Electric Membranes

Question 1

Nernst Equation

Answer 1

(60mv/Z)(log10(xout/xin))

Question 2

Resting potential potassium

Answer 2

~ -90 mV

Question 3

Resting potential sodium

Answer 3

+70 mV

Question 4

Undershoot

Answer 4

Caused by VGKC being open and VGNC being closed, Ek reached

Question 5

Upstroke

Answer 5

VGNC open, K channels overwhelmed, ENa reached

Question 6

Repolarization

Answer 6

VGKC opens, swamps VGNC, potential returns to negative toward ENaK (but undershoots)

Question 7

Refractory

Answer 7

cell cannot initiate an action potential

Question 8

Channel selectivity

Answer 8

how much a channel can specify which ion it wants to let pass

Question 9

Conductance

Answer 9

how much current changes when voltage potential changes (inverse of resistance); measured in Siemens (pS in cells)

Question 10

Permeation

Answer 10

all of the factors that contribute to how much ion can flow through a channel; specifically electrochemical gradient and physical size of the pore

Question 11

Reversal potential

Answer 11

the nernst potential for a multi-ion channel

Question 12

Time Constant Equation

Answer 12

tau = R * C or C/G

Question 13

Conduction velocities

Answer 13

Heart = 0.3-2 m/s
Axon = 120 m/s
Skeletal muscle = 5 m/s

Question 14

Conduction time (time to repolarization)

Answer 14

Heart = 200 ms
Skeletal muscle = 2 ms
Axon = 1 ms

Question 15

selectivity filter

Answer 15

a region that loosely binds ions to ensure specificity of ion channels

Question 16

Inactivation

Answer 16

As opposed to de-activation; inactivation is when the channel is plugged up.

Question 17

pacemaking

Answer 17

depends on non-specific cation channels

Question 18

Potassium channels (structure)

Answer 18

oligo-tetramer; IRK 2 transmembrane Vk 6 transmembrane domains; Kv has “P-loop” that is like tongue sticking into ice cream; Kv extra domains are the voltage sensor

Question 19

“the” IRK

Answer 19

gives muscle and cardiac cells higher resistance to accidental depolarization than other excitable cells; plugged by divalent cations

Question 20

ROMK

Answer 20

Renal outer medullary potassium channels; most prevalent epithelial potassium channels

Question 21

VGNC and VGCC

Answer 21

Like Kv but composed of only one protein with four transmembrane domains; VGCC in neurons and cardiac cells are different

Question 22

ENAC

Answer 22

Epithelial Sodium Channels; like IRK channels made up of four subunits, non identical; large extra-cellular domain

Question 23

CFTR

Answer 23

cystic fibrosis receptor Chloride receptor

Question 24

CLC channels

Answer 24

Chloride channels that are double barreled; they operate opposite P-pumps that are feeding protons into lysosomes; 12 domains.

Question 25

Ca activated Cl channels

Answer 25

Found in sweat glands that release Cl into the lumen of the gland

Question 26

Ligand gated ion channels

Answer 26

Excitatory: ACh and glutamine- cation channel
Inhibitory: GABA - Cl channel

Question 27

Nonselective sensation channels

Answer 27

Ca channels for sensing touch, heat, stretch, etc…

Question 28

Intracellular channels

Answer 28

Normally mediated by cAMP or cGMP