Membrane potential Flashcards
Electric forces are ______ than osmotic forces
way larger
Membrane potential
electrical differential across the cell membrane. Empirical
Equilibrium potential
calculated from the Nernst equation for a particular ion
True or False: Bulk solutions are always electrically neutral
True. This includes inside the cell
Nernst equation
Eeq = (62/z)log(Co/Ci)
What two forces govern passive movement of an ion across a membrane?
concentration difference and electrical potential difference (combine to make electrochemical gradient)
What does the Nernst equation tell us?
the electrical potential difference across the membrane that must exist if the ion is to be at equilibrium at given concentration
What is the equilibrium potential when an ion is at equal concentration across a membrane
zero
What does it mean when Vm is not the same as Ecl?
- the membrane is impermeable to Cl-
or - Cl- must be pumped across the membrane
Donna’s rule
[Ko][Clo]=[Ki][Cli]
Na/K pump ratio
3 Na+ (out) for 2 K+ (in), making it electrogenic (not electro-neutral
How do relative membrane potential depend on permeabilities to ions?
- Na+ is constantly leaking out of the cell trying to get to equilibrium (pulling Vm to Ena) and K+ is leaking out trying to pull Vm down to Ek
- The balance is different in different cells due to relative permeability (how many K+ or Na+ channels they have)
- this determines if Vm is closer to Ena or Ek
What is the primary short term determinant of membrane potential?
The relative membrane permeabilities to different ions (even if the Na/K pump stopped working, nothing really happens initially in most cells)
What is the driving force of an ion?
the difference between Vm - Ena or Vm - Ek
Why do changes in ECF levels of Na+ have little effect on the membrane potential?
the membrane is relatively impermeable to Na+
Why are cells very sensitive to K+ ECF changes?
- the cell membrane is much more permeable to potassium
- an increase in [K+] will reduce the efflux of K+ from the cell, causing the cell to depolarize and Ek moves closer to zero
- Because Vm falls between Ek and Ena, there is depolarization -> a modest change in [K+]o results in a large change in Vm
What are three treatments for hyperkalemia?
- sodium bicarbonate
- beta-2 adrenergic agonist to increase the activity of the Na-K ATPase pump
- give insulin and glucose to increase ATP supply for the Na-K ATPase pump
How is hyperkalemia diagnosed?
usually an EKG to detect cardiac arrhythmia followed by measuring plasma potassium ion concentration
