1.2- Membrane Physiology Flashcards
Give the structure of the lipid bilayer
Phospholipids (polar heads to water, non polar tail to tail)
Glycolipid (protein anchors)
Cholesterol & sphingomyelin (lipid rafts)
What is being partitioned with the plasma membrane/ blood vessel wall?
Intracellular fluid and extracellular fluid (interstitial fluid, blood plasma)
Why is there a difference between intracellular and extracellular components?
To establish and electrochemical gradient
What are the types of transport?
Pores (fastest)
Ion channels/solute carriers
ATPases (slowest)
Discuss aquaporin
Primarily “open” when inserted in a membrane- but some pores can be regulated via protein-protein interactions
There are 13 mammalian AQPs identified with greater densities on tissue type:
Adipocytes (AQP 7) Blood (AQP 1, 3, 9) & Blood vessels (AQP 1) CNS (AQP 0, 1 & 3-5) Epidermis (AQP 3) Skeletal muscle (AQP 4) Lungs (AQP 3-5) Kidney (AQP 1-4 & 7)
Discuss prototype AQP 2 which is located primarily in the kidney
In the kidney water wants to be moved from the atipical lumen side across the apical membrane into the cell allowing reabsorption of H2O, an osmotic gradient is needed for water to move. What determines H2O transport is basically the density of AQP 2 channels on this membrane, more channels= more H2O moves.
Regarding ion channels, what needs to be established across the membrane?
A concentration gradient
Ion channels are gated in that the permeable pathway is only open for a limited time, what is required to open this pathway?
An activator
What types of gates do ion channels have?
Voltage gated: small electrical potential difference needed across cell membrane
Ligand gated: specific signal needed
Other (eg. Stretch-activated): respond to mechanical deformation
Why do ion channels only allow a certain set of ions or a particular ion?
Due to the presence of a selectivity filter
Nicotinic AChR (nicotinic acetylcholine receptor) are important in transferring certain types of cell signals and ions, what does activation require?
2 ACh to bind to both the α-subunit binding pocket. Activation alters the selective filter thereby allowing cation flux across the membrane. A channel is especially important in neuromuscular and ganglionic function
ATPases: Prototype Na+ K+ ATPase
The use of energy to move or pump a substance is primary active transport. If it is used to establish a gradient and that gradient is used to move the substance, then it is secondary active transport.
Where can ATPases be?
On any membrane: plasma or intracellular
When would a pump be termed electrogenic?
If the pump moves an unequal number of ions either in or out of the plasma membrane (i.e. creating both concentration and electrical gradients)
Give an example of ABC binding transporter
The cystic fibrosis transmembrane regulator (CFTR). CFTR regulates Cl- movement, transporter poems when 2 ATP bind to associated nucleotide binding domains and undergo hydrolysis (acts like ligand channel due to activation)
Discuss the average P-type pump
On average this pump extrudes 3 Na+ & intrudes 2 K+
If the tissue is a gland or epithelial cell the pump is typically on the basolateral membrane
Ion movement has a number of steps where Na+ enters first followed by ATP hydrolysis, Na+ extrusion, K+ binding, loss of inorganic phosphate, ATP binding then K+ entry
Discuss solute carriers
Prototype: SGLT1
A solute binds to a site within the carrier protein on one side of the membrane. A conformational change happens allowing it to enter the cell. Solute is released. Carriers work in reverse directions as well
What are the names of solute carriers?
Solute carriers are named or classified by the direction and the number of solutes or ions being transported
Symport (cotransported
Antiport (countertransported)
Uniport
Discuss SGLT1 with regards to glucose
SGLT1- sodium glucose cotransporter 1
If a person is diabetic you could eclipse the vMax of SGLT1 in renal tubule cell, therefore glucose will be spilled in the urine. Losing glucose in diabetic hyperglycemic condition.
Regarding cell signaling what are the modes of communication?
Message travels some distance
Endocrine (hormone in blood to cell with receptor)
Neural (direct communication, targeted)
Paracrine/Autocrine (diffuse in distance around cell)
Message conveyed by direct contact
Gap junctions (most direct mode)
Paracrine
What are the types of receptors?
Environmental information: sensation receptors
Cell to cell communique: receptor(ligand)
Catalytic, G protein, ion channel linked, nuclear/cytosolic
What are some extracellular and intracellular receptor modifications?
Downregulation Upregulation Internalization Externalization Desensitization Sensitization
What are the steps in signaling
- Recognition (ensure ligand binds to receptor/ligand affinity)
- Transduction (move in for from cell surface to cell)
- Transmission (getting transduced signal to the right spot)
- Modulation of effector
- Response
- Termination (turn off else it continues: remove/block ligand)
What is Vm/ membrane potential?
When an electrode is placed within a cell membrane potential is measured, the precise value is determined by the difference in ion concentration between inside and outside the cell and how charges are balanced
Why does the electrode register a voltage difference
There is no charge imbalance across the membrane so there is no voltage difference
Give the ICF and ECF ion concentrations for the 4 primary ions
Na+ ICF: 12 ECF: 145
K+ ICF: 120 ECF: 4
Ca2+ ICF: 0.0001 ECF: 2.5
Cl- ICF:15 ECF: 110
How does one know how much voltage difference there will be?
Use of Nernst equation
What is the effect of ion potential on membrane potential?
Changing the ion concentration in the ECF such as the plasma alters the equilibrium potential for ion and potential alters membrane potential
What is the effect of current on membrane potential?
The direction of current flow across the membrane can cause depolarization(more positive) or hyperpolarization(more negative)
Cation efflux causes an outward current and hyperpolarizes membrane potential
Discuss action potential
The point where these voltage gated channels open is threshold
Increasing action potential past the threshold can cause an action potential in certain tissues like nerves
What are the types of epithelial flow?
Paracellular flow
Between a cell by lateral mechanisms
Transcellular flow
Apical membrane to basolateral membrane
