Transmembrane voltage

Ion channels are proteins which span the plasma membrane and can be opened by transmembrane voltage changes (voltage-dependent ion currents) or by binding of a neurotransmitter. Ion channels which are selective for Na+or Ca2+ ions cause excitation, ion channels with selectivity for Cl- or K+ usually cause inhibition of cells. 

DHP drugs bind allosterically. The open L-channel is somehat more permeable to the Ba ion than to the Ca ion but is very much less permeable to the Na ion. Nonetheless, because Na ion concentrations are so much higher than Ca ion concentrations, the actual fraction of charge carried by the two ions is not always so clear. There are a number of states that the L-channel can be in, aside from simply being open or closed. It is the distribution of L-channel molecules among the various states that is influenced by transmembrane voltage. From another view the rate constants between the states are functions of the transmembrane voltage. 

The absence of any indication of a counter ion movement calls attention to the likelihood that there is no SR transmembrane voltage difference. 

It follows from previous discussion that the destabilizing electrostatic contribution grows in absolute value with x (with increasing A.). But the influence of the nonuniform electrical force is overwhelmed by the stabilizing bending and stretching contributions. As a result, the traditional smectic model cannot explain how a small transmembrane voltage can lead to membrane breakdown. The obvious solution is to abandon this approach and to develop an alternative, such as the pore formation model. However, as we noticed before, this approach postulates rather than proves the appearance of hydrophobic pores. 

A premixture of 8 and soybean lecithin gave stable single channel currents with well-defined transitions between open and closed states with the 0.1-Is time scale. The conductance level detected was 6.1 0.5 pS at 0.5 M KCl solution. At various transmembrane voltages with different molar ratios of 8-to-lipid in the range 1/200 - 1/3000, an identical conductance level was always observed. This observation is therefore compatible with the original idea that monomeric 8 itself defines a pore mouth with a specified diameter in the single lipid layer. It gave a cation/anion... 

Rohr S Determination of impulse conduction characteristics at a microscopic scale in patterned growth heart cell cultures using multiple site optical recording of transmembrane voltage. J Cardiovasc Electrophysiol 1995 6 551-568. 

The crystal structure of a channel clarified the basis for selection of ions that can pass through the open channel pore and the mechanism by which the channel proteins sense changes in transmembrane voltage that control the open or closed conformational states of the channel (5). Thus, investigations of ion channel proteins employ fundamental physics to study the function of biologically critical proteins. 

Noebels Is anything known about whether external K" " ions could alter the Na pore in a way that transmembrane voltage wouldn t ... 

In their classic series of papers, Hodgkin and Huxley gave a quantitative description of the unique electrical behavior of the giant nerve fibers (axons) of squid. This behavior is described in terms of permeability of the surface membrane (measured as conductance per unit area of membrane) to different ion species, particularly Na+ and K+. The current carried by an ion species through the membrane is then calculated from the product of conductance and driving force on them (transmembrane voltage, V, minus ion equilibrium potential). The specific ionic conductances have several unique properties which challenge explanation at the molecular level ... 

The nature of the rearrangements in membrane molecules that give rise to the steep dependencies of sodium and potassium conductances on transmembrane voltage and their peculiar kinetics. There are no satisfactory... 

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