Phys 2

lipid rafts

microdomains within the phospholipid bilayer that act as a hotspot for signal transduction; contain cholesterol, sphingomyelin, glycoproteins

protein free lipid bilayers are impermeable to ___

ions and large, uncharged, polar molecules

substances that can diffuse directly through lipid bilayer

carbon dioxide and oxygen

molecules least able to pass by diffusion

ions

permeability is determined by

size, charge, lipid and water solubility

hydration shell

ions are surrounded by water molecules, must go through proteins that shield them from hydrophobic tails of phospholipids

uniporter

membrane transport protein that moves single specific molecule or ion via passive transport

ion channels

conduct ions at high rates; contain aqueous pores that shield contact from bilayer; may be highly selective and have gates; mediate passive transport

pumps (ATPases)

enzyme pump proteins that establish electrochemical gradients of ions by using energy to pump ions across bilayer

antiporters / exchangers

transport two substrates in the opposite direction

symporters / co-transporters

transports two substrates in the same direction

conduction rate of ion channels

10^7 - 10^8 ions/sec

passive transport

solutes move down chemical concentration or electrochemical gradient; no energy required

active transport

solute moves against gradient; mediated by transporters, requires energy

electrochemical gradient

net sum of electrical and chemical gradient; only applies to charged solutes

semipermeability

lipid soluble molecules freely cross, water soluble molecules require transport proteins to cross

primary active transport

transports solutes against a gradient and directly uses ATP

secondary active transport

solutes transported using a gradient established by primary active transport

coupled transport

proteins rely upon potential energy stored in electrochemical gradient for an ion; not enzymes - toggle proteins

ex of uniporter

GLUT

transporters have a ___

slower rate than channels (10² - 10^4 ions/sec)

ex of passive transport

ion channels, passive transporters, simple diffusion

ex primary active transport

Na+ K+ ATPase (Na+ pump)

ex secondary active transport

Na+ Ca2+ exchanger, Na+ glucose symporter

ex coupled transporter

symporter and antiporter

function of Na+ K+ pump

maintains osmotic balance and stabilizes cell volume by controlling ICF Na+ at lower concentrations

Na+ K+ ATPase

three Na+ taken out, two K+ taken in; causes overall positive charge extracellularly, and overall negative charge intracellularly

contribute to negative charge ICF

PS, phospholipids, anions left behind when K+ leaves cell

digoxin

purple foxglove - flower that was discovered to be treatment for congestive heart failure and dropsy; inhibits Na+ K+ pump

effects of Na+ K+ pump inhibition

decrease in ICF K+ and increase in ICF Na+ → drives Na+ into ICF because of gradient → reduces efficiency of Na+ Ca2+ exchanger → increase of ICF Ca2+ increases cardiac output (positive inotropic effect)

ICF Na+

5-15

ECF Na+

145

ICF K+

140

ECF K+

5

ICF Ca2+

10^-4 = 100 nM

Volta

pioneer of electricity and power; inventor of electrical battery; invented Voltaic pile to prove Galvani wrong - generated chemically

Luigi Galvani

“animal electricity” - bioelectricity

glucose transport

low concentration of glucose, glucose and Na+ go through Na+ driven glucose symporter; high concentration within intestinal lumen, glucose enters ECF through uniporter, Na through Na+K+ pump

Giovanni Aldini

nephew of Galvani; brought corpses “back to life” by making them move with electricity

leak channels

channels that allow ions and water through passively

fixed intracellular anions

cannot go through leak channels and are left behind by K+ ions; contribute to negative charge intracellularly

the thinness of the PM ____

allows for charges to interact on opposite sides of membrane

Nernst equation

describes voltage that will be created when K+ has attained electrochemical equilibrium

a large negative transmembrane voltage is important for ___

maintaining electrical excitability

electrochemical driving force

absolute difference between membrane potential and Nernst potential for that ion

depolarization

shift in voltage across membrane to less negative value; excitatory

hyperpolarization

shift in voltage across membrane to more negative value; inhibitory

dendrites

receive electrical signals

cell body

integrates incoming signals and generates outgoing signal to axon

axon

passes electrical signals to dendrites of another cell or effector cell

axon hillock

contains VGNCs and where APs occur

main excitable cells

muscle cells and neurons

neurons

specialized, terminally differentiated cell types; main excitable cells that can support action potential

local potential

change in membrane potential at nearby point of stimulation; graded, decremental, reversible

action potential

electrical signals produced by coordinated opening and closing of VGNCs; rapid depolarization followed by hyperpolarization; all or none, non-decremental, unidirectional, irreversible

ligand gated ion channels

proteins that open and close to let specific ions through when ligand binds to them

AP follows an all or none principle __

because of transient positive feedback

Hodgkin Cycle

describes how positive feedback at threshold potential leads to all or nothing event of AP; increase in permeability to Na+ → Na+ influx → membrane depolarization

VGKCs

allow for repolarization during recovery phase

selectivity of ion channels

charged parts of channel pore substitute for water molecules and allow ion to shed hydration sphere

Loligo

squid studied to understand APs because of its large axon

threshold

APs triggered when sufficient VGNCs open and result in depolarization inward

VGNC closed

ready to open, S4 repelled from ECF

VGNC open

conducting Na+; S4 repelled from ICF

VGNC inactivated

open but non-conducting within 1-2 ms; S4 repelled from ICF; inactivation gate swings shut

S4

voltage sensors for VGNC channel, movement results in opening of channel

repolarization

loss of positive K+ ions turn membrane negative again

absolute refractory period

no chance for another AP

Relative refractory period

could potentially have an AP, relative to strength of stimuli

hyperkalemia

elevated K+; results in less negative Nernst potential, causing VGNCs to be stuck in inactivation and refraction

local anesthetics

block pain by blocking inner mouth of VGNC channel; comes from cocaine

tetrodotoxin (TTX)

plugs extracellular mouth of channel like inactivation gate; found in animals because it is produced by symbiotic bacteria

3 Na+ ions bind to pump and trigger ___

Na dependent autophosphorylation; 1 ATP consumed

2 K+ ions bind to pump and trigger ___

dephosphorylation; triggers release of K+ ions