Ion Channel Gating

Question 1

Essence of Membrane currents

Answer 1

• Membrane currents are like a circuit with capacitance in parallel with variable resistors
• The ion drive is like held charge (capacitance) or a loaded spring
• The current is dependent on the resistance (the ion conductance)

Question 2

Measuring Ionic Current

Answer 2

• Permeability properties of channels

- Mechanisms by which channels open and close

Question 3

Voltage Clamps

Answer 3

• Used to measure ion currents
• Voltage is held constant
• By changing the voltage, you can study V-sensitive channels

Question 4

Current Clamps

Answer 4

• Current can be clamped for a set amplitude and time

Question 5

Define the current of an ion species

Answer 5

= (membrane conductance to the species) x (driving force for that species)

• DF = (Em - Eion)

Question 6

Conductance

Answer 6

• Em
• Type of ion
• Conc. of ion

Question 7

Permeability

Answer 7

• Em
• Type of ion (type/charge)
• NOT conc. (only likelihood of direction)

Question 8

Inward currents in VC

Answer 8

• Either +ve in or -ve out produces downward deflection

- Inward currents depolarise the cell