Transmembrane electrical potential

Individual polyethers exhibit varying specificities for cations. Some polyethers have found appHcation as components in ion-selective electrodes for use in clinical medicine or in laboratory studies involving transport studies or measurement of transmembrane electrical potential (4). The methyl ester of monensin [28636-21 -7] i2ls been incorporated into a membrane sHde assembly used for the assay of semm sodium (see Biosensors) (5). Studies directed toward the design of a lithium selective electrode resulted in the synthesis of a derivative of monensin lactone that is highly specific for lithium (6). 

Among the vitally necessary elements the most important are Fe, Zn, K, Ca, S. Some of them are imbedded in the stmcture of many ferments, amino acids, intracellular liquid, the other define transmembrane electrical potential. In the paper the contents of elements in whole blood and semm by X-ray fluorescence spectrometry is studied. 

Up to now in this chapter, we have concentrated on the measurement via electric field sensitive dyes of the transmembrane electrical potential, which by itself should produce a linear drop in the electrical potential across a membrane. However, at least through the lipid matrix of a cell membrane, the electrical potential, /, at any point does not change linearly across the membrane. Instead, it follows a complex profile (see Fig. 6). This is due to contributions other than the transmembrane electrical potential to /. The other contributions come from the surface potential and the dipole potential. Both of these can also be quantified via electric field sensitive dyes. 

Slow dyes that respond via a redistribution across the entire membrane (sometimes called Nemstain dyes) do so because of a change in the transmembrane electrical potential. As such, they can only be used as probes of the transmembrane potential and not as probes of the surface potential or the dipole potential. Dyes whose electric field sensing mechanism involves a movement between the aqueous medium and its adjacent membrane interface on one side of the membrane can, in principle, respond to changes in both the transmembrane electrical potential and the surface potential. Fast dyes that remain totally in the membrane phase (e.g., styrylpyridinium, annellated hemicyanine, and 3-hydroxyflavone dyes) respond to their local electric field strength, whatever its origin. Therefore, these dyes can, in principle, be used as probes of the transmembrane electrical potential, the surface potential, or the dipole potential. 

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... 

Hurwitz, S., Cohen, I., Bar, A. The transmembrane electrical potential difference in the uterus (shell gland) of birds. Comp. Biochem. PhysioL 35, 873 (1970)... 

FIGURE 11-33 Chloride-bicarbonate exchanger of the erythrocyte membrane. This cotransport system allows the entry and exit of HCOf without changes in the transmembrane electrical potential. Its role is to increase the C02-carrying capacity of the blood. 

FIGURE 11-36 Na+K+ ATPase. In animal cells, this active transport system is primarily responsible for setting and maintaining the intracellular concentrations of Na+ and K+ and for generating the transmembrane electrical potential. It does this by moving three Na+ out of the cell for every two K+ it moves in. The electrical potential is central to electrical signaling in neurons, and the gradient of Na+ is used to drive the uphill cotransport of solutes in many cell types. 

Individual polyethers exhibit varying specificities for cations. Some polyethers have found application as components in ion-selective electrodes for use in clinical medicine or in laboratory studies involving transport studies or measurement of transmembrane electrical potential. 

Fig. 5.—Stimulation of UDP-gIucose glucan Synthetase Activities by Conditions that Lead to Induction of a Transmembrane, Electrical Potential.169 The experiment was performed by using membrane vesicles prepared from developing cotton-fibers incorporation of radioactivity from UDP-D-[,4C]glucose into total /3-D-glucans was measured. Anion and cation concentrations were 50 mM valinomycin (VAL) was present at 5 u.M and UDP-glucose at 0.1 mM 1 /xCi per irmol. ...

Results of later studies by Delmer and coworkers189,179 provided some support for this hypothesis. Thus, it was shown that re-establishment of a transmembrane, electrical potential (positive-inside) across vesicles isolated from cotton fibers resulted in a 4-12-fold stimulation of /3-D-glucan synthesis from UDP-glucose (see Fig. 5). Such a potential was established by the addition of K+ in the presence of an imper-... 

---