Lecture 7 Terms/Questions

Question 1

Equilibrium Potential

Answer 1

• the membrane potential that EXACTLY OPPOSES the steady state electrochemical gradient for an ion
• follows the convention: “inside with respect to outside”

Question 2

Resting Membrane Potential

Answer 2

• special case of MP where there is steady-state balance b/t active transport & leakage of ions
• for most cells, RMP b/t -20 mV & -90 mV

Question 3

Na+/K+ ATPase

Answer 3

• pumps 2 K+ ions into cell, removes 3 Na+ ions (uses energy from ATP)

in order to do this:

1. hydrolyses ATP (uses energy from ATP)
2. several conformational changes (b/c it’s not a channel)

Question 4

Nernst Equation

Answer 4

the equation that determines the equilibrium potential for a single ion based on the ion concentrations inside & outside the cell
- we can calculate the equilibrium potential for any ion at 37 degrees celsius, given a concentration gradient

Eion = 61/z x log ([ion]out/[ion]in)

Question 5

Goldman Equation

Answer 5

predicts RMP considering:

• relative permeability of Na+, K+ & Cl-
• the concentrations inside & outside the cell

Question 6

Electrochemical Gradient

Answer 6

combination of an electrical gradient & chemical gradient

* - ions subjected to an electrochemical gradient will move

Question 7

Depolarization

Answer 7

more (+)

goes up

Question 8

Hyperpolarization

Answer 8

even more (-)

goes down

Question 9

Repolarization

Answer 9

more (-)

dips down more

Question 10

Relative Permeability

Answer 10

g

Question 11

Leakage Channel

Answer 11

ion channels that spend most of their time in ?

Question 12

How do ions cross the cell membrane?

Answer 12

move according to their concentration gradient

& with ATP ases and channels ?

Question 13

Does RMP represent equilibrium? Why or why not?

Answer 13

no - system is at STEADY STATE where the rate of leakage thru leakage channels is exactly balanced by active transport

NOT equilibrium b/c it requires constant energy!

Question 14

What kind of channels are responsible for the movement of ions across the cell membrane at RMP?

Answer 14

K+, Na+, Cl- ?

Question 15

How do these ion channels differ from voltage gated channels?

Answer 15

Ion channels may be specific for one ion or may allow ions of similar size & charge to pass

Voltage channels open and close in response to changes in membrane potential.

?

Question 16

How do these ion channels differ from ligand gated channels?

Answer 16

Ion channels may be specific for one ion or may allow ions of similar size & charge to pass

Ligand-gated ion channels open when a chemical ligand such as a neurotransmitter binds to the protein.
?

Question 17

What happens to equilibrium potential for K+ (=Ek) when [K]out increases to 25 mM?

Answer 17

-47 mM

so it depolarizes (more +)

Question 18

What happens to Ek when [K]out decreases to 2 mM?

Answer 18

-144 mM

so it hyperpolarizes (more -) ?

Question 19

What happens to Ek when [K]in decreases to 50 mM?

Answer 19

-61 mM

so it depolarizes (more +)

Question 20

What happens to ENa when [Na]out increases to 175 mM?

Answer 20

+65 mM

so it depolarizes (more +)

Question 21

What happens to ECl when [Cl-]in increases to 10 mM?

Answer 21

+63 mM

so it depolarizes

Question 22

What happens to RMP if [K]out decreases to 2 mM?

Answer 22

-89 mV

so hyperpolarization

Question 23

What happens to RMP if permeability of K (=Pk) decreases to 10?

Answer 23

-63 mV
so depolarization (more +)

Question 24

What happens to RMP if permeability of Na (=Pk) increases to 10,000?

Answer 24

+ 58 mV
(becomes very very +)
goes from 1 to 10 000

Question 25

What would happen to RMP if there were no leakage channels?

Answer 25

constant @ 0

- all would be 0 in the Goldman Equation

Question 26

Suppose that there are 1000 K+ leakage channels operating in the membrane & Pk = 75. What would happen to Pk if second messengers opened an additional 1000 channels? What would happen to RMP?

Answer 26

?

Question 27

What would happen to RMP if the Na+/K+ ATPase was blocked for a short time? For a long time?

Answer 27

establish only RMP @ -80mV

• 1st step transport of 3 & 2 (net loss of +1)
• depolarize b/c stopping electrogenic nature (more (-))
• Na+ & K+ will reach equilibrium eventually b/c nothing moving them back & forth

Question 28

When patients are rescued from hypothermia, potassium permeability of many cells dramatically increases. K+ leaks from cells into the extracellular fluid (& plasma). Elevated plasma potassium is predictive of a low chance for survival. Why is high serum K+ bad for you? Hint: think about what high K+ does to RMP. What cells need a hyperpolarized RMP in order to function?

Answer 28

d