L7 - ions and electrochemical equilibria at the membrane

Question 1

define patch clamping

Answer 1

measurement of electrical potential by placing electrode on membrane

Question 2

describe electrode of patch clamping technique

Answer 2

thin capillary tube filled with conducting solution and wire

Question 3

explain process of measuring intracellular/extracellular potential

Answer 3

1. electrode placed in electrode holders which are mounted in micromanipulators
2. place electrode inside / outside cell
3. connect to volt meter
4. compare to a reference point further away from cell (0V)

Question 4

explain process of patch clamping

Answer 4

1. electrode placed in electrode holders which are mounted in micromanipulators
2. tip of electrode broken and flamed in bunsen burner making it smooth
3. end brought in contact with membrane and suction applied
4. membrane is slightly sucked into the electrode
5. allows measurement of potential in a ‘patch’ of the membrane e.g where channels are

Question 5

what can patch clamping show you

Answer 5

how potential changes with the opening/closing of a channel within a patch in the membrane

Question 6

explain the setup of resting membrane potential

Answer 6

1. ATPase pump pumps 3Na out and 2K in
2. K+ channels are open so some flow out following conc gradient
3. therefore the inside is relatively more -ve
4. equilibrium created with no net flow of current

Question 7

how is this membrane potential intensified?

Answer 7

1. Cl- tries to follow the K+ but cannot pass through the channel so it accumulates on the inner membrane
2. K+ accumulates on the outer membrane surface (attracted to the Cl-) creating a ‘shell’

Question 8

explain the concept of the nernst equation

Answer 8

1. if conc gradient (of ion) is known, it can be used to calculate the membrane voltage using the nernst equation

Question 9

what is the nernst equation

Answer 9

for positive ions:
E = 58 x log conc out / conc in

E = ebm potential
58 in mV

for -ve ions just swap conc in / conc out