Electrical excitability

The focus of this section is the emission of ultraviolet and visible radiation following thermal or electrical excitation of atoms. Atomic emission spectroscopy has a long history. Qualitative applications based on the color of flames were used in the smelting of ores as early as 1550 and were more fully developed around 1830 with the observation of atomic spectra generated by flame emission and spark emission.Quantitative applications based on the atomic emission from electrical sparks were developed by Norman Lockyer (1836-1920) in the early 1870s, and quantitative applications based on flame emission were pioneered by IT. G. Lunde-gardh in 1930. Atomic emission based on emission from a plasma was introduced in 1964. 

Photopolymerization and Plasma Polymerization. The use of ultraviolet light alone (14) as well as the use of electrically excited plasmas or glow discharges to generate monomers capable of undergoing VDP have been explored. The products of these two processes, called plasma polymers, continue to receive considerable scientific attention. Interest in these approaches is enhanced by the fact that the feedstock material from which the monomer capable of VDP is generated is often inexpensive and readily available. In spite of these widespread scientific efforts, however, commercial use of the technologies is quite limited. 

Atomic Absorption/Emission Spectrometry. Atomic absorption or emission spectrometric methods are commonly used for inorganic elements in a variety of matrices. The general principles and appHcations have been reviewed (43). Flame-emission spectrometry allows detection at low levels (10 g). It has been claimed that flame methods give better reproducibiHty than electrical excitation methods, owing to better control of several variables involved in flame excitation. Detection limits for selected elements by flame-emission spectrometry given in Table 4. Inductively coupled plasma emission spectrometry may also be employed. 

Voltage-gated Ca2+ channels are Ca2+-selective pores in the plasma membrane of electrically excitable cells, such as neurons, muscle cells, (neuro) endocrine cells, and sensory cells. They open in response to membrane depolarization (e.g., an action potential) and permit the influx of Ca2+ along its electrochemical gradient into the cytoplasm. 

Like other voltage-gated cation channels, Ca2+ channels exist in at least three states A resting state stabilized at negative potentials (such as the resting potentials of most electrically excitable cells) that is a closed state from which the channel can open. The open state is induced by depolarization. Channels do not stay open indefinitely because they are turned off during prolonged depolarization by transition into an inactivated state. Inactivation is driven both by depolarization... 

Capellos and Suryanarayanan (Ref 28) described a ruby laser nanosecond flash photolysis system to study the chemical reactivity of electrically excited state of aromatic nitrocompds. The system was capable of recording absorption spectra of transient species with half-lives in the range of 20 nanoseconds (20 x lO sec) to 1 millisecond (1 O 3sec). Kinetic data pertaining to the lifetime of electronically excited states could be recorded by following the transient absorption as a function of time. Preliminary data on the spectroscopic and kinetic behavior of 1,4-dinitronaphthalene triplet excited state were obtained with this equipment... 

Muscle contraction is initiated by a signal from a motor nerve. This triggers an action potential, which is propagated along the muscle plasma membrane to the T-tubule system and the sarcotubular reticulum, where a sudden large electrically excited release of Ca " into the cytosol occurs. Accessory proteins closely associated with actin (troponins T, I, and C) together with tropomyosin mediate the Ca -dependent motor command within the sarcomere. Other accessory proteins (titin, nebulin, myomesin, etc.) serve to provide the myofibril with both stability... 

Striated muscle is composed of multinucleated muscle fiber cells surrounded by an electrically excitable plasma membrane, the sarcolemma. An individual muscle fiber cell, which may extend the entire length of the muscle, contains a bundle of many myofibrils arranged in parallel, embedded in intracellular fluid termed sarcoplasm. Within this fluid is contained glycogen, the high-energy compounds ATP and phosphocreatine, and the enzymes of glycolysis. 

Cardiac models are amongst the most advanced in silico tools for bio-med-icine, and the above scenario is bound to become reality rather sooner than later. Both cellular and whole organ models have aheady matured to a level where they have started to possess predictive power. We will now address some aspects of single cell model development (the cars ), and then look at how virtual cells interact to simulate the spreading wave of electrical excitation in anatomically representative, virtual hearts (the traffic ). 

Clearly, cardiac function may not be addressed exclusively on the basis of describing the working mechanisms of single cells. Both normal and disturbed heart rhythms are based on a spreading wave of electrical excitation, the meaningful investigation of which requires conduction pathways of at least hundreds if not thousands of cells in length. 

Meisel, I., Ehrhard, P., Simulation of electrically-excited flows in microchannels for mixing applications, in Proceedings of the 5th International Conference on Modeling and Simulation of Microsystems, San )uan, Puerto Rico, 22-25 April 2002, Computational Publications, Boston, pp. 62-65 (2002). 

While many biological molecules may be targets for oxidant stress and free radicals, it is clear that the cell membrane and its associated proteins may be particularly vulnerable. The ability of the cell to control its intracellular ionic environment as well as its ability to maintain a polarized membrane potential and electrical excitability depends on the activity of ion-translocating proteins such as channels, pumps and exchangers. Either direct or indirect disturbances of the activity of these ion translocators must ultimately underlie reperfiision and oxidant stress-induced arrhythmias in the heart. A number of studies have therefore investigated the effects of free radicals and oxidant stress on cellular electrophysiology and the activity of key membrane-bound ion translocating proteins. 

The electrical oscillations at the aqueous-organic interface or at membranes in the absence of any substances relative to the channel or gate were introduced. These oscillations might give some fundamental information on the electrical excitability in living organisms. Since the ion transfer at the aqueous-organic or aqueous-membrane interface and the interfacial adsorption are deeply concerned in the oscillation, it has been stressed that the voltammetry for the ion transfer at an interface of two immiscible electrolyte solutions is... 

H, and Albuquerque, E.X. Interaction of phencyclidine and its analogues on ionic channels of the electrically excitable membrane and nicotinic receptor Implications for behavioral effects. Mai Pharmacol 21 637-647, 1982. 

Albuquerque, E.X. Warnick, J.E. Aguayo, L.G. Ickowicz, R.K. Blaustein, M.P. Maayani, S. and Weinstein, H. Phencyclidine Differentiation of behaviorally active from inactive analogs based on interactions with channels of electrically excitable membranes and of cholinersic receptors. In Kamenka, J.M. Domino, E.F. and Geneste P., eds. Phencvclidine and Related Arvl hexvl ami nes Present and Future Appl i cat ions. Ann Arbor ... 

J.E. and Albuquerque, E. X. Descriminant effects of behavioral -ly active and inactive analogs of phencyclidine on membrane electrical excitability. J. Pharmacol Exp Ther 228 80-87, 1984. Albuquerque, E.X. Tsai, M.C. Aronstam, R.S Witkop, B. ... 

The relationship between the electrical excitation of the axon and the membrane potential was clarified by A. L. Hodgkin and A. P. Huxley in... 

Neuron The electrically excitable cell of the nervous system. 

The interaction of a beta particle and an orbital electron leads to electrical excitation and ionization of the orbital electron. These interactions cause the beta particle to lose energy in overcoming the electrical forces of the orbital electron. The electrical forces act over long distances therefore, the two particles do not have to come into direct contact for ionization to occur. 

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