PSYC 306 Lecture 3

The NA+-K+ Pump

The NA+-K+ Pump

Unidirectional pump where sodium wants to go inside the membrane but can only leave and potassium wants to enter the membrane. However, both want to go against the driving forces. 

Step 1 of NA+K+

• Step 1: 3 sodium ions bind to an ATP (inside)

  • Charge: -3

Step 2 of NA+K+

• The ATP burns off, changes shape, and allows sodium to leave through the pump 

Step 3 of NA+K+

•  potassium binds from outside 

  • Shape changes  

Step 4 of NA+K+

•  ion channel opens and allows potassium to go in 

Step 5 of NA+K+

• last phosphate from ATP falls off 

Importance of NA+-K+

• Regulates sodium and potassium in side the membrane 

  • A lot of potassium inside 

• maintain voltage equilibrium within a membrane

endocytosis

• Processes that bring molecules and cells into a eukaryotic cell 

• Plasma membrane folds in or invaginates around the material, forming a vesicle

exocytosis

• Material in vesicles is expelled from a cell 

• Other materials leave cells such as digestive enzymes and neurotransmitters

GI process

• Ligand signal binds to receptor 

• Receptor interacts with g protein 

• GDP falls off the alpha subunit 

• GTP binds to the alpha subunit 

• Alphas subunit falls off with disengaged GTP and bind to at a different spot AC

• Reduces production of cAMP

GS process

• Ligand signal binds to receptor 

• Receptor interacts with g protein 

• GDP falls off the alpha subunit 

• GTP binds to the alpha subunit 

• Alpha unit disengages

• Alpha binds to AC 

• When binded, it takes ATP and changes it to cAMP 

• cAMP binds to ion channel or regulatory cell of PKA 

Ion channel route GS

• open up and ions will flow (how we smell)

PKA route GS

• catalytic cell will bond to protein and phosphorylated 

GQ11

• Ligand signal binds to receptor 

• Receptor interacts with g protein 

• GDP falls off the alpha subunit 

• GTP binds to the alpha subunit 

• Alpha unit disengages

• Alpha subunit will disengage with GTP goes to PLC 

• Sever bond in PIP2

DAG route GQ11

• Interact with PKC 

  • Add phosphates 

IP3 route GQ11

• Every cell regulates calcium 

  • Pump out 

  • Pump in to intermembrane 

    • Store in endoplasmic reticulum 

• Bind to IP₃ receptor on ER 

  • Calcium will go from high to low 

  • Short time, bind to PKC 

  • Add phosphates (phosphorylates) 

GTPase

• Catalyzes the hydrolysis of GTP to GDP and inorganic phosphate

•  converted GTP to GDP 

  • Disengage 

    • GTPase 

      • Converts GTP to GDP

Phosphodiesterase

•  converts cAMP to AMP

Protein Phosphatase

• Regulates phosphate levels 

• removes a phosphate group from a protein

Signal amplification

• 1 messenger binding to receptor causes the activation of at least 10 G-proteins 

• Ach G protein activates at least 10 AC

• Each AC generates hundreds of cAMP molecules: 5000 cAMP 

• Each cAMP activates PKA: 5000 

• Ultimately each PKA creates the phosphorylation of 2,500,000 proteins 

Axon

Portion of nerve cell that carries nerve impulses away from the cell body

Dendrite

• any of the usually branching extensions of a neuron over which impulses travel toward the cell body compare axon

Cell body

• spherical part of a neuron that houses the nucleus.

Synapse

• Connection between axon terminal and dendrite 

Chemical synapse

• neurotransmitter

electrical synapse

• Gap junctions 

nerve

•  Bundle of axons from different neurons in the PNS

tract

 Bundle of axons from different neurons in the CNS

glial cells

• Release and reuptake neurotransmitters 

• Support neurons 

  • Provide nutrients and maintain the extracellular environment 

oligodendrocytes

• Myelinate axons in the CNS 

schwann cells

• Myelinate axons in the PNS

3 reasons why neurons are negative

• Sodium-potassium pump

• Non-permeable, like DNA

• Potassium leak channels trying to get membrane to -90

Driving force

• (Vm -Eion)

• Sign of the driving force indicates the direction of ionic flow 

Permeability

• Biological membranes are selectively permeable 

  • Allow some substances to pass while others are restricted

• Big force w/out open channels 

  • 0 ions will move

Permeability equation

i = Gion(Vm - Eion)

Action Potential Step 1

• presynaptic will release neurotransmitters

Action Potential Step 2

•  neurotransmitter binds to sodium-gated ion channels 

Action Potential Step 3

• ion channel will open and sodium flow from outside to in (EPSP)

Action Potential Step 4

• positive charge loves negative charge, so it will start to distribute throughout the dendrite 

Action Potential Step 5

• there will be a buildup of positive charge on the axon hillic bringing voltage to -45

Action Potential Step 6

•  a voltage gated sodium ion channel will open up and start to bring in sodium 

Action Potential Step 7

• when the gate becomes positive enough, the inactivation gate for the sodium channel will begin to close and reach its highest point (+20)

Action Potential Step 8

• when the inactivation gate closes, there is enough positive charge for potassium voltage channels to open 

Action Potential Step 9

• Potassium leaves, brings charge to -90

  • causes depolarization

Action Potential Step 10

• Activation gate for potassium closes, action potential returns to rest (-60)

Action Potential Step 11

• Chain reaction of action potential passing through axon through each node

Action Potential Step 12

• Opening up calcium channels, causes calcium to enter

Action Potential Step 13

• Influx of calcium in the synapse

Action Potential Step 14

Vesicular release

Manipulation of volted-gated sodium channels

Manipulation of volted-gated potassium channels

• Steps 1-7 will be the same, but there will continue to be negative in undershoot, thus it is take longer to repolarize

• Inactivation gate for sodium may reopen 

• Spike will be more narrow 

  • Undershoot quicker 

• Then calcium channel will be positive and more neurotransmitters will shoot out 

Salutary

From node to node to node

Multiple sclerosis

degeneration of myelin

Major Neurotransmitters

• Glutamate

• Glycine and GABA

Glutamate

• excitatory amino acid. Sodium comes through its voltage gated ion channels

Glycine and Gaba

• inhibitory amino acids. Chloride goes through their channels.

AMPA receptors

• Glutamate binds, sodium flows. Just like ligand gated ion channels. 

NMDA receptor

• Glutamate or glycine are the neurotransmitters. 

• In order for NMDA receptors to open, the cell needs to get depolarized first (more positive) for the magnesium block to get removed.

• Calcium flows through these channel

How neurotransmitters are released

• diffusion

• reuptake

• enzymes

diffusion

goes away

reuptake

blocked by a drug

enzymes present

breaks neurotransmitter apart

spatial summation

adds up messages at different synaptic sites

temporal summation

adds up potentials generated at the same sit, over time

agonists

• Mimic or potentiate the effect of a neurotransmitter

• Binds to same receptor as original

• Pretends to be the original neurotransmitter

antagonists

• Blocks the actions of neurotransmitter 

• Prevents from binding 

• Does not allow action to happen