Problem 2 For a vertebrate neuron you are studying at 25 °C, you have measured t
ID: 3477694 • Letter: P
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Problem 2 For a vertebrate neuron you are studying at 25 °C, you have measured the following intracellular and extracellular concentrations, although unfortunately you were not able to get accurate measurements of [Na*] (concentrations are in mM): [K1in = 145.5 [Mg2+]in = 2.2 [Na]in ? [Cl]in = 7.0 [A]in = 147.4 [K"]out = 4.2 [Mg2out 5.4 [Na+]out = ? [Cl-]out = 156.0 [A]out = 0 You determined that the membrane is impermeable to Mg and A:. You have also discovered that the permeability to K' is 50 times the Na* permeability, and the permeability to Cl is twice the permeability to Na* (a) Assuming this is a complete list of solutes present in the intracellular and extracellular solutions at significant concentrations, calculate [Na']n and [Na lout. (b) Calculate the membrane resting potential, Vrest. (c) You add an experimental drug to the extracellular solution that increases the permeability to K+ by 10%. What is the new resting potential Vrest? (d)You realize that in order for your experiment with the experimental drug to work, you need the resting potential to be the same as what you calculated in (b). What ion concentration(s) could you change to keep Vrest where you need (you can only change extracellular solution)? By how much would you change the concentration(s)?Explanation / Answer
(a) From the given intracellular and extracellular concentrations of K+ and Cl- and assuming the intracellular concentration of K+ is 50 times of Na+ as per the permeability difference the Intracellular concentration of Na+ is calculated to be 3.2, and from the Nernst equation, assuming that the equilibrium potential to be +60mv the outer cellular concentration of Na+ is calculated as 33.107.
(b) By applying all the given values in the Goldman-Hodgkin-Katz equation the membrane resting potential is found to be -0.0815
(c) Due to the 10% increase in the permeability of the K+ ion the resting potential falls to -0.0981
(d) In order to bring back the original membrane resting potential, the extracellular concentration is increased to 4.4.
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