PHAR 111 Physiology I

What are the most common membrane phospholipids?

Phosphatidylcholine (PC)

Phosphatidylethanolamine (PE)
Phosphatidylerserine (PS)

The phospholipid bilayer structure produces a natural barrier to what molecules?

positively charged

large

polar molecules

What is an example of a signaling phospholipid?

Phosphatidylinositol (PI) in IP3

works for Ca2+ release

What component makes the biological lipid layer fluid?

Cholesterol

What are some examples of Peripheral Membrane Proteins? Where are they located? What are their roles?

PI3 Kinase and RAS

Found in the Inner Leaflet of the Plasma Membrane

Regulates Membrane Structure & Function

What is the roles of Integral Membrane Proteins?

They are embedded in the Bilayer

They mediate Solute Transport and comprise the Major Drug Target Receptors, Transporters and Ion Channels
They have a polar amino acid head part outside and inside the membrane with a hydrophobic region inside the membrane and they undergo conformational changes.

What is diffusion?

PASSIVE / NO ENERGY solute transport Mediated by Ion Channels

Solutes Flow from High Concentration to Low Concentration
FAST Transport

What is active transport?

ENERGY required transport mediated by PUMPS & Exchangers

Moves Solutes Against Concentration Gradient

Often requires ATP Hydrolysis, Slow Transport

ex: Na+/K+ ATPase

What are the steps of Na+/K+ ATPase that contributes to Na+ and K+ gradients? What is the main function of the Na+/K+ pump?

1. 3 Na+ ions from the inside of the membrane attach to their binding site in the ATPase

2. ATP becomes phosphorylated; after ATP transfers a Pi to bind to the ATPase

3. Configuration change releases 3 Na+ outside the cell

4. Affinity of ATPase changes for 2 K+ from outside to bind into ATPase

5. Pi is released, ATPase reverts back to original position of opening to the inside of the membrane

6. The 2 K+ is released inside the cell

helps maintain the resting membrane potential

What is the extracellular and intracellular concentration of Na+?

Extracellular: 150+ mM

Intracellular: 5 mM

Nao / Nai = 30

What is the extracellular and intracellular concentration of K+?

Extracellular: 10^-5 mM

Intracellular: 140 mM

What is the extracellular and intracellular concentration of Ca2+?

Extracellular 2

Intracellular 1 x 0^-4

Cao / Caii = 20,000

There are way more Ca2+ outside the cell than inside the cell

Monoamine transporter (MAT) transports what type of NT into the cell using what ion gradient and solute transporter?

MAT uses Na+ gradient to invite NT floating in the synaptic cleft into the presynaptic terminal

Na+ is an ENERGY SOURCE because its going from low concentration to high concentration

NT = 5-HT, norepinephrine, dopamine

What drug class inhibits 5-HT reuptake?

SSRIs inhibits 5-HT reuptake which increases the duration of 5-HT recpetion activation following release of neurotransmitter

Vesicular Acetylcholine Transport (VAT) and the Vesicular Monoamine Transport (VMAT) uses what gradient to do what action?

uses the H+ gradient to transport neurotransmitters (NT) inside the vesicles.

Synaptic Vesicle Proton Pump H+-ATpases pump protons into vesicle producing a H+ gradient which can be used to do solute transport work

Stable Resting State of Biological Membrane can be mostly attributed to the ______

High Selective Permeability of the K+ ion. K+ can not freely enter and leave the cell

At rest, what is the relationship of K+ efflux and K+ influx?

K+ efflux = K+ influx, no Net K+
Resting Membrane Potential is at -70mV
Electric Force = Chemical Force

++++ outside

- inside

[K+] outside: Low

[K+] inside: High

What happens to K+ pumps when restoring resting membrane potential after stimulation? -70mV → -60 mV

Increased K+ efflux

K+ leak channel influx is weakened

Positive Charge Leaves Cell to repolarize membrane to resting mV

[K+]outside = low

[K+] inside = High

What happens to K+ pumps when restoring resting membrane potential after inhibition? -70mV → -80mV

hyperpolarization: inside of membrane becomes more negative

K+ enters the Cell, increased K+ Influx

[K+] outside is low

[K-] inside is high

Then, posiive charge enters, cell depolarizes membrane to resting

What type of protein are ION Channels?

integral membrane proteins: with the exception of leak channels they participate in SIGNALING functions

Where are ion channels located?

expressed in Plasma Membrane
Key Ion channels are also expressed in Intracellular Membranes (ER SR)

regulated by a SIGNAL

HIGHLY selective to which ion they allow

What are the different types of ion channels?

Voltage Activated (Gated) channel

Ligand Chemical Regulated

Leak Channels

Voltage Gated Channels

Excitable Cell (Neurons, muscle cells, etc) Membranes

Voltage-gated Na+, K+, and Ca2+ channels

Many types within each category, ex. Multiple Na+ voltage gated channels across the membrane

• Cells use Energy to Build ion gradients to serve as a biological signal to induce a cellular response (diffusion), solute transport work, neurotransmitter or glucose uptake

Activated, forms a change in voltage near the bilayer

Ligand Chemical Regulated channel (binding of a signal)

Many types within multiple mechanisms of Ligand Regulation

Controlled by Receptor Action of Channel Protein

Includes the major class of Neurotransmitter Regulated Channels

ex: Acetylcholine & Glutamine Receptors

Leak Channels

No Gates, Always Active, K+ Leak Channel Key to Biological membrane Function

What are the steps of Na+ voltage channel activity during an Action Potential

The Na+ voltage channel is open after a stimulus, domain switched to open and Na+ enters the cell to hyperpolarize the membrane

At the peak of the AP, the ball-in-chain closes and inactivates the channel. THEN K+ voltage gated channels are activated to drive the membrane potential back to -70mV.

During the closed Na+ volotage channel state, the membrane returns to resting state via K+ leak channels & Na+/K+ ATPase.

Ionotropic receptors are _______ membrane proteins that….

integral membrane proteins that open an ion conduction pathway when activated by a ligand signal

What is the difference between a voltage gated channel vs. iontropic receptor?

voltage gated are more selective, channel is specific to an element

ex. K+ ion gated channel

Ionotropic receptors allow for a MIX of ions to cross

What type of receptor is Acetylcholine? What type of signals do they produce? What is the receptor, NT, and conducting ion?

Ionotropic Receptor
Excitatory Signal / ACh/ Depolarizing

Conducting Ion: Na+ /Ca2+

What type of receptor is Glutamate receptor? What type of signals do they produce? What is the receptor, NT, and conducting ion?

2 Types:

Ionotropic: Glutamate receptors ex: AMPA & NMDA (Learning & Memory; Neuron Excitotoxicity)

Metabotropic: Glutamate receptors ex: mGluR, GPCRs
NT: Glutamate, Glycine

Glutamine Receptors require _______ for activation. Glutamate receptors are _______ of distinct subunits.

2 Glutamate ligand molecules, tetramers

• Upon binding, conformational changes in the LBD leaders to local conformational changes in the TMD, leading to activation

Glutamate Receptor conducts mostly _____ is an example of _____

Na+ , AMPAR

How does a Glutamate NMDA receptor activate?

1. 1 Glutamate AND Glycine bind to site

2. Mg2+ blocks ion flow when the membrane potential is negative

   1. The membrane depolarizes then Mg2+ is relieved so that Ca2+ can flow inside

What is a GABA Receptor?

Ionotropic: GABA receptors 9key drug targets for anxiety, epilepsy, etc)

Metabotropic: GABA receptors

uses neurotransmitter GABA as a ligand

NOTE: pentamers of 5 receptor subunits which in different combination confer unique functions

What happens when a GABA receptor is activated?

2 GABA ligand binds

The central pore of the receptor is able to mediate INWARD Cl- conductance. Cl- influx decreases neuronal excitability by making the membrane potential more negative— ie. hyperpolarization

What are cholinergic receptors?

AChRs are found in cholinergic synapses: nicotinic and muscarinic synapse

W

What are the steps of an ionotropic receptor at the Synapse?

1. An AP arrives in the presynaptic terminal

2. AP triggers neurotramitter release in the synaptic cleft

3. Neurotransmitters activate postsynaptic receptrs allowing the flow of positive chargers (Na+,Ca+)

4. The positive charge influx makes the membrane more positive, activating voltage-gated ion channels and AP stimulation.

What is a GEF

Guanine Nucelotide Exchange Factor (GEF’s for G alpha are activated cell surface receptors

What are the major steps of the GPCR second messenger-linked signalling pathway?

1. Epinephrine binds to the GPCR

2. The occupied receptor causes GTP to replace GDP bound to Gs and Gs gets activated

3. Gs (alpha subunit) moves to adenylyl cyclase (effector protein)

4. Adenylyl cyclase catalyzes the formation of cAMP

5. PKA is activated by cAMP briefly

6. Phosphorylation of cellular proteins by PKA causes the cellular response to epinephrine.

7. cAMP is degraded, reversing the activation of PKA

What are the major units in the Calcium/IP3 pathway

GPCR, Gprotein (Galpha, Gi, Gs), GEF (GTP + Ga), Phospholipase C-Beta, diacylgycerol (unactivated no ATP), IP3, Ca2+, protein kinase C, IP3 gated Ca2+ release channel

SOC Function

Ca2+ storage in the ER, can send a depletion signal to Ca2+ voltage channel of the extracellular membrane protein

Gq increases

Ca2+

Gs increase

cAMP

Gi decreases

cAMP

What is the pathway with Gs G-protein?