Miniaturization potential

Since the orexin receptors are Gq protein-coupled (Alexander et al. 2006), one may assume that this also holds true for the presynaptic orexin receptor(s), but so far no data are available. Nonetheless, the six studies carried out in central nervous preparations permit some conclusions on the post-G protein mechanisms. In all instances, the orexins increased the frequency of spontaneous inhibitory or excitatory postsynaptic potentials or currents. The results differed, however, with respect to the influence of tetrodotoxin. In the medial and lateral hypothalamus (van den Pol et al. 1998 Li et al. 2002), dorsal vagal complex (Davis et al. 2003), and caudal nucleus tractus solitarii (Smith et al. 2002), orexins increased the frequency of the miniature potentials or currents also in the presence of tetrodotoxin, suggesting that they directly influenced the vesicle release machinery (references in italics in Table 5). On the other hand, in the prefrontal cortex (Lambe and Aghajanian 2003) and lat-erodorsal tegmentum (Burlet et al. 2002), the orexins did not retain their facilitatory effect in the presence of tetrodotoxin, suggesting an effect further upstream e.g., on Ca2+ and/or K+ channels. 

Berberine was observed to reduce the amplitude of spontaneous miniature end plate potentials in the frog neuromuscular junction. At low concentrations, berberine diminished the frequency of miniature potentials, but increased it when the concentration exceeded a certain value [250]. 

This relation highlights the miniaturization potential that can be reached by adapting the channel radius a decrease in the dimension R impUes a decrease in the reactor volume as soon as the scale dependence of the limiting phenomenon m is positive. Almost aD the phenomena presented in Table 2.1 enable one to apply this strategy since their scale dependences are positive. Only homogeneous reactions make it impossible since they are not scale dependent, and other strategies are required for these reactions. For transfer phenomena, the miniaturization potential can be very large, since a two-fold decrease in the channel radius imphes a four-fold decrease in the reactor volume. 

The pursuit of further miniaturization of electronic circuits has made submicrometer resolution Hthography a cmcial element in future computer engineering. LB films have long been considered potential candidates for resist appHcations, because conventional spin-coated photoresist materials have large pinhole densities and variations of thickness. In contrast, LB films are two-dimensional, layered, crystalline soHds that provide high control of film thickness and are impermeable to plasma down to a thickness of 40 nm (46). The electron beam polymerization of CO-tricosenoic acid monolayers has been mentioned. Another monomeric amphiphile used in an attempt to develop electron-beam-resist materials is a-octadecylacryUc acid (8). 

A phenomenon known as silver migration has limited the use of silver plating in miniature circuit boards under a positive d-c potential within a damp environment silver can migrate across insulation. On drying, silver is found in the insulation or media creating a leakage path. Silver plating is forbidden in many military specifications for circuit boards. 

Microfabrication technology has made a considerable impact on the miniaturization of electrochemical sensors and systems. Such technology allows replacement of traditional bulky electrodes and beaker-type cells with mass-producible, easy-to-use sensor strips. These strips can be considered as disposable electrochemical cells onto which the sample droplet is placed. The development of microfabricated electrochemical systems has the potential to revolutionize the field of electroanaly-tical chemistry. 

A glass electrode, a thin-walled glass bulb containing an electrolyte, is much easier to use than a hydrogen electrode and has a potential that varies linearly with the pH of the solution outside the glass bulb (Fig. 12.11). Often there is a calomel electrode built into the probe that makes contact with the test solution through a miniature salt bridge. A pH meter therefore usually has only one probe, which forms a complete electrochemical cell once it is dipped into a solution. The meter is calibrated with a buffer of known pH, and the measured cell emf is then automatically converted into the pH of the solution, which is displayed. 

Sea urchin toxins extracted from spines or pedicellariae have a variety of pharmacological actions, including electrophysiological ones (75). Dialyzable toxins from Diadema caused a dose-dependent increase in the miniature end-plate potential frequency of frog sartorius muscle without influencing membrane potential (76). A toxin from the sea urchin Toxopneustes pUeolus causes a dose-dependent release of histamine (67). Toxic proteins from the same species also cause smooth muscle contracture in guinea pig ileum and uterus, and are cardiotoxic (77). 

A number of developments have increased the importance of capillary electrophoretic methods relative to pumped column methods in analysis. Interactions of analytes with the capillary wall are better understood, inspiring the development of means to minimize wall effects. Capillary electrophoresis (CE) has been standardized to the point of being useful as a routine technique. Incremental improvements in column coating techniques, buffer preparation, and injection techniques, combined with substantive advances in miniaturization and detection have potentiated rugged operation and high capacity massive parallelism in analysis. 

The development of protein chip assays to determine protein function using purified components is a rapidly advancing area. Automated systems for the assay of protein function on chips in parallel for thousands of proteins simultaneously will likely be available in the next few years. These miniaturized arrays will be useful for basic research as well as for diagnostics and drug development. For instance, the combination of protein chips with combinatorial chemistry will allow the simultaneous screening of vast collections of small molecules against vast collections of potential target proteins. 

The electrolyte volume of the STM cells is usually very small (ofthe order of a 100 pi in the above-described case) and evaporation of the solution can create problems in long-term experiments. Miniature reference electrodes, mostly saturated calomel electrodes (SCE), have been described in the literature [25], although they are hardly used anymore in our laboratory for practical reasons Cleaning the glassware in caroic acid becomes cumbersome. For most studies, a simple Pt wire, immersed directly into solution, is a convenient, low-noise quasireference electrode. The Pt wire is readily cleaned by holding it into a Bunsen flame, and it provides a fairly constant reference potential of fcj>i — + 0.55 0.05 V versus SCE for 0.1 M sulfuric or perchloric acid solutions (+ 0.67 0.05 V for 0.1 M nitric acid), which has to be checked from time to time and for different solutions. 

Petersons pH probe also was modified in order to give a miniature fiber optic sensor potentially suitable for glucose measurements90. Kopelman et al.91 developed a fiber-optic pH nanosensor for physiological measurements using a dual-emission sensitive dye. The performance of a pH sensor was reported92. An unclad fiber was dip-coated with a thin layer of porous cladding within which a pH-sensitive dye was entrapped. The fundamental... 

Peterson J.I., Goldstein S.R., A miniature fiberoptic pH sensor potentially suitable for glucose measurements, Diabetes Care 1982 5, 272. 

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