Ionic pump

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. 

The energy needed to transport ions across the membrane is obtained by the cell in chemical reactions occurring in it that is, the oxidation of organic substances with oxygen (for more details, see Section 30.2). Every second about 10 to 10 ions are transported across 1 m of membrane area. This process requires 20 to 30% of all energy generated by the cell. It has been calculated that the total power of the ionic pumps in the cells of the brain is about 1 watt. 

The potential depends upon the concentration of charged ions present, the relative membrane permeability to those ions and the presence of any ionic pumps that maintain a concentration gradient. The resting membrane potential is — 60 to — 90 mV, with the cells being negatively charged inside. 

Fig. 1. Summary of the most important actions of antiarrhythmic drugs on membrane channels, receptors, and ionic pumps in the heart. The drugs are arranged in a fashion similar to the columns, so that generally the entries for their predominant actions form a diagonal. Most of these drugs are already available in Europe and the USA, but aprindine, pirmenol, cibenzoline, and pilsicainide are only available in Japan. (Reproduced with permission from Ogawa et al., 1997.)...

Treatment of neuronal cultures with glutamate is accompanied by the loss of neuronal viability, reduced neuronal energy state (ATP level and mitochondrial membrane potential), and increased cytoplasmic mitochondrial Ca2+. This decrease in ATP results in failure of ionic pumps and increase in extracellular K+. These processes cause neuronal depolarization and release of glutamate, which over-stimulates NMDA receptors. The NMDA antagonist MK-801... 

Membrane-bound enzymes, particularly the ATPases involved in the ionic pumps for calcium, sodium and potassium, have been found to function abnormally in the brains of epileptic patients and animals. A reduction in Na+K+-ATPase activity has been reported in human focal epileptogenic tissue, but it is uncertain whether such changes are due to the disease itself or a reflection of drug treatment. Similar changes have, however, been reported in experimental animals following the localized application of alumina cream and in DBA/2 mice that exhibit sound-induced seizures a reduction in calcium-dependent ATPase has also been found in the brain of DBA/2 mice. Such findings are consistent with the hypothesis that a defect in ion channels may occur in epilepsy. 

All cells, including muscle and nerve cells, have inside them an intracellular fluid (ICF) which contains high levels of potassium, K+, phosphate ions, PC>43+, and protein and small amounts of Na+ ions and chlorine ions. Outside the cells in the extracellular fluid (ECF) consists mostly of sodium ions, Na+, chloride, Cl, and bicarbonate ions, HC03, but no protein, plus low concentrations of potassium ions. The inner layer of the cell membrane is negatively charged relative to the outside. When activity occurs then an ionic pumping action takes place to try to maintain the balance within the cells between the intra and extra flow of sodium and potassium... 

Carnosine (as well as anserine) exerts positive effect on oxidative phosphorylation in mitochondria and maintains P/O ratio in the in vitro experiments at higher level than that in control samples having no dipeptides added [79]. The same effect of the dipeptides was noted in terms of ionic pumps of skeletal muscles, such as Ca-pump and Na/K-pump. supporting their activity under unfavorable conditions [6,45]. 

Membrane proteins have multiple functions. They comprise enzymes acting on locally concentrated substrates transport systems of various kinds, including the ionic pumps responsible for bioelectric manifestations translocators serving in the specific delivery of proteins and other macromolecules across membranes electron-transfer chains and other components of protonmotive machineries photosystems and their ancillary cofactors and a variety of receptors involved in transmembrane signaling. 

Under normal conditions, the extraceUnlar concentration of calcium is in the milhmolar range (l(h M), whereas its intracellular concentration is less than l(h M. The cytoplasmic concentration of calcium is increased through the actions of receptor-operated channels, voltage-activated channels, or ionic pumps. In addition, calcium can be released from internal stores (see also Figure 103). 

Failure of Na+/K+ ATPase and other ionic pumps with loss of ionic gradients and net transfer of water from the extracellular to the intraceUular compartment... 

Energy failure with failure of cell membrane ionic pumps, similar to ischemia Hemiplegic Migraine... 

The major ionic pump that has received much attention in the myocardium is the Na /K -ATPase pump, which is the site of action for cardiac glycosides (Danger... 

Ionic pumps within membranes operate, over time, to produce markedly different concentrations of ions in the intracellular and extracellular volumes around cells. In cardiac cells, the sodium-potassium pump produces concentrations (millimoles per liter) for Purkinje cells as shown in Table 19.1. 

DiFrancesco, D. and D. Noble (1985). A model of cardiac electrical activity incorporating ionic pumps and concentration changes. Phil. Trans. R. Soc. Land. B 307,353-398. 

Passive. The energy delivered to the network must he positive for any excitation waveform, and all currents or voltages must he zero without excitation. As we know, tissue with electrodes does not fulfill this last requirement we know, for instance, that it contains cells with endogenic ionic pumps. 

FIGURE 17.2 Concept of a sodium-potassium ionic pump within flie phospholipid structure of flie cell membrane. The mcriecular pump structures are not exactly known. 

The electric nature of the membrane is usually modeled as distributed capacitors and resistors, as shown in Fig. 17.10. The value of is the membrane equivalent electric resistance. R, and /f, are the resistances of the external and internal membrane environments. The stored charge across the membrane is electrically represented by a capacitance C , and the action of the ionic pumps is represented by E . 

The membrane component of the background noise consists mainly of shot noise [8-11], that is the expected electrical noise created by the ions that cross the membrane by leakage or ionic pumps. The spectral density of shot noise is directly proportional to the unidirectional membrane current. Thus, the spectral density of the noise will increase by increasing the surface of the membrane patch, and consequently the total current (leakage and pumps). This implies that the noise conditions will be improved when current is recorded from a small piece of membrane (a patch). 

Lead biokinetics can potentially be affected by erythrocyte instability in ways such as increased erythrocyte fragility and brittleness due to lead s inhibitory effects on blood cell membrane stability, ionic pump activity, and ionic flux homeostasis. These abnormalities occur at chronic Pb exposures producing PbB of 50—60 pg/dl or higher, where numerous toxic endpoints have been triggered. 

Whether or not the active transport of monovalent cations is rapidly increased by serum was not known when our investigation was started. There were reports of a several-fold increase in the activity of the Na+K+ ATPase after serum feeding and this is the enzyme responsible for the action of the sodium pump , which pumps out Na+ and pumps in K+. 13,i4> However, the ATPase measurements were made 24 hours after serum addition and we were interested in rapid responses. The question of serum effects on cation transport is important because the maintenance of an asymmetric distribution of K+ and Na+ ions has a profound influence in the regulation of cell functions such as cell volume,<45) transport of non-electrolytes,membrane potential,activity of glycolytic enzymes ) and macromolecular synthesis. 7) Thus, alteration in ionic pumping activity is another potential point of control in linking surface and intracellular events. 

Pumping systems used on recent XPS spectrometers are typically (1) turbomole-cular pumps coupled with a rotary or membrane pump for the introduction chamber (a in Fig. 7) and (2) a cryogenic pump (b in Fig. 7) or an ionic pump with Ti subli-mator for the analysis chamber the second one being preferred to cryogenic pump on systems with imaging capacity to avoid vibrations. A detailed description of the vacuum technology can be found elsewhere. ... 

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