Ion Channels and Transporters

Question 1

Patch Clamp Method

Answer 1

• using a tiny glass pipette, suction a single ion channel

- apply suction to this cell membrane and pull that patch of membrane into the pipette

Question 2

Types of patch clamp methods

Answer 2

Cell-attached recording: all the current that flows when a single ion channel opens must flow into the pipette
Whole cell recording: the interior of the pipette becomes continuous with the cell cytoplasm, allowing electrical potentials and currents from the entire cell –> and can inject substances into the interior of a patched cell
Inside-out recording: (n) makes it possible to change the medium to which the intracellular surfae of the membrane is exposed (valuable when studying influences of intracellular molecules on ion channel functioning)
Outside-out recording: (u) optimal for studying how channel activity is influenced by extracellular chemical signals such as neurotransmitters

Question 3

clamping the cell at a depolarised value: sodium channels

Answer 3

macro response is sodium decreasing initially before returning to baseline

transient activation, subsequent inactivation

Question 4

clamping the cell at a depolarised value: potassium channels

Answer 4

sustained activation (opening / conductance of potassium) which matches macroscopic observations

Question 5

sodium response

Answer 5

• When at rest - the channels are closed
  
  • Once you turn on that clamp voltage, the channel opens (now permeable or conductive to sodium) - the sodium rushes into the cell
  • As it stays open for longer - the sodium starts to inactivate (the channel is open, but inactivated)
    The sodium channel then closes `

Question 6

potassium response

Answer 6

• Potassium stays closed (slower activation response)
  
  • When the Na starts inactivating, the K+ channel opens and potassium rushes out of the cell (contributes to the downward slope of the membrane potential
    Then closes (there’s no inactivation)

Question 7

structure of ion channels

Answer 7

protein folding
pore loops create a cavity inside the cell wall
the way that these structures become ion-specific or selective is largely structural in nature (how narrow or wide these channels are)

Question 8

There are other types of sensitivities than just voltage

Answer 8

• they can be sensitive to other molecules: neurotransmitters (hwne a neurotransmitter of interest passes, it will bind to the complex of the membrane pore, which will change the transmembrane pore and allow ions to go thru it)
• sensitive to pH of the fluid its suspended (acid sensing ion channel)
• sensitive to calcium (Ca activated K channel)
• cyclic nucleotide gated channel
• thermosensitive channel
• mechanosensitive channel

Question 9

active transporters

Answer 9

consume energy

- Has to do with  phosphorylation or dephosphorylation of molecules 
- To get an ion transfer against its concentration gradient - it costs energy (ATP) 
- These active transporters depend on energy - if you disrupt ATP synthesis, then less sodium gets through 
	○ Additionally, without potassium, you lose sodium translocation as well

Question 10

Ion exchangers (another way of transporting across concentration gradients)

Answer 10

• Antiporters (be permeable to one positive charge going in one direction, and a different charge in the other direction)
  ○ Na+ / Ca2+ exchanger
  ○ Na+ / H+ exchanger
  
  • Co-transporters (ions going in the same direction across the membrane)
    ○ Na+ / K+ / Cl- co-transporter
    ○ K+/Cl- co-transporter
    Na+ / neurotransmitter co-transporter GABA, domain