What can be inferred about the ion-transporting properties of a membrane from measurements of resting potential, tangential resistance, and tracer flux?
1981; Elsevier BV; Volume: 55; Issue: 1-2 Linguagem: Inglês
10.1016/0025-5564(81)90016-x
ISSN1879-3134
AutoresWilliam F. Pickard, John C. Galanis,
Tópico(s)Lipid Membrane Structure and Behavior
ResumoThe term transport ionophore is introduced and defined as a membrane inclusion which facilitates the passage of ions between the two aqueous phases bounding a bilayer membrane. This concept is then used to derive formulations for the membrane currents and the undirectional ion fluxes in terms of the several species of transport ionophores (which are presumed to be biochemically unambiguous) rather than in terms of the more traditional ion-specific channels and pumps (which are commonly thought to be of less than ideal selectivity). It is shown how membrane currents so defined can be reduced, by imposing a few simple but explicit conditions, to the usual simple equivalent circuit models or dichotomized into passive fluxes versus active fluxes; however, it is also shown that many experiments which seek such models or dichotomies fail to satisfy one or more of the imposed conditions and thus are not rigorously interpretable. Finally, it is concluded that the transport ionophore approach, though it fits much more naturally with the biochemical reality of the membrane than the more traditional approaches, will achieve its full potential only when the isolation and characterization of the several individual transport ionophores of an arbitrary membrane becomes more routinely possible.
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