2,117 research outputs found
Direct and specific activation of human inward rectifier K+ channels by membrane phosphatidylinositol 4,5-bisphosphate
No full textMany ion channels are modulated by phosphatidylinositol 4,5-bisphosphate (PIP(2)), but studies examining the PIP(2) dependence of channel activity have been limited to cell expression systems, which present difficulties for controlling membrane composition. We have characterized the PIP(2) dependence of purified human Kir2.1 and Kir2.2 activity using (86)Rb(+) flux and patch clamp assays in liposomes of defined composition. We definitively show that these channels are directly activated by PIP(2) and that PIP(2) is absolutely required in the membrane for channel activity. The results provide the first quantitative description of the dependence of eukaryotic Kir channel function on PIP(2) levels in the membrane; Kir2.1 shows measureable activity in as little as 0.01% PIP(2), and open probability increases to ?0.4 at 1% PIP(2). Activation of Kir2.1 by phosphatidylinositol phosphates is also highly selective for PIP(2); PI, PI(4)P, and PI(5)P do not activate channels, and PI(3,4,5)P(3) causes minimal activity. The PIP(2) dependence of eukaryotic Kir activity is almost exactly opposite that of KirBac1.1, which shows marked inhibition by PIP(2). This raises the interesting hypothesis that PIP(2) activation of eukaryotic channels reflects an evolutionary adaptation of the channel to the appearance of PIP(2) in the eukaryotic cell membrane
Dual-mode phospholipid regulation of human inward rectifying potassium channels
No full textThe lipid bilayer is a critical determinant of ion channel activity; however, efforts to define the lipid dependence of channel function have generally been limited to cellular expression systems in which the membrane composition cannot be fully controlled. We reconstituted purified human Kir2.1 and Kir2.2 channels into liposomes of defined composition to study their phospholipid dependence of activity using (86)Rb(+) flux and patch-clamp assays. Our results demonstrate that Kir2.1 and Kir2.2 have two distinct lipid requirements for activity: a specific requirement for phosphatidylinositol 4,5-bisphosphate (PIP(2)) and a nonspecific requirement for anionic phospholipids. Whereas we previously showed that PIP(2) increases the channel open probability, in this work we find that activation by POPG increases both the open probability and unitary conductance. Oleoyl CoA potently inhibits Kir2.1 by antagonizing the specific requirement for PIP(2), and EPC appears to antagonize activation by the nonspecific anionic requirement. Phosphatidylinositol phosphates can act on both lipid requirements, yielding variable and even opposite effects on Kir2.1 activity depending on the lipid background. Mutagenesis experiments point to the role of intracellular residues in activation by both PIP(2) and anionic phospholipids. In conclusion, we utilized purified proteins in defined lipid membranes to quantitatively determine the phospholipid requirements for human Kir channel activity
The Indian history of an American institution: Native Americans and Dartmouth
No full textAbout the Book
(from upne.com) Dartmouth College began life as an Indian school, a pretense that has since been abandoned. Still, the institution has a unique, if complicated, relationship with Native Americans and their history. Beginning with Samson Occom’s role as the first “development officer” of the college, Colin G. Calloway tells the entire, complex story of Dartmouth’s historical and ongoing relationship with Native Americans. Calloway recounts the struggles and achievements of Indian attendees and the history of Dartmouth alumni’s involvements with American Indian affairs. He also covers more recent developments, such as the mascot controversies, the emergence of an active Native American student organization, and the partial fulfillment of a promise deferred. This is a fascinating picture of an elite American institution and its troubled relationship— at times compassionate, at times conflicted—with Indians and Native American culture.
About the Author
(from upne.com) Colin G. Calloway is John Kimball Jr. 1943 Professor of History and Professor of Native American Studies at Dartmouth College. He is the author of numerous books, including One Vast Winter Count: The Native American West Before Lewis and Clark (2003), which won six best-book awards.
About the Electronic Publication
This electronic publication of The Indian History of an American Institution was made possible with the permission of the author. The University Press of New England created EPUB and PDF files from a scanned copy of the book.
Rights Information
Creative Commons Attribution-NonCommercial License © Trustees of Dartmouth Collegehttps://digitalcommons.dartmouth.edu/dartmouth_press/1004/thumbnail.jp
Expression and purification of recombinant human inward rectifier K+ (KCNJ) channels in Saccharomyces cerevisiae
No full textThe inward rectifier family of potassium (KCNJ) channels regulate vital cellular processes including cell volume, electrical excitability, and insulin secretion. Dysfunction of different isoforms have been linked to numerous diseases including Bartter's, Andersen-Tawil, Smith-Magenis Syndromes, Type II diabetes mellitus, and epilepsy, making them important targets for therapeutic intervention. Using a family-based approach, we succeeded in expressing 10 of 11 human KCNJ channels tested in Saccharomyces cerevisiae. GFP-fusion proteins showed that these channels traffic correctly to the plasma-membrane suggesting that the protein is functional. A 2-step purification process can be used to purify the KCNJ channels to >95% purity in a mono-dispersed form. After incorporation into liposomes, (86)Rb(+) flux assays confirm the functionality of the purified proteins as inward rectifier potassium channels
Underwater detection, classification and localisation: Improving the capabilities of towed sonar arrays
No full textThe end of the Cold War and the collapse of the Warsaw pact have resulted in a change of operational theatre for the naval forces of the North Atlantic Treaty Organisation (NATO). In particular, the focus of Anti Submarine Warfare forces has shifted from tracking Soviet nuclear ballistic missile submarine in the deep waters of the Atlantic ocean to hunting smaller and quieter Diesel electric submarines in coastal water. In most scenarios, towed array sonars are the best sensor to detect, classify and localise submarines. The long passive towed array sonars used during the Cold war are more difficult to use in coastal waters and are being replaced by most Navies by Low Frequency Active Sonars (LFAS) using a towed source and shorter towed receiving array. These shorter towed arrays can be used in both active and passive modes. In passive mode, their reduced size offer limited performance compared to their longer equivalent. In active mode, they can detect submarines at long ranges in shallow waters but are plagued by false alarms caused by echoes from features of the seafloor. This thesis deals with algorithms improving Detection, Classification and Localisation for towed sonar arrays, with a specific focus on LFAS sonars. In Chapter 2, we derive, analyse and apply to measured data a method for improving detection performance with short passive towed arrays. An important issue in detection of quiet acoustic source with short towed arrays is the improvement in signal-to-noise ratio (SNR) and bearing resolution for targets emitting low frequency signals. One of the techniques believed to improve these characteristics is Synthetic Aperture Sonar (SAS). The method is based on the artificial enlargement of a sonar array by coherently integrating acoustic snapshots at different antenna positions. We first derive theoretical measures of performance of passive SAS and report on its application in combination with other signal-processing algorithms. Its theoretical performance is compared with that of the frequently used incoherent integration. The used passive SAS algorithm is the method known as Extended Towed Array Measurement (ETAM) or the overlap correlator. It is based on the correlation of data snapshots on overlapping hydrophones. Correlation is a key issue in this method and since it is affected by noisy targets, some gain can be expected from noise cancellation. The influence on the performance of ETAM of a method of tow ship noise cancelling at hydrophone level (Inverse Beam Forming, IBF) is analysed. This approach increases ETAM performance by removing a loud and highly correlated noise source, the tow ship, and thus enhancing the other targets in the beam pattern. The results of the algorithms applied to two experimental datasets show that they bring an improvement close to theoretical expectations. Port starboard discrimination and the successful combination of IBF with ETAM make this approach innovative. In Chapter 3, methods for improving the localisation of a source with a short towed array are analysed and applied to data, both simulated and measured at sea. Localisation performance with sonar towed array is related to the array length. The knowledge of the position of a given acoustic source gives a critical tactical advantage to a ship. There are a limited number of ways to estimate the range of a source with a towed passive sonar, most requiring the towing platform to execute a manoeuvre. These manoeuvres are undesirable as they take a lot of time, cause bending of the towed array and can even put the towing platform in harm’s way. We present a number of source position estimation methods for both broadband and narrowband sources suitable for short towed arrays. Recursive methods based on the extended Kalman filter are first examined. A new method based on the integration of time delay of arrival measurements along the sonar path is described. We derive theoretical performance indicators and show that this method gives the possibility to estimate the position and speed of a source without a manoeuvre. In Chapter 4, the Classification performance of a broadband waveform is analysed and measured on data collected at sea. Like any long-range active sonar system, LFAS produces a large amount of unwanted sea bottom echoes or clutter. These echoes give rise to false alarms that increase the computational load of target trackers and jeopardise the correct classification of each echo. The number of false alarms due to clutter can be reduced either through echo classification techniques or through Doppler filtering provided the targets of interest are in motion. Much research has been carried out on waveform investigation for the efficient use of bandwidth capabilities of modern sonar transmitters. Among the quantity of waveforms, Binary Phase Shift Keyed (BPSK) pulses have emerged as exhibiting cross-correlation properties relevant to Doppler filtering while maintaining a range resolution comparable to Frequency Modulated (FM) pulses. We have successfully applied a false alarm reduction technique using contacts obtained with an FM pulse subsequently processed by Doppler filtering with a BPSK pulse. The Doppler classification performance for this pulse is evaluated on an experimental dataset and a few limitations of BPSK are identified.Aircraft Transport and OperationAerospace Engineerin
Zoledronic Acid Blocks Overactive Kir6.1/SUR2-Dependent KATP Channels in Skeletal Muscle and Osteoblasts in a Murine Model of Cantú Syndrome
No full textCantú syndrome (CS) is caused by the gain of function mutations in the ABCC9 and KCNJ8 genes encoding, respectively, for the sulfonylureas receptor type 2 (SUR2) and the inwardly rectifier potassium channel 6.1 (Kir6.1) of the ATP-sensitive potassium (KATP) channels. CS is a multi-organ condition with a cardiovascular phenotype, neuromuscular symptoms, and skeletal malformations. Glibenclamide has been proposed for use in CS, but even in animals, the drug is incompletely effective against severe mutations, including the Kir6.1wt/V65M. Patch-clamp experiments showed that zoledronic acid (ZOL) fully reduced the whole-cell KATP currents in bone calvaria cells from wild type (WT/WT) and heterozygous Kir6.1wt/V65MCS mice, with IC50 for ZOL block < 1 nM in each case. ZOL fully reduced KATP current in excised patches in skeletal muscle fibers in WT/WT and CS mice, with IC50 of 100 nM in each case. Interestingly, KATP currents in the bone of heterozygous SUR2wt/A478V mice were less sensitive to ZOL inhibition, showing an IC50 of ~500 nM and a slope of ~0.3. In homozygous SUR2A478V/A478V cells, ZOL failed to fully inhibit the KATP currents, causing only ~35% inhibition at 100 μM, but was responsive to glibenclamide. ZOL reduced the KATP currents in Kir6.1wt/VMCS mice in both skeletal muscle and bone cells but was not effective in the SUR2[A478V] mice fibers. These data indicate a subunit specificity of ZOL action that is important for appropriate CS therapies
Orbit design for future SpaceChip swarm missions in a planetary atmosphere
No full textThe effect of solar radiation pressure and atmospheric drag on the orbital dynamics of satellites-on-a-chip (SpaceChips) is exploited to design equatorial long-lived orbits about the oblate Earth. The orbit energy gain due to asymmetric solar radiation pressure, considering the Earth's shadow, is used to balance the energy loss due to atmospheric drag. Future missions for a swarm of SpaceChips are proposed, where a number of small devices are released from a conventional spacecraft to perform spatially distributed measurements of the conditions in the ionosphere and exosphere. It is shown that the orbit lifetime can be extended and indeed selected through solar radiation pressure and the end-of-life re-entry of the swarm can be ensured, by exploiting atmospheric drag
From selective permeation to physiology in potassium channels
No full textAbstract Highly K+-selective potassium channels are essential for electrical signaling The high selectivity of most K+ channels, with relative K+: Na+ permeabilities being as high as 100-1000:1 arises from the conserved so-called K+ channel selectivity filter (SF). Structural and computational studies have shown how the SF forms multiple sites that coordinate K+, by mimicking the water dipoles that coordinate K+ ions in solution, and thermodynamically favoring the binding of K+ over Na+. Selective conduction of K+ ions then results from a “knock-on” mechanism, whereby entering ions destabilize the next ion in the file. This review highlights key biophysical and biochemical research that provides insights to the atomic details of these processes. It then discusses how mutations that alter K+ selectivity and permeation in different K+ channels underlie multiple simple and complex diseases, illustrating how selectivity and permeation are central to physiology and to pathophysiology, and important for physiologists to be aware of
Zebrafish_KATP_Emfinger_et_al_RSOS_Data
No full textThis is the data for the paper: Expression and function of ATP-dependent potassium channels in zebrafish islet β-cells
Christopher H. Emfinger, Alecia Welscher, Zihan Yan, Yixi Wang, Hannah Conway, Jennifer B. Moss, Larry G. Moss, Maria S. Remedi, and Colin G. Nichols
These data are organized into sub-folders which include PCRs for the sorted cells (cf Figure 3), the whole islets (cf Figure 3), the electrophysiological records (cf Figures 2 and 4; raw and data-reduced, with subfolders for the ATP sensitivity, ADP activation, and pharmacology (Diazoxide and Pinacidil activation and glibenclamide and tolbutamide inhibition), as well as the injection studies (cf figure 1). These are uploaded as a single zip file for download. The raw electrophysiological traces are in pClamp-compatible file formats. The PCR gels are in PDFs. The data for injections are in an excel file with processing in a GraphPad prism
Pathophysiological consequences of KATP channel overactivity and pharmacological response to glibenclamide in skeletal muscle of a murine model of Cantù syndrome
No full textCantù syndrome (CS) arises from mutations i
- …
