Exam_III_Practice_Questions - MCB 401 - Exam III Practice...

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MCB 401 - Exam III Practice Questions 1 ) Indicate which of the following statements about inward-rectifier K+ channels is correct: 1. In the presence of MG2+ and polyamines, the open probability of these channels increases as the membrane is hyperpolarized. 2. The phenomenon of ion-channel blockade consists of the occlusion of the ion-permeation pathway by a non-permeant ion, or by an ion that permeates very slowly. 3. Ion-channel blockade in inward-rectifier K+ channel channels is a function of the applied voltage because these channels contain positively charged transmembrane segments that act as voltage sensors 4. A and B 5. All of the above Inward-rectifyers: they have IV’s that rectify inward. Bath membrane in equal concentrations of potassium; 150mM on each side. There are no Mg or polyamines. There is proton buffer to pH the solution. IV curve would be 1:1 through the origin with little curvature. Now lets go to the cell: we have NaCl on extracellular side and K+ on cytosolic side. The IV curve now looks to be more hyperpolarized, reversed towards the Nernst of -75 to -80mV and it will be more horizontal. Now if we add Mg and polyamines on both sides of the membrane: same resting potential, but now its levels off once it passes into the positive y region. If we keep depolarizing the membrane, it will go to zero because Mg and polyamines blockade the ion channel and reduce the current to zero. Because the membrane is depolarized, Mg and polyamines (positive charge) attempt to go to the extracellular side(?). Currents are always outward for potassium. Membrane potential never gets more negative than potassium’s Nernst. It’s never more positive than sodium’s Nernst. Objective
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Exam_III_Practice_Questions - MCB 401 - Exam III Practice...

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