Field intramembrane

The ideal electric field sensitive dye would respond to changes in intramembrane field strength or transmembrane electrical potential within femtoseconds the magnitude of its absorbance or fluorescence response would be enormous it would... 

Concerning your experiment on the measurement of intramembrane pH, pH indicators are charged molecules, which could conceivably migrate in or out of the membrane is response to electrical fields. Have you checked whether your indicators really stay in the membrane, and in the same place in the membrane, during the experiment ... 

How may such minute field strengths have macro effects This may be made understandable in terms of cooperative action. Consider, for example, the strands of intramembranous proteins that protrude from the phospholipid membrane. They contain charges, and each would react to an applied field. In a membrane at least 10% of the sites will be occupied by proteins. If each protein strand reacts to the field, the very small but coherent signals may be magnified by, for example, 1013 strands cm2. In growing bone cells subjected to a 100-Hz field, say, a significant effect becomes understandable. 

While perhaps overly schematic, this approach proved useful for two reasons first, because it provided terminology in which one can discuss the specific structural features of ionic channels, and second, because it allowed certain qualitative predictions to be made. Thus according to the scheme it is altogether clear that there must exist an electric transmembrane current due to displacement of the charged intramembrane particles in response to a field variation. This current has received the name of gating current, the origin of which is obvious in the model in question. 

A significant boom in AC dielectrophoretic research occurred when microfabrication became widely available. This enabled precise fabrication of electrode systems (surface patterned electrode arrays, posts, and related), which created very symmetric, reproducible nonuniform electric fields enabling cellular responses to such fields to be more precisely quantified. It became apparent that at radio frequencies, cells were selectively controlled due to their inherent intramembrane polarizability characteristics. This attribute was exploited to sort cells because one cell type responded in a unique fashion from other cells at specific AC frequencies. Genetically or geometrically similar cells were found to have more similar, but still distinct, responses at given frequencies [4, 5]. 

Xu, C. Loew, L. M. The effect of asymmetric surface potentials on the intramembrane electric field measured with voltage-sensitive dyes. Biophys. J. 2003, 84, 2768-2780. 

These effects of TPB are explained by postulating the rapid movement of TPB within the membrane according to the two-intramembrane-potential-well model proposed by Anderson et al. (1978) in the study of black lipid membranes. According to this model, TPB moves rapidly from one potential well, which exists just beneath the outer surface, to the other well close to the inner surface upon application of inside positive membrane potential (Fig. 4) and rapidly dissipates the electrical field in the center of the membrane. Equilibration of TPB concentrations between the well and the outer aqueous phase on each side of the membrane is estimated to be rather slow due to the cooperative interaction between TPB molecules. Biphasic decay kinetics of the carotenoid can be explained by the response of carotenoids to the field change in the center of... 

Matsuura K, Masamoto K, Itoh S and Nishimura M (1980) Effects of surface potential on the intramembrane electrical field measured with carotenoid spectral shift in chromatophores from Rhosopseudomonas sphaeroides, Biochim. Biophys Acta 547, 91-102... 

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