1. You have a cell and you know the concentrations of some ions, but not the oth

Question

1. You have a cell and you know the concentrations of some ions, but not the others. Intracellular Fluid] ? mM 142 mM ? mM 127 mM [Extracellular Fluidl INa'] IK'] [CI-I A-1 135 mM ? mM 140 mM Calculate the concentration of the unknown ions based on the following a) Use electrical neutrality to determine [K.J b) Use the Donoao rule to calculate ICI c) You know osmolarity is balanced, so use that to determine [Na. d.) Based on your identification of each ion concentration, what is the driving force for Na+ if K+ is 25 times more permeable than Na+?

Explanation / Answer

Part a-

Electrical neutrality comprises the equilibrium of negative and positive ions where net charge becomes zero. Therefore, we need to add moles of positive and negative ions separately to get the net zero charge.

In the table, we know that 142 mM is the highest molarity amongst all. Therefore, we would take this as reference. We will try to make 142 mM to all ions. Therefore, molarity of Potassium ions at extracellular fluid is zero.

Now sodium and potassium ions have difference of 7mM. therefore, intracellular fluid will have 7mM sodium concentration.

Part b-

Donnan formula suggests at equiblirum-

[Na1]/ [Na2]= [Cl1]/ [Cl2]

7/135 = [Cl1]/140

[Cl1] =7.26 mM

Part c-

Because here all ions are monovalent, therefore, we can consider their osmolarity as same as molarity. Therefore, the sodium concentration would be 7mM.

Part d-

If K+ ions are 25 times more permeable, then these ions will move faster towards extracellular matrix. Therefore, sodium ions must rapidly mover from Extracellular to intracellular matrix.

The driving force will be Extracellular to intracellular matrix.

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