Question

4) Recall that after the Na+ channels open the K+ channels open. Again to make the calculations relatively simple, solve the Goldman equation again with all resting conditions EXCEPT a 100 fold increase in potassium permeability. (2 points) [Hints, first, while I always stress the importance of units, in this case the simplified equation uses lumped constants (RT/F) and thus the units are factored in – so you can, this time, ignore the units. Second, remember that Cl- is a negative ion and thus in both the Nernst equation and Goldman equation you must remember to in and out concentrations are reversed relative to the cations]

To solve this equation, you will need to use the following concentrations inside (i) and outside (o) the cell and permeabilities (P) of sodium (Na+), potassium (K+) and chloride (Cl-) for the neuron: Ko = 5 (all) Ki = 150 Nao = 150 Nai = 15 Clo = 125 Cli = 9 PNa= 10-9, PK = 10-8 PCl = 10-9 (

All concentrations in mM and permeabilities are in units of cm/s but see “hints” below)

Answer #1

5) A new drug has been discovered that completely opens the
voltage-gated potassium channels. If this drug is used
experimentally on an isolated axon, the membrane potential can be
easily measured. Assume that this experiment provided the following
results. The extracellular Na+ is 145 mM and the extracellular K+
is 4mM, the measured membrane potential in the presence of the drug
is -94mV. Using this information, calculate the intracellular K+
concentration.
To solve this equation, you will need to use...

Plot the voltage of the cell using the original parameters for
Na, K and Cl, and changing sodium permeability from 1 to 10, 100,
1000 and up to 9999. Will the voltage keep increasing positively as
the permeability to sodium is increasing? Why?
Plot the voltage of the cell using the original parameters for
Na, K and Cl, and changing potassium permeability from 1 to 10,
100, 1000 and up to 9999. Will the voltage keep increasing
negatively as the...

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