Electrogenic pumping

From the point of view of the stoichiometry of the transported ions during active transport, the electroneutral pump, where there is no net charge transfer or change in the membrane potential, must be distinguished from the electrogenic pump connected with charge transfer. 

Waxman We saw the same thing in the optic nerve. We did not include an electrogenic pump into our model, because it would have been one more unconstrained variable. But there is no question, if you activate the ATPase, it can cause hyperpolarization. 

A.23.3 (a) (1) the partial permeability of the membrane to charged species, (2) the uniformity of charge distribution across the membrane, (3) the net equality of charge flux across the membrane, (4) tire applicability of the Donnan equilibrium for each ionic species to which the membrane is permeable enough to permit free distribution across the membrane, and, (5) the absence of an electrogenic pump and its resultant driving force. 

From this analysis it may be inferred that the limiting Ca + concentration (or activity) ratio that can be achieved by this electrogenic pump (i.e., AG = 0) is... 

Some useful theoretical approaches have been developed to describe the noise of many special transport mechanisms, such as ion channels, carriers, and electrogenic pumps (28-33). Unfortunately, there are few experimental studies of transport noise in biological membranes and lipid bilayers. 

Not much more is known about the expeditiousness which, in this context, may be defined as the rate at which the protonmotive force rises after the onset of the pump, but some general predictions can be made. The expeditiousness is the higher the fester the pumping rate of protons is relative to the conductance of passive ions, which tend to shunt the electrogenic pump effect, in other words, to maintain electroneutrality. We see that the two components of the protonmotive force, the electrical and the chemical PD, are controlled by different factors and may therefore develop at different rates, as is illustrated by the following two extreme conditions ... 

It is unlikely that the effect of valinomycin is due to a conductance change which would stimulate an electrogenic pump, since protonophores like TCS have much less effect than ionophores and lipid-permeable cations do not substitute for these ionophores [58]. The effect of K -ionophores must be attributed to a requirement of the pump enzyme for internal K" ". Under certain conditions transport could be shown to be driven by a large gradient in the absence of ATP [66],... 

Heinz, E. (1981) in C. Slayman (Ed.), Electrogenic Pumps, Yale University Press, New Haven, in press. 

Mullin and Noda have derived an equation for the membrane potential in the presence of electrogenic pumping under a steady state condition/... 

Jansen, J. K., and Nicholls, J. G., 1973, Conductance changes, an electrogenic pump and the hyperpolarization of leech neurones following impulses,/. Physiol. London) 229 635-655. 

FIGURE 12 Some ion pumps in the plasma membrane. The Na+/K+-ATPase of animal cells uses the energy of ATP hydrolysis to move three Na+ ions out of the cells and two K+ ions in, which results in the generation of ion gradients and a membrane potential. Plant, yeast, and fungal cells do not have a Na+/K+-ATPase, but instead have a H+-ATPase, as the electrogenic pump. The plasma membrane also contains a Ca +-ATPase that pumps Ca + out of cells to help keep the intracellular Ca + concentration low. 

Working on Nitella clavata, Kitasato put forward the hypothesis that a large passive influx of protons had to be correlated to an electrogenic efflux of protons. Therefore, he introduced Ch+ and Ch+, respectively, in the numerator and denominator of Equation (2), both terms being affected by a permeability factor Ph+ of high value. He assumed further that the electrogenic pump works as a current source, i.e., as though it has infinite impedance, and he described the membrane potential by the equation... 

Figure 2. Equivalent circuit suggested in Reference 9 for the cell membrane in the case of an electrogenic pump. 

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