w-3 ion channels and transporters

Question 1

The Patch Clamp Method

Answer 1

• Glass micropipette 1-3 μm diameter
  tip
• Inside-out recording enables control
  of intracellular medium (it is easier to
  change the bath solution rather than
  the pipette solution)
• Outside-in recording enables greater
  control of the extracellular medium

Question 2

Ohm’s law

Answer 2

V = ir

Question 3

Structure of a simple bacterial K+ channel
determined by crystallography

Answer 3

• 4 subunits each containing two membrane- spanning helical structures and a poor loop
• Pore loops form the pore for K+ ions
• Negatively charged helix from pore loop helps stabilize non- hydrated K+ ions
• Mouth of the channel is too narrow for larger ions (Cs+) and too large to stabilize a non- hydrated Na+ ion
  
  • Acts as a selectivity filter
• Four K + ion binding sites within the selectivity filter

Question 4

Voltage-gated chloride channels

Answer 4

• Cl - channels contribute to the excitability of a neuron, resting membrane potential, and cell volume
• Channel is a dimer of two identical subunits, each with an ion conduction pore
• No voltage sensor domain, rely on voltage-dependent movement of negatively charged amino acids near the selectivity filter

Question 5

Ligand-gated ion channels:

Answer 5

• There are many different types of ligands that can bind to and open ion channels
• Ligand-gated channels tend to be less selective regarding the ions that flow

Question 6

What active transporters establish the ion gradients that generate ion currents?

Answer 6

• ATPase Pumps
• Ion exchangers

Transport mechanisms can also transport other molecules in and out on intracellular vesicles.

Question 7

ATPase pumps:

Answer 7

• hydrolyze ATP to move ions against their concentration gradient
  
  • ~2/3 of brain’s total energy consumption

Question 8

Ion exchangers:

Answer 8

• move one ion against the concentration gradient using the energy of another ion move with/down its concentration gradient
  - Antiporters – moves ions in opposite directions
  - Co-transporters – moves ions in the same direction

Question 9

Translocation of Na + and K + by the Na+ pump:

Answer 9

• ATP hydrolysis/ phosphorylation causes conformational change that releases sodium ions and binds potassium ions
• 3 Na+/2 K+ exchange ratio
• Ion movements by the Na + pump are dependent on ATP and the presence of both ions

Question 10

Ion Exchangers

Answer 10

• Use the energy of one ion moving down its gradient to move another ion against its concentration gradient
• Cannot create energy, depend on gradient established by ion pump