Molecular ion channels

Fig. 8 Chemical structures of molecular ion channels with ion selectivity, 1,2. Schematical illustration of expected structures of a tail-to-tail dimer. The side chain opposite to the reader is eliminated for clarity.

Figure 41-9. Diagrammatic representation of the structures of two ion channels. The Roman numerals indicate the four subunits of each channel and the Arabic numerals the a-helical transmembrane domains of each subunit. The actual pores through which the ions pass are not shown but are formed by apposition of the various subunits. The specific areas of the subunits involved in the opening and closing of the channels are also not indicated. (After WKCatterall. Modified and reproduced from Hall ZW An Introduction to Molecular Neurobiology. Sinauer, 1992.)...

Over 40 different types of polypeptide toxins have been found in marine animals (i). Many of these toxins are exquisitely selective in their actions, affecting a single process or receptor at minute concentrations. So far the sea anemone and gastropod Conus) toxins have attracted the most attention as molecular probes of ion channels. In this chapter, we discuss several approaches which are being used to investigate, at the molecular level, the interactions of the sea anemone neurotoxic polypeptides with sodium channels. 

Birch and coworkers studied the time-intensity interrelationships for the sweetness of sucrose and thaumatin, and proposed three thematically different processes (see Fig. 47). In mechanism (1), the sweet stimuli approach the ion-channel, triggering site on the taste-cell membrane, where they bind, open the ion-channel (ionophore), and cause a flow of sodium and potassium ions into, or out of, the cell. Such a mechanism would correspond to a single molecular event, and would thus account for both time and intensity of response, the intensity of response being dependent on the ion flux achieved while the stimulus molecule binds to the ionophore. 

Chebib, M and Johnston, GA (2000) GABA-Activated ligand gated ion channels medicinal chemistry and molecular biology. J. Med. Chem. 43 1427-1447. 

Kuhse, J, Betz, H and Kirsch, J (1995) The inhibitory glycine receptor architecture, synaptic localization and molecular pathology of a postsynaptic ion-channel complex. Curr. Opin. Neurobiol. 5 318-323. 

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