Membrane Potential (Al Medhi)

Question 1

Functions of ionic concentration gradient

Answer 1

• Action potential
• Pace maker activity (heart/gut CYCLIC action potential)
• Signaling
• Cell volume homeostasis
• pH homeostasis

Question 2

Action potential

Answer 2

excitable cell function resulting from rapid change in membrane potential

Question 3

pace maker activity

Answer 3

sequential opening of ion channels at particular membrane potentials

Question 4

signaling

Answer 4

dependent in change in membrane potential (Ca2+ etc)

Question 5

Cell volume homeostasis

Answer 5

influx/efflux of ions determines water homeostasis

(aquaporins follow concentration gradient)

Question 6

pH homeostasis

Answer 6

concentration of hydrogen ions

many enzymes require a specific pH to act

Question 7

Na+

Answer 7

lower inside

higher outside

Question 8

K+

Answer 8

higher inside

lower outside

Question 9

Cl-

Answer 9

lower inside

higher outside

Question 10

HCO3-

Answer 10

lower inside

higher outside

Question 11

Ca2+

Answer 11

higher inside

lower outside

Question 12

Active Transporters

Answer 12

create concentration AND electrical gradient

electronegative charge INSIDE cell

more positive charge is exiting

Question 13

Na+-K+-ATPase

Answer 13

pump two K+ IN

pump 3 Na+ OUT

Question 14

What determines membrane resting potential?

Answer 14

Ion channels

Question 15

Uncharged molecules move across the membrane by:

Answer 15

passive transporters

Question 16

GLUT1 uses […] to drive glucose into the cell

Answer 16

The concentration gradient

*glucose is UNCHARGED

Question 17

Energy sources for charged molecules

Answer 17

concentration gradient

electrical charge gradient

Question 18

Nerst Equation

Question 19

Vm

Answer 19

resting membrane potential/equilibrium potential

Question 20

Vm for specific ions

Answer 20

Question 21

The Goldman Equation

Answer 21

describes the reversal potential across a membrane

(membrane potential at which there is no net flow of ions)

used for REAL cells → more than one ion channel is open

Question 22

Current direction

Answer 22

direction of movement of positive charge

Question 23

Ligand gated channels

Answer 23

follow concentration gradient

Question 24

4 primary voltage gated channels

Answer 24

Na+

K+

Cl-

Ca2+

Question 25

What amino acids sense voltage?

Answer 25

Lysine and arginine

positively charged

Question 26

mechanism of voltage-dependent gating

Answer 26

negative electrical field → inward pull → closes channel

depolarization (cell gets more positive) → outward push → conformational change → pore opens → hydrophobic loop blocks pore → inactivation (physically open but blocked: refractory period)

Question 27

action potential duration

Answer 27

should be about 1 ms

whole thing about 2 ms, including hyperpolarization and return to resting potential

Question 28

mechanism of inward rectification

Answer 28

hyperpolarization → inward rectifying potassium channels are opened (Kir)

• voltage current relationship is linear

1. channel opens briefly, potassium exits
2. from -25 to 25 mv, no current
3. >+50 mV, a very low slope outward rectifying current

Question 29

Outward non-rectification

Answer 29

• potassium pore is negatively charged
• in positive voltages, positive ions try to escape cell
• larger positively charged molecules (magnesium and polyamines) are pushed into potassium channels and block them
• → potassium is prevented from leaving cell

Question 30

Lidocaine

Answer 30

lidocaine: voltage-gate sodium channel blocker

local anesthetic