Electrical membrane characterization

From this brief historical perspective, it can be seen that metal oxides were the basis of inorganic membrane development. In this chapter we will try to examine, in a tutorial rather than complex form, the main features of the metal oxide based membranes, as an important part of the field of inorganic membranes. In this way, some paragraphs will be initially devoted to the fundamentals of membrane synthesis, covering the most common membrane making techniques. Structural, fimctional, and electrical membrane characterization methods will then be introduced. Finally, we... 

Gap junctions provide in the nervous system the structural correlate of one class of electrical synapses, characterized by very close apposition between the presynaptic and postsynaptic membranes. It should be noted, in this respect, that different junctional specializations can mediate different forms of electrical transmission between neurons (Bennett, 1997). Electrical synapses transmit preferentially, but not exclusively, low-frequency stimuli, that allow the rapid transfer of a presynaptic impulse into an electrical excitatory potential in the postjunctional cells. Electrical transmission, via the intercellular channels, can be bidirectional. The widely held opinion that electrical transmission is characteristic of lower vertebrates probably derives from the large cell systems in which electrical synapses were identified in the initial period of intracellular recording (reviewed by Bennett, 1997). Contradicting this view, electrotonic coupling between neurons has now been demonstrated in many areas of the mammalian central nervous system and has been implicated in neuronal synchronization. Gap junctional intercellular communication can occur between glial cells, glia and neurons, as well as between neurons. 

Fig. 18. Decay of the flash-induced field-indicating absorption change serving as a device for diagnosing the function of the ionophore valinmycin in chloroplasts (A) In the presence of 10 M K and 10 M Na but no valinomycin (B) in the presence of 10 M valinomycin and 10 M Na and (C) in the presence of 10 ° M valinomycin and 10 M of Na and 10 M of K. Figure source Junge and Schmid (1971) The mechanism of action of valinomycin on the thylakoid membrane. Characterization of the electric current density. J Membrane Biol 4 184. AA represents the absorbance change induced by a single (1) saturating flash.

W Junge and Schmid (1971) The mechanism of action of valinomycin on the thyiakoid membrane. Characterization of the electric current density. J Membrane Biol 4 179-192... 

Fortunately, AFM in conjunction with the colloid probe technique offers an alternative means of membrane surface electrical properties characterization. If a colloid probe is approached towards a surface it is possible to quantify the force of interaction. Figure 6.15 shows typical data for a Desal DK membrane, which is one of the least rough membranes [7]. 

Theoretical and experimental descriptions of three different types of electrical measurements commonly used for membrane characterization have been presented. Streaming potential, membrane potential, and impedance spectroscopy are nondestructive techniques and they can be carried out with the membranes in contact with electrolyte solutions, which allows characterization of membranes in working conditions , but they also permit us to established changes in the membrane characteristic parameters related to solution chemistry (ion size, charge, concentration, pH) and/or membrane structure. 

Researchers at the MoneU Center (Philadelphia, Pennsylvania) are using a variety of electrophysical and biochemical techniques to characterize the ionic currents produced in taste and olfactory receptor cells by chemical stimuli. These studies are concerned with the identification and pharmacology of the active ion channels and mode of production. One of the techniques employed by the MoneU researchers is that of "patch clamp." This method aUows for the study of the electrical properties of smaU patches of the ceU membrane. The program at MoneU has determined that odors stimulate intraceUular enzymes to produce cycUc adenosine 3, 5 -monophosphate (cAMP). This production of cAMP promotes opening of the ion channel, aUowing cations to enter and excite the ceU. MoneU s future studies wiU focus on the connection of cAMP, and the production of the electrical response to the brain. The patch clamp technique also may be a method to study the specificity of receptor ceUs to different odors, as weU as the adaptation to prolonged stimulation (3). 

An excellent review of experimental techniques for measuring electrical resistivity in aqueous solutions is available [34], Separators used in nonaqueous systems can be characterized by wetting them with a surfactant and measuring the electrical resistivity in an aqueous solution. Then the resistivity in a nonaqueous membrane can be estimated from Eq. (2). 

Finally, with regard to synaptic type, there is the well-characterized electrical synapse [20], where current can pass from cell to cell across regions of membrane... 

Sadoulet-Puccio, H. M., Khurana, T. S., Cohen, J. B., and Kundel, L. M. (1996). Cloning and characterization of the human homologue of a dystrophin related phosphopro-tein found at the Torpedo electric organ post-synaptic membrane. Hum. Mol. Genet. 4, 44489-44496. 

ENTER Membranes LLC has developed Teklon— a highly porous, ultrahigh molecular weight polyethylene separator for lithium-ion batteries. At the writing of this publication, the separator is available in small quantities. Pekala et al. characterized Celgard, Setela, and Teklon separators in terms of their physical, mechanical, and electrical properties. ... 

Polar Cell Systems for Membrane Transport Studies Direct current electrical measurement in epithelia steady-state and transient analysis, 171, 607 impedance analysis in tight epithelia, 171, 628 electrical impedance analysis of leaky epithelia theory, techniques, and leak artifact problems, 171, 642 patch-clamp experiments in epithelia activation by hormones or neurotransmitters, 171, 663 ionic permeation mechanisms in epithelia biionic potentials, dilution potentials, conductances, and streaming potentials, 171, 678 use of ionophores in epithelia characterizing membrane properties, 171, 715 cultures as epithelial models porous-bottom culture dishes for studying transport and differentiation, 171, 736 volume regulation in epithelia experimental approaches, 171, 744 scanning electrode localization of transport pathways in epithelial tissues, 171, 792. 

INTESTINE Characterization of a membrane potassium ion conductance in intestinal secretory cells using whole cell patch-clamp and calcium-sensitive dye techniques, 192, 309 isolation of intestinal epithelial cells and evaluation of transport functions, 192, 324 isolation of enterocyte membranes, 192, 341 established intestinal cell lines as model systems for electrolyte transport studies, 192, 354 sodium chloride transport pathways in intestinal membrane vesicles, 192, 389 advantages and limitations of vesicles for the characterization and the kinetic analysis of transport systems, 192, 409 isolation and reconstitution of the sodium-de-pendent glucose transporter, 192, 438 calcium transport by intestinal epithelial cell basolateral membrane, 192, 448 electrical measurements in large intestine (including cecum, colon, rectum), 192, 459... 

Glyceryl monooleate (22) bilayer lipid membrane Nanometer-sized, single-domain, Fe304 particles attached to BLMs Electrical measurements and reflection spectroscopy were used for characterization 795... 

Unlike transport across the membranes of the ER, transport across plasma membranes of bacteria often requires both hydrolysis of ATP and energy provided by the membrane electrical potential.33 38 44-48 Secretion into the periplasmic space has been well characterized but less is known about transport of proteins into the external membranes of E. coli48 A16 kDa periplasmic chaperone may be required.483... 

The nicotinic acetylcholine (ACh) receptor is a well-characterized receptor of this type consisting of five subunits. It is present on the skeletal muscle cell end-plate in the neuromuscular junction, at all autonomic ganglia, and in the central nervous system (CNS). The function of this receptor is to convert ACh binding into an electrical signal via increased Na+ or K+ permeability across the cell membrane (i.e., membrane depolarization). When two molecules of ACh bind to the a subunit of the receptor, a conformational change in the receptor induces opening of the channel to at least 0.65 nm for approximately 1-2 ms. 

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