Electrical Potentials in Biological Membrane Transport by Professor Dr. Erich Heinz (auth.)

By Professor Dr. Erich Heinz (auth.)

The fabric of this quantity was once initially deliberate to be integrated within the previous monograph Mechanics and Energetics of organic shipping. A separate and coherent therapy ofthe number of bioelectrical phenomena was once thought of most well known, ordinarily for didactic purposes. frequently, the biologist has to collect the foundations of bioelectricity he wishes from assorted resources and on assorted degrees. the current e-book intends to supply those ideas in a extra uniform context and in a kind adjusted to the issues of a biol­ ogist, instead of of a physicist or electric engineer. the most emphasis is wear the molecular point via referring to the bioelectrical phenomena, resembling the membrane diffusion potentials, pump potentials, or redox potentials, to the homes of the membrane involved, and, so far as attainable, to precise steps of shipping and metabolism of ions and nonelectrolytes. Little area is dedicated to the ordinary and frequent illustration of bioelectrical phe­ nomena by way of electric networks, of identical circuits with batteries, resistances, capacities and so on. that allows you to elucidate the elemental rules, the formal therapy is saved so simple as attainable, utilizing hugely Simplified versions, in line with organic structures. The corresponding equations are derived in methods: kinetically, i. e. by way of the legislations of Mass motion, in addition to energetically, i. e. , by way of Nonequilibrium Thermodynamics.

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In reality, however, this contribution is presumably decreasing accordingly as the system approaches the steady state, since the sum L H+ L ~ can hardly remain stable but is likely to increase under these conditions. lin [H+] = VH Lr ACh v~Lr + LH (57a) for the maximum ceiling, and for the PD to (57b) Also here, the contribution of the electrogenic pump to the overall PD is seemingly the same under all conditions, namely vHLr Ach. But for reasons similar v~ Lr + LH + L~ to those given for the condition of constant J r , this contribution is likely to decrease as 41 Treatment in Terms of Thermodynamics of Irreversible Processes (TIP) the system approaches the steady state, as the phenomenological coefficients cannot be expected to be constant over such a wide range.

A rapid electric response would make pumping energy available (or unavailable) for useful functions more swiftly, and well in advance of significant changes in chemical PD. , in mitochondria, chloroplasts, bacteriorhodopsin systems, etc. The corresponding time curves are complicated by transient deviations from electroneutrality. Preliminary equations of this kind, based on Simplifying assumptions, have been carried out for mitochondria by Mitchell (1968), and extended by Heinz (1981). 1). At the present juncture, a qualitative consideration may suffice provide a basic understanding.

For nonrheogenic antiport the electric PD, as a function of the activities of the solutes involved, can, in analogy to the electrically silent exchange pump, be adequately described by the Goldman-Hodgkin-Katz equation, but using only the rheogenic permeability coefficients for the transient and steady state as well. The terms symport and antiport are used as synonymous with cotransport and counter-transport, respectively. There is a certain tendency to prefer the latter for ion-linked secondary active transport of organic nutrients, such as sugars and amino acids, without any rational justification 47 Ionic Symporters and Antiporters For the rheogenic antiport the corresponding procedure is somewhat more complicated; for instance, the transient PO that may appear depends also on the movements ofthose ions which are not directly involved in the antiport, but are necessary to maintain electroneutrality.

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