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Voltage gated Ion Channels are a class of Trans membrane ion channels that are sensitive to the change in the potential difference across the membrane. Studies are done on the single channel dynamics to determine the voltage dependence of the sensitivity of these channels. Since these channels are made up of large super family of proteins their function is dependent on their protein conformation. These conformations are known as Global States which are in turn average of different microstates. Transition in these states is known as a Global Transition. These Global Transitions are dependent on change in voltage in the case of these ion channels. This voltage dependence was assumed to be due to the common structural feature (S4) seen among these proteins with 25 amino acid chain which possess charged amino acids. Its role was later confirmed by the mutations in this amino acid chain. This structural feature acts as a voltage sensor and is responsible for the opening and closing of the ion channels upon the change in the voltage. In the end it can be concluded that the voltage gated ion channels are a super family of proteins and the sensitivity of these ion channels is dependent on its protein’s Global Transition which is in turn dependent on the change in voltage which is sensed by a common structural feature possessed by them which acts as a voltage sensor.

Image Url : http://www.ncbi.nlm.nih.gov/books/NBK21608/

References:

1. Membrane and Cellular Biophysics, Mayer B. Jackson, Chapter: 1
2. Voltage-sensing residues in the S4 region of a mammalian K+ channel. Liman ER, Hess P, Weaver F, Koren G. Department of Cellular and Molecular Physiology, Harvard Medical School, Boston, Massachusetts 02115. Nature. 1991 Oct 24;353(6346):752-6.
3. Alteration of voltage-dependence of Shaker potassium channel by mutations in the S4 sequence. Papazian DM, Timpe LC, Jan YN, Jan LY. Department of Physiology, University of California, San Francisco. Nature. 1991 Jan 24;349(6307):305-10.
4. S4 mutations alter the single-channel gating kinetics of Shaker K+ channels. Shao XM, Papazian DM. Department of Physiology, School of Medicine, University of California, Los Angeles 90024-1751 Neuron. 1993 Aug;11(2):343-52.
5. Evidence for voltage-dependent S4 movement in sodium channels. Yang N, Horn R. Department of Physiology, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA Neuron. 1995 Jul;15(1):213-8.
6. S4 mutations alter gating currents of Shaker K channels. Perozo E, Santacruz-Toloza L, Stefani E, Bezanilla F, Papazian DM. Department of Chemistry and Biochemistry, UCLA 90024-1751. Biophys J. 1994 Feb;66(2 Pt 1):345-54.