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Unformatted text preview: 1 BME 417 HW3 Jing Liang 1. What are the major functional differences between the voltage sensitive K+ and Na+ ion channels? There are two major functional differences between the voltage sensitive K+ and Na+ ion channels. They have different gating characteristics, and they pass different ions. Na+ channels are activated at a lower potential, typically around -55mV – the threshold potential. The activation, i.e., the opening of the Na+ channels, allow the influx of Na+, causing further depolarization. The positive feedback is the basis for the rapid depolarization during the propagation of an action potential. K+ channel, on the other hand, is activated at higher potential, typically around the peak of an action potential – around +30mV. The opening of K+ channel causes the rapid repolarization of the membrane.  It was thought the only Na+ channels possess an inactivation gate. However, recent studies show that K+ channels, too, exhibit inactivation. The classic mechanism for the inactivation of Na+ channel is the ball and chain model. Whereby a charged peptide ‘plug’ hangs off the intracellular surface of the Na+ channel. When the membrane is depolarized, the intracellular surface of the membrane and the Na+ channel become positively charged. The negatively charged ‘plug’ is then attracted to the Na+ channel, closing the pore. Recent studies suggest that the charge affects only how fast the Na+ channel inactivates but it doesn’t decide whether it is going to inactivate. Hydrophobic interaction, instead of charge, is proposed to be the main force that binds the plug and inner pore. [2, 3, 4] The inactivation characteristics of K+ channel is more varied, and they display a wide variety of inactivation time courses. The proposed model for the inactivation of the fast inactivating N-type K+ channels is by a ball and chain model similar to that of 2...
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- Winter '07
- Ion channel, MacKinnon, Voltage-gated ion channel, k+ channel