Ion pumping

Maintenance of the concentration of various ions, both inside and outside the neutrophil, is crucial for cell function. Concentrations of ions such as Na+, K+, Cl, Ca2+ and H+ outside the neutrophil (i.e. in extracellular fluids) are 140, 5, 140, 2 and 100 mM, respectively. Inside the neutrophil, the concentrations of these ions are 20 mM, 120 mM, 80 mM, 100 nM and 100 mM, respectively. The transport of these ions into and out of the neutrophil is regulated by ion channels (which may exist in the open or closed states), ion pumps and ion transporters. 

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Modem UHV chambers are constmcted from stainless steel. The principal seals are metal-on-metal, thus the use of greases is avoided. A combination of pumps is nomially used, including ion pumps, turbomolecular pumps, cryopumps and mechanical (roughing) pumps. The entire system is generally heatable to 500 K. This bakeout for a period of... 

Few of the naturally occurring elements have significant amounts of radioactive isotopes, but there are many artificially produced radioactive species. Mass spectrometry can measure both radioactive and nonradioactive isotope ratios, but there are health and safety issues for the radioactive ones. However, modem isotope instmments are becoming so sensitive that only very small amounts of sample are needed. Where radioactive isotopes are a serious issue, the radioactive hazards can be minimized by using special inlet systems and ion pumps in place of rotary pumps for maintaining a vacuum. For example, mass spectrometry is now used in the analysis of Pu/ Pu ratios. 

Fig. 5. Plots of pump-down performance for pumps operating on 0.1-m-dia x 0.43-m-long stainless-steel tubing. Curves 1—4 are sputter-ion pumps of different makes curve 5 is Orbitron type and curve 6, LN-trapped oil DP. Pressure is measured using Bayard-Alpert gauge (BAG) (26). To convert Pa to...

Given the difficulty of obtaining three-dimensional crystals of membrane proteins, it is not surprising that the electron microscope technique is now widely used to study large membrane-bound complexes such as the acetylcholine receptor, rhodopsin, ion pumps, gap junctions, water channels and light-harvesting complexes, which crystallize in two dimensions. 

Such vessels can also be baked at a temperature of several hundred degrees, to drive off any gas adsorbed on metal surfaces. The pumping function of an ion gauge was developed into efficient ionic pumps and turbomolecular pumps , supplemented by low-temperature traps and cryopumps. Finally, sputter-ion pumps, which rely on sorption processes initiated by ionised gas, were introduced. A vacuum of 10 "-10 Torr, true UHV, became routinely accessible in the late 1950s, and surface science could be launched. 

Depletion of ATP in the cells prevents maintenance of the membrane potential, inhibits the functioning of ion pumps, and attenuates cellular signal transduction (e.g., formation of second messengers such as inositol phos phates or cyclic AMP). A marked ATP depletion ultimately impairs the activ-itv of the cell and leads to ceil death. 

Three kinds of equilibrium potentials are distinguishable. A metal-ion potential exists if a metal and its ions are present in balanced phases, e.g., zinc and zinc ions at the anode of the Daniell element. A redox potential can be found if both phases exchange electrons and the electron exchange is in equilibrium for example, the normal hydrogen half-cell with an electron transfer between hydrogen and protons at the platinum electrode. In the case where a couple of different ions are present, of which only one can cross the phase boundary — a situation which may exist at a semiperme-able membrane — one obtains a so called membrane potential. Well-known examples are the sodium/potassium ion pumps in human cells. 

One of the primary ways in which cold causes injury to cells is by the loss of the capability to regulate cellular volume. This occurs because of the decrease in the available energy (ATP) caused by hypothermia and ischemia which is needed by the membrane-bound ion pumps, the increased rate of leakage of ions through the plasma membrane, and the decreased activity of the membrane-bound ion pumps, especially the Na-pump. 

Hydrogen detection in this type of meter is achieved using an ion pump, mass spectrometry or thermal conductivity detectors. ... 

Purified membrane proteins or enzymes can be incorporated into these vesicles in order to assess what factors (eg, specific lipids or ancillary proteins) the proteins require to reconstitute their function. Investigations of purified proteins, eg, the Ca " ATPase of the sarcoplasmic reticulum, have in certain cases suggested that only a single protein and a single lipid are required to reconstitute an ion pump. 

Many environmental toxins interact with specific cellular receptors, including enzymes, ion channels and ion pumps, and thus provide natural tools for the study of cellular signalling pathways. Palytoxin, a compound isolated from the coelen-terate of genus Palythoa, is one such useful and intriguing compound. The structure of palytoxin was first determined in 1981 independently by Hirata (7) and Moore (2). As one of the most potent marine toxins known, palytoxin has been studied in a variety of systems ranging from erythrocytes to neurons. As a tumor promoter of the non 12-O-tetradecanoylphorbol-13-acetate (TPA) type, palytoxin can also be studied in the context of a growth control system. 

During the last year we have built an FTMS instrument specifically designed for laser-induced thermal desorption from single-crystal surfaces. Figure 5 is a perspective drawing of the Instrument. The chamber is pumped by a 150 1/s ion pump and has a base pressure of 2.0 X 10- torr. Gases are Introduced through sapphire-sealed leak valves from a diffusion pumped gas manifold. 

Our discussion here will concentrate on the various forms of the Ca " transport ATPases that occur in the sarcoplasmic reticulum of muscle cells of diverse fiber types and in the endoplasmic reticulum of nonmuscle cells (SERCA). The structure of these enzymes will be compared with the Ca transport ATPases of surface membranes (PMCA) [3,29-32,34] and with other ATP-dependent ion pumps that transport Na, K, andH [46,50-52]. 

The ATP molecule is a universal energy carrier in the cell, and it is the principal one. It will sustain all reactions and processes requiring Gibbs energy active ion transport (ion pump operation), biosynthesis of proteins and other substances, muscle contraction, and so on. It is also employed for temporary energy storage in the cell. 

In the past few years, erbium doped materials gained much attention in the field of optical communications, since the Er ion shows a broad optical emission at 1540 nm [111], within the main wavelengths window in the telecommunication technology. For this reason Er can be suitable as an active element for the generation and amplification of light in optical devices [112,113], also if limitations for the realization of an efficient planar amplifier are related to the small cross section for Er excitation (typically 10 -10 cm according to the matrix). In order to enhance Er ion pumping efficiency, a possible... 

Deprived of their substrate in severe or prolonged hypoxia, some ATPase-driven systems, including ion pumps, may become impaired. Further, with the decrease in the availability of O2 as its terminal electron acceptor, the mitochondrial transport chain becomes increasingly unable to accept reducing equivalents from cellular metabolic processes. Hence the intracellular pH falls, subjecting the cell as a whole to a reductive stress and favouring those enzyme systems with acid pH optima. 

Boundary membranes play a key role in the cells of all contemporary organisms, and simple models of membrane function are therefore of considerable interest. The interface of two immiscible liquids has been widely used for this purpose. For example, the fundamental processes of photosynthesis, biocatalysis, membrane fusion and interactions of cells, ion pumping, and electron transport have all been investigated in such interfacial systems. 

The reduction of O2 is usually believed to proceed accompanying the transfer of protons or other ions through a biomembrane [5], and the reaction rate or even the process is considered to vary depending on the kind of transferring ions. An ion channel or ion pump composed of membrane proteins has often been assumed in the explanation of the dependency of the reaction rate [5]. 

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