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#ion channel

2 public questions tagged with this topic.

Membrane Transportation

Which ion channel is involved in action potential generation?

Action potential propagation in excitable cells depends on rapid voltage dependent changes in sodium and potassium conductances. Resting potential near minus 70 millivolts maintained by K+ leak and Na+/K+ ATPase. Upon synaptic depolarization reaching threshold about minus 55 millivolts, voltage sensor S4 helices of sodium channels containing repeated Arg-X-X motifs move outward within 100 microseconds, opening activation gate formed by S6 crossing. Sodium electrochemical gradient strong due to 145 millimolar outside, 12 millimolar inside and negative membrane potential drives inward current, d

Ref: Alberts et al., Molecular Biology of the Cell, Chapter 11: Voltage-Gated Na+ Channels in Action Potentials.

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Membrane Transportation

The selectivity filter of an ion channel ensures:

Ion channels achieve selective conduction despite high throughput by incorporating a narrow selectivity filter that discriminates on basis of size, dehydration energy and electrostatic coordination. Pore domain S5, P-loop, S6 forms inverted teepee; P-loop folds as two short pore helices P1 and P2 scaffolding filter. In potassium channels carbonyl oxygens from TVGYG sequence replace hydration waters precisely matching potassium radius but requiring too large cavity for smaller sodium. In sodium channels DEKA motif and outer ring carboxylates create high field site preferring partially hydrated

Ref: Hille, Ion Channels of Excitable Membranes, Chapter 13: Selectivity Filter and Molecular Sieving.

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