Channel-mediated ion transport

It is well known that TEA is able to inhibit K+-channel mediated ion transport at both sides of plasma membranes [53, 54], and the present observations are consistent with this unique characteristic. 

The actual mechanism of channel-mediated ion transport is, so far, not established unequivocally. Alternative possibilities exist, sucb as formation of tubular bundles with holes large enough to serve as a conduit for water and ions. 

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. 

Fig. 10. Transport processes. Carrier mediated, via a neutral species (left), of an ion pair (centre). Channel mediated (right, top), gated channel (right, bottom).

Effects of the enniatins at lipid bilayers have been studied by several groups133,197,268>28s), Considerably higher concentrations of these antibiotics are required to obtain membrane conductance and potential values comparable with those induced by valinomycin and the macrotetrolides. Ivanov et al. observed first, second, and third power dependence of membrane conductance on enniatin B concentration, but only, first power dependence on the concentration of bis-enniatin B (cf. Section 5.1). They concluded that complexes with 1 1,2 1, and 3 2 carrier-cation stiochiometry are involved in the ion transport mediated by enniatin B and beauvericin. In the limiting case, stacking of many enniatin complex molecules can be postulated, which could lead to a channel mechanism of cation transfer by enniatin133. ... 

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