Lecture 2: Ion channels, Ionic Equilibria, RMP

Question 1

Why are biological membranes able to act as capacitors?

Answer 1

They can separate charge across the membrane since it is selectively permeable. It is not permeable to charged or large or hydrophilic substances, so since charged ions can’t cross membrane, leads to charge storing across the membrane

Question 2

Describe how the membrane is like a circuit

Answer 2

electromotive force (batteries) = potential energy from electrochemical gradients of ions, set up by Na+/K+ ATPase
capacitor = membrane, storage of charge
resistors = ion channels, conduct current
Na+ comes in, inwards current
K+ goes out, outwards current
Cl- comes in, OUTWARDS current

Question 3

Name 3 ways ion channels can be gated, give example of each

Answer 3

ligand gated = Ach receptors at neuromuscular junction
mechanically-gated = RyR receptors attached to CaV1.2 channels in the SR of skeletal muscle
voltage-gated = Na+ channels in the axons of neurons

Question 4

What key factors determine the resting membrane potential?

Answer 4

Activity of Na+/K+ ATPase
Permeability of membrane to various ions
K+ leak channels
Equilibrium potential of other ions

Question 5

What does depolarization/hyperpolarization mean?

Answer 5

depolarization = membrane potential gets more positive
hyperpolarization = membrane potential gets more negative

Question 6

What are the intra/extracellular concentrations of Na, K, Ca, Cl, HCO3, Pi

Answer 6

Na: 15/145
K: 140/4
Ca: 0/2.5
Cl: 25/100
HCO3: 12/24 mM
Pi: 0.6/1.2

Question 7

Define equilibrium potential

Answer 7

membrane potential of a cell only permeable to that ion, the potential at which there is no net movement of charge