Electric Membranes Flashcards
Nernst Equation
(60mv/Z)(log10(xout/xin))
Resting potential potassium
~ -90 mV
Resting potential sodium
+70 mV
Undershoot
Caused by VGKC being open and VGNC being closed, Ek reached
Upstroke
VGNC open, K channels overwhelmed, ENa reached
Repolarization
VGKC opens, swamps VGNC, potential returns to negative toward ENaK (but undershoots)
Refractory
cell cannot initiate an action potential
Channel selectivity
how much a channel can specify which ion it wants to let pass
Conductance
how much current changes when voltage potential changes (inverse of resistance); measured in Siemens (pS in cells)
Permeation
all of the factors that contribute to how much ion can flow through a channel; specifically electrochemical gradient and physical size of the pore
Reversal potential
the nernst potential for a multi-ion channel
Time Constant Equation
tau = R * C or C/G
Conduction velocities
Heart = 0.3-2 m/s
Axon = 120 m/s
Skeletal muscle = 5 m/s
Conduction time (time to repolarization)
Heart = 200 ms
Skeletal muscle = 2 ms
Axon = 1 ms
selectivity filter
a region that loosely binds ions to ensure specificity of ion channels
Inactivation
As opposed to de-activation; inactivation is when the channel is plugged up.
pacemaking
depends on non-specific cation channels
Potassium channels (structure)
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
“the” IRK
gives muscle and cardiac cells higher resistance to accidental depolarization than other excitable cells; plugged by divalent cations
ROMK
Renal outer medullary potassium channels; most prevalent epithelial potassium channels
VGNC and VGCC
Like Kv but composed of only one protein with four transmembrane domains; VGCC in neurons and cardiac cells are different
ENAC
Epithelial Sodium Channels; like IRK channels made up of four subunits, non identical; large extra-cellular domain
CFTR
cystic fibrosis receptor Chloride receptor
CLC channels
Chloride channels that are double barreled; they operate opposite P-pumps that are feeding protons into lysosomes; 12 domains.
Ca activated Cl channels
Found in sweat glands that release Cl into the lumen of the gland
Ligand gated ion channels
Excitatory: ACh and glutamine- cation channel
Inhibitory: GABA - Cl channel
Nonselective sensation channels
Ca channels for sensing touch, heat, stretch, etc…
Intracellular channels
Normally mediated by cAMP or cGMP
