1. Patch clamp recording of a single ion channel yields the following results: H

Question

1. Patch clamp recording of a single ion channel yields the following results: Holding Potential (mV) Measured Current (pA) -100 -1.0 -50 0.0 0 +1.0 +50 +2.0 +100 +3.0

A) Draw a graph of the current (on the vertical axis)-voltage relation for this channel. B) What is the electrical resistance (in ohms) of this channel? (keep in mind mV = 10-3 volts, pA = 10-12 amperes, and an ohm is a derived unit that is equivalent to a volt/ampere, i.e. a V/A) C) What is the conductance of this channel in siemens (S)? (keep in mind 1 S = 1/ohm). D) What would be the equivalent conductance of 1,000 of these channels opened at the same time?

2. Assume that the ion channel described in question 1 was selectively permeable to ion X+1. Use the graph you made for Question 1 to help answer the following questions (note: no calculations are necessary!) A) What is the equilibrium potential for ion X+1? B) Is ion X+1 in higher concentration inside or outside the cell? (keep in mind that negative currents indicate inwardly-directed current, whereas positive currents represent current flowing out of the cell).

3. Lethal injection can involve intravenous delivery of a highly concentrated potassiumchloride solution. As such, extracellular K+ concentration may increase up to as much as 100 mM. For a typical neuron: A) What would be the equilibrium potential for K+ in neurons under such circumstances (assume that intracellular K+ concentration remains at 100 mM)? B) What would be the new resting potential (just give an approximate value – no calculation is necessary)? C) This question is not scored (you don’t need to write anything down): in your head, consider why such high extracellular K+ would cause neurons to stop firing?

Need help with 2(A) and 3(A,B).

Explanation / Answer

2(A) At equilibrium potential no flow of ions takes place or current is zero which is happening at -50mV so -50mV is the equilibrium potential.

3(A) http://www.indiana.edu/~nimsmsf/P215/p215notes/PPlectures/Printables/Membpotentials.pdf

Equilibruim potrerential given by Nerst equation

-Ex=(61/z)log[Xo]/[Xi]

Resting potential=-0.65 to- 0.95mV

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