: We will ignore Cl- and Ca2+. Set PK=30 and PNa=1 and use PK/PNa=30 to make the calculation easier. Actual permeabilities are challenging to measure so we use a ratio.

Values for mammalian muscle from Table 12.1. Nao=145 mM, Nai=12 mM; Ko=4 mM and Ki=155 mM.
Values for squid axon are Nao=440 mM, Nai=50 mM; Ko=20 mM and Ki=400 mM.
Show your arithmetic for full credit and label units.

1. Use the GHK equation to calculate the resting Vm with PK/PNa=30. Compare the mammalian Vm with the squid axon. Why are the ion concentrations so different?
2. Calculate the relative PK/PNa permeability for mammalian muscle during an AP when the Vm=10 and at the peak when Vm = +40 mV.
3. Electrical excitability is much more complex than understanding the membrane potential at a given point in time in a given neuron. But for our goals, we will utilize the GHK equation to consider what happens in status epilepticus—a type of seizure that does not stop of its own accord but is a life-threatening emergency. A full understanding of the ionic mechanisms has been explored in patients and the changes involve K+, Na+, Cl-, Ca2+, H+ and HCO3-. Values for these ions were measured at rest and during an epileptic seizure. Calculate the Vm during rest and during the seizure based on the measured K+ and Na+
   Source: doi: https://doi.org/10.3389/fncel.2015.00419 (Links to an external site.)
   FIGURE 1 Ion concentration changes during seizures. An intracellular recording from a CA3 hippocampal neuron during a seizure-like event in vitro demonstrates typical neuronal membrane potential changes which accompany seizure episodes.
   Rest: Nao=145 mM, Nai=10 mM; Ko=4 mM and Ki=96 mM.
   During a seizure: Nao=139 mM, Nai=55 mM; Ko=12 mM and Ki=94 mM.