Potential cell membrane

Other auxin-like herbicides (2,48) include the chlorobenzoic acids, eg, dicamba and chloramben, and miscellaneous compounds such as picloram, a substituted picolinic acid, and naptalam (see Table 1). Naptalam is not halogenated and is reported to function as an antiauxin, competitively blocking lAA action (199). TIBA is an antiauxin used in receptor site and other plant growth studies at the molecular level (201). Diclofop-methyl and diclofop are also potent, rapid inhibitors of auxin-stimulated response in monocots (93,94). Diclofop is reported to act as a proton ionophore, dissipating cell membrane potential and perturbing membrane functions. 

Bello-Reuss, E., T.P. Grady, and L. Reuss. 1981. Mechanism of the effect of cyanide on cell membrane potentials in Necturus gall-bladder epithelium. Jour. Physiol. 314 343-357. 

Ion-selective microelectrodes [18, 70,71, 164] are chiefly used for measurement of ion activities in individual cells and in intracellular liquid. They were developed from micropipettes, which are miniature liquid bridges used for measurement of cell membrane potentials [94]. Micropipettes and ion-selective microelectrodes are made using commercial drawing devices. Ion-selective... 

Alkali metal transport in biochemistry is a vital process in maintenance of cell membrane potentials of use, for example, in nerve signal transduction and is at the core of some of the early work on artificial ionophores that mimic natural ion carriers such as valinomycin. Ionophore mediated ion transport is much slower than transport through cation and anion ion channel proteins, however. 

In order to avoid chemical compounds at all, it is also possible to apply a high voltage to kill microbes on surfaces. It was found that a direct current kills E. coli cells, probably by heat or by hydrogen peroxide formation [84], Microbial cells can be effectively killed by using pulsed electric fields (PEF), probably by frequently disturbing the cell membrane potential [85], PEF that was found to lower microbial cell numbers in food and drinks was also shown to effectively kill E. coli and Listeria innocua cells attached to polystyrene beads [86], This demonstrates the potential of applying this purely physical method to surfaces as well. 

Electrochemical research on DNA is of great relevance to explain many biological mechanisms. The DNA-modified electrode is a very good model for simulating the nucleic acid interaction with cell membranes, potential environmental carcinogenic compounds and to clarify the mechanisms of action of drugs used as chemotherapeutic agents. 

Potassium channels are key regulators of cell excitability in the brain and also in other electrically active tissues such as the heart. They control cell membrane potential and... 

The heart depends on the synchronous integration of electrical impulse transmission and myocardial tissue rcsponsc to cany exit its function as a pump. When the impulse is released from the SA node, excitation of the heart tis.sue takes place in an orderly manner by a spread of the impulse ihmughout the specialised autontatic fibers in the atria, the AV node, and the Purkinje fiber network in the ventricles. This spreading of impulses produces a characteristic clectro-atdiographic pattern that cun be equated to predictable myo-caidial cell membrane potentials and Nu and K fluxes In and out of the cell. 

When making actual intracellular measurements, the microelectrodes are mounted in micromanipulators for cell penetration. It has been found that beveling the tip of the micropipet ISE aids in the ability to enter the cell and also enables the fabrication of electrodes with smaller tip diameters of O.I (im. Once inside the cell, single-barrel liquid membrane micro-ISEs (as described above) allow for the measurement of only steady-state ion activities. For excitable cells, where ion levels change rapidly, one cannot differentiate the potential changes resulting from variations in the intracellular activity of a specific ion and the living cell membrane potential. For such situations, double-barrel-type liquid membrane micro-ISEs have been developed (K2). 

The purpose of the reference barrel is to allow for the simultaneous measurement of the cell membrane potential while measuring the intracellular ion activities with the ISE portion of the device. Tims, in practice, a second single-barrel reference micropipet electrode is placed in the bathing solution outside the cell so that the potential between the two KCl-filled electrodes can always be monitored to obtain the instantaneous cell membrane potential (E ). The potential of the liquid membrane ISE barrel can also be monitored versus the external reference electrode. In this manner, potential changes due to variations in the cell membrane potential can be taken into account when calculating the intracellular ion activities. Alternatively, only the potential difference between both barrels of the electrode could be monitored. This potential should only be dependent on the intracellular activity of the analyte ion (not affected by the cell membrane potential). For certain ion measurements, e.g., K using a valinomycin based liquid micropipet electrode, leakage of K+ from the reference barrel could present a problem. In such cases, the reference barrel and the outer reference pipet should be filled with a solution other than 3 M KCl. 

Aside from intracellular work, the liquid membrane micro-ISEs described above may also be used for extracellular studies involving a wide range of tissues. For example, accumulation and depletion of ions that flow across extracellular space between nerve groups in the brain can be easily monitored by these types of microelectrodes (N2). The size of the electrodes used in such studies need only be 2-4 pm. In these experiments, the ISEs are placed in the extracellular fluid and ion activities may be directly monitored without concern for the cells membrane potentials. 

The ion selectivity data clearly indicate that veiy specific ion-solvent interactions take place in the vicinal water and that these bear little resemblance to expectations from bulk-phase observations. This, in turn, means that such quantities as the classical standard ion activity coefficients are not applicable, and hence osmotic coefficients must also differ from the expected values. In fact, the use of the generally accepted osmotic coefficients is simply inappropriate, and unusual osmotic behavior must be anticipated. Likewise, if the activity coefficients display anomalous behavior so must cell membrane potentials. In other words, ion distribution and the osmotic behavior of cells must be influenced by vicinal water, and models of cell volume regulation must anticipate and take into account this aspect (see also Wiggins, 1979). 

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