Lipids sodium/potassium

As detailed in chapter 17, biological membranes are basically lipid—think fat or oil—in nature with some attached proteins. As such, these thin sheets of phospholipids and proteins are nearly impermeable to charged particles such as sodium, potassium, or chloride ions. While the isolation of the cell interior from the exterior ionic environment is critical in many ways, it is also true that controlled permeability to ions may be critical. In fact, it is the near-impermeability of biological membranes to ions that permits control of ion transport across them by certain, specific proteins. 

While there is little evidence to suggest that alcohol produces its pharmacological effect via a specific "alcohol receptor", some lipids do show a particular vulnerability to the disorganizing effects of the drug. For example, alcohol selectively inhibits monoamine oxidase-B, and not the A form, in human platelets and brain similarly, it inhibits sodium/ potassium-dependent adenosine triphosphatase in the neuronal membrane but not in the glial membrane. 

Ion channels are ubiquitous and undoubtedly occur in the lipid bilayer of all cell membranes. They have many functions and some are critical to cellular activity. These include the generation of cellular energy, the production of electric signals in the nervous system, and a variety of signal-transduction processes. The inorganic ions involved in this signaling include sodium, potassium, and calcium. Each... 

Further sequelae to lipid peroxidation include inhibition of membrane-bound, phospholipid-dependent sodium-potassium ATPase and calcium ATPase with changes in the electrolyte milieu, especially calcium overloading of the cell with subsequent further cell damage and cell death as well as inhibition of adenylate cyclase. This results in loss of function in the mitochondria and microsomes. Damage to the DNA leads to enzyme defects or impaired enzyme synthesis, which triggers further metabolic changes. This also causes a cellular overload with calcium and subsequent activation of... 

Tears comprise inorganic electrolytes - sodium, potassium and some calcium ions, chloride and hydrogencarbonate counterions - as well as glucose. The macromolecular components include some albumin, globulins and lysozyme. Lipids which form a monolayer over the tear... 

Consider a typical eukaryotic cell, for instance, a muscle cell. By weight, the cell is about 75% water. However, this estimate fails to convey the truly aqueous nature of the cell a far more realistic description is in terms of mole ratios. Because of the low molecular weight of water, the nominal 75% water translates into a very large number of moles of water relative to the number of moles of other cell constituents. Thus, the aqueous nature of the cell is better illustrated by noting that for every 20,000 water molecules there are only about 75 lipid molecules, 100 sodium, potassium, and chloride ions (with at most a few hundred other small molecules or ions), and only one or two protein molecules. By sheer numbers water molecules totally dominate, and in this perspective life is merely some complex biochemistry in an extensive matrix of water, stabilized by a few lipids and macromolecules. The two dominating factors in cell biology are thus, simply, water molecules and interfaces. 

See also Passive Transport Mechanisms, Sodium-Potassium Pump, Lipid Bilayer... 

The U. S. Department of Agriculture maintains the USDA National Nutrient Database for Standard Reference, which contains over 7000 food items with data on the energy content, minerals, vitamins, and other properties of nutritional interest. The table here includes about 600 common foods extracted from that database. The properties listed are the energy content (in effect, the enthalpy of combustion) the content of carbohydrates, proteins, and lipids (fats) the cholesterol content and the amount of sodium, potassium, calcium, magnesium, iron, copper, zinc, manganese, phosphorus, and selenium. AU values are given for a 100 gram sample of the food. 

M. L. Ahrens, Electrostatic Control by Lipids upon the Membrane-Bound Sodium-Potassium ATPase. II. The Influence of Surface Potential upon the Activating Ion Equilibria, Biochim. Biophys. Acta 732(1), 1-10 (1983). 

In most large automated biochemistry analyzers electrode concentrations are evaluated in the diluted sample by ISEs, by the so-called indirect method. A special compartment for the determination of sodium, potassium, and chloride is integrated. The ISEs have replaced flame photometry as well as coulo-metry to a large extent. However, the compatibility as well as interpretability of the results is problematic in many cases (see above). Since the ion-selective assays strictly respond to molal single-ion activities in the aqueous phase, the comparability to direct measurements is weak. A volume displacement effect by lipids and proteins even affects the accuracy and comparability in diluted samples with buffered ionic strength. 

Among these chemicals are silver nitrate - added to allow separation of cisitrans isomers, particularly for lipid analyses potassium oxalate - added to allow discrimination of polyphosphoinositides magnesium acetate - added to help in the separation of phospholipids ammonimn sulfate - added so that the plate is self-charring (after heating) carbomer -added for the analysis of mannitol/sorbitol and sodium hydroxide - added to improve the separation of bases and organometallics. 

In addition to protein and lipids, the red cell also contains electrolytes sodium, potassium, chlorides, carbonate, and others. Their exchanges are important in maintaining the integrity of the red cell structure and physiology. 

Among the requirements for enzyme activity are ATP, Mg, Na", and lipids. The requirement for ATP is not absolute. The hydrolysis of ITP, GTP, and CTP can replace that of ATP, but these nucleotides are much less effective than ATP. The hydrolysis of UTP is ineffective in the sodium-potassium—dependent ATPase (Na K ATPase). 

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