Functional Interactions between KCNE1 C-Terminus and the KCNQ1 Channel

The KCNE1 gene product (minK protein) associates with the cardiac KvLQT1 potassium channel (encoded by KCNQ1) to create the cardiac slowly activating delayed rectifier, IKs. Mutations throughout both genes are linked to the hereditary cardiac arrhythmias in the Long QT Syndrome (LQTS). KCNE1 exerts its specific regulation of KCNQ1 activation via interactions between membrane-spanning segments of the two proteins. Less detailed attention has been focused on the role of the KCNE1 C-terminus in regulating channel behavior. We analyzed the effects of an LQT5 point mutation (D76N) and the truncation of the entire C-terminus (Δ70) on channel regulation, assembly and interaction. Both mutations significantly shifted voltage dependence of activation in the depolarizing direction and decreased IKs current density. They also accelerated rates of channel deactivation but notably, did not affect activation kinetics. Truncation of the C-terminus reduced the apparent affinity of KCNE1 for KCNQ1, resulting in impaired channel formation and presentation of KCNQ1/KCNE1 complexes to the surface. Complete saturation of KCNQ1 channels with KCNE1-Δ70 could be achieved by relative over-expression of the KCNE subunit. Rate-dependent facilitation of K+ conductance, a key property of IKs that enables action potential shortening at higher heart rates, was defective for both KCNE1 C-terminal mutations, and may contribute to the clinical phenotype of arrhythmias triggered by heart rate elevations during exercise in LQTS mutations. These results support several roles for KCNE1 C-terminus interaction with KCNQ1: regulation of channel assembly, open-state destabilization, and kinetics of channel deactivation

Green hay application and diverse seeding approaches to restore grazed lowland meadows: progress after 4 years and effects of a flood risk gradient

The two most common approaches to target species introduction in European meadow restoration are green‐hay transfer from species‐rich donor sites and the use of diverse seed mixtures reflecting the chosen target community. The potential of both approaches to restore species‐rich grassland has been variously reviewed, but very few studies have experimentally compared them at one and the same site. Moreover, studies involving one or both approaches have rarely taken into account environmental gradients at a site, and measured the impacts of such gradients on restoration outcomes. Such gradients do e.g. exist during grassland restoration on former arable land in river floodplains, where gradients in the occurrence of flooding, and in associated edaphic characteristics such as nutrient availability, might affect restoration outcomes. Using a randomised complete block experimental design, based on five different indicators of restoration progress, we compared the usefulness of green‐hay application and diverse‐seeding to restore species‐rich grazed meadows of the MG5 grassland type according to the British National Vegetation Classification, and also investigated how restoration outcomes differed after four years between areas within experimental plots characterized by high flood risk, and areas characterized by low flood risk. Overall, both restoration approaches yielded similar results over the course of the experiment, whereas high flood risk levels and associated edaphic factors such as high availability of phosphorus negatively affected restoration progress particularly in terms of floristic similarity to restoration targets. These results highlight the need to take into account environmental gradients during meadow restoration

Mesotrophic basiphilous communities affected by changes in soil properties in two dune slack chronosequences

Two soil chronosequences were investigated to identify soil properties related to acidification during succession of dune slack vegetation. One chronosequence was associated with a primary succession series on a wet beach plain on the Dutch island of Schiermonnikoog, the other with a succession series after sod cutting in a secondary (blown out) slack on the island of Terschelling (the Koegelwieck). Both chronosequences include a succession sequence which starts from bare sand, proceeds to basiphilous, mesotrophic (low productivity) vegetation types (Junco baltici-Schoenetum nigricantis) with many rare species, and ends with productive shrubbery or forested, acidified organically enriched soils with little floristic value. The pH decreased with time in both chronosequences. In the beach plain this was correlated with an increase in organic matter and a decrease in salt content. In the blown out slack the pH decrease was correlated with an increase of organic matter and with an increase in exchangeable bases, except for Ca, on the exchange complex. The faster organic matter increase and pH decrease in the blown out slack chronosequence resulted in a relatively short persistence of mesotrophic vegetation type with endangered basiphilous species. The mesotrophic basiphilous vegetation persists for a longer time (c. 20-25 years) in the initially calcareous beach plain chronosequence with a high acid buffering capacity as compared to the Koegelwieck chronosequence with a low acid buffering capacity

Atmospheric deposition of acidifying and eutrophicating substances in dune slacks

The atmospheric input of nitrogen and potantial acid, and the composition of the leachate from the topsoil layer are quantified for eight dune slack sites differing in plant composition, on the Frisian islands of Terschelling and Schiermonnikoog. Basiphilous mesotrophic communities with many rare plant species grow in one site on Terschelling and two sites on Schiermonnikoog. Samples were taken in the period mid May 1992 - mid May 1993. Bulk atmospheric nitrogen deposition measured in an open collector was between 15-20 kg ha(-1) yr(-1) for the eight sites. On Terschelling, the deposition was slightly higher than on Schiermonnikoog. Ammonium was a third of the total amount of nitrogen deposited on Terschelling and half the amount of nitrogen deposited on Schiermonnikoog. The deposition of potential acid varied from 490 to 810 mol ha(-1) yr(-1). On Terschelling, the amount of potential acid was highest and around 800 mol ha(-1) yr(-1) for both sites. On Schiermonnikoog, the amount of potential acid was lowest for the dune slacks in the north-western part of the island and it showed an increase for slacks towards the eastern part of the island. Calcium is the main cation leached from the topsoil followed by sodium, magnesium and potassium. Nitrogen or ammonium hardly leached from the topsoil layer. The shift from basiphilous pioneer communities toward older and more acid stages of dune slack succession appears to be caused primarily by leaching of base cations rather than eutrophication