of electrophysiological changes induced by light in plant cells was constructed. Its main components were a xenon arc lamp, an electronic shutter, a liquid light-guide, a computer equipped with an analog-to-digital converter and a computer program that controlled the shutter and data acquisition. The apparatus was used to examine transient changes in membrane potential (Vm) that occur upon illumination in Arabidopsis leaves. Light-on induced a transient hyperpolarization of 4 mV after a lag time of 0.53 s. It was followed by a much larger transient depolarization that peaked 31 s after light-on. The Vm returned to near its original value after approximately 3 min. The early changes in Vm have been proposed to result from effects of photosynthetically produced ATP on the activities of H(+)-ATPases and K+ channels at the plasma membrane. The kinetics of the initial hyperpolarization were found to be reasonably consistent with such a mechanism. It is expected that the apparatus described here will be useful in future investigations of this and other electrophysiological responses to light.

Chronic kidney disease prevalence and secular trends in a UK population: the impact of MDRD and CKD-EPI formulae.

INTRODUCTION: Most UK laboratories use the MDRD4 formula to estimate glomerular filtration rate (eGFR), but this may exaggerate chronic kidney disease (CKD) prevalence. In a large adult population, we examined the impact of the more accurate CKD-EPI formulae on prevalence estimates, and on secular trends in prevalence. METHODS: We extracted all serum creatinine (SCr) results for adults, processed in our laboratory during two 1-year periods (2004, 2009-10). To minimize the effect of acute illness, a patient's lowest SCr was used for each period. eGFR (traceable to isotope dilution mass spectrometry value) was calculated using the MDRD4 and CKD-EPI formulae. Prevalence estimates were compared, with sub-group analysis by age and sex. RESULTS: In 2004, 102 322 patients had SCr tested (35.4% of the adult population), rising to 123 121 (42.3%) in 2009-10. The proportion tested rose with age to 86% of 85- to 89-year olds. The prevalence of CKD stages 3-5 was lower with the CKD-EPI formulae than the MDRD4 formula. The CKD-EPI formulae reclassified 17 014 patients (5.8%) to milder stages of CKD, most commonly from eGFR 60-89 ml/min/1.73m(2) and CKD stage 3A, in women, and in those <70 years old. 5172 patients (1.8%), mostly elderly women, were reclassified to more severe stages of CKD. Between the two time periods, the prevalence of CKD stages 3-5 rose from 5.44% to 5.63% of the population using MDRD4, but was static at 4.94% with CKD-EPI. CONCLUSION: The CKD-EPI formulae, which are more accurate than the MDRD4 formula at higher GFR, reduced the estimated prevalence of CKD stages 3-5 by 0.5% in 2004 and 0.7% in 2009-10. The greatest reclassification was seen in CKD 3A, particularly amongst middle-aged females. The minor rise in CKD prevalence between 2004 and 2009-10 seen with the MDRD4 formula was not confirmed with the CKD-EPI formulae. The CKD-EPI formulae may reduce overdiagnosis of CKD, but further assessment in the elderly is required before widespread implementation.

Ion channels and the transduction of light signals.

Studies of biological light-sensing mechanisms are revealing important roles for ion channels. Photosensory transduction in plants is no exception. In this article, the evidence that ion channels perform such signal-transducing functions in the complex array of mechanisms that bring about plant photomorphogenesis will be reviewed and discussed. The examples selected for discussion range from light-gradient detection in unicellular algae to the photocontrol of stem growth in Arabidopsis. Also included is some discussion of the technical aspects of studies that combine electrophysiology and photobiology.

Influence of electrolytes on growth, phototropism, nutation and surface potential in etiolated cucumber seedlings.

A variety of electrolytes (10-30 mol m-3) increased the relative growth rate of etiolated cucumber (Cucumis sativus L. cv. Burpee's Pickler) hypocotyls by 20-50% relative to water-only controls. The nonelectrolyte mannitol inhibited growth by 10%. All salts tested were effective, regardless of chemical composition or valence. Measurements of cell-sap osmolality ruled out an osmotic mechanism for the growth stimulation by electrolytes. This, and the nonspecificity of the response, indicate that an electrical property of the solutions was responsible for their growth-stimulating activity. Measurements of surface electrical potential supported this reasoning. Treatment with electrolytes also enhanced nutation and altered the pattern of phototropic curvature development. A novel analytical method for quantitating these effects on growth was developed. The evidence indicates that electrolytes influence an electrophysiological parameter that is involved in the control of cell expansion and the coordination of growth underlying tropisms and nutations.

Mechanism of blue-light-induced plasma-membrane depolarization in etiolated cucumber hypocotyls.

A large, transient depolarization of the plasma membrane precedes the rapid blue-light (BL)-induced growth suppression in etiolated seedlings of Cucumis sativus L. The mechanism of this voltage transient was investigated by applying inhibitors of ion channels and the plasma-membrane H(+)-ATPase, by manipulating extracellular ion concentrations, and by measuring cell input resistance and ATP levels. The depolarizing phase was not affected by Ca(2+)-channel blockers (verapamil, La3+) or by reducing extracellular free Ca2+ by treatment with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). However, these treatments did reduce the rate of repolarization, indicating an inward movement of Ca2+ is involved. No effects of the K(+)-channel blocker tetraethylammonium (TEA+) were detected. Vanadate and KCN, used to inhibit the H(+)-ATPase, reduced or completely inhibited the BL-induced depolarization. Levels of ATP increased by 11-26% after 1-2 min of BL. Input resistance of trichrome cells, measured with double-barreled microelectrodes, remained constant during the onset of the depolarization but decreased as the membrane voltage became more positive than -90 mV. The results indicate that the depolarization mechanism initially involves inactivation of the H(+)-ATPase with subsequent transient activation of one or more types of ion channels.

Anion channels and the stimulation of anthocyanin accumulation by blue light in Arabidopsis seedlings.

Activation of anion channels by blue light begins within seconds of irradiation in seedlings and is related to the ensuing growth inhibition. 5-Nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) is a potent, selective, and reversible blocker of these anion channels in Arabidopsis thaliana. Here we show that 20 microM NPPB blocked 72% of the blue-light-induced accumulation of anthocyanin pigments in seedlings. Feeding biosynthetic intermediates to wild-type and tt5 seedlings provided evidence that NPPB prevented blue light from up-regulating one or more steps between and including phenylalanine ammonia lyase and chalcone isomerase. NPPB was found to have no significant effect on the blue-light-induced increase in transcript levels of PAL1, CHS, CHI, or DFR, which are genes that encode anthocyanin-biosynthetic enzymes. Immunoblots revealed that NPPB also did not inhibit the accumulation of the chalcone synthase, chalcone isomerase, or flavanone-3-hydroxylase proteins. This is in contrast to the reduced anthocyanin accumulation displayed by a mutant lacking the HY4 blue-light receptor, as hy4 displayed reduced expression of the above enzymes. Taken together, the data indicate that blue light acting through HY4 leads to an increase in the amount of biosynthetic enzymes but blue light must also act through a separate, anion-channel-dependent system to create a fully functional biosynthetic pathway.

Nonselective block by La3+ of Arabidopsis ion channels involved in signal transduction.

Lanthanide ions such as La3+ are frequently used as blockers to test the involvement of calcium channels in plant and animal signal transduction pathways. For example, the large rise in cytoplasmic Ca2+ concentration triggered by cold shock in Arabidopsis seedlings is effectively blocked by 10 mM La3+ and we show here that the simultaneous large membrane depolarization is similarly blocked. However, a pharmacological tool is only as useful as it is selective and the specificity of La3+ for calcium channels was brought into question by our finding that it also blocked a blue light (BL)-induced depolarization that results from anion channel activation and believed not to involve calcium channels. This unexpected inhibitory effect of La3+ on the BL-induced depolarization is explained by our finding that 10 mM La3+ directly and completely blocked the BL-activated anion channel when applied to excised patches. We have investigated the ability of La3+ to block noncalcium channels in Arabidopsis. In addition to the BL-activated anion channel, 10 mM La3+ blocked a cation channel and a stretch-activated channel in patches of plasma membrane excised from hypocotyl cells. In root cells, 10 mM La3+ inhibited the activity of an outward-rectifying potassium channel at the whole cell and single-channel level by 47% and 58%, respectively. We conclude that La3+ is a nonspecific blocker of multiple ionic conductances in Arabidopsis and may disrupt signal transduction processes independently of any effect on Ca2+ channels.

An anion channel in Arabidopsis hypocotyls activated by blue light.

A rapid, transient depolarization of the plasma membrane in seedling stems is one of the earliest effects of blue light detected in plants. It appears to play a role in transducing blue light into inhibition of hypocotyl (stem) elongation, and perhaps other responses. The possibility that activation of a Cl- conductance is part of the depolarization mechanism was raised previously and addressed here. By patch clamping hypocotyl cells isolated from dark-grown (etiolated) Arabidopsis seedlings, blue light was found to activate an anion channel residing at the plasma membrane. An anion-channel blocker commonly known as NPPB 15-nitro-2-(3-phenylpropylamino)-benzoic acid] potently and reversibly blocked this anion channel. NPPB also blocked the blue-light-induced depolarization in vivo and decreased the inhibitory effect of blue light on hypocotyl elongation. These results indicate that activation of this anion channel plays a role in transducing blue light into growth inhibition.

Sequential and coordinated action of phytochromes A and B during Arabidopsis stem growth revealed by kinetic analysis.

Photoreceptor proteins of the phytochrome family mediate light-induced inhibition of stem (hypocotyl) elongation during the development of photoautotrophy in seedlings. Analyses of overt mutant phenotypes have established the importance of phytochromes A and B (phyA and phyB) in this developmental process, but kinetic information that would augment emerging molecular models of phytochrome signal transduction is absent. We have addressed this deficiency by genetically dissecting phytochrome-response kinetics, after having solved the technical issues that previously limited growth studies of small Arabidopsis seedlings. We show here, with resolution on the order of minutes, that phyA initiated hypocotyl growth inhibition upon the onset of continuous red light. This primary contribution of phyA began to decrease after 3 hr of irradiation, the same time at which immunochemically detectable phyA disappeared and an exclusively phyB-dependent phase of inhibition began. The sequential and coordinated actions of phyA and phyB in red light were not observed in far-red light, which inhibited growth persistently through an exclusively phyA-mediated pathway.