Sandbox WWC3

From Proteopedia

Revision as of 00:33, 13 April 2016 by Landon Edwards (Talk | contribs)
Jump to: navigation, search

Sodium channels [1] are voltage gated integral membrane proteins found in muscles and neurons that selectively allow for the diffusion of sodium ions across the membrane. These proteins important for all cells but are specifically responsible initiating electrical signaling in these cells [2] and are commonly targets of drugs and mutation. Each sodium channel is composed of two subunits: the alpha subunit, which is the ion channel transmembrane domain [1], and two beta subunits that modulate channel gating and regulate the channel expression in the membrane [3]. The alpha subunit is able to function independently of the beta subunit[3] .

Insert caption here

Drag the structure with the mouse to rotate

Contents

Function

Sodium channels initiate action potentials in nerve and muscle cells. These electrical signals initiate the contraction of muscles and the release of neurotransmitters. The electrical signal is propagated when the sodium channel allows the influx of sodium ions. These positively charged ions depolarize the resting membrane potential of -70mV to +40mV, which creates the electrical signal that is sent along the length of the cell.The initial influx of sodium ions is often activated by the binding of a neurotransmitter to receptors on the post-synaptic membrane [4]. Then, as the sodium ions depolarize the membrane potential. more sodium channels open, and the action potential moves along the length of the muscle or nerve. The channels inactivate after 1-2ms [5] and the depolarization is then reversed by the efflux of potassium ions out of potassium channel[5]. This information was first discovered by Hodgkin and Huxley in 1952[5]. For more information on the role of sodium channels in electrical signaling, click here.

Structure

As noted above, the sodium channel consists of an alpha and two beta subunits. However, the alpha subunit is the only part necessary for the function of the channel [1]. The alpha subunit, depicted right, consists of four repeating structures, named I through IV [6] and shown in different colors . These structures consist of six transmembrane alpha helices named S1 through S6 [6]. Interestingly, each repeating subunit resembles a bacterial K+ channel [6]. These subunits fold together to form a central pore, and this complete structure resembles a bacterial Ca2+ channel [6].

Gating

The S4 segments consist of repeated motifs of a positively charged residue (usually Arg) followed by two hydrophobic residues [2].

Medical Implications

References

  1. ↑ 1.0 1.1 1.2 https://en.wikipedia.org/wiki/Sodium_channel
  2. ↑ 2.0 2.1 Payandeh J, Scheuer T, Zheng N, Catterall WA. The crystal structure of a voltage-gated sodium channel. Nature. 2011 Jul 10;475(7356):353-8. doi: 10.1038/nature10238. PMID:21743477 doi:10.1038/nature10238
  3. ↑ 3.0 3.1 Isom LL. Sodium channel beta subunits: anything but auxiliary. Neuroscientist. 2001 Feb;7(1):42-54. PMID:11486343
  4. ↑ https://en.wikipedia.org/wiki/Neurotransmission
  5. ↑ 5.0 5.1 5.2 Catterall WA. Voltage-gated sodium channels at 60: structure, function and pathophysiology. J Physiol. 2012 Jun 1;590(11):2577-89. doi: 10.1113/jphysiol.2011.224204. Epub, 2012 Apr 2. PMID:22473783 doi:http://dx.doi.org/10.1113/jphysiol.2011.224204
  6. ↑ 6.0 6.1 6.2 6.3 Marban E, Yamagishi T, Tomaselli GF. Structure and function of voltage-gated sodium channels. J Physiol. 1998 May 1;508 ( Pt 3):647-57. doi: 10.1111/j.1469-7793.1998.647bp.x. PMID:9518722 doi:http://dx.doi.org/10.1111/j.1469-7793.1998.647bp.x
Retrieved from "http://52.214.119.220/wiki/index.php/Sandbox_WWC3"
Personal tools